Stringer foam
 

Hey guys, I've got the stringers on my 74' 23sf cleaned out and I'm about ready to fill them back up and continue on with the rebuild. I was wondering what type of closed cell foam to use, like specific brands and densities? How much foam am I going to need? Also, is there anything I should know before doing this? I was thinking of maybe bracing the stringers shell so the foam doesn't make the fiberglass expand or anything like that. All input is welcome. And if anybody could explain how I upload images to this post that would be great also.

I would use no less than 8 lb density myself but that is because I only believe in doing a job once. The 8 lb is nice and hard. You may be able to get away with 4lb if you layer up the glass cap good. Quantities should.be calculated using dimensions inside cavities to be filled and a good online volume calculator. Figure 10-15% extra for waste and learning curve..... with the foam you're damned to get it all out of the container you mixed it in so you lose some there too. Buy lots of mixing containers. Best but most expensive way is to make sure your pour expands over the top, then cut/ belt sand down to finished dimension. As far as bracing, you can use a 2x4 or straight edge braced off hull sides/ other stringers. Word to the wise: do one at a time and be patient!

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

Now you are referring to the filled stringer boxes and not foam poured loosely between, correct?

Cap the stringers w glass first.

Drill holes in the top of the cap.

Go in small batches low to high.

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.

This video from Metan Marine shows you how they foam stringers on their builds. See 10:14 - 11:00. You can thank Mike B. for contributing technical information to the site :) Looks like 2 or 3lb foam to me . . . that's just a guess.

https://www.youtube.com/watch?v=ZPj4rBlZyPo

When lost, the hulls are found.

Yes hooligan, I was referring to the stringer boxes. I figured that they put foam in it for a reason so I was going to replace all of it, even the loose foam on the outer side of those boxes. All of the foam in the back half of the boat was wet and holding small amounts of water. I appreciate the info and input from everyone so far

I think I figured out how to post pics also. Here's a few to show y'all what's going on at the moment..