Aluminum Boat Cabins

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Kevin Morin
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Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 1:32 pm

Thread Goals:

This thread is a companion to the Marine Tanks and Work Methods threads close by on the Metal subdivision of the Boatbuilding Materials section of the Forum and there a plenty of details that will rely on posts in the other threads. This information appears elsewhere on the web but is posted to help round out some of the other topics being explored so that Glen-L's Forum has more complete builders' reference to go with the many plans packages offered.

As preface in (other) metal working threads I've observed that it seems a lack of tutorial level material for the owner builder may keep potential metal boat builders away from aluminum versions of their boat project. However, there are more than enough cost related factors- very expensive welding equipment, very extensive welding practice period to become proficient to perform all welds in a fully welded aluminum boat, and extremely expensive materials- all of which contribute to boat builders planning to work in other materials.

What I'd like to accomplish by posting these various threads here at Glen-L's Building Forum is to reduce the lack of information available to metal boat builders and educate those who are interested in the details of what needs to be accomplished so the potential builder is able to make an informed decision about the material of their boat project.

This thread does not offer plans; it explores designs and methods to build the shapes in the design concepts shown. However, there are cabin designs in the Glen-L catalog that could be used with these work methods to build a boat cabin. I will not be using any of the specific cabin plans from the catalog as examples because I did these drawings years ago for a couple of friends who were at the stage of adding cabins to their own boats.

If any Glen-L reader (mod/admin.) finds that I've already posted this here??? Please let me link to that post and I'll bump it up and use any original (if it exists) and not re-post all this info.

As always, I encourage any boat builder to acquire the habit of drawing before building, that includes lofting or full size drawing, model making and otherwise planning all the steps be taken before you even pick up a power tool.

Background on Design:

I've discussed with a lot of owner/builders what "to do" about cabins, pilot houses, dog houses, weather helms, all terms used to describe small cabins on small boats. Few more difficult design projects exist in my experience drawing small boats than to make a stand alone or walk around cabin look well integrated to the boat. Building these cabins can be difficult if the builder doesn't think ahead to joints, structural elements and overall design. So this thread has a strong design and preplanning focus; however using existing plans works great because there are no dimensions (sets of drawings or dimensions for building) provided here.

Most of my cabins have ended up looking like something off a corn combine, functional and industrial not very 'boat like' or nautical. I'd like that to have been different but unfortunately for my building career it was not. That doesn't mean you can't draw something more imaginative or with more attractive proportions for your own boat, its just the sad truth of most of my work. I'd prefer not to refer to my own designs as 'agricultural' but I do admit that I've not been able to draw a really nice cabin to go with a few sheer-lines that still remain attractive in my eyes, years after they're built.

I have yet to see a stand-up house or weather helm that looks genuinely appealing to my eye, but as with all things; "beauty is in the eye of the beholder" - we all like different lines and proportions, some find one look or design appealing and his next door neighbor doesn't care for it at all.

So this thread won't be able to help you with the best looking designs, and it won't explore very deeply all the preliminary sketches that will make your cabin project look the best. It has to be the readers' understanding that since the cabin has to suit you..... you have to draw or copy the image of the cabin you want. I'm going to explore how anyone with welding skills and some aluminum working experience can design and build a stand alone/walk around cabin for a boat.

You may build your cabin without welding skills or equipment- by using various techniques and hiring the welding done for you. We will try to explore those details as the examples are presented.

Glen-L Catalog Cabin Designs:

The catalog section (here) has several cabins plans packages, I suggest you look at them and find the general direction you're interested in among those designs. Also, you may find a picture of a cabin on a boat that you like, great! use that as your planned model and begin drawing there. The Glen-L cabins won't use or show the methods we'll explore here. But, you can use those dimensions, and redraw those plans using the ideas we'll explore in this thread and that includes modifications. What you would gain by using those designs are #1 proportions- design proportions are partly mechanical and partly artist. #2 ergo-metric dimensions- human spaces use dimensions that need to be observed- if the cabin is too short to stand under- well- you'd have to sit not stand! #3 proportionality to the boats' LOA again a combination of art and experience that could well guide a new cabin builder.

Next point, as introduction, is based on the old saying that 'there's more than one way to skin a cat' -not that I've actually met anyone that has skinned a cat; this method could be changed in countless ways to improve it for your use. My intent is not to try to claim the last word in this area of many boats- instead; I'm giving a basic "how too" .... so you have something to rely on if you're
going to work on your boat to build a closed in helm.

