Strip foam boat building

[svfrolic]

I am looking for some input about building small (canoe size) boat using foam strips glassed (or "kevlared") from both sides.
As the core material I was thinking about 6 lb polyurethane foam. I was thinking about 1x1/2'' strips (wooden boat builder use cedar strips 3/4x1/4") cut from block of foam.
It went through my mind using polystyrene foam like surfboard builder use but this is much weaker material...however works in surfboards...
If anybody used this method I would appreciate any info.

 

[TeddyDiver]

Why?
BR Teddy

 

[PAR]

When "designing" a cored composite, you need to investigate the strength and stiffness necessary for the loads you expect. Taking a guess at core thickness, density and sheathing schedules is a guarantee for disappointment.

For an overview of the process have a look at:
http://boatdesign.net/articles/foam-core/
which will get you in the ballpark for core thickness, density, etc.

Lastly, a surfboard's loads are considerable different than that of a boat, which is why the core and sheathing scantlings seem so light. If you try to use wooden core dimensions, for a foam core composite, things will break pretty quickly once you get it it.

 

[DCockey]

John Lindahl builds A Cats using carbon/epoxy over foam strips. He uses a set of CNC cut female molds spaced 6" apart, closer than is needed for wood strips. He cuts strips of foam with beads and coves (same shape as used for wood strip canoes). The inside of the station molds are then "planked" with the strips and a layer of carbon cloth and epoxy is applied inside the strips. The hull haves are removed from the mold stations and glued together. The outside is then covered with a layer cloth and epoxy. I've seen part of a hull and the workmanship is excellent. I assumed it was vacuum bagged but Lindahl said he just "knows how to use a squeege".

More information on his website http://lindahlcompositedesign.weebly.com/lr4-build.html
and also in an article from the Spring 2012 issue of Epoxyworks
http://www.epoxyworks.com/34/pdf/Foam Strip Plank.pdf

 

[DCockey]

svfrolic, why are you interested in using foam rather than wood strips? Weight savings is possible with good engineering. My guess is using foam would be more expensive.

 

[svfrolic]

svfrolic, why are you interested in using foam rather than wood strips? Weight savings is possible with good engineering. My guess is using foam would be more expensive.

Time saving.

 

[svfrolic]

John Lindahl builds A Cats (...). I've seen part of a hull and the workmanship is excellent. I assumed it was vacuum bagged but Lindahl said he just "knows how to use a squeege".

Yes, I have seen it. very good work indeed.

 

[svfrolic]

Why?
BR Teddy

Why not?

 

[svfrolic]

When "designing" a cored composite, you need to investigate the strength and stiffness necessary for the loads you expect. Taking a guess at core thickness, density and sheathing schedules is a guarantee for disappointment.

For an overview of the process have a look at:
http://boatdesign.net/articles/foam-core/
which will get you in the ballpark for core thickness, density, etc.

I think about building a canoe (not an ocean going vessel) they used to build them from bark;-)

 

[DCockey]

Time saving.

Where would the reduction in time come from?

Based on Lindahl's experience using foam strips may require twice as many molds, which would increase time for making and aligning the molds.

Cutting strips? I wouldn't expect any difference in time if you have use of a power saw.

Fairing?

 

[TeddyDiver]

Why not?

Reasons my friend, you must have a reason to do what ever you do. Why not is not a reason. There's no time saving, that's at vaste of time (except a good lesson )

 

[PAR]

Composite hull building, regardless of hull type isn't very fast, nor typically cost effective, for a one off. In most cases you need to justify the material and labor cost increases, with some element(s) of the SOR. Simply put, a one off composite build (canoe) will be a more costly and a more time consuming project, unless you can qualify these aspects of the build with something. Build speed wouldn't be one of those things you could use for this justification, unless you where looking to produce several hulls of the same type off the same jig.

 

[Oyster]

Time saving.

No way that building with foam is quicker than any wood in small boats. In the beginning your frame or building jig will take additional time, almost as much if not more time that it takes to rough in your hull shape, if you get things correct. Buy a Kevlar canoe and maybe dress it up and you will have not only money in the bank but time on your hands to visit the water while quite possibly no additional back strain too in many cases.

 

[svfrolic]

Where would the reduction in time come from

I have actually a coworker who used to build boats that way. He said that it is a weekend project. Maybe a long weekend;-)
Foam boat should be easier to strip and sand. Stripping and fairing foam shouldn't take more than a day (at last that is what takes to strip and sand male mold for building Kevlar canoe:
http://www.myrabo.com/k-canoe/Kevlar 2007/02-solo-foam.htm)
Glassing would take 3-4 hours for each side.
Then a day for finishing (gunwales, seats, yoke etc.)
No, I am not going to do luster Awlgrip finish, it is a canoe not a Hinckley
I don't say no to wooden one, I am just considering different options.
For the lowest cost, building time and weight I should probably chose SOF boat. We just had a shop talk about foam strip boats so I was interested if anybody else used that method.

 

[svfrolic]

Reasons my friend, you must have a reason to do what ever you do. Why not is not a reason. There's no time saving, that's at vaste of time (except a good lesson )

I just feel like I want to build something. I like projects. Is that a reason?