new member, eager to learn, need some suggestions for step 1, design!

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gomoto
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new member, eager to learn, need some suggestions for step 1, design!

Postby gomoto » Wed Jun 15, 2016 3:45 pm

Hi everyone, said a quick hello in the introduction forum with a bit of background on myself. I am in the planning stages of an aluminum boat build i've been building in my head for quite some time, and am looking for input on what i'm planning, ya's or na's to my ideas so to speak.
I live in southern bc, on shuswap lake, that is where the boat will spend 95% of it's time. It's a large lake, and we get some nasty storms, so here is what i'm looking at:
Oal in the 18 to 19 ft range, i want to build as much performance into the hull as possible. I'm thinking somewhere in the 14 to 18 degree deadrise for a good ride in the chop, not looking for a flat bottom, shallow water boat. Suggestions on this? I also plan on welding uneven channel on over the chine seam to provide a flat/reverse chine for better performance. How wide can i go here, is 5" better than 3"? Is a reverse angle better than flat? Trade offs to performance?
I'm planning on single outboard power, bigger the better within reason, and building an extension, continuing the hull surface back, but not full width, with a step on top full width of transom. Is there an optimum length/ width for this type of mount? As per kevin morin, an angle of 18 to 20 degrees at the mount to optimize trim will be used.
Would a delta pad design be beneficial for this hull, even if shallow water running is of no concern? Would the extra lift help top speed, or would i simply be counteracting the ride of the deeper vee?
Would adding another uneven channel between the chine and keel on each side help performance at all?
I hope i'm not asking too many questions at once here, but like i said, i'd like to add as much performance/efficiency to the hull as possible, i don't mind the extra work, after all, that's why we build them ourselves, right?! Thank you for any input, and i look forward to being a part of this forum and getting to know everyone, cheers! Garry

Kevin Morin
Posts: 638
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Wed Jun 15, 2016 6:06 pm

gomoto, great to hear about a new builder/owner of a welded aluminum boat.
gomoto wrote:Oal in the 18 to 19 ft range,

Before going too much further, is this a sit down helm or a center console stand up helm design boat? The reason to ask is about the LOA (length over all) versus the deadrise angle or V of the bottom? I think the sit down helm is often a full width dash at the forward end of the cockpit in this size range, and the center console has a bit more walk around room? The prior design is often called a run-about while the center console is a little bit more fishing oriented over just burning gas and enjoying the ride in great scenery?

gomoto wrote:i want to build as much performance into the hull as possible


sometimes when we're in the design phase terminology can be misunderstood- does the word "performance" mean top speed? or turning radius or the sea keeping by the bow in head seas? Not trying to be difficult but performance does have synonyms that could mean several attributes to the hull?

gomoto wrote: I'm thinking somewhere in the 14 to 18 degree deadrise for a good ride in the chop, not looking for a flat bottom, shallow water boat. Suggestions on this?


There are two basic planing hull types one is monohedron where the V is constant from bow to stern, the other is 'warped' where the V aft is most often steeper, sharper, deeper forward- so both hull types may take a head sea with low impact. The problem in boat design is that light weight, smaller boats (20' LOA is small) tend to roll a great deal if they have an 18 degree bottom at the transom and that is extremely fatigueing to people in boats under 25-28'. So this matter of design has occupied many designers for many years, and is an important point for your research.

gomoto wrote:I also plan on welding uneven channel on over the chine seam to provide a flat/reverse chine for better performance.


Channel shapes are usually a C or E without the middle appendage and are not commonly added to hulls at the chine- but angles or L's, uneven and otherwise are often added to chines for several purposes. Also, chine flats, or a simple plate that is welded to the bottom's outer most edge (inner chine) is very regularly seen in welded plate boat design and construction.

Chine flats accomplish many benefits to welded plate hulls. First they increase the beam at the waterline so the boat floats in less water. Next they offer a wider planing waterline that provides greater stability when running, turning and they also provide both spray deflection ("drying out the hull") and longitudinal stiffness to the hull.

There are designers who put chine flats on horizontal and those who angle them down, I've not heard of may chine flats that are angled down much more than 5 degs from horizontal, but that doesn't mean they don't exist or there may be benefits to that design. I've generally followed the (US Navy's) David Taylor Model Basin studies done for Riverine Warfare hulls in the 60's where the 5 deg figure was originated - as near as I know?