Last, in way of introduction, most of the time I use illustration sketches to help my limp writing as I describe the ideas being presented. In these images I try to color different parts different colors so the parts are not all shades of gray. Being aluminum colored makes it hard to 'see' what pieces are fitted/formed/fabricated together; if you realize I'm not making a paint scheme suggestion in the sketches I think it helps to get the ideas across if the parts are different colors as well as different shapes?

This thread is intended to give a proposed method to make welded aluminum pilot house for those who are at that stage of their build or modifications. I hope that you're able to get a foundation for your project and as you draw and explore you're able to expand these ideas to adapt them for your own uses.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 1:48 pm

To begin I'd offer opinions on some basics based on my experiences as references for your planning. I think its best to start with a 'box' that you cabin will fit into? The box has beam/width, the cabin top or height and the length dimensions that you can draw to scale of use CAD to make a box that will contain your design.

The size of the boat is going to have the most influence on the cabin, especially the beam. If the chines are 5' wide, 6' or 7'- then I'd say that the deck edge will be just a bit wider than that dimension; so the width of the house is this deck width, minus twice the walk around space?

How much space is needed to walk around the cabin? If you're a heavy displacement, old, broke down welder like me, at least 12" of deck space is probably the minimum and 18" would be nice but that would mean the cabin were only 22"-28" full width on a 5' chine hull.

Going around the width dimension a few times, maybe chalking the shop floor or putting some chairs next to the desk and walking between them is worth the time. The wider the chines/deck the wider the cabin can be while still allowing walking space between the topsides or guard deck and the cabin sides.

Next is the height of the cabin top, I built a skiff with a brother-in-law who is short like me and every tall friend who's gone on that boat has cussed us for out lack of consideration. On the other hand, its very comfortable for everyone in the family so you'll need to make plans for this second critical dimension with an eye to the crew too!

A reminder that most of the skiffs with stand up helms have a very disproportionate 'outhouse' looking appearance helm due to the sides heights compared to the top of the helm structure. This is one of the main challenges in my view of trying to make a skiff look good with a helm. (Some of the most attractive solutions are to provide a 'sit down' helm where the sheer and the cabin top lines are more closely aligned, vertically, and therefore they look better.)

Last but not least, is the fore and aft distance or length of the cabin structure. This can be as short as just 'wings' or spray shields along side the helm or console and it could be long enough for an entire group of 6 to stand and sit in the cabin. Again this is a design decision for the owner builder to make based on the used of the boat and its weather helm structure. So we could say that the minimum was as T-top & windscreen and the max is (say) a 12' long full cabin for a the entire crew to sit for coffee while underway?

Image

Here is a stand up helm that I did for a skiff a few years past. The skipper wanted 6'2" in the centerline of the cambered top, a 14" deck space on both sides, and a four person cabin. Two seated at the helm or dash, and two standing or sitting behind them max occupancy. The cabin needed a sliding lockable door/hatch/passageway and if possible it shouldn't look like it was built for agricultural purposes.

Image

How did it work out? Well it sure is tall, even with all the work (4x the "needed" labor) the curves didn't soften the lines that much. The cabin is a hard design job in my opinion and even with the cut and curved, then welded lines in this cabin making a stand up helm fit the boat and look good is a challenge.

You'll probably see the brow is curved to try to make that flat line more like the sheer? There's a break in the cabin sides that were originally going to be use for a hand rail mount but that was later deleted. The break was more than a few hours of work to cut and fit just to get a line on the cabin that was curved like the sheer.

Image

The cabin shown here is now combined with the final skiff; (trailer is pitched down the driveway ramp to the shop door) it sure looks tall and all my design and building of horizontal/fore & aft curved lines hasn't fooled my eye very much! In the end it was the best I could do at the time and I did spend much more time than I should have building this complex form- in my attempt to make the cabin look more integrated to the rest of the hull lines.

Above we've talked about the 'box' or rough dimensions of beam, height and length, once those are drawn; planning can continue.

Image

This stand up helm only had three sides and is owner designed and built in a Glen-L/K.Hankinson Chinook design. These cabin surfaces are more simplified, the shapes are all much smaller due to the size of the boat. Regardless of your boat size and design complexity, I hope to give some ideas about how to plan, then build, your own cabin structure as we move along here.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 2:08 pm

The terms dog house, weather helm, pilot house, stand up cabin, and others are used referring to a group of shapes, not all identical but like the word 'dory', in boating language, different people use the term for different boats in different locations. I'm going to use cabin now, to simplify the wording and below I'd like to introduce other terms.

