Thread: My upside down "boat" with wheels

Howdy Brad,

Lightweight boat building methods will work very nicely for a trailer too.

Boats work through using the furniture to support the sides and bottoms rather than having something separate to fulfil those functions.

Do you have anything drawn up yet?

Michael

Originally Posted by Boatmik

Howdy Brad,

Do you have anything drawn up yet?

Michael

Hi Michael, You could certainly say I've wasted some time on thinking about this project. Images attached. The current thinking is;

Floor 15mm, walls and roof 15/12mm, tailgate, 12mm. It is intended that the outside part of the deck under the bed plus the partitioning between the wheel arch areas and the kitchen would all add to the structure. I'd most likely have a couple of support rails going across the inside of the roof (only one shown at this point). The rear frame around the opening adds to the cross bracing as does the tailgate when closed as it would lip over and be locked to the rear during travel when forces are at their greatest. The spare wheel carrier as shown would be self supporting back to the chassis in the closed position to minimize stress on the tailgate. The length of the wall not including the tailgate is 2300 and max height is 1400.

For the construction I think it should be a fairly simple stitch and glue process. The difficult part would be achieving the curves in the front, roof and tailgate. For finishing I'm thinking a layer of fibreglass to the outside and epoxy on the inside. I'd probably then finish it off with a single pack paint inside and out. On all the corners I'd radius them say to around 6mm before finishing. The checkerplate around the base would only be a glue on for stone protection and not part of the structure at all.

A bit more info. Finished width of the box is 1600. The ply will be exterior grade. That's assuming that I use a single thickness of ply and no laminations. The epoxy will most likely be Bote Cote with the various additives as required.

I've made enquiries locally for a TAFE short course on fibreglassing but no one seems to run them anymore until they get the demand. However there are a few steps to get over before I get to that one.

One of the main detailing things I keep coming back to is if the side sheets finish over the edge of the roof sheet or vice versa. It would be easier to cut the roof sheet sides parallel and then route the side walls to the profile. If the side walls are cut to shape first, then they need to be more accurate. but at least then I can stand and brace them, get the support rails on, and then the roof. Sounds like an easier process to me. I suppose that the beauty of stitch and glue is that things don't have to be "perfect" before using the epoxy.

Another consideration is the tailgate. It needs to close perfectly to the main body. I could make the two together and then cut the joint to ensure a match but this seems unwieldly to me. Once the body is made I should be able to use it as a mould and stitch up the tailgate before gluing to ensure a match.

Howdy,

I just have the link in my clipboard ... so here are common epoxy/ply boatbuilding joints

There is a good argument for using timber in the corners to join the ply along with the Plasterboard/Drywall screws for quick assembly and then removing them.

The glassing is a trivial process. You will have a chance to practice on the big flat surfaces of the sides - you can preglass them on the flat. I do tend to push people toward very light glass as it is easier to use and offers much the same protection as a much heavier glass.

A lot of the background thinking of modern structures is on my FAQ page.
FAQ - Boat Building and Repair Methods - Plywood Epoxy Fibreglass Cedar Strip - Michael Storer Wooden Boat Plans

If you read that you will have a more directed bunch of questions even if you disagree!

MIK

Hi Mik,

Thanks for your generous input. I've read most of the information contained in your links and am now informed past the point of having a clear direction! I imagined I would cut everything out, stitch it all in place, glue it, and then epoxy and glass it. Seemed straight forward enough! Each piece would rely on the adjoining pieces to retain its position and shape during this process. I'll call this the linear approach.

I totally see the logic in pre-finishing large surfaces horizontally before installing but not sure how this affects the gluing and glassing in the joint areas. I'm wondering now if "pre-fabricating" the various pieces, including the roof, and then assembling them is the better way to go. This would save a lot of working at awkward angles, inside a relatively enclosed space, and sore backs. On the downside, it would require a lot more precision and possibly some jigs set up to make each component. This method also requires a "concurrent" approach where several skills are needed at the same time throughout the project where my imagined "linear" approach separates each of these.