Width of chine flats is another well discussed point of design. I've added them to hulls from a few inches to nearly a foot wide on a 32'er. Can't say there is a fixed rule of thumb. They sure do work to make a low cost addition to the beam at the waterline.

gomoto wrote:How wide can i go here, is 5" better than 3"? Is a reverse angle better than flat? Trade offs to performance?


Noted above, this is a design discussion still being held, I'm not sure there's a hard and fast agreement about the effects, of different widths and angles of "look down" Surely if the angle got so steep it was drag (?) that would be poor design, where is that point? Can't say... I'd say it was fine to add a 3-5 flat to a 18-20' hull; but my reason would be as much to get a 70" bottom (chine to chine) out of a 60 sheet as to expect any radical performance enhancements. If you draw less water (wider chine dim.) you take less power to get 'up' so that aspect (not all aspects) of 'performance' is enhanced.

gomoto wrote:I'm planning on single outboard power, bigger the better within reason, and building an extension, continuing the hull surface back, but not full width, with a step on top full width of transom. Is there an optimum length/ width for this type of mount?


Well if you've reviewed the 'stern design cycle' post here you'll see there are too many combinations of geometry to discuss effectively. I don't know of any hard and fast percentages of the overall chine beam to suggest for a single engine bottom extension.

gomoto wrote:Would a delta pad design be beneficial for this hull, even if shallow water running is of no concern?


The designers who incorporate Delta pads all say they make a difference? The hulls without this flat are not often close enough in displacement, LOA and bottom deadrise along with engine and loads to run side by side and make any decent comparison so we're not sure on this count?

gomoto wrote:Would adding another uneven channel between the chine and keel on each side help performance at all?


As before many planing hulls of this class, regardless of length, have unequal leg angle extrusions on the bottom as 'spray rails' and many designers have argued that these provide various performance enhancements. I've added unequal legged angles to the bottom of planing skiffs for many years- it won't hurt to put the longs outside the hull with other framing inside.

gomoto wrote:I hope i'm not asking too many questions at once here, but like i said, i'd like to add as much performance/efficiency to the hull as possible


Not too many questions, but using the words performance and efficiency together may not clear? Often you give one to get the other in boats.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

gomoto
Posts: 6
Joined: Wed Jun 15, 2016 2:39 pm

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby gomoto » Wed Jun 15, 2016 7:17 pm

Thank you very much for your reply kevin, i have read many of your posts, and find them very helpful and informative, and done in such a way as to keep ego's out of the conversation, most forums quickly turn into battles and insults, which helps no one learning a thing. I'll see if i can clear up some questions you had.
Performance to me for this boat i guess is a combination of factors, speed is important, but i'm not building a drag boat, so some speed will be compromised for a smooth ride in chop, although i don't want a boat that rocks too much either. That was my thinking with the wider chine extrusions, coupled with a delta pad bottom, there may be a sweet spot there of a fairly steep deadrise, coupled with enough flat hull area, to resist excessive rocking, while still cutting through waves quite well, and enough lift to carry good speed on flat water. Efficiency i would describe as a hull that rides high enough while planing to obtain low fuel consumption for any given speed.
The boat will have a side by side seating arrangement, with full dashboard and windshield, opening in center, with probably a flat floor on the bow 4 to 6 inches below sheer height. This would be a typical runabout, or lake boat. By moving the outboard behind the transom, i would still have a pretty good deck space for fishing.
My build plan is for 3/16" bottom and 1/8" sides.i don't think i need to go heavier than that, as i'm not planning on hitting rocks!
Several years ago a friend and i built six 10 and 12 foot welded aluminum fly fishing punts, which he sold to friends. We used .100" throughout, and i welded them. The first one i tigged, took forever! We rented a mig setup to do the rest. I set very high standards for myself for quality of work, so i will not proceed until i'm happy with each step of construction, so i plan on doing this right! I haven't found a set of plans yet, trying to set in my head the major criteria i want, then find plans that come as close to that as i can. Thank you again for your input!