These terms are NOT 'right', they're not the only word for the part of piece I'm describing they're just a set of terms I'll use as I write. Lots of times reading online, I can clearly see various posters using terms that each considers to mean something the other person doesn't seem to 'get'. So if you have different words to describe these pieces of design ideas, please don't hesitate to add to the wording here?

The Deck of a boat is a surface exposed to the elements (not always uncovered) but that surface becomes a Sole when you put in in a cabin! But in welded skiffs, many times the cabins we're discussing are welded directly to the deck -does that mean the deck became a sole inside the cabin? and if the cabin is only three sided -what then?

I hope this helps readers to see that my attempt to define terms will hopefully reduce confusion in the thread? A good nautical terms list might be helpful if the labels for parts are not clearly understood, but aluminum boat 'parts' do get called by their other materials boats' forerunners.

Image

(in my terminology not the dictionary's) The top surface of the cabin is the top, the ball cap like visor at above the windows at the forward end is a brow- but does get called a visor. Glass windows are mounted to the windscreen even if the sides and after bulkhead may screen wind their orientation to the bow changes their names. So the term "forward panel or side panel" may be used to discuss the windscreen (glass) framing materials because we're talking in terms of welded aluminum building. I ofter refer to the entire layer of panels on edge above the lower panels as the window band, and the windscreen is the glass in the forward panel in that horizontal organization of the cabin.

The vertical structural members in the windscreen structure are Struts and the cabin corners at the height of the windscreen level may be called struts too? In the model above, the bend on the edges of some thin plate, forward and side panels, are fit together and welded forming a welded angle strut at the corners of this simple cabin.

In the following illustrations I've used a series of 'pizza pans' as building blocks. The reason to use this method is to create a light wt. shape that is strong compared to its wt. and to reduce as much as possible for the newer builder, welding distortion from internal framing element needed to stiffen the thinner materials of most cabins of this type.

A note about welding frames to thin materials: I use the term thin for 1/8" (0.125", 3mm) and thinner metal. I call material thicker than 1/4" (0.25", 6mm) plate and sometimes I'll use plate/sheet for these terms instead to mean a wider range of materials. I'm not sure where these terms of use are really defined as I've read lots of articles with different terms. I'm suggesting that most smaller cabin structures are adequately built of 1/8" sheet.

Welding edges is somewhat different in terms of distortion than welding 'in the field'. Edges are more often solid welds, or continuous welds, while framing inside a cabin is usually 'stitched' or intermittent welded in a pattern that holds the frame to the skin of the cabin but is not continuous.

Small short welds in proportion to the thickness of the 1/8" house lower topsides or window band panels- to attach framing to these panels is often put in too wide, or, too big in cross section and not proportional to the thickness of the materials. This usually results in a large bulge on the outside call 'print through' and also contracts the entire panel surface causing wrinkles or waves.

Therefore, one of the best reasons to (design &) build of bent 'pizza pans' is to allow the press brake to put strain hardened edges on the cabin's building blocks so there is little or no interior framing required to be welded in the middle of the various panels or.... 'in the field' of those panels.

Image

Here is a smaller three sided cabin where no framing is needed except one horizontal bar (brown) that ties the lower panels' top edges to one another and provides a base for the upper panels to sit upon.

The 'dodger' or forward lower bulkhead is a conic or cylindrical section. This can be cold formed with minimal effort using a few wood braces and some tack strips and is easily built - but could be rolled by a shop with a pyramid rolls as well. Just another design element that can stress the panels of thin metal cabin, reducing framing, and therefore reducing welding but at the same time adding some pleasant geometry to the cabin's overall look.

Each panel's edges are (would be) welded to the adjoining panels' with vertical down butt fillets or a horizontal T-fillet; as a result no required side wall framing elements beyond the edges of the pans have to be added. Also true in the window band design where window cutouts can be done before or after the tack and weld of this model of cabin- the bends along the panels edges serve more than one purpose and are worth consideration in the design. The edges of the glass cutouts are "protected" from the welds' distortions by the pans' edges being press braked and hardened and stiffened in both directions.

