Stringer foam

[Bigshrimpin]

Originally Posted by kmoose

I have to ask why re-foam? Is there any structural benefit of adding the foam back other than flotation? I seriously doubt the amount of foam in the stringers would do much to keep one afloat offsetting the engine or other heavy objects.

Each sq ft of foam is equal to roughly 60lbs of flotation. Submerged weight of fiberglass (.33 k factor) and aluminum (.63 k factor) is very different from the weight on land. This manual explains how to calculate your flotation needs. Page 20 (or page 24 of the pdf)

http://www.uscgboating.org/regulatio.../FLOTATION.pdf

On a 23ft seacraft each stringer is roughly average of 15 inches deep x 2 stringers x 16ft +/- . . . that's a LOT of flotation just in the stringer foam. If you round it to 1 cubic ft for each foot of stringer . . . that's approx 32 cubic ft x 60lbs = 1920lbs of flotation.

If the hull is solid glass (which it isn't) but just for the explanation let's say the hull weight 2600lb was solid glass . . . the submerged weight would be 2600 x .33 = 858lbs of flotation would be needed to float the hull. When you factor in plywood cores and balsa cored decks . . . it'll weigh even less. Even the motor (assuming it's a 50/50 mix of steel (.88) and aluminum (.63) = 1.51/2 = .755 k ) so a motor underwater only weighs 75% of what it does when it's not submerged. A 600lbs motor would only weigh 450lbs underwater. My point is that the stringers full of DRY foam is PLENTY of flotation for 23 with motor and people.