Kevin Morin
Posts: 638
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Thu Jun 16, 2016 9:26 am

gomoto, I agree- lots of times, what could be simple exchange of opinion or discussion of sequence of design or build can end up without any real communications and I've been involved in my share of those, just because I've built before and offered to TRY to help inform others- online. Some sites are taken over by a few who don't know, or haven't built themselves but are less than welcoming to those who have- so those sites aren't frequented by many experienced designers or builders as a result of the tone of their threads.

Glen-L's forum is a very decorous and a positive site where learning is welcomed by posters and readers alike.

gomoto wrote:Performance to me for this boat i guess is a combination of factors, speed is important, but I'm not building a drag boat, so some speed will be compromised for a smooth ride in chop, although i don't want a boat that rocks too much either.


Actually, I don't see (top) speed and deep V's are a trade-off really? The sharper/higher deadrise angle/more V'd a bottom; the faster you can go. In my experience the human body is the sole limitation on speed in boats- (horsepower being unlimited) because it's our ability to take impact that limits top speed; rarely is a welded metal hull going to have impact problems - but our carcasses do! I said that to say - speed into a chop and top end speed are not exclusive of one another- but roll or rocking on the at-rest waterline comes from that very steep bottom.

The open ocean 27deg or greater deadrise, bikini freighters of boat racing fame roll so much at rest they're regularly driven in flat calm waters at low speeds. So your idea of adding chine flats, or, as I mentioned many designers warp the bottom from the stern to the bow- work to reduce roll, while leaving a sharp entry for smooth running into a chop.

gomoto wrote: That was my thinking with the wider chine extrusions, coupled with a delta pad bottom, there may be a sweet spot there of a fairly steep deadrise, coupled with enough flat hull area, to resist excessive rocking, while still cutting through waves quite well, and enough lift to carry good speed on flat water.


That description of a hull design purpose is just what hundreds of designers have worked to provide for many years! And the design features you've mentioned are all looking for that 'sweet spot' of a proportional combination of these design elements to result in a good all around performing boat- so you know you're on the right path- its well traveled.

gomoto wrote:Efficiency i would describe as a hull that rides high enough while planing to obtain low fuel consumption for any given speed.


This again agrees with most run-about designers' goals and they do add chines, some turn them down aft, and Delta Pads and those flats at the keel are in different proportions so now it becomes a matter of combining these elements in some proportion into a design. I'd suggest (if you're drawing for yourself) that you consider investing in some study plans to see what other designs 'say' or used? This gives you some references and proportions as a basis for your own decisions?

Image

This skiff above, one of mine from the 1980's, has a nearly flat bottom aft. However, you can see that by running the chines all the way to the sheer, the bow is very sharp angle of entry. Her job was to float rivers and plane in shallow water but then to go out in saltwater and run well into a 2-3 sea. She was a bit lightly built to do this well in the salt, but when she finally got enough power to push her with a good load the shape did run well in both conditions. (She is 18' LOA and didn't have seats or hand rails when this test run was made.)

She's shown as an example (perhaps extreme case?) of warping the bottom to preform in two conditions- the bow is sharpened to take a sea head on with minimal impact and the stern is only cambered 4" in 60" to provide a nice flat planing surface. She would plane five adults with a 50 hp 2stroke, but when she ended up with a 70hp four stroke she lifted half dozen people and gear, and ran well even in 4' head sea- but at that height of waves she could not hold speed due to launching off waves. She was very stable at rest due to her almost flat after sections.

I built this boat in a 22' LOA and 72" chines that was used to fish 6 people in 15 miles offshore regularly, but her sides were taller by a foot. The warped hull can provide a runabout performance with more stability at rest, by using a combination of chine flats and deadrise changes.

{ FULL DISCLOSURE: I'm not selling designs, boat plans or offering any of my past work for sale. This image, and all others I post, are for visual comparisons and to contribute to the discussion by the Forum readers only. }

The rest of your boat's design goals sound very much in keeping with other successful designs out there. I'd say looking at the Glen-L catalog's Chinook is a good place to begin, not that you'd finish her foredeck in a cuddy or an open console, but she has a good smooth entry and planes well with reasonable power. I've been able to see two of these hulls built in my area both modified from the stock plans by the builders, and both resulted in very nicely running hulls- discussing salt water performance.

The hull is about 10deg or so at the stern if I recall, but sharper forward and both run into head seas easily. The hull doesn't have a delta pad, but they both get up on a plane in a few boat lengths with light loads and still get up with heavier fuel and larger crews. This hull doesn't have a chine flat that I recall but, depending on your building skills one could be added.

