Is under-floor flotation foam structural in 1992 1800 XR?

[harryharls]

Hi,

As per title, I need to know if the nasty foam that was filling the entire under-floor area is a structural component of the boat. I had a rotten area of floor and have now ended up stripping out the lot, including the two main stringers. I don't really want to put the foam back. The above deck 'boxes' that were foam filled were also rotten in places so they've all been cut out too. I want a much cleaner, more open look once it's finished. My thoughts are that I could install ribs (lateral reinforcing boards, I think they're called ribs!) from the stringers to the boat sides at the plywood floor joints. Would the ribs be adequate reinforcement in place of foam if the foam was indeed there for structural reasons? The hull is fairly thin and deflects considerably if stood on.

[mmwjr]

It’s not structural but flotation, required for smaller boats per regulations.

[harryharls]

Hmmm, actually, I think I've changed my mind. I think I will reinstall the foam under the deck after all. I don't want to go to all this trouble and then be dissatisfied with an end result and wish I'd put foam back in! Sorry to have wasted anyone's time, although others may be interested to know at some point if the foam has a structural purpose or not...I very much suspect it does considering how thin the hull is. My main reason for not reinstalling foam was because the pre-existing foam was quite wet in some areas and much of the ply it was in contact with had rotted completely (black), even on upper surfaces. In an ideal world I would have drainage through the two main stringers but I'm not sure any water would be able to get out once it got in because of the nature of the foam.

[harryharls]

Oh it's not structural? Could my idea of using lateral ribs work then?

[harryharls]

I know about the USCG regs for flotation on craft under 20' but I'm in the UK, not sure those rules apply here?

[harryharls]

The foam also acts as support for the floor though, the original floor is only 12mm ply (half inch), presumably because of the support that the foam offers.

[harryharls]

I seem to be having a conversation with myself here but I've made my mind up now; I'm putting foam back! Case closed

[mmwjr]

Like arguing with yourself do ya?