Notes on Metal Boat Building Methods

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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Kevin Morin
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Sat Jan 02, 2016 3:56 pm

I made a few remarks in the previous posts about relative accuracy or error in paper plans and I'd like to take a post to explore what I was talking about. The reason to use full size aluminum extrusion battens for full size lofting or model expansion (to be explored more in future posts here) is so important to understand that I'd like to expand on this topic.

IF this is already information your work experience has made clear, then no need to take time with this discussion. If you're not sure what I'm talking about in those previous remarks, this 'fact of life' post is intended to help you understand why I'm made a big deal out of the effects of aluminum battens in full sized work.

First, plans are drawn on paper and they are drawn to scale, if this principle is not clear to you... please look up one of the many online articles and read about this idea, I'm ASSUMING here, you're at least aware of the idea and practice of proportionality in the practice using a scale ruler? (not intending to make an 'ass' our of 'u' and 'ME' I'd need you to take the time to find these explanations)

Scale rulers are very commonly "three bladed" in cross section with two different scales on each blades' two sides. The rulers shown in the images to follow are for the purpose of illustration and not intended to represent all scales.

Let's relate a skiff of 20' LOA to a scale drawing. Scale and paper size are related to boat size. I a 20' LOA boat is drawn in 3"=1'0" then the boat will be physically 60" long on paper- where each 3" piece of paper boat equals 1'-0" of plans boat. So that scale would require a long sheet of paper. To fit this same boat, in scale, onto a smaller piece of paper the scale could be reduced to (let's say) 1/8" = 1'-0". Now the 20' boat would only take up (20 ft. )x(0.125"/ft) or 2.5" of paper!

That's pretty small, so let's increase the scale to 3/4" = 1'-0" where .75" x 20' = 15" of length on paper- in the scale chosen.

PAPER note: for those who don't know, paper sizes can be recalled like this: 8 1/2" x 11" is an A; double the short side and it becomes B or 11"x17"; double the short side and you have C or 22"x17"; double the short side and you have D 22"x34" and double the short side and you get E size or 34"x44".

Now, to use Architectural size pages start with 9"x12" and continue as with ANSI sizes, and then there are other size systems that can correlated to these basic sizes.

So our 3/4"=1'-0" boat that is 20'LOA could be shown as 15" measured in inches, in scale, on a B size piece of paper that is laid longwise side to side or "landscape".

NOW- to the meat of this post's points to consider in regards paper plans. How wide is a pencil line on paper? Well if we use 'full Scale" that is full inches to measure this line's width, the could probably vary from 1/64" for a finely sharpened hard lead up to maybe as wide as 1/16th inch for a softer lead and the width could vary along the curved line as the lead wore away while marking!!! (last point is kind of important)

What is the width of that same identical line in scale?

Image
Just above is an image of a scale ruler being shown marking an offset. The scale shown is 1&1/2"= 1'-0" and the scale portion of the ruler is shown to the left where the pencil mark is being made at 3-1/2" of the foot. The three full divisions to the right show that the total being marked is 3' 3-1/2". What I'd like to call to your attention is the size of a pencil line in width at this scale.

In this scale ruler on plans task the drafter is 'putting down' a measurement.

Image
This second sketch shows the scale ruler being used for a different task; in this image the rule is being used to 'take off' the measurement and the scale is different that the previous image.

The pencil lines or plans lines are the same width; but the scales are different so the rule's markings are either closer together or farther apart.

What is the measurement taken off shown in the second image? How does the pencil width effect the ability of the drafter/builder to 'take off' accurate measurements due to the effect of wide lines and small scale? What if the pencil line were even wider than one shown?

how much error are we talking about? Well look at the second image (close above) and estimate what fraction of a FOOT could be error! It would be easy to find an inch or more of error in normal plans and there are some drawings where this could be more than an inch- several inches.

I hope to have made the point that using scale plans there is a error potential when you're reading off the plans- even is the designer has given you a "table of offsets" which is merely the designer/drafter doing the exact process shown in the last image above; there is a potential for measuring error in the 'take off' procedure.

Now let's complicate things little bit to make the next step in this discussion clear as well. If plans papers are moist or too dried, paper will shrink and expand, if plans are 'blue lined' or copied then lines can "bloom" or become foggy and vague- wide lines are harder to 'take off' than sharp narrow crisp edged lines.

(Also) IF plans are reproduced in some types of printing, they can become pixelated or have different widths. Therefore... when a builder gets plans on paper, which are drawn to scale, there can be automatic and naturally occurring errors of some fractions of an inch: even in the best plans available.

This is one reason many plans services provide paper patterns, actual full size patterns to be placed on the work materials that don't require lofting, taking off or laying down- the 'real size' pattern is provided. Not a bad way to go, but not something that all plans packages off.

What happens when you read a plan's dimensions (take off) and then lay it out full sized? There are two steps of potential error- one in both operations- the take off dimension is not clear due to line width and scale; and the laying down dimension is subject to marking error.

Looking above in the first image, again, the most reliable method of marking an offset on a grid line is shown. The V tip is exactly at the point of the measurement. This is done by placing the pencil (or preferably scribe tip- on the measured location (tape,scale,story stick) and making a V using the tip only, and marking on the metal with the scribe.

I prefer a small black reference mark as contrast and background exactly like the struck lines in previous posts.

Image
This sketch of a layout grid of station lines on paper shows a series of V's marked along the station lines from the left reference line (in this case it could be Plan View of a Keel -straight line in Plan).

This exercise was a conversion of scale- only. The original plans were in a very small scale, and therefore the pencil lines of the plan were almost 2" wide!!!! So the drawing here was part of the steps required to scale up to a larger scale drawing of 1-1/2" = 1'-0".

The chine (Plan View) was 'taken off' as a series of offset-distances-from-keel in Plan in one scale and then using the other side of the Scale Rule, they were 'laid down' to the reading as close as possible to that reading- which we've reviewed may not have been all that accurate?

For the sake of this image; the left most straight line is a reference line like a Plan View Keel. The next line rightward in the pic (top of image) is like a chine in Plan View aft on most planing hulls and is a reference line to the curve being formed. The next right line could be the keel in Profile View, and the farthest right may be some reference to the curves that will be drawn in Profile.. this is not a plans explanation- the illustration was part of previous discussion online.

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What will have to be done with these V marked offsets? The process is the same for most curves we'll discuss- the batten had to be passed through the points to draw a fair curve. This is just a reminder of that process while on the drawing table.

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The sketch above shows a fair curve drawn through the points, first taken off a scale drawing, then put down, laid down, lofted to the offset grid stations of the larger scale plans. This same process is done and called lofting if the eventual scale is 1"=1" or 'real dimensions'.

I hope that you can see the curve shows there were errors in the measuring and marking process? The V's are not all at the exact intersection of the Station Grid lines. What had happened by using the batten? THE ERRORS HAVE BEEN DETECTED AND CORRECTED!!! That is a very big deal, very important and critical point of using aluminum battens for drawing tools in the full size work.

