How to build a plywood velomobile...
March 15, 2012 1:03 AM
How would you build a plywood kayak without fiberglass?
I'm not actually building a kayak, but I'm using the "stitch and glue" technique in an attempt to build a velomobile from plywood. So waterproofing isn't an issue, but...
Everything I've read about stitch and glue kayaks indicates that the fiberglass is crucial not only for waterproofing but also for strength. I understand why this is, but I'm wondering if something else can serve that purpose - cross-sectional bulkheads, maybe?
I dove into this project on the assumption that people MUST have built plywood kayaks and canoes before fiberglass existed, right? Now I'm starting to wonder.
I'm not actually building a kayak, but I'm using the "stitch and glue" technique in an attempt to build a velomobile from plywood. So waterproofing isn't an issue, but...
Everything I've read about stitch and glue kayaks indicates that the fiberglass is crucial not only for waterproofing but also for strength. I understand why this is, but I'm wondering if something else can serve that purpose - cross-sectional bulkheads, maybe?
I dove into this project on the assumption that people MUST have built plywood kayaks and canoes before fiberglass existed, right? Now I'm starting to wonder.
I would look into box joints with strong glue, after assembling a rig or other system to cut them accurately and quickly. (There might be a more special name than 'box joint" for when you use it to join sheets that nearly flat together, instead of at a sharp angle, but I wouldn't know it).
You haven't said why you want to avoid fibreglass, which makes it hard to know which alternative solution wouldn't fall afoul of the same issue.
I haven't used fibreglass (though I've watched). I suspect it's probably so universally used for this because it can be fast and easy and simple. If you're under the impression that it's difficult and people only use it because of waterproofing, you might want to double-check those assumptions - they could be leading you towards making things harder on yourself than necessary.
posted by -harlequin- at 2:20 AM on March 15, 2012
You haven't said why you want to avoid fibreglass, which makes it hard to know which alternative solution wouldn't fall afoul of the same issue.
I haven't used fibreglass (though I've watched). I suspect it's probably so universally used for this because it can be fast and easy and simple. If you're under the impression that it's difficult and people only use it because of waterproofing, you might want to double-check those assumptions - they could be leading you towards making things harder on yourself than necessary.
posted by -harlequin- at 2:20 AM on March 15, 2012
Thanks, victory_laser! The "Light Sculling Training Boat" from the first link goes a long way toward confirming my guess that, with sufficiently strong bulkheads and other interior support, I'll be able to make something that works from 1/8" plywood.
harlequin, good question! I'm trying to avoid fiberglass (1) because I don't like to spend time with epoxy fumes and (2) because fiberglassing over wood, as far as I can tell, makes it nearly impossible to re-use or decompose. Of course, plywood already has its internal glues, but since I'm not using marine-grade plywood these are fairly water-soluble. I don't mind using fiberglass tape to join sheets, as in victory_laser's first link. I just don't want to be glassing the whole thing, as others have done.
posted by sibilatorix at 2:34 AM on March 15, 2012
harlequin, good question! I'm trying to avoid fiberglass (1) because I don't like to spend time with epoxy fumes and (2) because fiberglassing over wood, as far as I can tell, makes it nearly impossible to re-use or decompose. Of course, plywood already has its internal glues, but since I'm not using marine-grade plywood these are fairly water-soluble. I don't mind using fiberglass tape to join sheets, as in victory_laser's first link. I just don't want to be glassing the whole thing, as others have done.
posted by sibilatorix at 2:34 AM on March 15, 2012
there was a discussion on the Dutch recumbent group recently mentioning an M5 prototype "Kalisvaart" velo, which was built using traditional kayak joints. Not sure about the fiberglass.
But that's in Dutch; I don't think the actual bike was found there.
They do mention a link to a French discussion on wooden VMs, that has quite a few pictures and links; maybe someone there can help you?
My online French is not good enough to get at the details, but maybe you'll do better.
posted by gijsvs at 2:38 AM on March 15, 2012
But that's in Dutch; I don't think the actual bike was found there.
They do mention a link to a French discussion on wooden VMs, that has quite a few pictures and links; maybe someone there can help you?
My online French is not good enough to get at the details, but maybe you'll do better.
posted by gijsvs at 2:38 AM on March 15, 2012
gijsvs, thanks! I've followed most of the discussion of wood VMs - some are strip-built and some are stitch and glue, but they've all been completely fiberglassed as far as I can tell, with the possible exception of plywoodvelomobile.blogspot.com, though it has an internal frame. The French thread is one I've looked through before, I believe.
