Support for new floor

mjwag

Recruit
Joined
Feb 15, 2026
Messages
2
Hello all, my son recently purchased a 14' 1981 Forester tri-hull for $200 including motor and trailer. It was obvious upon purchasing the boat that the deck was in need of repairs but for $200 he couldn't pass it up.
After a summer's use of it we've decided to tear into the floor to see what we had to work with. After removing a couple hundred pounds of soaked open cell foam I was surprised to find only one single stringer running up the center of the boat. (Which fortunately is solid with no visible cracks) I figured there would for sure be some sort of support below where the deck and hull walls meet.
I am planning on glassing in a new marine plywood floor but my question is - will tabbing the floor to the walls be sufficient enough structurally? Obviously it was good enough for the boat to be built that way but it just concerns me.
My second question is - could I add stringers equally spaced on both sides of the original center stringer, or would that make the boat too rigid per it's original design causing more problems down the road?
Thanks in advance!

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tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
19,024
At one point the foam was closed cell, but over time, it can become saturated leading folks to think it is open cell.

It looks like there is only room for 1 stringer, and I agree with @racerone that the foam was serving as some structural rigidity.

If you wanted to 'beef-up' the structure, you could add some ribs stemming out from the center stringer. Speaking of which, I'd do a few core samples of that stringer, since it was probably exposed to a lot of moisture from the wet foam. It could look/feel solid only to be soft/soggy on the inside.
 

MikeSchinlaub

Senior Chief Petty Officer
Joined
Jan 14, 2025
Messages
701
Looks to me like the floor rests on the hull at the sides. When you're ready to install, bed that whole area in some resin putty and put as much weight on it as you can overnight.
 

mjwag

Recruit
Joined
Feb 15, 2026
Messages
2
At one point the foam was closed cell, but over time, it can become saturated leading folks to think it is open cell.

It looks like there is only room for 1 stringer, and I agree with @racerone that the foam was serving as some structural rigidity.

If you wanted to 'beef-up' the structure, you could add some ribs stemming out from the center stringer. Speaking of which, I'd do a few core samples of that stringer, since it was probably exposed to a lot of moisture from the wet foam. It could look/feel solid only to be soft/soggy on the inside.
Thanks for your response and I agree with what you're saying. I do plan on pouring foam underneath the deck, do you think 4lb foam is sufficient?
 
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