Floor replacment

Hello everyone! I'm currious about how you would replace the floor in a 78 nautique. The boat came from the factory with wood support under a few locations, mainly up front. Other than that, it was just fiberglass laid on top of foam (not sure what weight). I'm currently fixing a few rotten locations in the stringers, but will soon be moving on to the floor and foam. Obviously I had to do all of this because water made its way into the foam, and eventually the stringers. This leads me to believe the foam wasn't helpful in preventing the stringer rot, and makes me want to go with out the foam now. I'm currious if anyone knows the following things..

1.) is the foam structural in a 78? and therefore, manditory to replace?
2.) would it be better to add a layer of something under the fiberglass floor (ie ply wood)?
3.) If so, should I add from the current stringer height, or shave off the thickness of plywood to bring the floor to the same final height?

I really want to make sure the finished boat isn't going to have a weak floor, or allow water to get in again. My thinking is that poor maintence allone may have done this damage, but the floor wasnt exactly "thick n heavy" from the factory either. Any thoughts would be helpful. I've been reading about floor replacment online and most ski boats have plywood under the floor so it's strange to me this boat didnt have it.

OK, I did a search and am not finding anything on OMB board. Can you describe it and what it's made of?

I have a friend who restored an old Mustang in the past and is a builder.   He's telling me that a product called Advantech is the way to go on my project. It's a brand of OSB/chipboard that's got enough waterproof glue holding it together that they guarantee it for 50 years. The plus side is that it's $28 a sheet vs $75 for marine plywood and it will be covered by glass and carpet. The downside is that it goes against anything I've ever heard about what wood to use in a boat.

I've always heard that the only difference between treated plywood and marine is that the marine doesn't have any voids or patches in it. I replaced my floor about 6 years ago. I used 3/4 treated plywood and put 9 coats of polyurethene on it (including the edges) and put clear silicon on all the seams after screwing it down. Also, make sure the floor is slightly higher on the outside against the walls so water will not puddle there. I used shims to raise the floor, because that was where my floor went bad, water seeped in the edge and delaminated the plywood. That Advantech looks like dark brown particle board. Two of my friends put it in their houses. I don't know about using it in a boat.

Nida-core is cool looking stuff. The website is http://www.nida-core.com

I think Nidacore's number is HP88 you can buy it in a Hard Pannel Made to the size you need.
3/4 thick is plenty. When you screw it down, just oversize the holes fill with kitty hair to prevent crush of material.

Yeah, I think I may have to go with Nida Core but even though I have a catalog downloaded now the prices are not listed so I dont know how much the cost will be to have them cut me out floor pieces on a CNC. I'm going to call a rep soon and have them estimate a price for me though.

Yeah this is becoming quite confusing, but I think I'm getting closer to the finish line. All of the products made with "skins" are going to weigh too much to ship, but the good news is I think the core is really all I want anyhow. The core material is pre fabricated with "fur" to crate a great bonding surface when I go to laminate a skin of fibergalss. That should be ideal for making the boat light, yet still resistant to rot. I'll post some pictures when I get things started. Oh yeah, last but not least. I found another company that makes this type of material (polypropyline honeycomb) here in Michigan! They're still working on a quote, but the shipping cost will be free if they're competitive with the pricing! :) You can get info about this company here, http://plascore.com