I'll have to look into that M5 prototype; I haven't heard of it before. Thanks for the links! I'll dive into google translate in the morning, perhaps.
posted by sibilatorix at 2:48 AM on March 15, 2012
I'll have to look into that M5 prototype; I haven't heard of it before. Thanks for the links! I'll dive into google translate in the morning, perhaps.
posted by sibilatorix at 2:48 AM on March 15, 2012
The stitch-and-glue method is very strong, fast and quick - this is why it's so popular. It's particularly so where the desugn has compound curves.
There are alternatives, but they will be much more time-consuming, exacting in the work and probably not as strong. Any method that uses internal bulkheads will dramatically increase the weight overall.
You could use battens inside the joint, but they will have to be shaped to fit the sheet angles and each side of each joint would have to be fitted and glued separately. You could also use thicker ply on one side of each joint and lap the thinner sheet over the edge of the thicker sheet. Again, time consuming and relatively heavy.
For what I assume is a non weight-bearing body, you should aim for the absolute minimum weight, expecially given that you have to use your body to move the whole thing. The most effective way to do this is stich-and-glue.
There is absolutely no need to 'glass over the whole sheets - just use the tape and then fair the edges in with body filler. Using 1/8" ply, you should be able to make the entire body without reinforcement except for where mounting points are attached. The fumes (and polyester or vinyl ester resin would be fine - epoxy is overkill for this) are not great, but either of those resins cure quickly and the fumes will be gone before long. If you use epoxy, the fumes will be worse and wil hang around longer. The glue on plywood is not water soluble, by the way - the only real difference between marine ply and exterior ply is the surface finish (and the price), although there are some specialty marine plywoods that are a lot stronger and this is reflected in the price also. Just plain exterior ply should be perfect for your needs. Assuming you are making a curved body, the plywood will be pretty much impossible to re-use, as it will permanently take on the curves quite quickly.
If you are making this to your own design, I recommend making a mock-up of the body in cardboard first. tape the joints together, fiddle until you are happy wit the design, then use the cardboard panels as patterns to cut the ply.
Have fun - it sounds like a great project!
I was a boatbuilder in a previous life, if that matters.
posted by dg at 2:57 AM on March 15, 2012
There are alternatives, but they will be much more time-consuming, exacting in the work and probably not as strong. Any method that uses internal bulkheads will dramatically increase the weight overall.
You could use battens inside the joint, but they will have to be shaped to fit the sheet angles and each side of each joint would have to be fitted and glued separately. You could also use thicker ply on one side of each joint and lap the thinner sheet over the edge of the thicker sheet. Again, time consuming and relatively heavy.
For what I assume is a non weight-bearing body, you should aim for the absolute minimum weight, expecially given that you have to use your body to move the whole thing. The most effective way to do this is stich-and-glue.
There is absolutely no need to 'glass over the whole sheets - just use the tape and then fair the edges in with body filler. Using 1/8" ply, you should be able to make the entire body without reinforcement except for where mounting points are attached. The fumes (and polyester or vinyl ester resin would be fine - epoxy is overkill for this) are not great, but either of those resins cure quickly and the fumes will be gone before long. If you use epoxy, the fumes will be worse and wil hang around longer. The glue on plywood is not water soluble, by the way - the only real difference between marine ply and exterior ply is the surface finish (and the price), although there are some specialty marine plywoods that are a lot stronger and this is reflected in the price also. Just plain exterior ply should be perfect for your needs. Assuming you are making a curved body, the plywood will be pretty much impossible to re-use, as it will permanently take on the curves quite quickly.
If you are making this to your own design, I recommend making a mock-up of the body in cardboard first. tape the joints together, fiddle until you are happy wit the design, then use the cardboard panels as patterns to cut the ply.
Have fun - it sounds like a great project!
I was a boatbuilder in a previous life, if that matters.
posted by dg at 2:57 AM on March 15, 2012
You might look at acoustic guitar construction for more ideas. There are rows of tiny glue blocks along the insides of the corner joints, and stiffening ribs across the wide panels.
I wonder whether you could substitute a glue-soaked canvas tape of some sort for fiberglass at the joints.
I agree with dg that this plywood is never going to be useful for anything else again.
posted by jon1270 at 3:42 AM on March 15, 2012
I wonder whether you could substitute a glue-soaked canvas tape of some sort for fiberglass at the joints.