Starting to the lower left the first V is the bow end of the change scale curve and we'll hold the batten to that point- so it's OK. But the next Station Grid V is 'short' - that is the mark is inside the location the batten shows as 'fair'. The next grid point is off too. That third Station Grid mark is 'wide' or 'outside' the curve's fair line. Moving back along the new curve, toward the top of the sketch of the new curve, there are lots of various errors of various differing amounts.

The concept used was to anchor to the reference line aft.
Next use the bow point as 'good' and then best fit- make the batten lay fair as close as possible to the majority of the tips of each V at the Station Grid intersection. The builder's/drafter's/designer's eye is the control of the batten's fair line. But remember- the batten is selected so it can't kink like a chain could. The batten as tool will bend to a fair curve, but the curve has to be controlled by the eye of the builder.

What are the implications? Anyone can take standard paper drawings and loft/rescale those plans and correct normally occurring errors in measurement and layout- resulting in clean, fair, full sized boat lines; (that when) accurately cut, fit and assembled as boat parts- will build a fair hull if they take time to apply aluminum extrusions as drafting battens to fair their curves.

That may not seem significant if you're not involved in trying to find out how to handle long curves in metal; but it will be if you decide to buy a plans package and do all the traditional (per computer) stages of work with your own hands.

Now, what do NC cut packages do? First computers have many different 'line fairing' routines- second lines have no 'thickness' or 'width' in a computer- so the measuring errors are gone! Second when the NC table is given commands to cut- the cuts are usually so close to exact we can't hardly measure the 'errors'- not so with us humans.

Therefore all this type of consideration of concept and practice of working metal is not of concern to those who chose to afford the Plans with Cut Files packages. This work we're discussing in detail is done for you- and the associated costs are relative to having a skilled tradesman do these steps for you, by hand.

Let's take some real world curved boat parts as examples next?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Sat Jan 02, 2016 4:46 pm

One part of metal boats that is often curved is the 'transverse deck beam'. This element can be pressed/bent/kinked with a hydraulic jack frame in segments, it can be rolled with pyramid rolls or it can be cut, all have reasons for consideration which we're not discussing in this post.

This post will just discuss the layout and marking of a either a pattern deck beam for cutting or roll template for comparison. The method will be 'Expansion of a Circle' which is very commonly used for these shapes where an arc is drawn from a set of given aspects of the boats' design.

In these images the boat was a 50 or 60' long so the deck camber or amount of curvature was 6" in 16' of beam. That doesn't matter- since you could calculate any camber you need and follow a similar method to get this curve. There are (free) online calculators to help you save all the layout too! The purpose here is to incorporate some of the steps we've covered above so they relate to common skiff layout work.

As mentioned - choose the amount of deck curvature- the amount of arc rise from the side to center of the boat's deck (the illustrations will show 6" but a skiff would likely have less than 2"). Decks, cabin tops, transoms, frame sections, all use camber layout in some designs.

Image
This first sketch above, shows the various steps to take
#1 draw a half circle of the radius of the full camber (say 1-1/2" but shown here as 6")
#2 Walk your dividers up and down the 1/4 circle arc until there are four even divisions of the ARC. This is not a division of the radius at the baseline!!!

The orientation planes are present to make sure you 'see' where this arc/camber/expanded circle is planned in the hull.

Image
Next, above, #3 draw verticals from the even arc end's to the baseline these verticals are the 'baseline offsets' for the arc's grid line measurements. One important graphic fact to make clear; the four divisions of the radius line (on the baseline) at the lower edge of our half circle are NOT even, but they will be evenly distributed when the circle expands.

"Half Breadth" is the term for an offset from centerline; so a 1/4 Half Breadth is 1/4 the distance from centerline to the sheer line at that Station of the Hull. 1/2- Half Breadth is 1/2 the distance from the Keel Plane to the Sheer.

Image
This image may not be the most effective at showing the expansion of values so I'd ask for any comments if this causes confusion? The four levels of the 1/4 circumference arc's divisions by length- are moved to three verticals at even divisions #4 of the radius of 1/2 the FULL width of the deck beam, and the 4th is the outboard or sheer/chine location of the end of the camber frame, zero ht.

In this image I made each quadrant a different color to help show it was equal width and still show where that (1/4 of the final frame's half) began and ended from the center or Keel Plane outward. At the sheer edge, the ht of the deck frame curvature is 0- at the Keel/centerline the hit is Max Camber Height. (reminder; the discussion for this original sketch was a 6" rise in a 16'6" beam so the expansion shows 8'-3" of expansion.)

All of the ht.s found in the original 1/4 circle are measured and marked vertically from the baseline- not at any radius angle. All lines have a height mark V at their side as shown in the previous post on measuring and marking.

Image
Above the layout's goal of an expanded circle is drawn BUTTTT the PC CAD tool didn't line up with the marks exactly !!! sorry the arc line should (and will) intersect with each of the three verticals with the V marks AND the outboard most point will be at the baseline while the center will be a tangent to the original circle's top most (12:00) position/point.

Image
In this sketch of a batten run between the points of the expanded circle- I show one clamp in the middle so that the marking locations would be visible. If I showed 4 or 6 clamps in that area, which could be needed?? then the image would be too densely populated to give the idea.

Image
How many clamps you need will be determined by the batten's stiffness and the amount of arc/camber the frame has. The line along the angle, once fair, would be marked with ink for visual reference then a scribe and then cut- band saw, skill saw, jig saw, and faired once that operation was done.

The purpose of this post was to begin to apply the concept of accurately marking from and baseline, a series of offsets as V's at 90degs to a grid or Station line an then to run a batten through the points, and finally to mark a fair curve for cutting.

There are other places in normal building where this set of techniques if used and they could serve as a good example of these principles.

Cheers,
Kevin Morin
Kenai,AK
Kevin Morin

Kevin Morin
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Wed Jan 06, 2016 4:09 pm

This post introduces the application of off the shelf extrusions used as battens for tapering other extrusions. Outside many skiffs spray rails are employed to deflect water from running up the topsides but these extrusions welded to the topsides out side the hull also act as longitudinals to reduce hull panel size and stiffen the overall boat.

Some designers, builders and buyers don't care for the lines of their boats being interrupted by extrusions, so all the longs are inside and not as discussed here. There remain entirely different series of work techniques and layout methods to deal with inside longitudinals of all forms, so we're just discussing those which might be installed outside - specifically angles or hull stiffener extrusions that may need to be tapered for both looks, flexibility and ease of installation.