There are few other metal boats in the catalog that would make a good reference or basis hull design as well. The Specmar (NC Cut File part of the catalog here) boats do have deeper V's typically and are designed for a little more high end using deeper and heavier hull scantlings to sustain the higher performing hulls.

Glad you have both MIG and TIG aluminum welding experience, that sure can be a tall obstacle to a new builder. I've tried to help in that category before and had both great success and utter failure- that is trying to help someone learn to weld by correspondence! If you've welded 0.100" (probably 5052?) with MIG then you're already aware of the bead types, some idea about sequence of welding and adjusting the weld to the metal- all important lessons for the new builder/welder in aluminum.

If you're drawing the hull yourself (?) the lower tier cost marine hull software is New Wave/ProSurf (Steven Hollister?) and Delftship Pro (Martin von Engeland; Holland). Rhino Marine is a bit more and the other suites of programs get into serious money. My experience is that the look and feel of the software's interface will be the biggest effect on your work with that software. So, if you're interviewing software? I wouldn't recommend getting familiar with them all (time!); first, I'd pick a price range after researching, then I'd see if there were free or sample (time limited) copies and then I'd spend some time and try to gauge which seems most intuitive to you? That has shown, in the past, to be the most important predictor of the time it will take to learn and use.

Of course being a plate boat you an draw her by hand, as we all did for so many years! The only hard part of that is to find the bow cone apex, which the software solves by working out surface tensions in color graphics allowing a designer to see if the plates/sheets can be 'developed' from flat material. That step can be time consuming by hand- I usually made a builder's plate model rather than to fiddle on the drawing board to find that out.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

gomoto
Posts: 6
Joined: Wed Jun 15, 2016 2:39 pm

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby gomoto » Thu Jun 16, 2016 11:22 am

Thank you kevin, again, your explanations are spot on and easy to understand. I'm happy my ideas seem to follow the general design of what makes a good hull. The idea of a warped hull makes sense, and provides just what i'm looking for in regards to handling. This boat would also make the odd trip to bc's coast for some salmon fishing, so being able to feel secure in our somewhat protected coastal waters is important.
I like the looks of the skiff you built, with a windshield and side by side seating, that's pretty much what i'm picturing mine to be. I think i will be buying plans, and any mods i will make off those. My skills with tools in my hands are much better than computer skills, so i don't think i'll attempt designing from scratch! I read your post on building the model to take off panel sizes, was very interesting, and will be re-reading that one again. I've also read many of your posts on welding, and have learned a lot. Your cold wire feed tig gun looks like something you could use to hunt aliens, as well as weld a boat!
If i decide to go with a delta pad (i will research as much as i can regarding proportions and advantages), would you suggest welding a longitudinal (1/4" by 2" bar for example) on top of the seams, following the diagonal? I would also like to extend these pieces (bottom sheeting and longs) into the outboard extension, so the extension is an integral part of the hull, not just welded onto the transom, i think this would add strength to the hull. Any thoughts on this?
As for cross frames (that the longs get notched into), could i keep those short, say deck height, from transom to dashboard? I would build a full bulk head for the dash area, but would prefer to keep the area under the gunwhales clear for fishing rod storage if possible. I had an idea that i could get a piece of sheet press braked, to use as the top and inside gunwhale surfaces, from transom to dash, with cut outs to be able to store rods inside, saving me welding an extra seam on top, inside surface, while providing a clean look and strength of a 90 degree bend ( i hope i've explained that clearly enough!) I think the cockpit sides would be straight from transom to dash, to allow me to do this. Do you see any issues with this plan?
I am also hoping the deck (floor?) could be high enough to be self draining, but not sure if that's possible in a 19' boat, will have to study some plans!
It seems by studying many other builds on here that bar stock for longs is used most often, is there any advantage to using boxed type material,.especially in the aft section of the hull? Bar stock would seem much easier to build with, and if adequate, that's probably the way i would go.
I'm happy to have confirmation that most of my design ideas for the hull agree with what is generally accepted as good design. I like to have a clear vision in my head about what direction i want to go, and your advice is helping me a great deal with narrowing that down, thanks again for your time kevin, and i hope this discussion will help others with this stage of their builds, cheers! Garry

Kevin Morin
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Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Sun Jun 19, 2016 3:52 pm

gomoto, I'll try to reply to some of the last post, but don't hesitate to repost the questions if I'm not 'getting it'. Things have gotten busy here, so my replies have suffered for timeliness and content.