OK, I've tried to define some terms, given a basic idea of how to create the planning box, shown a few examples of this idea of a building-block cabin of bent pans from thin materials so I'll move to some examples of this type of construction.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 2:29 pm

Some of the sketches shown below in this post present various design suggestions that may help inspire your ideas as you work inside the design or planning box? (I have used some of these variations in different cabins over the years but 90% of that work was not photographed- who cared back then? )

Image

Above, is the top view of a pair of panels or "pans" as I've called them to give the idea of a shallow sided, wide, flat, thin material, formed piece of metal. The width is not important, you could divide the longest run of your cabin design by three or four or five, and discover the best or most attractive set of lines for the panel intersections.

If your cabin were 4' at the 'break' between the window band and the lowers- then the panels shown 3' tall in this sketch would be 4' tall.

I'd call attention to the corners show with the 1/2 radius because this can become an issue depending on your forming work supplier/fab shop. The various alloys 5052, 5083, 5086 come in various H-numbers that describe their post smelting properties and some of these, H-321 for example in 5083, have shown they require very wide radius bending dies to avoid stress cracks. On the other hand, 5052 in H-32 can be bent with a much tighter radius or nose bar (some use a steel knife-edge nose bar) and still not strain crack.

A word of caution (from someone who's RE-bought metal due to plenty of damaged material over the years ) to anyone not used to this fact of aluminum life: pay attention to this detail- closely. Do make sure you know what the results of bending the material you have, in the direction (sheet orientation) you plan to use your sheet goods, with the die or nose bar your service plans to offer you!!! (No sniveling! if you 'trust' the shop and all your work comes back cracked out and useless.)

(NOTE: the pan sides' bends do not have to be 90 deg's as shown. They could be less than 90 and therefore have a better single edge-weld seam while not including a close metal to metal space to promote crevice corrosion sites.)

These following images are just offered to show the flexibility of this method of design then construction of the cabin. These examples of the lower shape of the cabin, fit inside the 'design box' mentioned above, their foot print on the deck are suggestions of how this could be modified for your preferences, where even an inch or two of curve/bend/non-planar shape can improve the appearance of your designs.

Image

Image

Image

IN the three images above, the second and third show a provision for the next basic structure. A flat plane in brown begins to show where the helm area or dash could be included in the transition plate or median band at the top of the lowers and bottom of the window band.

These three images simply vary the basic building blocks introduced so far. Obviously entire panels of the cabin's lower supports could be done in single sheets with or without bent corners. However if the panels were not 'pizza pans' then interior framing elements would have to be added and they are not in our discussion at this point.

Image

The sketch above shows some 'pans'/panels are sloped along the forward bulkhead so the two forward most, side panels are bent to accommodate this angle. These two lower panels would not have parallel side bends, but will work fine for the method being shown.

Image

Above is a combination of the previous ideas using a rolled or cold formed forward dodger to give a less angular and more rounded shape to the forward lower part of the cabin.

This set of pans or bent panels becomes very stiff when welded to the deck of an aluminum boat. But it is much more work to build inside the skiff crawling around on your knees. So the next post will show a method to assemble this cabin off the boat, at working heights where easier work conditions can mean better fits and more uniform proportional welding.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 2:44 pm

I know that many owners who'd consider doing their own cabins will have their own way of dealing with the work flow of fabrication. I'm showing one method I've used for decades because it has helped make cabin building faster with less crawling on the knees, something in which I may put too much importance? To keep off my knees I'll do a lot of work that allows me to stay upright and I've shown the Davis Jig complete hull rotisserie in the Work Methods thread. However, the importance to me (older, slower, heavier displacement) - may not be there for your younger stronger and more flexible knees and backs! (then) Ignore this method and just build inside your boat- but this method sure can help with accuracy and ease of build.

Image

On top of saw horses I put down a working surface, flat and fairly stiff- by butt jointing with ply under the joints, a particle board or plywood working surface to layout the bottom of the cabin.

NOTE: if your deck is cambered (?) then I'd make the cabin on a flat version of that same deck and mark the camber cuts into the lower edge after the entire cabin is complete. This assumes the cabin will be mounted on the deck and welded direct and not to a 'kicker plate' or to some other coaming- we'll discuss those types of options much later in this thread- for now? Let's assume we're working on a flat surface as the lower plane of the cabin build.

Image

lapping the pieces needed to support the shape, I lap and miter the corners but T butts would work as well.

Image

My goal is to get a flat surface that is stable and so I back the joints with ply and use dry wall screws to put on doubles or fish plates underneath.

Image

Then I draw the actual pans' lower edges as they will stand on the tack up jig, notice all this work is done at waist level- that's appealing for old backs supported by shaky knees. The pans themselves can be used to trace the outlines and the inner perimeter can be drawn by using a centerline board or aluminum straight edge then key offsets from centerline can be taken from the dimensions of the plans. The key dimensions would come from your plans developed in plan view.