Image
Above, the first image in this post, shows a set of saw horses with cutting or set up boards that are holding a series of pipe type furniture clamps that have a 2" x 2" x1/4" angle extrusion mounted. The full 25' of the extrusion is skipped to focus on the end to be tapered. The taper will be done in a curve so the final, cut legs of the extrusion will lay to the hull evenly as it tapers and the outer apex of the legs will be curved in relation to the topsides (or bottom ) once installed. These tapered legs form a nice V for the welds that hold these tapered section to the hull plate.

Image
Next, above, we'll zoom in closer and get around to the end of the set up to mark the tapering curve.

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In this next sketch view above, the vise-grip pliers have been hidden to show the curve, and to show the approximate tangent point to this 5' long curve. The taper shown here as 5', is arbitrary for the sketch. Very often longer and more gradual tapers- 6-8' are used in order to make the transition less abrupt to the eye.

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Again, in this view above, the view point is changed a little downward to make the relationship clear. I think the progression of these images will explain what's being accomplished? The tools are used to hold the 2x2 to mark and a 1-1/2"x3/16" angle is being used to batten the curve, there are two fixed clamps back behind the tangent point holding both extrusions, the work and the battens' edges common - that is the reference or baseline in this marking set up.

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Here above, the view is from the top of the work set up. Notice the relative positions of clamps or grips and what is being used as a baseline versus the curved sweep to the left end of the work.

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Cutting these curves is not show yet, next post or two will address some of the work techniques there, but the resulting even, double sided curving tapers are shown in an end on view. This image suffers a bit in perspective but the three examples are rotated at different aspects to make their tapering edges as clear as can be seen at screen resolution.

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In this image perhaps too close up?? it may a few seconds study to see how close up the narrow ends are show and with some slow tracing of the eye along the outside edges of these three examples of the same angle rolled to different Up aspects; I hope the results of a reliable and good quality angle extrusion tapering method shows up?

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In this sketch of a 'hull stiffener' extrusion the principles we've been discussing are shown applied to that extrusion shape. An example of the native extrusion is shown in the center foreground for anyone familiar with this pattern extrusion. bending this material around the side of a skiff is very easy along the main topsides where the curve is only a few inches in 15feet. However if you wanted to wrap this 2" tall and 3" wide (at the base) extrusion forward of the almost straight run of the topsides- well its a lot of work!

However if the legs were tapered as shown in the images above, in this post, then the flexibility will increase as the legs get reduced as they taper forward.

Image
This sketch above, is another point of view change to help make the tapering and curved pieces more easily seen as they might mount on the topsides of a boat.

The right hand image (just above) of the leg tapered extrusion shows yet another use for battened curves in tapering this extrusion. If a centerline 'orange peel' or 'trumpet bell shaped' piece of the flat top surface were removed from the native extrusion, using the exact same methods we've been exploring; this extrusion could be tapered in both width and height and further enhance its looks when installed on a boat's sides.

This 2nd taper would be marked 'back to back', cut, cleaned out, sides beveled and then the entire end would be pulled together and tacked (3 dimes or so) progressing from the Zero end to the widest end- not welded solid at that time. Once the entire tapered end were installed to the hull then all the welds would be finished and I'd expect this tapered to flat would be dressed clean and sanded to finish with the rest of the extrusion.

Image
Photo above shows a 4" x 3" angle that was ripped to 4" x 2" then tapered on both legs as a spray rail and hull topsides stiffener. This extrusion was stitched to the topsides using TIG by cutting short bevels deeply into the 1/4" wall of the extrusion to allow a very narrow top face of the weld and also deep penetration on the stitch welds.

Extrusions arranged in this fashion act to deflect spray more effectively than simply relying on the rub rail or other topsides shapes and contribute to a dry skiff.

Image
This very old photo of a 18's skiff I did many years ago shows the effect on the skiff design of tapering extrusions. The topsides has a 1/2 pipe as the panel stiffener, tapered (slightly different technique than we're exploring but similar) and the two angles that are show sweeping up to the sheer are tapered exactly as shown in the sketches in this post.

Image
Scans of old hard copy photos from glossy prints aren't all that high quality! This image shows the same skiff from another angle, again, included here to advocate for tapering extrusions as both ease of building while wrapping the shape with different extrusions and for the aesthetic contribution to the overall look of the boat- depending on design of course.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Thu Jan 07, 2016 11:17 pm

WE've explored accurate layout of curves and straight lines, tool selection and even cutting technique to some degree, but I forgot to mention one very useful method of handling extrusions for cuts.

Regardless if you're splitting or slitting pipe, tapering extrusions' legs, or making other longwise cuts in narrow pieces the following method allows good control, safe work conditions and usually results in high quality cuts because the saw table is stabilized on the cutting boards.

Image
Above is a sketch of two 2x6 cutting boards laying on a set of saw horses. The two 2x6's are clamped underneath holding a 1" pipe to be slit. This technique applies to many different extrusions that need to be tapered, split or slit and should have been included in the previous discussion of tapered curve marking (and cutting) of angles.

In the case of ripping a small bore pipe, an angle extrusion held firmly to the side of the pipe/tube extrusion will allow the marker reference line to be inked onto the surface, and a scribe will then follow with cut line that is visible when when cutting. By putting screw drivers into the cut (saw kerf) behind the blades' track, the pipe can be kept open and not bind the blade.

Since pan spray is used in the operation as well, rinsing the entire pipe with acetone can be very noxious, so charcoal filters on the half face APR or doing the rinse outside are called for to use acetone to rinse the grease out of the slit pipe. If the pipe is cut in half, then acetone rags can clean up the interior of both halves easily without using nearly as much solvent.

The saw horses shown are welded of saddled pipe and are not really needed unless you have to support 25' or larger boats, but they do have many purposes in the boat shop, they are welded not collapsible but will hold several tons and remain stable.

If the angle marked in the previous post about battening a curve on a tapered extrusion's legs were cut with a skill saw? The angle could be clamped between the two cutting boards where one leg would be flat to the cutting surface and the cuts SHOULD proceed from the wide end of off cut- tapered end of the extrusion- and move toward the long end, other wise the tiny thin off cut will (may) roll up in the saw blade due to the sharp, thin and weak remnant taken off the side of the extrusion.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Fri Jan 08, 2016 6:27 pm

So far we've focused on my ideas (experiences) about some of the common errors I've seen in working in sheet metal goods involved in building welded aluminum boats. My purpose has been to make sure that you at least one good way to get accurate layout, marking and cutting, we've sort of skipped fairing for now.

IN preparation for the next major topic I'd like to offer a preface that readers can use as a huge helping of salt- as in the phrase- take that with a grain of salt. I'm not advocating my boat building methods are the end all, be all, final word on the subject; instead I'm offering a review and explanation of a series of methods of metal working that can work as I've used them.

With that said, I'd refer you to the many boat building books that cover these subjects we're moving to explore next. This lofting or laying down or modeling a boat from plans. To do this here, I will provide a series of sketches and perhaps photographic images to support the text but UNDERLYING all this information is the fact that I rarely use traditional ring type frames to build welded boats.