You are most welcome for any comments I've returned that can help your learning and thought process in planning your welded aluminum boat.

#1 Warped vs Monohedron or fixed deadrise: speed kills. The main difference in application of the two hull groups is entry (read slam or impact) at high speeds. To explore this as briefly as possible the faster a boat goes the farther aft the running waterlines show up in Plan View. So a 80mph bikini freighter in the open ocean is running on a 2' fore and aft "wing" the width of the chines at the stern of the hull. This looks like a jet plane in Plan View. (think F-104; F-115 Eagle looking down) When the bow is up at these speeds, the boat can become airborne in less than one second.

What goes up must come down. When the boat comes down the speed of the object determines the hardness of the water. (read that again if its not intuitively obvious?) So a supersonic bullet hits water and disintegrates but a boat just bounces off 'concrete'.

The Super V (greater than 25deg deadrise up to 30deg) comes down and the narrowest part of the hull (keel) touches first and the rate of 'widening' of the hull is the deadrise angle. So a Jon boat (flat or 0Deg deadrise) adds 100% of all displacement as soon as it touches after the jump but... (thankfully) the deep V enters the 'hard' (high Reynold's Number) water over more fractions of a second soooo....

When going very fast, the reentry of the deeper V is 'softer' than the less V's bottom.

Enter the runabout. The warped bottom hull is NEVER (not some, not a little, not Ever) supposed to be kept a speeds that launch off a wave. They will do this if there is adequate horse power and an ill educated helmsman, however their purpose is not to maintain high speeds while pitching about the bow- their purpose is to adapt to the sea state conditions - the helmsman is expected to moderate speed when the bow pitches up so high that the hull will launch. Coming down on the water with a warped hull is closer to a jon boat than a deep V.

When does all this happen? as speeds above 25mph in waves or chop that allows the two hull types to pitch up by the bow, and use a swell or wind chop as a ramp; as general rule.

What are good transom angles for the transom of a runabout? 8 to 14 deg are the most common range of the warped bottom deadrise angles. Those same bow angles may range from twice to three times that range all depending on #1 the amount of rise of the Chine in Profile View, & #2 the beam of the inner chine aft as it rises and closes the stem (Plan View) compared with the Profile View depth of keel line.

Once you spend time with the lines of planing hulls, these two statements will make more sense- at the first reading it may sound kind of 'inside baseball' or marine design- but I stated them so you'll have some rules of thumb to begin considering that group of hulls which may be most suitable for your overall hull concept.

Gomoto, don't discount plywood designs in the search for a good design for your application. Any flat sheet material design can be converted to sheet metal/plate materials. I'm not saying the conversion is automatic or one equals the other- just noting that if you can cut plywood to built a boat hull that same hull can be made of sheet metal.

Kind of narrow focus on the topic of deadrise, classes and hull use by speed in this post.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Joined: Thu Jan 24, 2008 11:36 am
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Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Mon Jun 20, 2016 9:34 am

gomoto, back to some of your questions/remarks/ideas above.

In regard the idea of chine flats versus no flats in metal boats. Chine flats allow a hull transition from running to at rest that is widely considered a gain to the hull - enough gain to include flats in most planing hull's designs- but surely not all designers agree with their gains or value of the efforts to include them.

When the boat is at rest- let's use two side by side jon boats, with identical LOA's, to make it simple- the chine beam and the overall displacement are what governs the depth of the keel at rest. The total wt/displacement of the boat, expressed over the area (volume) of the waterplane determines how deep she sits at rest.

That means if one jon boat is 4' wide at the chine and the other 5' wide - both being the same length and all up weight- the wider boat will sit in less water. The narrower hull will take another inch or two of depth to displace the same amount of water (wt of water displaced is force of buoyancy upward). Now back to chine flats on V bottom planing hulls.


With the hull at rest, a 5' wide 10 deg V bottom hull will draw -let's say 8". But if that same hull has two 6" chine flats- the bottom is now a combination of the V in the middle (60" wide) but the chines have an added foot of beam (6' beam at waterline)- therefore at rest this hull, with the same V (deadrise angle) bottom plates will now sit higher in the water at rest.

