Aluminum Boat Cabins

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

Re: Aluminum Boat Cabins

Post by Kevin Morin » Sun Aug 05, 2018 3:46 pm

Yofish, that standing seam roofing take off solves some really big shape and forming issues for skiff (and larger boats') cabin tops that I hadn't "seen" until re-reading this thread.

One of the shapes that is most attractive on a skiff cabin - regardless of size- is the "whale back" - or compound curved cabin top. However that shape requires 'gores' or pieces of sheet that are trimmed out of square so they result in a camber -side to side on the top; AND a fore and aft curve as viewed from the side.

A sheet can be formed to a cylinder, cone or flat but not a compound curve unless it is stretched- shrunk or otherwise "deformed" from its originally uniform flat surface. If a skiff cabin were formed with an English Wheel it could probably be "whale backed" into a compound curve- but the labor and tooling sure would make it a big cost in time and effort.

One thing that is always attractive about small boats- especially in the wooden plank pulling boats like the Whitehall, for example, is their wine glass stern, and round bilges combined with a little compound curvature of their bow sections. These boats are made from flat planks which are 'skewed' to one another- that is each few inches of hull is a plank that is both curved and slightly twisted, only meeting the next plank at a slight overlap.

I think a series of U shaped 'planks' of aluminum, press braked into 10-12" wide pieces would allow a skiff cabin top to be formed into compound curvature by the standing seam joint you show? Each plank would only have a very slight fore and aft 'bow' (curvature in Profile View) but.... the standing seam between adjacent 'planks' or panels would allow that bow to open or close- slightly bend the corners of their press formed short vertical legs- in and out? This would allow the one curvature (fore and aft) while their arrangement in cross section over the rolled rectangular tube would provide the side to side (Body Section) curvature.

I haven't tried it but it seems that these panels would allow for a very nicely compound or whale back shape on a cabin top?

Are the tubes you label as clips full length? seems like they would need to be in order to seal the skip welded standing seam between 'planks'?

Thanks for the post- interesting idea on this design element- I've used almost exclusively cylindrical shapes- side to side curves in all my past cabins - but they'd all look better with a compound shape- I think this method would provide that?

Cheers,
Kevin Morin
Kenai
Kevin Morin

North
Posts: 294
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Aluminum Boat Cabins

Post by North » Wed Aug 08, 2018 8:14 pm

Yofish - I am sure that (as an amateur, first time builder..) I would be happy and content with any of the boats or cabin tops which you have still been less than happy with...

I will ask a dumb question - is what you are describing in your drawing similar to what Kevin did for the cabin side's (about halfway down page 1) - using preformed/ pre-bent panels except that in the roof the weld edge would be hid by tubing?
If so, do I understand correctly that the main reason for doing this would be to add curve or shape without having to do long welds (heat/ distortion) involved in welding two or more flat pieces together together?

Do either of you have any pics of larger cabin tops/ roofs made from a single flat sheet/ panel (with reinforcements welded below to retain shape)?
Do they really look that bad?? and therefore I should really consider using Yofish's method perhaps with 2 or 4 ???? panels to achieve a decent shape and look??? With 4 panels you would then see 3 pipes running fore/aft concealing the weld seams.
Kevin - you mentioned potentially using "planks" of aluminum of say 12" wide - I am just concerned that having 6 pipes running fore/aft may look a bit busy on my top - could I get away with wider planks / less pipe/joints of would the transitions be too harsh?

In the pic of the "Wilkes Workboat" - not sure if Kevin would have built this one.. if not, could either of you comment on the number of panels / reinforcing tube underneath, etc which would perhaps be used to create a roof that size?

please see attached pic of a sample cabin roof, which I would be ecstatic with.... which looks like a single sheet on top of tub crossmembers.
Attachments
sample cabin top.jpg

Kevin Morin
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Re: Aluminum Boat Cabins

Post by Kevin Morin » Thu Aug 09, 2018 11:23 am

North,
North wrote: I will ask a dumb question - is what you are describing in your drawing similar to what Kevin did for the cabin side's (about halfway down page 1) - using preformed/ pre-bent panels except that in the roof the weld edge would be hid by tubing?
yes, that is essentially what is being shown- but... the orientation is with legs up not 'inside' the cabin. Yofish's reason to consider this is to avoid full length welds in thin material. Unless you consistently make a weld cross section MAX section = 1.1 or 1.15 section of the parent material (thinner metal begets are smaller weld) then.... the resulting contraction usually makes a pretty unsightly set of waves in the finished materials. BUTT welds in two adjacent sheets of 1/8" or thinner material that are 8-10' long (!! read: cabin top length wise/fore and aft) will almost assuredly result in some real distortion.

