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I know it is long, but I wanted to put it all together for context and because the questions are interrelated.
Ohhhhkaaay, a few things, Be forewarned that. like the Pirahna Brothers, I use sarcasm. And if you thought yours was long… Gah - here goes my evening.
Background: Newbie here, and I’m looking to build a folding or 2 part paddleboard so it will fit in the car/van but still have an 11-12’ board with 32" beam. It will probably be a displacement design as it’s all lakes in my home of colorado, but I might still do traditional design so I can use it when we do drive to TX or CA for beach weeks. I’m big (>200), so need a big/sturdy board and ideally could use it with the dear wife (DW) for sit on kayaking. It will probably only see 100-300 hs of water time a year and will be garage kept.
Background - pretty much everything you describe has been tried one by one…with at best limited success. Attempting to do them all together is a nightmare waiting to happen.
Let’s start with the folding aspect. You’re talking about a hilariously long and wide thing, with a lot of area. The static loads alone are gonna require a REALLY STRONG system to hold it together, and then you have dynamic loads, like waves and wakes and chop and so on. Okay, neat, you come up with something, carbon fiber, titanium, whatever, you still need a really rugged substructure to fasten it to, tied into the rest of the board and real rigid. Which will be at the very least heavy, plus expensive. People have been trying to come up with a working folding board for at least forty years that I know of. Note I say trying. Not succeeding.
As has been suggested, and I will note kindly suggested, get a roof rack. Lose the folding idea.
I’ve read a ton here and other places as well and plan to eventually post my build here (and probably Instructables). I’ve never built a board or boat but and good at building things. However I hate epoxy/fiberglass and react badly enough to it I’ll probably avoid it if I can avoid it even it impacts my design choices. Since I’ve never built a boat/board (and have an inflatable), my DW is not really on board, so I need to do it cheap for now to prove the idea. (I’m an inventor with many patents and think my design could be patented but will likely post full plans online even if I file a patent so DIYs can do it themselves).
Uh huh. Don’t enumerate your mature poultry as ovae…
Here are my 3 first sets of design questions
- Materials
My first group of question is materials. My real preference is to get stuff on its way to the landfill or well used, but that has been very limited in choices so far.
1.1) I know I could do a stitch/glue plywood, but locally I cannot get 4mm or 5mm marine. I can get 1/4 underlayment, but then it’s going to be heavy (~60lb of wood + PMF coating ). I’ve got 1x4 furring and 3/8 exterior ply I can use for stringers/folding connections on any of the builds. I know I could make this design work and build that all in for < $80.
Awright, lauan is cheaper and lighter than underlayment. Stitch and glue is overrated, speaking as a guy who does build boats. It’s also heavy and expensive, what with the fillets of resin plus filler in every join and seam. There have been a lot of very successful hollow wooden boards built, the tech and instructions are out there, interior bulkheads and formers made of ply and such, reinforced with wood. Not a bad way to go. Requires very good woodworking skills and tooling.
The rest of the materials are foam. If I go any foam route, I’ll probably have a plywood standing platform, so I only need enough strength or the occasional misstep and crashes.
Bzzzzzt- wrong answer.
Just to start with, putting a single-point 100kg load in the middle of something that long is gonna make for considerable stress. And that’s just the static load. Dynamic loads, like waves breaking on it or even when you have the nose and tail supported (say, paddling across a boat wake) and the center ( with you on it) unsupported- Ungood.
1.2) Locally, I can find polyisocyanurate foam used for cheap ($10 for 3 1"x4’x8’ sheets or $15 for 3" 4x8 sheets), and with that, I can use low-cost Polyester resin such as Boatyard resin which is $14/gallon. https://www.bottompaintstore.com/Boatyard-Polyester-Resin-Gallon?gclid=C…. I’ve read most of the thread here that mention that type of foam, and it does not seem to be well respected. It is also pretty heavy (3" 4x8 is like 30lb before any glassing work). Also not sure how well it will handle building a hinge connection with the weight. So I have that way down on my list, but if anyone has positive experiences to report, I might reconsider because I can use polyester resin which, while not as good as epoxy, is better than PMF and the total cost for a higher-end finish is still reasonable.