One easy to see change is the wider bottom will have less distance to go 'upward' to be on plane, so less horsepower will 'get it out of the hole'. Next the wider hull will actually carry more ultimate load (for any inch the load pushes the boat down in the water- more water is displaced by the wider hull) and last when the boat enters a wave, regardless of attitude or heading, the wider hull offers more lift/pitch/buoyancy than the comparable narrower hull.

Now, the down side of chine flats with respect to these few points. Speed kills. If your boat will go faster than 30mph- and certainly faster than 40 mph- wide chines become a potential problem as they change the waterplane size very rapidly. At higher speeds chines should be smaller, say only an inch or two wide at the most. The reason is the effect of wetted area on drag. If a boat is traveling between 16 and 25 mph and you put a bucket in the water over the side (not recommended just an example) the boat will turn to the side of the drag- perhaps roll or snap the line?

A wide chine flat (greater than 4" wide) on a high speed hull in balance- running in good trim at high (>30mph) may become a 'bucket over the side' if the water surface were to be deeper (wave face, wind ripples, small roll of the hull) on one side wetting the entire chine's length from the leading edge of the running waterline forward. This would result in a slewing actions pulling the helm to the side and turning the hull while heeling into the turn. Not good.

So chine flats can be too wide for any given hull's designed speed, but if they're used on warped hulls of moderate speed they can make a major contribution to the at rest waterline and all up displacement.

I hope this is making sense- mostly must remarks on proportions so when you look at different designs you're more able to 'see' some of the factors that influenced the designers' decisions?

Cheers,
Kevin Morin
Kevin Morin

gomoto
Posts: 6
Joined: Wed Jun 15, 2016 2:39 pm

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby gomoto » Mon Jun 20, 2016 1:22 pm

Thanks Kevin, that all makes sense and gives me lots to think about. I'm back in camp working for a while again in northern alberta, so won't have a lot of time on here either,.internet is hit and miss! Lots of time to think though, so i will be putting your info to use!

Kevin Morin
Posts: 638
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Mon Jun 20, 2016 1:36 pm

gomoto,
hull longitudinals should be looked at first as making smaller unsupported areas of hull plate/sheet/sheathing. So a 4x20 clear sheet may flex and bend if the edges aren't trapped to some frame. Lets call those two edges the keel and the chine with a topsides to hold at the chine and another bottom piece or even VKB (vertical keel bar) to trap the other edge.

Now, even with some shape support- warped or twisted, the sheet could flex or bend under enough load- like running in the water at 25mph! The longs reduce the size of panels that unsupported (where that is needed). Once they're welded to the hull plate they become effectively "angles" since their one edge is held to the hull plate/skin/sheet. Their job is to increase the amount of force it takes to bend the hull inward.

Bending metal is easier to do the thinner the cross section. So a 1/4" x 2" flat bar will bend with less force across the 2" face- bending just 1/4" of metal instead of the 'hard way' or trying to hold the bar on the tall edge and bend the 2" direction. The same is true for a 3/16" x 3" bar and so forth as the cross section increases. But the 3" bar is deeper (wider?) than the 2" bar so it will take more force to bend the first over the last.

Hull longs are being loaded (bending direction) over their widest dimension (on edge) so once they're welded to the hull plate- the depth of the bar/longitudinals increases the resistance of the hull plate/panel/sheeting to bending inward by the addition of a bar. Not 100% of the bar's strength is added to the entire surface of the hull panel... but with a series of longs inside the hull its surface becomes many times stiffer to bending inward (or outward).

Flat Bars will bend on edge and there are rolling machines designed to do that exact job- roll the 'hard way' and make various radius rings that are like a flat circle cut of plate. Using deeper (wider bar) stock for after longs where there is little curvature to the hull works well, but as you go forward in most planing hull shapes the same flat bar material creates a builder's headache unless you have a ring rolls and someone skilled enough to operate it. (practice with this and all forming equipment amounts to a full time trade).

Planning hull longitudinals in a planing boat could be said to be simple in the after 2/3's and more complicated in the forward 1/3. Longs are not always run on hull diagonals, and some designers call for the longs to be aligned with the buttock lines so their bends in the forward 1/3 of the hull are more manageable compared to forming a flat bar along a diagonal.