Let's spend a few lines to understand this difference in my personal building methods versus a more conventional and traditional method of construction. Glen-L plans packages will all have a set of transverse frames that are built and lined up on a keel or strong back frame then covered with longitudinals and finally hull sheathing. That method works well and is the best, safest in regard error, and the most reliable technique of building welded metal boats.

However, I learned to build the entire hull as a shell and then frame inside once the hull shell was tacked and trued to shape. I taught myself to do this method because I could not afford to compete with Seattle area skiff prices if I used conventional framing methods- as I was paying Alaskan wages for the framing work- which is not a small amount of labor or metal.

Image
This photograph of a hull bottom of a 25' offshore skiff shows all hull panels are assembled but there are not transverse shaping frames in the design or method- there are some female molded former under the hull, not shown here.

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Above a photo of a 14'er's bottom on the fixture being tacked up. These are the only transverse in this building method until the entire hull form is tacked up.

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Above is a photo of the 14' with all major hull panels tacked edge to edge- laid out and cut to offset tables on a grid of the outline of the plate model's details of the little boat. The framing was added after this stage.

I am not trying to explain this method of building in its entirety. I'm showing that the most important thing in welded metal boats is the hull panel outlines being accurately laid out and cut- then tacked to their adjacent edges so the correct hull shape results. I will be using some of these images to explore the details that apply to plans where the builder begins with a frame set and then adds hull plating.

What does that mean for someone reading who would purchase a Glen-L plans package and begin to build their own welded aluminum boat? It means that I've spent a large amount of time making hull panels and hull seams super accurate and the information you read here will allow you to use your frame set to build an extremely fair, very cleanly joined and utterly smooth hull- because your boat is not focused on the labor - it will be focused on good work, final product quality, and seams that will weld easily due to the precise fits.

Will I be encouraging you to give up your frame set? NO. Will I be offering you a means to build without your frames for the plans you purchase? NO. Will this set of posts provide you information to improve you fit and finish using your Glen-L Plans sets' frames? YES.

I will use some examples of my technique of sheet fitting, and for other fits, to show you how to get 'perfect' fits on your plans package's frame sets. However, you can avoid all this work but purchasing the NC cut plans packages that would allow you to ignore ALL this planning and work and simply begin tacking up from accurately cut parts!!!

So let's discuss plans for a while in order to set the stage from this phase of the exploration of work methods.

Cheers,
Kevin Morin
Kenai AK
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Fri Jan 08, 2016 6:47 pm

In order to fully explore the various building methods from the last post, I thought I'd offer some links to explore that can help you see more about what I've given just a few lines.

http://www.amazon.com/Devlins-Boatbuild ... 0071579907
This builder works in plywood and glues but forms his boats just like a plate first welded boat, and has a book that shows how he does the planning and layout. I will be presenting something very similar in the next few posts.

http://www.bookdepository.com/Building- ... 0071427975
John Gardner is considered to be the bridge between the past methods of building (in wood) and the modern era of small boat building. I have copies of this book and read it over and over to explore his many worthwhile details of layout and lofting.

http://www.kastenmarine.com/frames_first.htm
Michael Kasten has a design office and seems to specialize in welded metal boats both steel and aluminum. He has many great articles on his website that are informative and interesting regarding metal boat building and the various points of view on method and theory.

http://www.glen-l.com/designs/hankinson/aluminumbb.html
Right here on the Glen-L site is a great discussion of lots of points that I'm skipping over! All of Mr. Hankinsen's points are important to review and soak up, as his knowledge, experience and insight are worth your time as a fundamental aspects of learning to build in welded metal.

Just a 'catch up' post to give some more scope to our ongoing exploration of metal boat building in welded aluminum. Incidentally paper or hardcopy books are becoming a thing of the past. But they can be cheap! I use the book selling site Alibris.com where I find many copies of these and other books for a few dollars, and I have to say, I do like hard copy of lots of these books that were never published in digital format, so this online source has been one good way to buy all the marine books I wanted for a fraction of the cover price!

cheers,
Kevin Morin
Kenai, AK
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Re: Notes on Metal Boat Building Methods

Postby steveh41 » Sat Jan 09, 2016 9:53 am

Kevin,

Many thanks for the time taken to produce this comprehensive and very informative thread! Makes me want to try a build in aluminum... (if my wife sees this I'll be in deep trouble! :lol: )

Regards,

Steve
The longest journey begins with a single step… then repeat as necessary!

Kevin Morin
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Sat Jan 09, 2016 12:48 pm

steve41, thanks for the encouragement, we've a ways to go!

While I don't want to see you in a conflict with the 1st Mate, I do hope the series will help DE-mystify the metal building process so more people would consider building for themselves in aluminum.

The late, great designer of boats, Wm Garden whose work included cradle boats and some of the first mega-yachts built used to say about aluminum that if it just smelled like wood and had a little color variation aluminum would be the perfect boat building material. I think it is the best material, the Miracle Metal, so I'm trying to encourage others to explore it more thoroughly for their own projects.

More to come.

Cheers,
Kevin Morin
Kenai, AK
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Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Mon Jan 11, 2016 5:52 pm

As I plan to show how to use a builder's plate model to find hull panel outlines for the 'skin-first' method and to expand on that same technique as it can result in perfect fits for hull panels on a set of frames, I think we should review hull lines drawings' basics. This information could be too rudimentary for many Forum readers who have already built their own boats (?) however, I've included this review of drawing techniques here to make sure that someone coming new to boat building has a complete step-by-step overview that can lead them to a solo build.

The basics of drawing a set of boat lines will be shown as one method, there are other introduction in books, online sources, and even correspondence courses that teach all of this in more detail so anyone seriously interested can use this abbreviated presentation in conjunction with other sources to more fully understand the skills involved. I'm focused on the critical path details, not a comprehensive drafting course.

That doesn't mean I won't try to address any questions you have left after reading this series of the Methods of Work thread.

First, we need to review some drafting basics, relying on pictures to convey most of the information, then we will need to do an exercise that confirms you can follow the ideas in the steps to convert a curve from one scale to another, then we can move forward to explore the plate model work method.

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First, above, the paper is mounted, usually with tape strips or dots to a board or other hard surface with at least on straight edge, this edge is where the T square rides and this is where long parallel lines on the paper are drawn. These lines would be references or baselines they would typically be the Keel line in Plan View, or a waterline or baseline or perhaps a Keel line in Profile, and in many cases they could be simply a reference /baseline for construction and drawing purposes and not permanent elements of the final drawing.

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The next set of basics is shown above where the T square is used with a 30/60/90 drafting triangle to make grid lines (Station lines) where the spacing of this grid is usually uniform (some exceptions at the ends of the Stations' grid set) so a dividers is set on a scale ruler's edge to a given distance (in scale) and the distance of each grid to the next is 'walked off' so they are uniform distance apart, not measured on the scale where error can be induced more easily.