It is key to your planning that if any pans are not vertical, if any panels will be curved or conic that provisions are made to layout and fit the curves on this forming jig or fixture to accommodate the curves as they meet this surface, not as mere vertical intersections.

Image

The key to making this wood and metal layout and tacking jig work is the 'tab' or 'tack strips'. I refer to these small 1" x 1" x 1/8" (very rough size- anything will work but they don't need to be 4" x 4" x 3/16" stock) squares of aluminum with a couple of dry wall screw sized holes- tabs/tack strips/tack tabs for want of better terms? These tack strips are screwed to the working layout surface at points that will restrict location of the shape of the pans to be tacked on.

Image

Again working at bench top height, above; the pans are aligned and tacked to the wooden work surface to begin the build. Shown here very shortened in the vertical! (Big sized cabin shown or short lower panels! not a small doghouse set of proportions in area to ht of lower panels.)

Once the first vertical is tacked to the base and the second one added next to it; the their inner edges can be tacked (adjoining edges) where the result is a stiff shape what will retain its form while the transition plate or dash board panel is added (tacked).

The cabin can be left on this jig or removed if a few tie bars are laid along the lower edges to hold shape in both directions until the cabin can be tacked to the deck.

Next we'll go back to some design ideas and discuss one of the least appreciated pieces of the cabin- the brow. But to get there, we'll look first at the cabin top panel and various methods of designing forming and assembling that element of the house.

Cheers,
Kevin Morin
Kenai, AK
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Re: Aluminum Boat Cabins

Post by Dave Grason » Sat Feb 20, 2016 7:34 pm

Kevin Morin wrote: ...it sure looks tall and all my design and building of horizontal/fore & aft curved lines hasn't fooled my eye very much! In the end it was the best I could do at the time and I did spend much more time than I should have building this complex form- in my attempt to make the cabin look more integrated to the rest of the hull lines.
Well... maybe you're not happy with it but you can rest assured that it looks damn good from here in Tennessee. Wow, what I wouldn't give to be able to stamp MY name on work like this!
Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 8:09 pm

Thanks Dave, as always, the welcome and comments at Glen-L are generous.

I'm not disappointed with the skiff, the nature of small boats and stand up weather helms- or cabins- is just what it is. I'm just sniveling that as someone who's spent some hours drawing boats- those lines might be a little sweeter if I could have lowered that cabin! But that domino just knocks over another one in the design helix, so I, like all designers, had chased my tail enough and had to build what was drawn!

More cabin methods coming.

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 8:40 pm

To design the brow we'd have to have a top of some kind to mount the brow because as I hope the sketches show... the brow is a surface mounted to the forward edge of the cabin top. To put on the top we'll need to hold it in shape and do some fitting before we can install a top. First we need to address the shape of the top so we'll discuss camber frame layout.

The top of most cabins have camber or curvature; upward in this case. A cambered surface or a 'camber' is part of a cylinder, but as I've heard and used the term the amount of curve is usually very slight or shallow. This means the radius of the camber's cylinder is big and the center may be fifty feet from the cambered deck? Not very easy to layout a camber if the compass needs to be 25 or 50' long.

IN the accompanying Work Methods thread we've already explored the idea of expanding a circle so that work method would be used here- to make the cabin top's temporary formers. These can be wood with tack strips on the edges but many times the cabin top can be marked without any tacking to the sides.

How does this fit into the cabin top? First both temporary frames shown below will need to be 'projected' onto the wind screen's forward panel top edge, as a curve, and then to the same framing element at the aft end of the cabin- if one is used. In both cases a straight edge slowly moved over the two formers and touching the two panels to be cut, provide the marks for these two projected cambers.

Once marked, they can be cut in place, or the two panels (not shown) can be removed and battened fair, then cut on the bench and retacked to the cabin frame.

Image

To add the top, hold its shape down onto the two wooden formers, shown above, while adding some permanent aluminum frames. These pieces of temporary wooden formers need to be layout and cut to the camber of the cabin top. (expanding a circle/camber layout in the Work Methods thread) This method could be used to layout and cut metal frames for wider spans or 'walk-on-top' cabins where the top becomes a deck and has to hold crew. Since we're not addressing that in this thread, we're just trying to show methods to shape and form a cabin to keep off weather so this cabin top framing could be left without interior framing.