In the forward sections of a planing hull- the chines turn in and upward, and the keel rises and the boat 'gets sharp'. So longs may have to be cut to fit out of plate, if they're not rolled of bar? This is a more complicated layout and shaping job than some others depending on the level of your plans package and its extent of lofting? For example an NC cut file package will have these cut for you, but a lines drawing plan that expects you to loft the diagonals yourself- will not. I'm not sure which level of patterns or lofting you'd see in any given plans set. Glen-L's plans often include full size patterns but I'm not sure what extent these forward diagonal curves are provided for any given plans package?

Transverse framing is usually used to hold and support the longitudinal elements for building purposes and end up adding some support to make the span of any long- shorter and therefore a greater stiffness to the hull panels between transverse frames. Transverse frames do not HAVE TO, touch the hull plate but they very often do and are welded as part of the overall weld out scheme.

Angle extrusions, T shapes, and specially shaped channels are all used to help stiffen hull panels as longs in different designs. I usually try to run the longs outside the hull, and bulkheads/transverse inside so the two don't have to intersect- but its not always possible. Outside angles on the bottom work as 'mini-keels' and wear plates as well as (stiffening) longs. Inside, these same angles are harder to install, have to intersect through any xverse elements so I find it easier to put them outside. They do more work and all their structural work in that location.

Spray rails, outside the hull on the topsides can help deflect spray, bump against docks, and they also stiffen the hull longitudinally like interior framing does. Exterior longs can be welded full length or left stitched, I prefer to leave them stitched unless I'm using their closed volume for keel coolers but other builders I know insist they be welded fully.

Just more notes on some various methods of combining materials into your boat's framing plans.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Wed Jun 22, 2016 11:34 am

gomoto,
On the topic of self bailing decks in small welded boats. Pluses and minuses exist in all cases of small boats, and some designers have stated that boat design is a series of compromises - "give and get" ending in a small boat. The smaller the boat the bigger the impact of some design features- for example a 12' long welded boat with a 27 deg deadrise would probably not weigh (displace) enough to sit on its keel without significant ballast! The all up displacement would be so little that this size boat would lay on her side- keel to chine acting as 'chines' in a conventional hull.

So too, decks in small boats have various considerations that need attention. First, if the boat is narrow chine, deeper V the deck could be lower (in relation to the chines) than a flatter bottom boat, with less V; because the volume of the V is greater than the flatter bottom boat's (for the same chine BOA beam overall). However, if the boat is significantly wider, say it has two 6" chine flats so the BOA of the chines is 12" wider then; a below decks volume and lower waterline on the hull- means you could have a deck low in the hulls that was still self bailing.

Some people view the below decks volume as a catastrophic safety flotation and it can contribute to that but being located so low in the hull if the boat is swamped in a seaway it will roll keel up if that is the only flotation in the entire swamped hull? However, if the flotation under the decks is covered with a few inches of water or even a foot, it can self bail and raise the hull up to the surface again- but not if she's filled to the gunwales.- that's when the flotation under the deck tends to roll her.

Now a self bailing deck is merely deck above the the loaded waterline, with sufficient freeing ports to allow the water to leave the deck as contained by the hull's topsides. This is where things get tricky or at least need to be discussed VERY clearly before decisions are made about the deck and scuppers/freeing ports. The design of any boat will result in a hull wt. (areas of materials times their wt per area) so you can find an estimated waterline and that can give the underwater volume (62lb/ft^3 for water as buoyancy) and that should give a rough waterline confirmation. Incidentally it doesn't matter if the waterline you choose is off, the volume below the waterline can be adjusted up and down to meet your all up displacement.

Now comes the design decision- how much above the Load Waterline will you plan the deck line? And then the second issue is the design and construction of the scuppers/freeing ports- to get rid of water off the deck. If the deck is only an 1" above the load waterline you'll need some form of check valve in the scuppers/freeing ports- if the deck is 4" to 6" above the load waterline- the sides will get 'too short' and you'll be sitting and walking higher up in the hull than is good for stability.