The Iso foam isn’t bad for some things. I’ve built boat stuff, insulated fish holds and so on from it. Typically it’s foil surfaced and glass won’t stick to it. Works fine with polyester resin just fine. Problems include how much foam comes away with the foil when you rip it off the sheet. And how you’re gonna deal with that.
1.3 I can keep looking for XPS or EPS scraps (or give up and buy XPS sheets for about $70 or EPS for $50). There are choices of compression strength (25psi 15psi 10psi), and I could not find good threads on the tradeoffs. To support the folding/hinge, I will have two 3/8" plywood stringers so I am curious how the PSI /rigidity trades off with two singers. (2 would be 24" apart to be under my feet). Since either is lighter than either plywood or poly iso, I like these choices a bit more, But since I hate epoxy and polyester will melt it(unless I add coating), I am tempted to do PMF (more below) on it and am not sure if it will then be strong enough for my mass, specially lower density EPS. Any comments on strength/density needed?
Awright, gluing stuff together, scraps and what have you - but what are you gonna do to stick this jigsaw together? Also, adding a coating, yeah, that’s nice, but just how well is the coating sticking to the foam? How well will the resin stick to the coating? Will it fail in shear under stress? Glue as a barrier coat has been used for polyester ding repairs on styrene foam boards, which are really small and structurally tied in to the rest of the glass. It used to be hard to get decent epoxy for repairs, which is why we did it.
1.4 The crazy idea – I have dozens of sheets of 3/8" white form core board (paper on both sides of foam use for academic projects) and think I could build a board for the cost of glue. To test it I build a small grid of knock-down interlocking 4" strips separated by about 4" horizontally and vertically. With that I put a 3/8" foam board piece on top and stood on it. The paper cracked and dented under my 200+ lb on one foot, but it did not break. Then added a coating of 6mil polyester fabric + titebond glue and let it dry overnight. I could then stand on that piece without any cracking. I can make a denser grid, maybe 2" or 3" spacing, and then add 2 layers on the top with layers of fabric/glue between each. (I’ll use to glue to waterproof the paper layers as well) and then coat with PMF and use a plywood standing board. I’ve not estimated total weight, but the sheets are light, and since the major of the volume is air in the grid, I think it might be lighter than XPS. Does anyone think this is just too crazy to try? Or crazy enough to keep exploring.
Heh, I am not gonna discuss single crazy ideas. - look, I’m glad you did a test. But… you didn’t do the right test. You simply made your sandwich and set it on the floor and stood on it to see if it would squish. Yeah, that’s nice- if you are gonna use it only on solid surfaces.
Now, make up a version of your sandwich, say eight feet long. Put it on a couple of sawhorses seven feet apart and then try standing on it. I’d maybe put a mattress on the floor first.
Okay, if you wanted to, you could probably make a very nice hollow board with this 3/8 stuff, similar construction to the hollow wooden boards. You will need to reinforce ( glass or carbon fiber) every piece. And glass them into position. This becomes…interesting.
- Layers
2.1 For either foam choice, I’ll need layers. Some ISO sheets have foil; some have glass mats. I’m wondering if adding glue or polyresin to those glass mat facings would make up for the fragility of the ISO sheets (though it will add weight).
The foil is to help with R-rating. The glass mat is so you can resin the stuff ( say to make a boat deck) and add another layer or several of mat for strength and abrasion resistance.
2.2 Similarly, for XPS, everyone seems to glue the foam to foam. I was wondering if adding a layer of fabric+glue between the two layers would provide added strength? I have a lot of free polyester poster fabric that is very strong (I can hang my 200lb from a 1" strip of it uncoated). If I do, would titebond or gorilla glue or foam be better between the sheets/fabric lamination?
