Replacing stringers/bulkheads on my South Coast 22 with XPS foam?

[skipperdee]

Last year I received a free South Coast 22 and have been slowly fixing it up with a steep learning curve. Very grateful for all of the advice received so far.

Now, I have my sights set on redoing the interior hull. The bulkheads and stringers are rotted out and need to be replaced. I've seen some videos on YouTube of people replacing rotted bulkheads and stringers with XPS foam (something like this) and glassing it over with several coats of epoxy resin and cloth.

What do people think? XPS foam advertises as 'impervious to water' and I like how light and easy to shape it would be for all those tricky curves. Cost is also always a factor in my decisions--the cost of the foam is less than plywood, but I'm wondering how much resin and fiberglass will be needed and whether that might end up costing more than traditional ply.

Any advice is always appreciated. Happy sailing!

 

[MikeHoncho]

It would cost more and take more time than replacing them with plywood.

 

[LloydB]

Make cardboard templates to cut new plywood parts with a jigsaw if the rotted parts wont work as templates. Tricky curves can be quickly dealt with coarse\fine sandpaper and a small electric sander.

 

[jssailem]

XPS foam advertises as 'impervious to water'

That is not quite a correct interpretation of the marketing words used. The product is said to be "Water resistant"

Yes XPS foam would be easy to shape. But it would not provide any strength. The use of "several coats of epoxy resin and cloth." would give you a brittle skin on a weak core. Bulkheads are like framing members in house construction. They support the shape of the hull maintaining a rigid frame to hold the hull in the desired shape as the water, wind and sails apply forces to squeeze, pull and push the boat about. Plywood is used to resist these forces when set in the boat as a "BULK HEAD".

No XPS foam even with epoxy resin and cloth would not serve as a bulk head, in my opinion.

 

[Hollyberry]

Your glass/epoxy work would need to provide pretty well all the strength.. "a few layers of glass and cloth" wouldn't do it. New wood will give you structural integrity much more easily..

 

[rgranger]

I have seen many examples of stringers being made out of resin soaked glass over a form …I’ve done it myself….it hardly maters what is used to make the form and foam is often used to lay out the shape of the stringer. The rigidity comes from the resin soaked glass cloth. The rigidity comes from two walls of the stringer being bonded together (through the foam) and also to the hull and stresses to the hull are thus transferred to a larger area. Sort of how an egg gets its strength. I have not seen any examples of a DIY bulkhead replacement using foam as the core. I’m sure it has been done but I have not seen anyone on here bragging about the results.