So those are the bushes that you need to beat around several times to make a sealed deck/self bailing deck design in a small craft. I realize that you're busy so I'm not waiting for replies, just trying to deal with all the questions in a single post so you've got references as your i'net time allows.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 638
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Sun Jun 26, 2016 10:22 am

gomoto, just another note about framing.

gomoto wrote:As for cross frames (that the longs get notched into), could i keep those short, say deck height, from transom to dashboard?


You can use whatever style and size frames you wanted- they do not need to run above the deck- IF there is sufficient "side deck"/ "guard deck" /sheer clamp to resist side to side flex/distortion/bending. So a boat with a small 2" extrusion at the topsides won't have the resistance to deforming (without vertical transverse ribs running to the gunwale top) as say the same design with an 8" wide plate up there- legs or gussets supporting underneath and some extrusions on the inside and outside of that same plate.

The wider plate at the sheer will act as a beam section to resist movement toward the keel plane and back- the same job that taller transverse frames do for a sheer with no plate on top- or less width to that plate.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

gomoto
Posts: 6
Joined: Wed Jun 15, 2016 2:39 pm

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby gomoto » Tue Jun 28, 2016 4:50 am

Thanks Kevin, once again, your wealth of knowledge on the subject is amazing, i hope you seriously consider writing a book on boat design and construction, maybe a retirement project for yourself? You have a knack for explaining things very clearly, i would buy your book!
I looked at the plans you suggested, the chinook i believe, and i like that one, i even like it with the cuddy! I assumed a boat that small wouldn't work with a walk around cuddy like that, but is something to consider! Just one more decision i guess! You have given me plenty to think about just in the design stages, and i will spend some time trying to narrow things down and make some choices, thank you again, looking forward to your book!

Kevin Morin
Posts: 638
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: new member, eager to learn, need some suggestions for step 1, design!

Postby Kevin Morin » Tue Jun 28, 2016 10:21 am

gomoto, thanks for the vote of confidence in the book idea but.... I'm not sure that's really on the bucket list? Instead, I've decided to leave a series of articles and illustrations of various topics related to small welded aluminum boats, and a goodly number of them are here because of the home building focus of the site and Glen-L Catalog of designs.

The subject is covered by several good authors but each has found it only possible to provide a guide, and overview of the subject instead of trying to do a full 'how to' version on building. So by remarking in online conversations as they happen, and as they apply to different live examples of decisions to be made in existing builds (or design planning) then I think I'd make a larger educational contribution than a step by step book.

The effort to write and publish, for little or no return, is out of proportion to the gain for the author. Of all boats built, few are welded aluminum by their owners' hands. So, I think its more use to me and the potential builder to just post on sites where the subject comes up, and see if I could help those new builders to avoid some of my countless mistakes over trying to author a tomb to do that job?

Please let me know if there are specific questions (remaining or new ) that I might try to answer and others here could find enjoyable to read as well?

As to the Chinook, I'm not sure that the cuddy version is walk around? Perhaps I misunderstood your remarks but I'm almost sure the cuddy would reach the sheer, even if there were a narrow walking deck alongside the trunk to allow you access to the bow cleat area (foredeck). When I use the term walk around I typically expect to see a deck level passage on both sides of a larger center located cabin- a weather helm/dog house/pilot house that does not reach the two topsides' sheer, but instead is free standing and you can walk around that structure or design element. If a cuddy cabin has two side decks (sheer clamps/guard decks) 6-8" wide to all footing to reach the foredeck, I wouldn't use the term walk around because of the deck level change in that design. Just trying to clear up the terms used in our discussions.

I've seen the Chinook built with a free standing house (weather helm/dog house/pilot house) and seen one with a full forward cabin, bunks, head and all; but the latter was stretched 3' to to 23' LOA about) to get the deck space 'back' from the enlarged forward cabin. Both boats run well in salt water here in the Cook Inlet.

Also for your consideration in the Glen-L book are the snake shooters, I believe there are a couple of sizes (16-20' ??) and a couple of different bottom deadrise angles (up to 12deg.?) as measured at the transom. The reason to mention these hulls is their intended use is shallow running and decent to high speeds, and at least one of them has a step through windscreen design so they're already offered in the classic run-about configuration.

If I did a book it seems it would be best done by using a current build as the subject of photos, videos, and set ups to show the various considerations to be made in the build. The design part of such a project is an entire discussion of its own- IMO- and involves even fewer potential readers so planning such an adventure is and extensive exercise in itself.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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