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Canoe building question

CanoeCritter

Member
Jul 5, 2011
5
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I was wondering if anyone has tried to build a wooden strip canoe using a foam core instead of the wood strips. The foam I am considering is the type used in construction.

Would it retain enough strength?
Would the epoxy properly adhere to the foam?
And any other questions I should be asking.

CanoeCritter
 

project

Member
Jun 1, 2011
15
0
The foam works great for building a light, strong boat if done right..I havent built a canoe out of it but have built aircraft components and hovercrafts using similar methods and the strength is incredible if done properly ..
 

beekeeper

Well-Known Member
Mar 4, 2009
1,573
18
project said:
The foam works great for building a light, strong boat if done right..I havent built a canoe out of it but have built aircraft components and hovercrafts using similar methods and the strength is incredible if done properly ..
What construction methods, or designs are used to achieve the strength? Will these translate to home built paddle boat designs?
CanoeCritter asked about subbing foam for wood strips. A foam boat built this way, would not be as strong as the wooden boat. It may be lighter, but would it be strong enough? "Strong enough" could only be answered by the user.

beekeeper
 

swampwood

Well-Known Member
Aug 6, 2010
274
2
Bayou State - Louisiana
project said:
The foam works great for building a light, strong boat if done right..I havent built a canoe out of it but have built aircraft components and hovercrafts using similar methods and the strength is incredible if done properly ..
Project,
Please explain, The right way to use foam in building construction? Or show some pics of its use? or both :idea:
 

beekeeper

Well-Known Member
Mar 4, 2009
1,573
18
CanoeCritter said:
I was wondering if anyone has tried to build a wooden strip canoe using a foam core instead of the wood strips. The foam I am considering is the type used in construction.

Would it retain enough strength?
Would the epoxy properly adhere to the foam?
And any other questions I should be asking.

CanoeCritter
I may have been wrong about the foam strips. Check this link:
http://www.amateurboatbuilding.com/arti ... index.html

Somebody needs to build a foam boat. Why aren't they common?

beekeeper
 

JEM

Well-Known Member
puncture resistence is the biggest reason. In buildng with foam core, you have to apply fiberglass on each side of the foam core to create a composite sandwich. By the time you build up enough skin thickness on the outer part of the hull to be puncture resistent, the skin is strong enough on it's own not to need a foam core or fiberglass skin on the hull interior. This happens on smaller craft that don't get on plane or need to with stand extreme loads. There are some canoe manufactures that use some foam core (in conjunction with more fiberglass) to add extra stiffness on the hull bottom like:



See the long diamond at the hull bottom? It's used in the area of higher stress. Keep in mind they make their hull sides vert thin to save weight. You have to mount your seat on the hull bottom because the sides are not strong enough to support hanging a seat from the gunwales. The book "Building Your Own Kevlar Canoe" show how to make a mold to create a one-off kevelar boat from a foam plug and use foam ribs to strengthen the hull as needed. Good read. Here's a build log of that book.

http://www.myrabo.com/k-canoe/kevlar2007solo.htm

I think that would be a fun project. But my thoughts are if you're going to go through all the trouble of making a mold, why not just use wood so you could pop off several hulls? In the book, it tells you your foam plug will likely get tore up when you remove the hull from the mold. Anyway, build a small paddlecraft entirely from foam core is possible, but it gets to be a waste of time and material.

But! What about building up from foam core, then just taking out the foam for the top 75% of the hull sides? Apply some packing tape to the outside of the foam you will remove before applying fiberglass. It should peel right out. Glass in the foam on the bottm hull interior and up the sides? Then you'd have it. Be warned though: Unless you're usng closed cell foam, reparing foam core could get ugly. That's why I'm a fan of wood. But to each their own.
 

Kayak Jack

Well-Known Member
Aug 26, 2003
13,532
96
82
Okemos / East Lansing Michigan
JEM said:
<SNIP> Unless you're using closed cell foam, repairing foam core could get ugly. That's why I'm a fan of wood. But to each their own.
I concur. Glass ADDS strength to that of the core. Trying to use the outer skin as the sole, or primary, source of strength is in between very difficult and beyond a point of diminishing returns. People stare in awe at a wooden boat; no one says "Oooo" or "Ahhhh" over a chunk of foam.
 

project

Member
Jun 1, 2011
15
0
Sorry its taken me so long to reply.. glass on foam can be made to be very light and strong if done right but its not cheap and is very time consuming.I built some test panels a couple of years ago of 1/2 blue board from lowes laminated with 3 layers of 3 oz carbon fiber on all sides that resulted in extremely strong panels. Now the big question is would it be worth it? I would have to say no for a few reasons, the expense of the carbon fiber cloth, the extra time it would take to build all the panels and the expense of the vacuum bagging equipment. For me personally I would rather have the beauty of the wood to look at and by the time you would finish one composite boat, you could be on your 3rd wooden one.
 