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This picture of a blue page of drafting paper with the upper Profile and lower Plan view show a typical set of lines with names attached. We're going to walk through an exercise that could apply to any of these lines being measured or 'taken off' then moved to another scale and 'put down' or 'laid down' on another grid set in a larger scale. This reminds everyone of the types of lines and locations we might see them on a set of paper plans.

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Above, is a 3D image in perspective view of the lines are they'd be seen on the final boat, but perspective views cannot give us real world dimensions to measure and therefore cut material. This image is included to help associate the flat lines on the blue (and brown) paper shown above and following; with those lines position on a boat's full shape.

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Some boat builders have angels working with them and here is a picture of a little wooden boat, almost as cute as the angel in the foreground, with the hull lines labeled to further reference the flat lines drawings. (In the absence of a picture of pretty girls in bikinis smiling on the deck of an all mahogany runabout from Italy, I figured a pretty girl would still liven up the post?)

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Last sketch correlating the positions on the hull of the named lines we're seeing in flat projection on drawing paper, here above, is a double ended dory shape with two chines. all the lines' labels remain the same in each rotated view, just as they do on flat views when drafted in the three primary Views.

For more on this topic, if it remains unclear; I posted a series exploring the Lines of a Hull a few threads down (?) so that may help explore the overall discussion of the hull intersection lines as they're drawn, FLAT as projections and NOT in perspective. That last is key for our work methods and understanding, even though I'm using 3D illustrations in most cases to try to explain these ideas.

Now let's do the exercise in curve scaling, by setting up a set of two scaled grids, draw on set of curves, the "take off the offsets" and "lay down" those same offsets and finally batten or fair the offset table into clean curves.

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Above the exercise's first few steps are shown all together in one image.
#1 a grid of Station lines are drawn at right angles to two right to left reference lines and two shorter baselines are drawn parallel offset from those two main references lines there could be like the Keel in Plan and Waterline in Profile but are not intended to be in this exercise.
The Grid is divided into 1" units so that 9 spaces will have 10 Grid lines or 9 Stations if the first line is 0 numbered, and the total length on paper will be 9" long and we'll be drawing curves related to a 18' overall skiff with a scale or 1/2" - 1'-0" or 1:24 ratio of paper dimensions to the real world full sized boat.

the next grid set will be three time this size or 1-1/2"= 1'-0" or 1:8 ratio and the grid lines will be 27" from 1-10; the same for Stations which will be 0-9 still at 27" physical inches on paper. Our proposed 24" wide 36" long paper (D sized) will work for both drawings.

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This image above of two sheets of paper, one above the other shows the method used by many drafters of putting a well measured and marked grid on the opaque page below a translucent of film page that allows the grid layout and drawing work to traced accurately from page to page without all the trouble and time needed to measure each new page's grid. Accurate tracing is much faster than individual measured and drawn grid lines. This method retains grid sets of different scale for reuse when drawing in different LOA' and different scales.

#2 the curves are 'anchored' as we've previously discussed at the tangent points and just to their left (in these images where the baselines are) then are shown curving to the right. It doesn't matter if the lines in your work curve in either direction or both in one, what matters is the lines are drawn fair and clearly result in a clean line at each grid/Station line intersection.

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A reminder image, previously shown but re-posted here to summarize the drafting board elements of drawing a curve with a batten. Key elements are the wt.'s ability to hold or clamp the batten in place so it will not move without the drafter's hand and will remain where it was left so the fairing process can be controlled by the drafter.

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Above is a point of view change for this stage in the curve scaling exercise showing the parts to the drawing already defined and labeled here for correlation to the step taken so far.

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#3 Next step in the exercise; information/data/measurement are 'taken off' the paper of the 1/2"=1'0" grid lines page and recorded in a Table of Offsets as distances from the reference line to the curve's intersection along the grid or Station line. The 1/2" scale side of the ruler is shown rolled to hold the scale side edge on the paper and measure from a reference line (a convenient straight line- not necessarily the keel in either view FOR THIS EXAMPLE)

This 1/2 scale dimension is reads 5' 3 & 1/2" but often tables of offsets will read to the nearest 1/8". 1/2 in is 4/8" so this entry might be 5-3-4 where by position in the numeric string excludes the need to include feet and inch or eighth inch labels - the first character is always feet the second always whole inches and the last figure is always whole 1/8 of inches. Not always used but common enough in traditional plans that new builder is cautioned to look closely at the offsets labels to make sure they're understood.

Moving along each curve; Station by Station intersection measure the offset form the same reference of baseline and record that dimension in real world feet and inches, this table will be used to 'lay down' on the next larger scale grid to reproduce these curves in larger size, and could be used full size to put down on a 5'x 20' sheet of metal.

Once the curves' offsets are taken off you'd move to the other larger, scaled grid lines set and lay down those same points in the corresponding locations.

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Along the way we'd have created a Table of Offsets with measurements at each grid/Station line that would hold this type of information. PLEASE NOTICE,the dimensions show here correspond to a different scale!!!! the first measurement shown above could confuse the reader is not observed and noted!!! I had drawn these images sets of this discussion years ago and this abbreviated use of the images could lead to confusion, care should be taken associating the text and images for this set of taking off and laying down sketches.

Notice, also, that it does not matter for the skills being introduced in this exercise which references lines are used as long as the same reference line used to lay down the same offsets taken up? it is important to recall this images shows dimensions taken off and recorded to the 1/2" to one eighth inch, but that most Tables of Offsets record to 1/8" I hope this detail helps make the inherent error of paper plan measurement clear to the reader? The width of a pencil line or copier line on paper when scaled could be several 1/8" or even larger.

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#4 Laying Down. The sketch just above shows the scale ruler rotated to 1-1/2' = 1'-0" so; the grid spacing has been swapped on the drafting table to the appropriator 27" long grid set of Stations as we begin to put down or lay down the previously taken up offsets prior to fitting the curves.

Note that the first station scaled offset was 5'-5-1/2" but now is 3'-5'-1/1"- Please ignore this and simply look at the idea of the first value of the Table of Offsets being laid down in the corresponding location and all other related points are likewise correlated to their location on the first scaled drawing.

[For the graphically astute reader; I needed to scale the size of the scale ruler in each image set to get the 1/2" scale and the 1-1/2" scales to correlate to the fixed size of the paper lines model and I did not bother... so the images don't match in offsets shown as taken off and laid down, your indulgence in my laziness is appreciated the images are nearly 10 years old.]

Each Station of the Table of Offset's grid to curve intersection is marked with a V the apex of which is the scale fraction marks, which results in a set of V's marked to the grid or Station lines.

[img]http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Hull%20Lines/CurvesScaling_6a.jpg[\img]
This is a sketch of the laid down larger scale curves' intersection on the 1-1/2" scale grid where only one curve is shown marked.

