How squishy is the foam? I'm just thinking about ways to do it, and if you set it up in a shaper you could have a powerfeed and keep things consistent for width and finish of the cut.

it's fairly rigid. If you were to hold a 1.5" x 1.5" x 8 foot from one end, it probably wouldn't flex 2 inches on the extreme end. It machines like butter.

Check this thread lot of good stuff.
http://www.catsailor.com/forums/ubbthreads.php?ubb=showflat&Number=217766&page=1

A tip for one off customs. Have paper templates of what you want the core to look like between the female forms so you can make sure what you just built, matches what you designed(you may need templates for the form too, depending on what technique you use). Having the ability to make additional templates at 2AM, when things start looking odd and you need to check places you don't have templates for, helps. Some CAD programs can put alignment marks on 8.5x11 paper so you can tape them together to make big drawings.

The issue is, core strips don't usually bend the way the CAD curve-fit "bends". Sometimes the strips don't lay up perfectly on a form. Curve-fits have assumptions that physically translates into compression or tension on the strips between female forms. If you create a curve-fit that assumes no tension or compression on the strip at the forms, friction on the real strip produces compression and tension. You can minimize this by using a curve-fit that approximates your strips and by making a CAD drawing of a strip built core but there are a lot of variables in assembly. If you make a CAD drawing of the strips, the CAD can give you measurements from one end of the core strip, to where the female forms touch that strip. You can measure and mark the strip so you can check to see the strip lays in the female forms they way it should. ALL of this is a pain in the butt but it beats discovering your hulls are different and having to build a third one, to match one of the first 2.

For boats built from good plans, this all been sorted out.

I don't want to start a discussion on merits of materials but you can use cedar instead of foam. Depending on where you are, there can be a huge price difference between foam and cedar and you will need less material in the laminate. Cut the strips out of 1-3" thick planks.

Wood battens, were used for "curve fits" once a upon a time. I read a article last year about simulating wood batten curves with CAD curve-fits. This went a long way toward explaining why I had such a bi**h of a time getting the real world to match what I created on a computer.

I like it im getting lots of great info and I appreciate all of it, you guys rock

Assume 64 sq. ft. area for an A-Class cat hull.
5.3#/cu.ft.foam (3/8" thick) equals 10.6 lb. and cost for material and labor cutting strips is $370.
21.2#/cu.ft. white cedar (1/4" thick) equals 28.26 lb. and cost is $512.

What would an an appropriate amount if Nomex cost?

Nomex needs to go into a mold

1/4" (8mm)white ceder with 2 oz glass on each side and some reinforcement on the inside would make a very strong hull.

8mm of white ceder is roughly/sorta/depending the equivalent of 2mm bidirectional carbon

I would probably use 3mm or 2mm as a core

I think im going with Core-cell, for the prototype boat. will make changes in production boats if need be.

Yes, cos no-one can afford to use it in production boats! Good choice for your prototype tho'. Don't bother with routing long strips, do vertical wider strips and glue them with PU adhesive [Gorilla grip]

the best thing about corecell with regards to this project is how well it takes to heat forming. Either buy yourself an old domestic oven from Craig's list or make a heating box ( for small projects these are often made with timber, fibreglass insulation and a couple of heat guns) and you will able to shape wide transverse runs of foam and do minimum fairing or gluing.

Corecell is probably the best foam on the market, however, it is banned in the F18 class, not worthwhile on a boat built with a chopper gun or inferior to nomex for high end builds. As a result we see very little of it in beach cat land.

With quite a few hundred hours invested in a strip-plank project I feel confident when advicing: Stay away from the devils building method if you want a fast build

Jake, which foam? There are sooo many different types of foam available it can be overwhelming...right now I have 7 different types of extruded polystyrene in my shop, along with Rohacell and Nomex for use as cores in molds. All the polystyrenes act differently and most wouldn't be suitable for a boat building project but they exist!

Quick word on foam. There are several types I used 3/8 Divinycell H80 and H60 on my project a bit cheaper than core-cell and does not need to be heated. I bought full sheets and ripped them to strips then used a router and cut it with a “canoe bit” which has a combo bead and cove blade. There are two main thoughts on foam stripping horizontal or vertical, the farrier guys like the vertical method. It looks like a good method - but did not work with my design. I used the older horizontal method. Gorilla glue worked good to glue the strips together and fares out well.

Am I reading you right? You can sand gorilla glue to shape?

Pete when I glued the strips with epoxy it did not sand at the same rate as the foam and wanted to dish between the glue and foam.

With Gorilla the dried glue it is about the same density as the foam and sands out fare. Rememeber this is a thin line of glue that may come out between the stips.

Okay, thanks.

Here is picture of a sanded hull with a little help.

Also - if you wet the surfaces before you apply the gorilla glue, the glue will foam as it cures. More water makes it foam more.