If a 2"x 1/4", or 1-1/3" x 3/16" flat bar is laid flat to the cabin top, and a smaller 1" x 1/4" is centered below it, and both held to the curvature of the cabin top, comforting to the two wooden camber formers- then stitch welded; this will hold a tremendous load in just fractions of an inch of depth. These provide an extremely low profile or shallow frame that doesn't have to be fit except for length and still delivers 100lb. sq foot loading in a 1/8" cabin top.

Back to a cabin brow, now that we've begun to explore where to hang one.

One final note; the two pieces of the window band that meet at the cabin's forward corners are bent/flanged/curved inward. They need not be- these corners can also be turned outward, and a slit segment of pipe welded to the out turned edges to form a very smooth exterior strut at the cabin corners. That is the construction of the welded cabin shown above.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 8:56 pm

First, I'll digress a bit. Windscreens can rake (lean) aft, be plumb (vertical) or rake forward, and almost all of mine will be shown forward. Here's what I've seen and think is the reason, and I prefer to see the glass panels lean aft for sleeker looks. If a green one ever comes aboard over the bow it would be curling downward as it traveled aft. So if the glass panels raked forward they'd be more or less parallel to the impact instead of leaned aft where the impacting water would be more at 90degs to that panel. Plumb windscreens are in between the two but considered in this rationalization as more toward the 'take-it-on-the-chin' kind of design than 'go with the flow' forward raking windscreen. Impact on forward raking screens is much less than on after leaning cabin windscreens, not that small boats should be called on to be in those weather conditions.

Next; cabin space is more or less premium boat space and giving up floor because the glass rakes aft, well, it drives lots of skiff owners and builders to adopt the forward rake so they can get closer to the glass, put their electronics overhead in the area above the glass, and make the helm more compact fore and aft.

Image

Here's a picture off the web of an aft raked glass cabin of about the class we're discussing, I'm sure you've seen more of the type? I think the cabin floor/deck/sole area lost by standing aft away from the glass rake may be a poor cost choice, given the effort and materials to build any cabin? I always want to maximize the deck/sole/floor but then 'its in the eyes of the skipper' that beautiful designs are decided.

Image

Here (above) is a plastic composite cabin and it may be sitting on a fuel cell? not sure on that, but the lines mean that the crew is aft the windscreen by a few feet more than is absolutely needed so I'm repeating the 'get close to the glass' idea that is allowed by the forward raking screen.

OK... back to the progress of designing and building your own cabin.

Image

Again we're looking a sketch (above) our example cabin. The temporary wood formers, cut to a camber, have tacking tabs screwed to their trimmed-to-fit inside ends and are tacked inside the window band panels. The forward panels' top camber is done by projection; lay a straight edge along the two formers' top edges and mark the curve for and aft (add a bar or angle above the opening aft) and then these pieces can be cut in place (jig saw) or taken down and cut (band saw and belt sander) and retacked while the two wood camber frames hold the sides' locations. (previous post)

Now....
Image

Drape the top panel blank, shown here (Above) already somewhat fit to along the sides. Mark the overhangs if there will be one, mark a brow radius if there will be one, and mark the aft overhang to your plans from the 'design box' in the first few posts.

A trammel bar, radius bar, wooden compass bar- whatever term you call this piece of wood or metal with a couple holes is shown located at the after edge of the top and then striking off a curve along the forward edge of the overhanging cabin top. The distance of overhang is up to you, some like them wider or farther fore and aft, others tighter to the windscreen. If the radius of this top edge's forward curve is not centered on the cabin top as I show here.... then you'll have to put a bar or plate aft the cabin top's aft edge and set up some way to run the trammel bar from there! The farther away, clearly the wider and slower arc you will describe along the forward edge of the cabin top as you define the brow's aft and upper intersection line.

Image

This picture shows a skiff with a cabin top brow that is a very long, slow arc; so the center is likely aft the long full cabin? In other words this brow's radius is so long it isn't even on top of the cabin! Some brow arcs may need to be laid out like a camber or expanded circle and not drawn with a trammel bar.

Image

This sketch, from a discusion kens and I had about his cabin design on Double Eagle (?? not sure on that design name) some while back, shows another shorter radius curved brow, center is probably on the cabin top, maybe even forward of the aft most edge? So one design feature that will influence the look of this visor/brow/cabin top trim item is the side to side curvature.