tx river rat

Well-Known Member
Feb 23, 2007
3,043
2
Waco Tx
Kirk
I just posted that thread a few weeks ago. I am still playing with it and will build one sometime in the future.
Foam can be used for making molds ,core for structures, used in the lost wax process. kelvar outside covering , a lot of uses.
First kelvar or carbon fiber is to expensive and labor intensive. not an option for me,
6 ounce glass inside and out ,epoxy and the dowling pattern do several things that I explained in the thread. Contrary to what jack stated you are not just using the outside skin, with the dowels you a have a rigid impact resistant unit where the load is spread completely thru it.
It isnt going to look like wood true ,well it could if Sondra got out her paint brushes ,but a good paint job and it would be a nice looking boat.
Somewhere on the web there is a race boat built using this method ,I think it was built for the Yukon race. I think with a knife a can of spray foam you could patch a hole pretty quick and do it right.
Taking a lick, I was very impressed with the impact resistance when I used a hammer on it 30 times ,I dont think a wood boat would do any better.
Ron
 

JEM

Well-Known Member
Ron,

The biggest concern I'd have for this type boat is the sheer strength of the foam. Another boat website, which shall remain nameless because I'll hear the "click-click" of Chuck's double barrel shotgun if I do mention it, built a simple canoe out of 1/2 foam and biax cloth. They said it latest about 3 months before the blue foam started sheer in the middle. They built it from foam strips bonded together with epoxy and covered in fiberglass. I would have thought the epoxy would have prevented the sheering.

However: Your dowels might prevent all that.

Now they do make specific boat building foam that won't sheer but it's VERY expensive.
 

tx river rat

Well-Known Member
Feb 23, 2007
3,043
2
Waco Tx
Matt
You are dead on on the shearing, but the dowel stop that, also there are several other ways to do it ,if you can isolate small areas of foam the problem is minimized, also 1 inch foam will be three times as tough done this way as 1/2 will be .
Planes built from regular Styrofoam with a covering of Dynell have been flying for years. I believe the pioneer of this process in planes was Ken Rand with his KR1. Lot of stress and vibrations on a wing and they were very impact resistant.
Ron
Dang I guess I need to build one and give it a good test.
 

CanoeCritter

Member
Jul 5, 2011
5
0
I have been checking out these posts and some others "from web sites that we wont mention here" and so far I have come up with two major concerns.
First is the sheer strength, second is the compression strength. Ron's use of dowels seems to help with the compression, it would seem to me that it would help with the sheer as well. It would be interesting to see some test results on this. I wonder if in addition to the dowels that if you would drill holes through the foam, leave the holes open, and let the epoxy bond directly to both sides if that wouldn't fix the sheer issue.

Yes there is foam that is specially designed for boat building; however, they are very expensive and just as heavy, if not more, than wood. If I was to go that route I would stick to using wood.

On the other hand I would hate to spend the money to build a canoe from foam that didn't last and fall apart on me while on a multiple day trip.

If i'm not mistaken I think the boat that was built for the race did win the race but it was also beginning to fall apart at the end but i'm not sure if they used the dowels in their construction.

Ron please keep us updated on your progress.

Thank you all for your input.

Critter
 

project

Member
Jun 1, 2011
15
0
The trick is covering all sides of the foam, not just the top and bottom. If the foam is totaly encapsulated in the carbon the strength becomes unbelievable and the foam becomes irrelevant but again, the time and expense makes it impractical.
 

tx river rat

Well-Known Member
Feb 23, 2007
3,043
2
Waco Tx
Project is right on enclosing the foam, again not using anything but fiberglass, no carbon,
there are several more ways to strengthen the hull, one is at each joint use a wood dust @epoxy mix between the edges for bonding then grove out a 1/4 inch deep and run this mix down the seams for a wear point and stiffener , running a layer of glass cloth will do the same thing or a thin piece of wood, this isolates the different section making them smaller units .
The dowels work as a truss for strength also shear and transfer impacts forces to the inside skin, I like the dowels for a couple reasons over just holes .one is the finish ,epoxy shrinks when drying, so you wind up with a bunch of dimples.the epoxy is flexible the wood dowels are stiffer under compression.
There is more of this type construction than most folks realize, planes we have mentioned, they build houses using one lb foam with wood epoxyed on each side . if you buy a travel trailer with a fiberglass outside , most are one inch foam with a layer of glass glued on each side.and wood on the other.
If and when I build one it will get a workout , I use a boat pretty rough.
On another forum I frequent a gentleman there built one from 3/4 foam and has been using it for a few months now ,no dowels or stiffeners and so far seems to be working well.
Ron
I think it would be neat to build a 20 or 25 lb 16 ft boat :D
 

project

Member
Jun 1, 2011
15
0
The only reason i use carbon as an example is because it enables you to use multiple layers of lighter cloth and result in a stronger part.. Fiberglass can be used in the same manner, it just has less strength and higher weight.. the techniques is the same.
 

project

Member
Jun 1, 2011
15
0
JEM said:
It seems like you'd get a lighter boat building a foam plug mold and then popping off a fiberglass hull with selected foam-fiberglass stiffeners... like in the book.
You would.. you could even pull a mould off a wooden canoe and not even use foam at all except for stiffeners.