Foam core for lightweight boat building?

John Robinson

John Robinson

Well-known member
I remember from my old sailing days most racing boats were built out of a sandwich construction, either balsa core, foam core or hexel honey comb. I'm sure I can just google foam core for boats, but does anybody know a good source for this type of foam? As I recall balsa core had problems with inevitable water penetration and resulting rot.
 
I would go one step further and get an engineered product. There used to be a company called Penske Plastics, and UFO composites, there was one company near Notre Dame and a couple of others. I'd have to do some digging. I do know that Penske Plastics was recently acquired as I still visit with some old friends who worked with me on that project. Last name of BonJovi sound familiar? That was one fun and very wild project. We were making a boat be very quiet and had the technology to reduce the decibels inside a sportboat by 16db to begin with. Wanted it quieter, how much did you want to spend?. Quite impressive.

Anyway, what we basically had was an urethane foam that had fiberglass reinforcing strands throughout. I won't get into details as I could probably get in trouble but the composites made were truly remarkable. Customizable in terms of strength and weight, sound damping qualities and so on.

I'd bet if you googled reinforced urethane foam cores you would find what you are looking for. There was also a companiy in Michigan we were workling with. Somewhere near where all the tulip bulbs are grown if I recall.

Mark W
 
http://www.fiberglasswarehouse.com/index.php

This place cells various core materials including divincell foam and balsa wood.

The issue with these foam cores and "light weight" boat construction is that you need a lot of glass to keep the core from delaminating. Lots of glass means not so light boat, but lighter than wood cored.

Glen-L also supplies pre cut lapstrake and cold molded foam for some of their kits.
 
That is the benefit to purchasing some of the materials I mentioned. The fiberglass starnds are foamed in to the core when being manufactured. It gives you the strength you need and maintains lightweight benefits. I wish I could recall the name of some of these places. The owner of one of them used to post on here once in awhile.

Mark W
 

basic how to article. They also sell the core materials.

http://boatbuildercentral.com/howto/foam1.php

Foam core for smaller boats is about the same weight as ply core and costs more. 1/4" foam core is not that much lighter than 1/4" ply and the glass/epoxy is the same.

In bigger boats requiring thicker laminations the weight savings of the foam core vs. ply starts to add up. The bigger the boat the more weight savings can be achieved with the use of foam core. For high performance or racing boats the weight savings start to pay off in terms of performance, fuel savings, winning races, etc.
 
Clark Craft had it when I was building the BB2 and I think World Panel had something like that too. I always thought a sneak out of Royalex would be cool, one of the big canoe makers used it in tripping canoes.
 
The reason I'm thinking foam core on my small marsh boat is that my buddy wanted a boat with a very curved deck, curving in two directions, so was thinking about forming the deck and constructing with foam and fiberglass sandwich, then epoxing the deck to the stitch and glue plywood lower hull. See my marsh boat plans post.

Thanks,
John
 
Foam core materials won’t bend any differently than plywood. They can only bend in one direction to form cylindrical or conical shapes, not more complex shapes.

What you may be thinking of is shaping the foam by cutting to shape similar to carving pink insulation foam for decoys or like the foam boats here and at the refuge. In this case you would essentially be making a male mold to laminate the fiberglass to. The other option to make a complex curved deck would be to strip plank the deck using 3/4" X 1/4" strips of cedar or a similar light and clear wood.
 
I thought I had seen a boat building product that was made 4" or so foam squares attached to some kind of fabric, similar to the way balsa core is manufactured. This allows it to follow complex curves. I may be mistaken. If I can't go the foam route I'll probably do a double diagonal cold molded cedar ala the Gougeon Brothers method used on larger sailboats, but I'm open to suggestions.

Thanks, John
 
Divinycell makes a foam that is scored in two directions but not all the way through and has a skrim on one face. It is for small radius curves, but takes a huge amount of epoxy to fill all the scores once in place.

Cold molding with thin plywood would work for the double camber deck. Okoume comes as thin as 3mm which bends like paper, a real PITA some times.
 

ay not be good for a small boat, but I've seen chicken wire inserted into a cavity and (spray can) foam insulation added a bit at a time. Some guys make bait boxes under a seat double walled and fill the "cavity" with spray can foam. I've used 1/2" foam sheets on top of the hull bottom and put 1/4 ext. ply over that. (keeps feet off the bottom & adds floatation) , same thing can be done to the sides. The 1/2" foam sheets flex a bit and are easy to work with. > insulation dept. & Home Depot - Lowe's - etc. MUCH cheaper than a 'BOAT SUPPLY'. Comes in different thicknesses - 1/2" flexes better & can be added to, to be as thick as you want.
 