By orienting the materials' welds on edges that are pressed into the various panels- the distortion is limited to the leg on which the welds are located-not to the main sheet. I suggest the 'pizza pan' cabin building blocks for a very similar reason Yofish suggests the 'standing seam' solution for a cabin top.

It is important to note: sheets are regularly available in most LMS 6' wide in both 12' and 20' lengths. So... if your cabin top was only 6' or less side to side- this entire discussion can be solved by the method in the picture you posted. That cabin top is a cylindrical development- not compound. The cabin top beams are transverse- and they're reasonably rolled uniformly- so they create a surface with only one direction of curvature.

IF>>>> you built one of these and it was too wide for the material- let's say 7' wide and you could only get 6' wide sheets- THEN: you could orient the weld seam over one of the rolled, curved beams and make that butt weld seam with a full back up and located on one of the beams. This would result in a decent seam, with little distortion if welded using a collar tie (temporarily side to side at ends of the beam) and short welds (8" or less) staggered/stitched onto the transverse weld seam orientation.

North, the panels Yofish is suggesting could be done with 2- each 3'6" wide. So a single seam down the centerline of the cabin (on top) would be uncluttered and allow a stitched seam to be covered with slit tube/pipe. THEN you'd have to separate my remarks - I was slightly changing the subject to compound shapes. That is where the multiple panel approach (I compared that idea to wooden plank boats' getting compound shapes from flat wood planks) comes in. Using Yofish's idea; then a more complex cabin to shape could be achieved with flat material bending in two directions in smaller individual pieces- so instead of 'tearing' a sheet- or EWheeling as plastic deformation into the sheet; the shape could be obtained by using the 'planks' relative shift from one another.

not sure about reference to Wilkes Workboat?? link?

if you're happy with a single piece top cylindrical shape? great- then my remarks (on a slight derivative idea; compound curvature) are not applicable to your project.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

North
Posts: 294
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Aluminum Boat Cabins

Post by North » Thu Aug 09, 2018 4:29 pm

thanks for the great explanations, as always Kevin!
I will not know dimensions until the late fall, but will take all of this into consideration at that time.
The "Wilkes worked" boat was a pic on page 1 of this thread.

Yofish
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Joined: Wed Jul 04, 2018 9:40 pm

Re: Aluminum Boat Cabins

Post by Yofish » Thu Aug 09, 2018 11:20 pm

Lordy. I apologise for not paying attention here but I've been busy with sooo many things. It's getting towards fall here in AK and I'm rather behind where I want to be. Anyway, once again, Kevin explained ME better than ME can...

I WILL add some later.

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

Re: Aluminum Boat Cabins

Post by Kevin Morin » Thu Aug 09, 2018 11:42 pm

North, the Hewescraft named "Wilkes Worked" has a standard single curve (cylindrical) top panel as near as I know about all Hewes boats?
Their factory is near Puget Sound somewhere so they have access to 8' x 30' sheets (any all other sizes!) in almost any alloy or thickness. So I doubt their factory produced boats have top weld seam issues due to supply?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

North
Posts: 294
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Aluminum Boat Cabins

Post by North » Fri Aug 10, 2018 3:26 pm

I would certainly appreciate the advice and help of Kevin and Yofish, once i begin to work on it in the late fall.

A couple of notes:
- i don't really need a large, enclosed deck at the bow as no v-berth needed for sleeping. I would like to incorporate perhaps a sit down head into the cabin / console area.
-as the boat is 25' long, 8 ft beam, i don't think i would have quite enough space (both space inside and to walk around) if i had a walk around /pilot house type cabin
- i am thinking of something like the pic attached, where the cabin walls run just to the gunwhales and not all the way to the floor, as required with a walk around cabin. I think this will give more space and save weights as walls are only needed from the sheer up.
- i would like to make a walk through cabin where the front middle window or a side window is basically attached as a sort of hinged man-door which can be opened to walk through the cabin and get to the bow - set the anchor, lines, etc.
I will add a one or two step raised floor at the bow so you have about knee deep "protection" as you are up there = about the same as in the stern.
- if i build something like the attached pic, i would like to incorporate larger windows / lexan and make them able to slide out completely - in tracks to be stored on bored in fair weather.
Attachments
nice cabin3.jpg
nice cabin2.jpg
nice cabin.jpg