That really opens up a discussion of the geometry of these shapes- what combination of flats, cylinders or cones are used to attain these boat cabin shapes?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sat Feb 20, 2016 9:07 pm

The geometry of the brow is a series of interesting cylindrical sections. If a cylinder is cut lengthwise, it will produce a uniformly rolled surface- like part of a pipe cut lengthwise, and if there were two or more of these surfaces, they can be intersected again in countless angles of intersection.

Image

Here is a blue cabin top with camber, and for the sake of making it a solid there's a vertical edge on all sides . To the left is a brown cylinder, the entire cylinder is shown so the idea of a section is more obvious, the purpose is to visualize the easy geometry of the brow's pieces.
One key point is the radius of the cylinder has been closely matched to the cabin top width to achieve an intersection that extends forward of the brow, a distance already planned.

Image

In this image, above, the two geometric objects, the brow's theoretical cylinder and the cabin top's cylindrical section (due to camber on top) are intersected with the cabin top pushing through the brow's rough cylinder. The reason to show this is that this is the shape that is being designed. A brow is will come out of the surface of the larger (left side) cylinder and meet the cabin top along the line where the top is 'sticking out' of in this sketch.

Image

By making the brow cylinder 'see through' again we can see how these two sets of surfaces intersect.

[NOTICE: in order to make the SketchUP software model faster- years ago when I made these sketches I left the curves at a very coarse faceting setting. So the curves in most of these images will be 'faceted' or have angle points or line segments instead of smooth curves we'd expect to see like the photographs in the previous posts.]

Image

We really don't need the whole cylinder anymore to see the 'blank' piece of plate or sheet that is used to form the brow. So here that is trimmed to a smaller piece of the cylinder, and the cabin top is gone to leave us the brow's pattern image in blue.

Image

To clarify the images in several views, here's a sketch of the same cabin top with a brow added in different angles of view. The idea I'd hoped to convey is the brow (here shown below the cabin top) can be considered just a plate draped over a curve cut in the cabin top- held at an angle to the cabin top in Profile View.

There are some other design considerations and we'll look at them next.

Cheers,
Kevin Morin
Kenai, AK
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Re: Aluminum Boat Cabins

Post by kens » Sun Feb 21, 2016 8:08 am

Kevin,
yeah we had a thread going about a house for my Double Eagle, . After I got home from a tour of Afghanistan, I was immediately put off by dealing with my plastic tarps covering my boat, I sent it out that same day to a fabricator and had a T-top installed. He did a fine job, but it is a T-top, not a house. The canvas guy worked with the t-top guy and a custom canvas cover was done at the same time.
I now wish I had a house as soon as I picked it up from the fab shop. As soon as I got it outside the building, I saw the 'lines' that I was talking about in the thread. The lines that remove the 'phone booth' look of a small pilot house. Alas, I had just paid for the t-top and it is now mine.
The first thing I noticed is that the 'lines' are smaller at the top, the sides cant in towards the top. This takes away the squarish lines of a phone booth. Any way you look at it from front, back, or side, the lines cant in at the top. This was the missing link that was in our thread about a house for my Double Eagle. Had I been aware of these lines, I would have built a house a long time ago,
The T-top carries with it a bit of modern 'sporty' look, aesthetics. I think a house along similar lines would do the same. You have a keen eye for sweet lines on your forward rake glass, it is proportioned right. Can you take a look with a keen eye look at the lines Im speaking of here, the canted sides, maybe we can convolute a new idea here.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sun Feb 21, 2016 3:00 pm

kens, were you referring to image files in your post? I didn't see anything attached or (maybe) I missed what you were discussing?

Sloping stand up helms inward is a good way to help the lines, and that includes all four sides in some cabins. Problem is really that no matter what we put up... boats under about 30' usually have sides that are proportionally lower by comparison to a fixed 6'-2" to 6'-6" cabin ht. So no matter what design we use there's a factor of 'too-tall', until the LOA starts to climb with the boat's proportions.

I'll keep showing my image set to example cabin so others can reference this method.