Awright, to begin with- cloth between foam layers will add some stiffness. They used something similar with cold-molded boat construction and Really Good Glue for PT boats back when. But that’s not the issue. This will be, as surfboards are, a monocoque structure, the strength is in the skin.
Now, I’m real glad you have all this free polyester fabric. I’m sure it has an ultimate strength that will hold you. But it will stretch before that, which in turn will make for some very interesting things going on as the board flexes and shear happens. Make yourself a sail or some pants or something. Fibrrglass and carbon and for that matter Kevlar stretch little if at all. Which is why they are the laminating fabric of choice.
2.3 If using PVA glue (titebond) and doing layers to avoid delamination, is it best to let it set but not cure and then add the next layer or let it cure, sand a bit, then add next layer?
Personally, I would glue, place, glue, place until you have it completely layered, then weight the living phuque out of it, use a roller to get air bubbles out of it first of course. But again, I wouldn’t do this in the first place unless you are effectively making a 3" plus thick blank out of it and even then…
- Skin/Covering:
3.1 I am leading to PMF – titebond II over the fabric. Most people use canvas or bed sheets (canvas) or fiberglass. But I’ve also seen various posts say it is important for strengths that the glue be absorbed by the material, but glass is not absorbing, just filling the gaps. So I thought the polyester fabric poster material I have would be sufficient/good since it will not mold if wet. Any comments on that?
Yeah, comments above. Look, back when there were some very cheap department/dollar store import boards that were fabric covered foam. As boogie boards they wrked badly, as surfboards they most definitely snapped like breadsticks.
Resin permeates the weave of the glass cloth, not the fibers. Neat. And irrelevant… Our British friends refer to boats built of resin and fiberglass as GRP, Glass Reinforced Plastic, which is a helluva sight more accurate than what we call them, ‘fiberglass’ . And the strength is in the skin.
Fabric over all- yeah, well, it might keep water out until it wears or gets cut. Strength, no. In boat work they used to do canvas or muslin (sheeting) set in adhesive over thin planked lightweight decks where abrasion and impact didn’t figure into it. Used to, now they are typically glassed. With…
3.2 My second choice is the Boatyard polyester resin which will make a nicer /stronger finish (but cost 2x). This is an unknown formulation for $40/gallon – does anyone have experience/comments on it.
It’s not a bad product…for boats. Typically it’s an inexpensive waxed sandable resin which means if you are doing multiple layers you need to do them all at once, which gets kinda messy. Or else grind and grind and grind. It’s quite good with mat or woven roving, heavy heavy stuff, not so great with cloth. .
3.3 A more traditional poly resin would be $60 and epoxy $80-150 + glass. I know resins are both stronger, but I can do PMF for the whole board for <$20). Given my very limited use per year and uncertainty about the folding design, I’ve also wondered if the PMF would also help highlight any design flaws with less testing than the stronger resin-based covering. Does anyone with experience want to comment on that?
Terry
Yeah, well, a few suggestions.
I remember reading a history of a particular aircraft where it was noted that the minor flaws were such that they completely hid the major flaws. When testing, you want to change one variable, not a bunch of them, lest you find that you have no idea what went right or wrong in the overall train wreck.
Look, I applaud your desire to reuse and recycle materials. The surf biz is amazingly wasteful, just to start with. But that is a major project in itself.
Then there is the radically different structure you want to try, construction, materials and so on. Oh, and making it folding.
As the cliche goes, how do you eat an elephant? One bite at a time.
The methods now used in surfboard construction came about very gradually, trial and many errors. A lot of them failed. Probably including much of what you want to try all at once.
So maybe you want to at this gradually, one thing at a time. Or, opon reflection, you may decide that the time and expense in the several (many) iterations to get any one of these things right are not worth it and buying something off the rack is a better use of that time and money.
hope that’s of use
doc …