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#5 Above, the batten has been run through the points or the apexes of each Station offset as it has been measured from its reference line along the grid to the new intersection point which defines where the batten will be held by the drafting wts. or by clamps if these were being drawn full size.

"Best fit curve" means to batten through as many points as possible, while staying as close the remaining points as possible; all the while keeping the batten fair with no hoggs, kinks or flats. Battens are supposed to have the properties we've already discussed so best fit is the job a batten was designed to do.

The points in this sketch show that most of the Vs' apexes are not exactly on the curve HOWEVER... if the differences or errors were scaled and recorded (Corrected Table of Offsets) the error will probably correlate to a pencil width in the previous scale. VERY important fact there, and one that makes the overall method we're using that much more valid- battens an correct curve's measurement errors to a very small correction allowing hand drawn designs to be built skin-first OR to take off hull panels accurate to less than 1/8th sheet thickness for frame-first building.

Please feel free to correct, question, instruct or remark about the posts here, the primary goal is to record method of work that will allow anyone to buy Glen-L plans and follow accepted (but not as widely practiced) metal working methods to build their own welded aluminum boat. This section introduces the basics of drafting in flat views (projections) the lines, next we'll take the lines off and make a model in 3D.

This type of building relies on work methods that the computer could do for you and is presented for those who'd like to consider doing all the build steps themselves. However, as recently notified here, Glen-L has a new association with a pre-cut boat kit supplier where you can skip all this level of detail in this drafting and modeling series of posts and go directly to the build process. We won't be showing building sequence and technique discussions in the near future! However, we'll try to get to those before this series is done.

Next, is a discussion further of lines drawings, then some model building so we can move on to taking off plate shapes as outlines for full size layout.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

North
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Re: Notes on Metal Boat Building Methods

Postby North » Tue Jan 12, 2016 12:50 pm

Hi Kevin (and everyone..),

Not sure if you would include this here, or perhaps I could start a different thread, but I am hoping Kevin (or anyone with the knowledge/experience) can walk through the basics for surface prep / finish choices on aluminum boats.

I am at the stage on my build where I will be soon wanting to paint the bottom - I will be leaving the topsides bare..
I have read many posts and articles on line, where a multitude of approaches have been recommended, but the info is somewhat disjointed: Some suggest sand/soda blasting, and then etching, priming and painting. I do NOT have access to a blaster, so I am hoping that others who suggest sanding and then etching, priming and painting are correct as well.

In addition to the question of recommended processes and hopefully even material/ brand choices, I have a special request to see what product and sequence would best be suited to fair the couple of low / recessed areas I have in the bottom from excessive heat (I know, this should have been avoided, and was for the most part in the topsides, but the bottom sits as is) So, I would like to fair the bottom as best possible and have received some recommendations from my local marine suppliers for products like Metal Weld (by Systems Three). It is basically a prepared epoxy and filler/thickener mixture which is thick enough to fair / fill gaps, etc and is formulated for adhesion to metal. It is likely not easily sandable and therefore if I use it, I would plan on building up slowly, and not putting on too much, even if it leaved the spots a bit low - I figure I could add some lightweight, easily sandable filler later after priming, if desired??
Or, am I way of and you would recommend something totally different....I have some left over West Systems epoxy from my glass sailboat, and could use various fillers with it, but I am not sure if it would be best directly on sanded aluminum, or after etching/ priming, ect....

Any help would be appreciated!

PS. I likely should have spent more time trying to straighten/ push out the couple of recessed areas, which are the "starved cow" between a couple of frames, but at present the stringers and frames are welded to the hull and engine girders are welded to the hull. There is no movement / flex in panels if I stand on either the high or low spots in the 3/16" hull. It likely would not greatly affect performance, but I would just like it to look fair when it's on the trailer for the winters, so I am willing to do a bit of fairing if that's achievable!

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Tue Jan 12, 2016 3:02 pm

North, mechanical attachment coupled with chemical film bonding is generally accepted as the best all around marine paint adhesion plan.

Mechanical attachment comes from the paint's inner film- primer- setting up or curing around a microscopically rough surface of metal the best way to get this is sand blasting- there is wide discussion on which blast media is best or most effective in aluminum alloys. Next best is to abrade the surface with a sander, usually rotary, and grits can be discussed all day where coarse versus fine would need grit numbers to get realistic. Last mechanical roughing would be a wire brush with fine wires, and again probably rotary power tool.

The mechanical abrasions all achieve some degree of what called an anchor pattern which is the name of the picture of a cross section of the metal very magnified to show these intentional but very short measurement irregularities; at a scale they can be discussed as distinct from one another. The impact of high speed grit particles creates the most 'gripping' points for the paint film the hold to in its hardened state; hence the term anchor pattern.

Once any anchor pattern is put on the metal surface a chemical bond very thin film, often and commonly Chromium Oxide, from an allodyne solution added to wet rinse water used to flush and dilute the acid that has just removed the aluminum oxide film. If aluminum oxide is allowed to reform the chrome oxide bond is lowered and there is more 'room' to get water under the coating systems.

Then primer and paint, I'm not up to speed on any brands for any products, so choosing those is not something I can help recommend. As to the methods above, used in descending order they are from most preferred to least effective and you could then fit your project into the spectrum of paint facts and continue from there.

As to hull distortion, this unfortunately is one of the most common problems with first time welded builders due to their need to absorb potentially an incredible volume of information in a short time in order to do the work their boat project requires to finish and get in the water. Hull welding is a fairly in depth discussion which is usually only summarized or shown by a few not-inclusive examples. So over welding is pretty common, regardless of what the references or plans say is adequate.

If the hull's distortion is welded in, as you appear to describe, my only solution is cut out the support's/frame's/longitudinal's welds to release than panel form support, use (add) exterior shaping elements tacked outside the hull to hold the desired final shape, then either sister or replace the interior framing elements to support the corrected hull panel shape and welding a little more planned and judicious weld pattern in the panel's interior support elements - this time.

I've only used fairing compounds on masts, deck fixtures and related welded/fabbed equipment enclosures that were mounted on glass boats where white gel coat/gloss enamel was the finish spec. So we built the anchor winch or chair base pedestal or Med Mast and after lots of sanding and prep, "bondo-ed" these primer coated welded fixtures and sanded again to a fine grit (220), then finished painting- the finish in those projects cost more by twice than the underlying metal work. We had to hire automotive body fender guys to do this work with any real skill as the metal workers in the shop had no 'touch' for that level of finish sanding in varied color layers.

I'm aware that mega-yachts are blasted, primer coated and then fairing compound is applied and long board sanded to make them mirror smooth , before the other layers cover the fairing layer and topcoat is added. I have no experience with any of these hull fairing products and can't remark about them in any constructive way. I used automotive grade bondo between two layers of primer and top coated with gloss white.