The bonus of the linear approach is that I don't have to learn fibreglassing until later in the process. I'm open to both methods as there are positives to each. I have a couple of basic questions which may help me find a direction.

1. Do I actually need to fibreglass the outside? Could it not be epoxied and then painted? What are the bonuses of the fibreglass? The ply should have inherent strength, and an epoxy coat should make the ply waterproof. (pardon my possible stupidity here)

2. For the concurrent approach, do you fibreglass the sheets leaving the edges bare? I have assumed for the gluing of the sheets you need bare timber for best results. Does it require more skill overall?

3. I see value in an epoxy coat on the interior to make sure there is no differential expansion/contraction to the outside. Is a single coat sufficient for this? I can see applying multiple coats of epoxy to the underside of the ceiling would be a total nightmare. (better to flip the whole thing)

Another approach I'm wondering about, is to build the top half separate to the bottom half with a joint maybe at the bed base line. This would allow better access internally for finishing, and the final joints are straight. Each side section would then be less than a sheet width.

If anyone has looked at my images and knows how they would build it, I'd appreciate your input.

Thanks for your patience.

Okay, a bit more clarity this morning. Pre-glassing the sides is a great idea and now I've thought about it, it sounds straight forward enough. I'll use masking tape to protect the edges and once the sides are in place the roof will then sit over the walls so that all works. I will also try to pre-glass the base to save having to turn the whole thing upside down too many times. It would be fantastic to also pre-glass the roof but due to the curved shape this may not be possible, plus it relies on the walls to define its shape.

I'm also reviewing the ply thicknesses. The base will be screwed/bolted to the chassis so this needs to be sturdy. So I may up this to 18mm. The sides should be good at 15mm max. The roof I'm now thinking can be reduced to 9mm if done in a single sheet. I'll add a couple more roof support rails to reduce the drummyness.(word?)

For the joints I like the timber fillet approach but would prefer to go to a "fillet" profile, that is a square cut diagonally. This would be much more aesthetic internally. If the joints between sheets are kept mainly below the bed level then I can go to butt straps to make things easier.

Q. instead of scarfing sheets, can you route a half depth rebate say 6 x the thickness of the sheet to both sheets and lap them together? Would this be sufficient? I've seen this done but it's not promoted by any boat building site.

All the best,

Just wondering, is your project to be used on an existing off-road box trailer, or is it the whole kit&caboodle, coupling to number plate?

Hi Mob. It's all totally brand spanking new. So the chassis will be made by me to suit.

You can even do without the Chassis if you want and carry the loads in the box structure. But it might be hard to get it past the rego people.

We had already talked about this project in the background but decided to move it here because other people would be able to use it.

Originally Posted by indiedog

Hi Mik,

Thanks for your generous input. I've read most of the information contained in your links and am now informed past the point of having a clear direction!

Hmm ... OK your questions below will resimplify.

I totally see the logic in pre-finishing large surfaces horizontally before installing but not sure how this affects the gluing and glassing in the joint areas. I'm wondering now if "pre-fabricating" the various pieces, including the roof, and then assembling them is the better way to go. This would save a lot of working at awkward angles, inside a relatively enclosed space, and sore backs. On the downside, it would require a lot more precision and possibly some jigs set up to make each component. This method also requires a "concurrent" approach where several skills are needed at the same time throughout the project where my imagined "linear" approach separates each of these.

Like almost all of what you have drawn up is rectilinear - this sort of structure is really easy to set up in terms of prefab and assemble. The fiddly bit will be the roof which will take a couple of layers of thinner ply to pull off. Not a biggie but a considered approach.

The thing that makes such structures work are enclosed spaces because they deal with torsional as well as all other loads. You can cut holes into these sorts of spaces if you leave a margin around the hole.

The bonus of the linear approach is that I don't have to learn fibreglassing until later in the process. I'm open to both methods as there are positives to each. I have a couple of basic questions which may help me find a direction.