North
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Location: Nova Scotia

Re: Aluminum Boat Cabins

Post by North » Fri Aug 10, 2018 3:26 pm

1 more pic
Attachments
nice smaller cabin.jpg

North
Posts: 294
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Aluminum Boat Cabins

Post by North » Wed Nov 27, 2019 7:31 pm

Hi Kevin, Yofish and others..

I may finally get around to welding in some type of cabin this winter ( to replace the temporary bimini top i have used for 4 summers now)- per previous posts I am planning a somewhat curved aluminum sheet roof (likely from 2 sheets of 4' x 8' material or perhaps 4' x 10', placed side by side so i have an edge pressed along the long side and weld the two sheets together along this seam, hidden later with a half pipe.) I plan on having a downturned edge or lip bent on the outer edge as well.

the boats length is 25' and beam is 8', but i do need to measure the beam at the points where the fore and aft ends of the roof will be placed above the sheer or gunwale.

I plan on having as little side material as needed to be strong enough to hold up the roof (i.e. I plan to have as large of sliding/ removable lexan side windows as possible).

If the roof is supported underneath by crossmembers (channel, rectangle tube,etc) i am wondering what thickness of material to choose for the roof to keep weight down, yet still allow reasonable welding (not for experts like you guys..) and minimize distortion.
I would appreciate your advice. The boat hull and side are 3/16" but i did weld a thin skin on top of the swim platform which I added a bit hastily last spring before launch. With my mig setup, i managed to blow a few holes in that thin material where my fit-up was a bit wide or sloppy..although i don't know the thickness of hand... i would say 1/16" or less.

I used most of my leftover material welding in floor panels, so i will be purchasing new sheets and can choose what best suits..keeping weight and price of material as low as reasonable..

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

Re: Aluminum Boat Cabins

Post by Kevin Morin » Tue Dec 03, 2019 11:08 am

North, I'd say the first step in the design helix is to establish the wt that will be carried by the cabin top panel? Many of the boats you show will have crew walking on them with rafts, pots or buoy's lashed down for want of deck space and a need to stow these items for running.

If you're not carrying much up there then you can make the top of whatever material you can weld? I can't always tell from your posts what thicknesses are involved exactly ?? so you'd have to offer dimensions to get any really informed replies?

Window bands on skiffs, as shown in the images I've posted, can be as simple as bands of sheet around the cutouts; or inside or outside the cabin you can incorporate extrusions welded (stitched is adequate) to the bands of sheet left between cutouts. Depending on the speed, load and seas a hull sees will govern if the framing is adequate!!

For example a slow displacement hull with a fairly narrow (vertically) window band and 6" between widow cut outs could get by with 0.160" or 5/32" side sheets and little extrusion framing inside the verticals. In fact, if you used the pan braked method, even 1/8" is more than adequate due to the vertical edges of adjoining panels forming a T with the sides of the cabin.

However, if that same boat were a 20knot planing hull(?) then corner and vertical framing elements inside the cabin would be needed due to the slamming/pounding/pitching at speed that would be acting on the mass above the 'break' in the cabin walls or attachment at the sheer in some cases. In the case of 1/8" cabin window band sheets; I'd suggest all planing boats have some framing inside each cabin side upright sheet. Using a U extrusion, or even pressed U of some kind is most effective as they're light wt but offer good side to side stiffness, and wiring and cabling can be run up and down from the top to the helm.

House top beams to support a top panel can be reinforced as shown in the previous illustrations and walked on by an adult crew member- with a simple 1/8" 5086 alloy cabin top panel.

As always with new builders I suggest it is worth the time to mock up a section of the weld being proposed - in order to assess if you need to A) practice more? or B) change the scantlings of the proposed parts to allow your current skills to weld that section?

Drawing a plan is always best practice, everyone I know who builds does this step- helps to create a Bill of Materials and would allow others to look with you to see if they notice any potential areas of improvement?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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