Cheers,
Kevin Morin
Kevin Morin

North
Posts: 283
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Notes on Metal Boat Building Methods

Postby North » Wed Jan 13, 2016 11:47 am

Hi Kevin - thanks for taking the time for the detailed response!

I understand that you do not have any specific primer/ paint brand recommendation. After blasting or abrading, can you recommend what etch or allodyne solution you (or other frequent builders) would commonly use, prior to priming? Is it a brand name/ readily available or a "homemade" concoction, where I would search locally for allodyne or other specific products?

I did watch a video on youtube which showed the use of Dupont's materials ( 225s Step A for cleaning I believe/ similar to Alumaprep) and 226S Step B (allodyne) for etching. He used full strength but mentioned it is normally diluted...

I would just like to hear what is common / accepted in marine industry before buying. using any products, if possible.

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Wed Jan 13, 2016 12:35 pm

North,

here are links to the chemicals I've used, I'm not sure of their geographic distribution in retail stores?
http://www.superkleendirect.com/zepa-lume.aspx This is the acid I used most often, it is stocked locally by a few suppliers, but I've heard from builders in different areas that they are not allowed to buy it in their area- Florida I think was on poster's area?

http://www.chemical-supermarket.com/home.php?cat=109 I've used the 1201, but this is the only product I've found locally. This stuff could be rated hazardous? in shipping terms, so, again, I'm not sure of distribution or availability.

Needless to say, anyone considering these two materials in their work should get their MSDS and read how many different ways this stuff will kill or injure and add PPE to make sure you're safe.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Thu Jan 14, 2016 5:38 pm

I don't think Glen-L Forum readers need too much instruction in lofting or drawing but I want to introduce plate models. So without these potentially redundant posts about drawing or rescaling- the images I'll use to explore a plate model might seem confusing. We'll need to be reading the same lines, from the same views, with the same names and view point terminology.

I know that lots of Glen-L Forum builders have done this, lines drawing work, redrawing, lofting or fairing work on their projects but I'll guess there are also newer builders or even future builders who have not collected all this information in one place -yet? With that in mind, this post intends to a) reinforce some techniques we've already seen, b) review some terms and c) reinforce the views of a set of hull lines so the reader is prepared to make their own plate model.

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Above the first sketch in this post of a sheet of blue paper with two sets of hull lines labeled with the terms we use to describe that particular line. The upper set of lines shows a Profile (or side) View of the boat's main lines; Keel, Chine(s), Draft Waterline, Sheer, Bow Stem and Transom. The lower set of lines are only 1/2 the boat but the same set of lines is shown. Note that the reverse chine is flat or there would be two lines in Profile? The chine flat diminishes to 0 width at the bow stem? (hard to weld) and the topsides have a nearly straight sheer, in Profile View?

There's a little V in the boat, since the keel is below the chine in Profile- how much V would only become apparent when the Body Plan or Section Plan view was constructed from the offsets in these two views.

The lower set of lines are based on the keel in Plan View so that plane is merely a line on this flat page view of the top of the boat? Also, the lower set of lines will be symmetrical around the keel line (the reference and baseline in this case) so the other side is not drawn- no need to spend paper or time.

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This sketch, above, shows a similar set of lines from another perspective of the page and there are labels with line leaders to the various lines drawn. The purpose is to correlate the text above, and this image to see which lines are grid, waterlines, hull lines and so forth. Being able to understand this jumble of lines does take some time, and the image here is supplied to relate names to these lines.

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Here, above, the image closes in (zoom) a little to label various parts of the sets of lines introduced in the previous images. Has the forefoot of the bottom/keel intersection and the lower end of the bow stem been drawn fair? Or is there a hogg at the waterline in this view? There is no sheer line drawn in either view at this point of the lines drawing.

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Close up image of the Profile View lines so a detail of the stern area can be seen. Again, the labels are intended to help correlate the lines in this view to others AND to hopefully cement these relationships in different views to the lines drawing.

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Zoomed back a little, view of the blue paper working page shows a series of reference and baselines that are placed on the Profile and Plan View reference lines (draft waterline in Profile and keel in Plan) and from these lines we can begin to add the curves of the design. Offsets from the two references could be; design draft in Profile establishing the keel depth? Chine Beam Overall as a straight line offset from the keel in Plan View? Chine to Keel Depth (making a V) in Profile...

We're not discussing those design decisions we're merely reviewing the methods that could be used to set out the references and baselines of curves as they my be offset from a couple of straight lines- one the draft of working waterline in Profile View, the other a keel (plane) in Plan View.

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Above, an image showing a series of V's that result from different PROFILE separations from Chine and Keel in plan view- which one is required is a design decision which would then be drawn with the same techniques. The depth shown in the middle of each cross section is the depth from keel to chine in Profile View. Also included in this sketch are two bottom frame profiles of EACH cross sections; one is cambered downward the other is flat chine to keel- there is an entire design discussion around this a facet of design of metal boats, one we'll touch on briefly in the future, but will not try to explore in depth.

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In this sketch a keel curve has been added to a baseline in the Profile View. The forefoot has been drawn up to the lower edge of the bow stem or the intersection of the two topsides at the bow- in this View. It appears more work will have to be done to 'fair' the two lines - after baseline and forward bow stem - to one another!

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This photo of a Glen-L Chinook by Chris Stephl, of Soldotna, Alaska, shows the forefoot of the keel line smoothly faired to the bow stem! That implies we need to 'go back to the drawing board' with our previous examples- our forefoot needs to fair into the bow stem without a hogg!

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Above is a 3D sketch of the flat plane of the keel and forefoot we're discussing in the other (flat) images. This is intended to make sure we realize the chine in the Profile View is 1/2the chine beam closer to us, but all the lines are on one flat page! the keel bottom, and forefoot and bow stem are all drawn 'on this plane of glass'.

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In this image of another boat, not shown above, from the same views, Profile View above the Plan View, lots of references are shown marked on the grid of Stations and working waterline (above) and keel (below) so that curves could be 'fit' to their respective references. Not all curves will be single sweeps- that is a baseline combined with a fair sweep departing at a tangent point, however.

This design has a small reverse chine plate forward and then the topsides intersects the bottom for a single chine aft design. The bow is very full - far forward, where this bow forms an almost barge-like fulness in the forward 1/3 this hull is designed to carry commercial loads of fish through a surf and bow lift or pitch is more desirable than a sharper entry as might be more useful on boats that are intended to carry less load in a sea.

However, the drawing techniques used for these two different boats is the same; using a grid in scale, and basing the lines on two parrallel references, we can set baselines for curves as offsets from the references, using design figures we've evolved or are Taken Off of the plans drawings we've been given on paper but want to change scale or fair in a larger scale. Using drawing tools, scale ruler, dividers, battens and batten weights and a little practice we can recreate the curves of the design plans we're building.