1. Do I actually need to fibreglass the outside? Could it not be epoxied and then painted? What are the bonuses of the fibreglass? The ply should have inherent strength, and an epoxy coat should make the ply waterproof. (pardon my possible stupidity here)

The glassing is quite tolerant to new people. Particularly on the flat a panel at a time. It is not essential but is one of the ways of making sure the structure is good for the really long term. It will still be pretty good with just the three coats of epoxy. The glass would make it more tolerant to stone damage and also any defects in the wood.

2. For the concurrent approach, do you fibreglass the sheets leaving the edges bare? I have assumed for the gluing of the sheets you need bare timber for best results. Does it require more skill overall?

Lets call it prefab. You would fibreglass the whole outside of everthing except the roof panel - adding glass will make it too hard to bend. So one strategy is to glass everything else and grind the edges down so you can run a tape along the joins.

3. I see value in an epoxy coat on the interior to make sure there is no differential expansion/contraction to the outside. Is a single coat sufficient for this? I can see applying multiple coats of epoxy to the underside of the ceiling would be a total nightmare. (better to flip the whole thing)

If it was a boat for this type of construction we rely on sealing all surfaces with three coats of epoxy to prevent moisture making the timber swell and shrink. That way all the paint never cracks up. There are condensation problems in trailers. For example if the canvas cover gets put away wet ... there might be several days or weeks where the interior is at very high humidity. The epoxy approach prevents this from becoming a serious structural issue.

Another approach I'm wondering about, is to build the top half separate to the bottom half with a joint maybe at the bed base line. This would allow better access internally for finishing, and the final joints are straight. Each side section would then be less than a sheet width.

If you box in the bed it will hold the sides up at the right angle ready for more work. That bed is the structure everything hangs off. If there was a boxed in storage unit or two helping to support the sides and roof then the structure would be really stiff without any separate structure to try and keep things stiff and torsion free. Also your doors would always close!

MIK

Actually looking more closely at the roof most of it could be one sheet - not laminated and you could use "bendy ply" for the radiussed bit between the front and the roof.

MIK

Originally Posted by indiedog

Okay, a bit more clarity this morning. Pre-glassing the sides is a great idea and now I've thought about it, it sounds straight forward enough. I'll use masking tape to protect the edges and once the sides are in place the roof will then sit over the walls so that all works. I will also try to pre-glass the base to save having to turn the whole thing upside down too many times. It would be fantastic to also pre-glass the roof but due to the curved shape this may not be possible, plus it relies on the walls to define its shape.

I'm also reviewing the ply thicknesses. The base will be screwed/bolted to the chassis so this needs to be sturdy. So I may up this to 18mm. The sides should be good at 15mm max. The roof I'm now thinking can be reduced to 9mm if done in a single sheet. I'll add a couple more roof support rails to reduce the drummyness.(word?)

The structure would be find in 9mm all round as a base point - you could go lighter but there would need to be more internal boxed in structure to stop things drumming. Where you need to attach it to the chassis just glue in back up pads to bring the local thickness to 18.

For the joints I like the timber fillet approach but would prefer to go to a "fillet" profile, that is a square cut diagonally. This would be much more aesthetic internally. If the joints between sheets are kept mainly below the bed level then I can go to butt straps to make things easier.

No worries at all.

Q. instead of scarfing sheets, can you route a half depth rebate say 6 x the thickness of the sheet to both sheets and lap them together? Would this be sufficient? I've seen this done but it's not promoted by any boat building site.

The general criteria for boats against domestic carpentry is the strength of the joins. However for this type of structure it is not going to be under a huge amount of load so you could make a compromise in the strength. The glass on the outside will help a bit too. I do like the look of a properly made and applied buttstrap and don't like scarfs much, though on some structures you end up with so many buttstraps (clinker boats) it will look pretty dicky going that way.

