I'm rebuilding the rear bench seat in my 94' Crownline because the plywood is all rotted. It's too bad too because the vinyl is in good shape.

Anyway, I'm wondering if anyone has found any alternatives to using plywood. I know newer boats have plastic tubs that make up the frame but I have no idea what kind of plastic it is or if you can buy that material in 4x8 sheets.

If I can find something that comes in 4x8 3/8" thickness that would be sweet. It would never rot and it would probably be a heck of a lot lighter too.

Any tips would be appreciated.

nidacore
http://www.nida-core.com/

Just spent half an hour reading their site. Interesting stuff.

Do you know if it is possible to use mechanical fasteners (screws/bolts) to assemble or does it have to be glued?

GlassDave would be the person to ask. I have never used it but have reaserched the $hit out of it for the same reason as you. I want to redo my seat base and a few other things to save some weight.

Just because the wood is rotted does not mean you have to replace the vinyl..if your careful with removing the staples you can reuse the skin's,you just have to be sure you make the wood structure the same as the old one was..their is nothing wrong with using wood as long as its properly sealed..i usually coat the wood with resin and a this piece of fiberglass mat to try and protect it then ill paint over the fiberglass with some 2 part polyurethane paint..i did this to my donzi seats like 18 yrs ago and they are still solid as a rock...make sure you use stainless staples..

The thing to use is actually PVC foam board.

http://www.bertram31.com/proj/tips/pvc.htm

No you can not use fasteners. If you want to put screwes into it you have to router out the area were you want to put screws in and glass in a block of wood.

There are also PVC alternatives.

What Marc said, PVC board. Its what any good boat builder has been using for quite a few years now. It takes a staple, can be glued, can be mechanically fastened, & is available in many thicknesses. Can be bought at any plastics wholesale house, such as Farco Plastics, etc. It also comes in different finish grades, which denotes price. You can definately buy the lesser grade for marine upholstery construction, as it will never be seen. White is the most popular color for your needs, but comes in gray, tan, etc. Good stuff.

Thanks for the help guys. I found some 10mm PVC Board locally that goes for $97 a sheet (4x8'). Seems like a no brainer.