Hi John,
I agree with the responses you have gotten so far and would add a few more suggestions.

1. Don't adapt a wooden boat design to foam core - unless you are a structural engineer. Start with a foam core boat design.
2. The weight savings won't be significant until you get into a boat 20FT+
3. It will cost a lot more to make than wood/glass - at any size. Would be cheaper to buy a bigger motor to make up for the "extra" weight..
4. Don't confuse flotation foam with structural foam - they are totally different, and I wouldn't recommend using flotation foam for structural elements.

I also considered using some foam core structures in a small boat and concluded that it wasn't worth the hassle or expense.
The wooden boat forum has some good advice on boat buiding - look it up if you haven't already.

http://www.woodenboat.com/forum/index.php

keep us posted - I have enjoyed your last project!

Dave
 
Thanks to both of you for the links. I especially like the foam strip method on the first link.

I am open to any and all ideas, please bear in mind this is our own design based on shapes I have seen of photos of various marsh boats in the boat list section of our duckboats site, so we aren't adapting a wooden design per se, we are trying to decide which method will be easiest to build the lines and curves we drew up. We are also looking at the option of building a model with chines that would be easier as a stitch and glue plywood boat.

Weight is definitely an issue, but that's not the reason I'm thinking about foam-glass for this boat, I realize that depending on layers of cloth and thickness of resin either method will weigh pretty much the same on this size boat. The only reason I'm considereing foam-glass construction is due to the complex curves of the design. We might try bending sheets of thin plywood and convert the design slightly to truncated cone and cylinder shapes for simplicity.

Regarding a larger motor, though we will have a square transom in case we ever want to put a little motor on, these boats are intended to be paddled, poled or pulled along while walking in shallow water. We plan to either tow them or place them across our larger Snow Goose to transport to some nice little duck holes off the river that are too small and shallow for our larger V-bottom Devlins. So very simple, no motor use. My buddy just emailed me his thought that we will build his boat in four days and launch on the fifth. I dared him to post that over here. I guess thats why we never let him bid on landscape projects, he always under-estimates jobs by about 75%!

Since we are building two, and our performance criteria is simply to float us level with a small load, be a stable sitting-shooting platform and be light enough to carry in the back of a pick up truck, I will probably experiment with different design and construction on mine.

Thanks, John
 
I think plywood is the way to go. I have read a ton on small boats along the same lines as your after. IMHO curved Okhume plywood is the best weight to strength material that is useable in a home workshop. You could go with cedar strip using bead and cove. Your hull shape should be no big deal, but there is a ton of work in those things. I think the next step up is vaccume bagged carbon fiber/Kevlar similar to the Poke boats.

GL
 
Built a few boats using this type of product. It can bend in more than one direction, weight can be varied depending upon the density of the board you desire, thickness can be varied to whatever you like. Product is structual and some of the foams have flotation capabilities. Need a carbide blade to cut the stuff.

Please note that Michigan Composites is just an example of one company that makes this type of product. I had a great relationship with PEnske Plastics in Mt Juliet TN (I think).

Stuff is amazing. Check it out.

http://www.michigancomposites.com/

Mark W
 
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John,
I am going to take some pictures of a Canoe that is being built in the shop at work by our IT guy. He is almost done with it and it has way more shape than you will need for the top of your boat design. He used the strip built method over a jig. The strips act as core and are typ 1 inch by about 5/16 with a cove and bead. They are temp stapled to the jig as the yellow glue sets as you plank. the strips bend easy and allow compound curves to be developed. Once the planking is finished the outer skin of glass and epoxy is put on. Then pop the part off and cover the inside with cloth and epoxy to develop the cored panel. With the curves and the two skins the part is very stiff and resists deflection well and is very light. It builds fast if you stay away from fancy inlays and patterns and intend to paint not varnish the part.
This link shows a similar canoe and how the build method allows very complex curves to be developed.
Not hard and not expensive if you have a table saw and a router.
I like the foams and nida core but if you are not vacbagging and infusing resin into the core voids you will be just as easily served by the wood core.

Also, once you have one done, you can pop a part off of it by moulding glass alone right off without much trouble, just a heavier part due to the required laminations to get the same stiffness.

http://www.greenval.com/winisk.html
 
This picture shows how much curve can be easily achieved. It show a hull being built without staples for varnish finnish which slows down the work to a few strips at a time. But with staples into the jig ribs a guy can do one side a night using yellow glue. Pull the staples, sand and then epoxy and cloth.


http://www.greenval.com/interclamp.jpg
 
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