I agree with dg that this plywood is never going to be useful for anything else again.
posted by jon1270 at 3:42 AM on March 15, 2012
Just glassing the joints is probably a good bet if you really don't want to cover the entire vehicle in glass.
Certainly it is possible to build from plywood without stich & glue (or tack & tape). Glue and screw is the name of the game, but of course, you need framing to screw into (and because this is somewhat heavy and time-consuming, you probably want a simple shape to minimize the number of joints). I've built a small punt (8ft long!) using this method (Luan ply, spruce, PL Premium adhesive, screws). I highly recommend Dynamite Payson's book Instant Boats for construction details if you choose to go this way. His other book, Build the New Instant Boats, is good for tack & tape methods.
posted by ssg at 9:22 AM on March 15, 2012
Certainly it is possible to build from plywood without stich & glue (or tack & tape). Glue and screw is the name of the game, but of course, you need framing to screw into (and because this is somewhat heavy and time-consuming, you probably want a simple shape to minimize the number of joints). I've built a small punt (8ft long!) using this method (Luan ply, spruce, PL Premium adhesive, screws). I highly recommend Dynamite Payson's book Instant Boats for construction details if you choose to go this way. His other book, Build the New Instant Boats, is good for tack & tape methods.
posted by ssg at 9:22 AM on March 15, 2012
Thanks for all the input!
dg - I've already spent many, many hours drawing designs and making cardboard mock-ups. I assumed the glue in exterior ply was water-soluble because in a few of my bending attempts (for other projects) I've de-laminated it. Perhaps it was the wood breaking down...
I'm still a little worried because this actually IS planned as a weight-bearing body. I have some interior structure designed in at the moment, but I'm afraid I may have to add to it. What I have now is a series of five cross-sectional bulkheads down the length of the velo. I hope that those, with the possible addition of an inner layer of paneling in some places, will be sufficient. We'll see...
posted by sibilatorix at 5:49 PM on March 15, 2012
dg - I've already spent many, many hours drawing designs and making cardboard mock-ups. I assumed the glue in exterior ply was water-soluble because in a few of my bending attempts (for other projects) I've de-laminated it. Perhaps it was the wood breaking down...
I'm still a little worried because this actually IS planned as a weight-bearing body. I have some interior structure designed in at the moment, but I'm afraid I may have to add to it. What I have now is a series of five cross-sectional bulkheads down the length of the velo. I hope that those, with the possible addition of an inner layer of paneling in some places, will be sufficient. We'll see...
posted by sibilatorix at 5:49 PM on March 15, 2012
Yeah, it's the bond between the laminations and the glue breaking, most likely. If you need to do tighter bends, you might need to invest in some good-quality marine ply and make sure it has an 'A' bond. You can also get ply designed specifically for tight bends, but you do sacrifice some structural strength.
If you need the body to have structural strength and have the time/equipment, an alternative would be 'cold moulding', where you make a 'mould' out of frames, then temporarily fasten strips of thin plywood to the frames (edge glued together) and then add another layer diagonally (and more layers if you need more strength). You then remove the shell from the mould and you have a very strong, light body with no need for internal frames to take a fair amount of structural stress. I think this is far more work than you are interested in, though and requires quite a lot of working with epoxy glues.
It sounds like the structure you are planning will be plenty strong anyway, but don't forget to pay careful attention to weight - every time you add an item, think carefully about how much it weights and whether there is an alternative material or method. It's amazing how fast weight can add up and how hard it can be to reduce the weight later.
posted by dg at 6:57 PM on March 15, 2012
If you need the body to have structural strength and have the time/equipment, an alternative would be 'cold moulding', where you make a 'mould' out of frames, then temporarily fasten strips of thin plywood to the frames (edge glued together) and then add another layer diagonally (and more layers if you need more strength). You then remove the shell from the mould and you have a very strong, light body with no need for internal frames to take a fair amount of structural stress. I think this is far more work than you are interested in, though and requires quite a lot of working with epoxy glues.
It sounds like the structure you are planning will be plenty strong anyway, but don't forget to pay careful attention to weight - every time you add an item, think carefully about how much it weights and whether there is an alternative material or method. It's amazing how fast weight can add up and how hard it can be to reduce the weight later.
posted by dg at 6:57 PM on March 15, 2012
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http://koti.kapsi.fi/hvartial/#XX1
Bark Canoes and Skin Boats of North America (google books)
posted by victory_laser at 1:09 AM on March 15, 2012