Cheers,
Kevin Morin
Kenai, AK
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Re: Aluminum Boat Cabins

Post by kens » Sun Feb 21, 2016 4:26 pm

I didn't refer to any particular image file, but I do remember us discussing a house for my build, we had a rather long thread going. If I had more time, I would have used the lines in the post you put up last Saturday, that was in our thread of long time ago.
But, when I got back from Afghanistan, I wanted a canvas top RIGHT NOW, and I went with a T-top from a local yard, and the custom canvas work along with it.
The thing that was bugging me all along is the same as you mention in your above post,; on a smaller boat a stand-up house looks 'too tall' if the boat is under 30'. That was exactly my quandary.
Here is a link to my boat up and running, with the T-top.:
https://www.youtube.com/watch?v=inT-vDWh2I8

If I had a hard sided house, it would have a really tall look to it, like a phone booth. Notice how all sides of the t-top cant inward at the top, this helps take away the phone booth look. I would like to see some lines of a hard sided , small house, with a brow, and a generous top for shade, with the canted sides. I think the 'canted sides' is the key word in the lines I wanted to see.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Mon Feb 22, 2016 1:14 pm

kens, you can draw on top of pictures and so take one of your boat's images and just color in (pen or marker) the pipe areas. When you do? I think what comes up is something in design called "white area" sometimes termed "negative space" where the pipes are what allow this top to look less top heavy. In other words the T-top is top heavy too, it just has lots of space that allows the eye to perceive the build as 'balanced'

The cabins in our sketched images aren't sloped much just to make drafting easier, but the photos of the cabin I showed in previous posts are leaned in a little. What happens when you lean in the sides of a tiny stand up helm/dog house/weather helms' sides is the interior space is lost - fast.

Let's put a "boat driver" inside the cabin; his feet must be put in the floor plan with his shoulder against the side wall. So if the cabin 3-6" wide and leans in 3" per side, the shoulders of the driver have now a 3' wide cabin to fit inside- the feet are inside or toward the keel from the sides by the distance of he shoulders' overhang of the stance- so this method of improving looks rapidly gives up the most critical reason to put cabin on skiffs; sheltered space.

Online, you can find several dealers/builders' boats with pipe frame helms and compare them to the same T-top when the canvass is installed? I find the 'look' changes from visually proportional to outhouse, just by adding the side canvasses back onto the pipe frame. This leaves me to conclude that the open web frame look of the pipe shelters is what gives the proportional look.

Of course, looks being as subjective as we've all seen in terms of both overall design and feature-by-feature- my view of the ht to length ratios of a cabin may be different from yours or anyone else?

kens, try the exercise of coloring in your top's corners and side frame opening on printer paper images of your boat and see if you find what I'm asserting about white space in a design?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Sun Feb 28, 2016 3:33 pm

We were at the discussion of the brow, and while you may feel this is too esoteric to spend time explaining or discussing (?? ) I think that different boats' brows and the impact on the looks of the boats makes this worth exploring?

Thankfully, anyone who's in disagreement with my reasons for posting this can click away and avoid the next few posts about this detail of cabin design. Just a note about this set of images, they're made with the curves in a very coarse or faceted display, the line segments in these curves are angled, so the what I'm calling curves show up like a bunch of hogged points in what otherwise would be curves.

Image

Above I'd mentioned that the radius of the brow is set by the radius (distance this center is aft the windscreen) the arc was drawn or designed. Here, a pair of cylinders of different radii show the effects of the very gently curing brow (longer radius) from one that is nearly semi-circular where the radius is much shorter.

Image

Maybe you'll recall this image of the compass bar/trammel used to layout this curve? IF the radius (circle's) center were behind the cabin top's after edge- farther and farther- the radius becoming larger and larger means the curve would become softer and less circular.

Image

Also, above, we saw examples of the angle of the brow to the cabin top or to the waterline? Here we're looking at one fixed camber with one fixed radius but different angles of rake of the brow and what that series of changes could mean to the looks of the cabin.

So when you look at pictures of various designs of cabins, regardless of how those cabins integrate to that particular boat, the brow is designed by using different combinations of radius of these two curves; radius of the brow in plan (or cylindrical diameter), and the camber or radius of the cabin top (done by expansion of the circle).

Image

Let's combine rake and radius to see the combinations' effects on the brow. This image begins to explore the countless combinations of these two design variables- angle to the waterline in Profile View and Radius of the Brow in Plan View, to start defining the effects of these two related decisions in your design.

The reason so show just the various combinations is to illustrate how these to sets of curves/surface radii result in different shapes- all of which can be developed of flat sheet stock but some may, if their radii is too tight to bend cold, need to be rolled to form the curves drawn?

Image

Here is the same idea as the image above with more selections and combinations of the rake and radius. It might be a worthwhile exercise if you're still seeing a fog in this thread?? to compare these two sketches to the many online photos of boat cabins- showing different brows. I hope this helps to inform you ( a little more) what is involved in the design process of the cabin brow?

If the ideas aren't clear? please post a pointer to the text and image that causes the confusion so I can find that and try to improve my explanation of the idea or concept in question?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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