Drawing the plans in larger scale helps to allow more accurate offsets to be taken, helps to fair curves of hogs, hollows and flats at a scale that our eye may see more easily, and allows a more accurate plate model to be built, which is our goal.

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A pair of lines compared in two views; the chine show in this drawing could be either line- the upper chine, #2, in the Profile View coupled with a narrowed set of chines #2 in Plan View would result in a much finer entry at the waterline, however- the other set of lines would offer more lift of the bow (pitch) because the V of the bottom would be flatter and wider- so all waterlines (plan view of the water at that level on the boat vertically) would be rounder and not as sharp.

Are there any other errors in this set of draft- working- comparative- lines?

But the image shows that the designer/drafter/builder have to faithfully draw the lines in both views that correlate to one another- we have not constructed the Body Section or Station Plan view of the boat at this point. The point in this image is that both sets of three curves in #1, and #2 are fair to their respective baselines and reference lines! There are in fact countless numbers of fair lines possible, what we've explored in the previous posts is a method to faithfully reproduce those in the plans drawings use techniques that reduce error- not redesign the boat!

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The sheer line is changed in this view from the same boat with a straight (Profile View) sheer.

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Another sheer line, fair and reasonably proportional to the LOA but not the same curves as the previous versions of this Profile View.

Summary of this post; Lines of the Profile and Plan views can be drawn together on one grid/Station set with one view above the other. The curves can be put down using reference baselines offset to the two main long lines of the grid (working/Draft Waterline in Profile & Keel in Plan Views). Also we an use the previous lesson's methods to create a series of offsets along the grid so we can faithfully reproduce the curves as they were drawn by the designer of the original plans. Combining all the layout and drafting techniques shown above we could reproduce a set of lines to a larger scale- including full sized (called lofting) and increase the accuracy of all curves, offsets and hull dimensions.

What was not shown? This was not a design exercise- design was noted but not explored. The information about why any reference or baseline was where is shown is not provided except in brief association to a few example lines that have the visible differences. Sheers are shown changed, chines are varied and some implications are given but the underlying 'why' is only briefly discussed- to show that you might want to make these changes but not how.

WHAT was NOT shown was how the bow conic sections (forefoot and chine combinations) are developed- that is not important if you have plans. That design question is dealt with in other books and perhaps online as well? Our examples were here to draw in changing scales not to design so the bow cone design exercise was totally not mentioned or shown, it would be wise for the potential self-designer-builder to add very significantly to this short outline of drawing techniques before attempting to draw and build this set of curves.

Now we might try a plate model?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 697
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Notes on Metal Boat Building Methods

Postby Kevin Morin » Tue Jan 19, 2016 5:51 pm

So far in our review of redrawing a set of lines, we've looked at the side/Profile and the top/Plan views, but we haven't worked on the section/Body plan view or Station View. That's where we need to do next.

The images are all three from one single step because this is an introduction to this set of views. If you haven't had time to glance at the post below regarding hull lines, in which I tried to sketch sheets of glass as hull intersection planes, where a line on the surface of those three sets of glass pane are the lines we'd see on the plans in flat (stacked up to add lines but of 0/zero thickness)- then this may be confusing?

I've tried to use three different 3D views of the same couple of points in the modeling/drawing process so that I'm reinforcing the concept shown.

Image

This sketch, above, hopes to introduce the fundamentals of finding the information to construct the Body Plan/Station view of the boat's lines. the blue page at the bottom is one we've viewed before, it has a two sets of lines, one below the other of the Plan view below (to the left) of the Profile view (to the right and above the Plan). The Plan is half the lines (port side) where the Profile shows the keel, chine(s) and sheer.

One important item here; a new baseline is added below the Profile view lines, this will be a reference for all the points in the Body Plan ABOVE, this arbitrary line. The dividers are used to show how the information is taken off, a scale ruler will induce error as we've seen. Dividers with sharp pointed tips would be able to 'poke/prick/pin-point' the lines intersections and reduce error as well as their hinge adjusting screw making their measurement firmly locked in while transferring to the Station Card.

The card shown will make more work sense as we move to other stages of hte plate model, so its important to note this could be another piece of paper on a separate grid. I needed to put the dividers and the taken-off together with the 'laid down' information all in one sketch... so I decided to make each station a single stiff backed paper card or rectangle.

This will be the technique to make a plate model- so using it now will not hurt our concept.

ALL elevations above the baseline for all station information will be taken from Profile, above the baseline.
All Offsets from Keel or Half-Breadths will be taken from the Plan View keel (on edge, seen only as a line in Plan).

In this image the Station Card is shown with the vertical Keel Plane (line on end of the keel plane's forward edge) aligned to the Station #3 (stations are numbered from 0 ) so the various offsets/elevations can be shown in one sketch.

Image
The second sketch, above, is really the same information as the first- there are two points being plotted on the Station Card. The Station Card is located aligned to the Keel Plane where the Keel plane is a line in Plan view (from the top) and the Keel plane is a line in Body Plan (from the forward edge). The purpose is to use this second view to correlate the views, and what information comes from what position and related to that same distance/information/date/offset/elevation- in another view.

I tried this skecth with the Station Card directly on the Station #3 Grid line... but that interferred with the images of taking off distances too much.. so I move the Station card aft, to give more room for the dividers' images. Note; this image is not aligned where it will truly associate to the lines/stations/grid- the card of Display of Information is AFT the Station #3 line.

The two points we're looking at in all these views are the Elevation of the keel above baseline in Profile and that keel point's OFFSET= 0 because the point is ON the KEEL plane. Next we're marking the two reference lines on the Body Station Card for the offset of the Inner Chine from the Plan View. There is no elevation information shown with dividers in this set of views BUTTTTT... however the elevation of the inner chine is shown- without dividers, and will be shown again.

Therefore- the line of the Section through the boat at this Station; can be found from the keel point elevation from Profile PLUS that points zero offset therefore located in the vertical Keel Plane line AND... the half breadth of the inner chine (laid out on the baseline in the horizontal) then raised to the Elevation of the Inner chine- shown on the Card but not shown with a divider- yet.

Notice the V angled line from the keel to the inner chine? that is a section through the bottom panel at his location along the Stations.

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Last image in this post, above, shows the Station Card rolled on its side so that the 'UP' orientation is the same as the Profile View lines set. This is just another attempt to orient the new boat lines drafter with the process of taking off the two views' shape information and collecting that information onto a series of Station Cards (which could be a single sheet of paper where all these references were 'stacked') so the fundamentals of creating a builder's plate model can be more fully explore in later posts.

When you try to save those thousands of words by using a picture to illustrate the goal information to be conveyed- designing the images is not always as easy as I'd like! If these images leave your understanding of the graphic relationships between 3D boat lines and the traditional 2D drawing methods' representation of that information? Please take time to post a question. There's little point in posting if I'm confusing readers about this series of operations on the drawing table.

Next we'll get a little more in detail about the Body Plan and move on to a plate model.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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