I would suggest that you review the structure and work out where you could incorporate some boxed in volume as storage. Overhead rack at the top front corner and at the rear as well? Remember they can have access holes as long as you leave a margin.

Best wishes
Michael

This is an interesting idea, I cant see any problems with ply and epoxy construction, MIK has pointed you in the right direction about that.
But my first suggestion is to move the spare... do you really want to lift it as well as the attached canvas every time you set up camp? I would also give some thought to making sure the joint between the tailgate and body is waterproof when you are camping. This is more important than waterproof for travel because you dont need water falling on your bed in the middle of the night.
Just a few thoughts,
Tom (who has been wet in leaky pop tops)

Originally Posted by Boatmik

The thing that makes such structures work are enclosed spaces because they deal with torsional as well as all other loads. You can cut holes into these sorts of spaces if you leave a margin around the hole.MIK

Thanks Mik. The structure under the bed I always thought would be a big part of the overall structure. There are effectively 2 torsion boxes down each side with intermediate dividers to add stiffness. And there is one across the front but this has no dividers and one end is open for the kitchen. The bed deck in the middle is liftable to access the storage but the perimeter binds all the boxes together. At the rear I've designed essentially a portal frame to brace the sides and roof. Portals assume the "ground" or in this case the floor, won't move. In my case, the floor will be fixed down to to the steel chassis. So I'm sort of assuming the floor is my "ground" and will brace everything else.

You can even do without the Chassis if you want and carry the loads in the box structure. But it might be hard to get it past the rego people

Hmmm, I think it could be a bit of a leap too far for them yes. I love the idea that even the drawbar could be ply, and that the shape of things follows and indicates the associated forces, but maybe not this time.

If it was a boat for this type of construction we rely on sealing all surfaces with three coats of epoxy to prevent moisture making the timber swell and shrink. That way all the paint never cracks up. There are condensation problems in trailers. For example if the canvas cover gets put away wet ... there might be several days or weeks where the interior is at very high humidity. The epoxy approach prevents this from becoming a serious structural issue.

Good point. 3 coats it is. If done wet on wet pre-fabbed, it shouldn't be too bad.

I would suggest that you review the structure and work out where you could incorporate some boxed in volume as storage. Overhead rack at the top front corner and at the rear as well? Remember they can have access holes as long as you leave a margin.

I don't mind the idea of overhead storage at the front which adds to the structure (see attached long section. Sorry see next post) but not sure I want to box it in too much at the rear. The "portal frame" as outlined above will brace the opening at all times. I've considered another smaller portal halfway towards the front and this would stiffen both the walls and roof.

The tailgate I believe can be made to brace the whole thing during transport. I've designed a raised lip on the body set in from the edge which is to help shed any water, plus fit neatly inside and seal to the tailgate for both structural integration and dust/water protection.

This is an interesting idea, I cant see any problems with ply and epoxy construction, MIK has pointed you in the right direction about that.
But my first suggestion is to move the spare... do you really want to lift it as well as the attached canvas every time you set up camp? I would also give some thought to making sure the joint between the tailgate and body is waterproof when you are camping. This is more important than waterproof for travel because you dont need water falling on your bed in the middle of the night.
Just a few thoughts,
Tom (who has been wet in leaky pop tops)

Hi Tom and thanks. I agree, the spare on the tailgate makes life harder initially, but in that location it's always out of the way and doesn't take up valuable space for other items. Still open to review though. Gas struts do great things these days so it shouldn't be too bad to lift. You'll see that the tailgate has a spoiler at the top. In the open position this stops most water from the tailgate running into the joint. The body roof is designed with a slight fall away from the joint. There is also a raised section I've designed inside the back end of the body to act as a gutter for any water that makes it through the joint and sheds it to the sides and down. (pics may show this) I haven't worked out yet how to seal properly between the tailgate and body while the tailgate is up though. Suggestions? And leaky tents are painfull too!!

Thanks guys, I'm learning lots, love it.