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Using foam to make seats for Nesting Spindrift?

7 posts in this topic

I've been thinking of using Urethane expanding foam to add removable seats to the rear half of my Nesting Spindrift. This would also add buoyance if the boat was swamped or capsized. I was wondering if anyone had done this and what type of foam to use. I see that you can get the foam in various weights. I was thinking I might wrap the foam in fiberglass after it was shaped to add strength if necessary but if the foam was strong enough to sit on without reinforcement that would make the job easier.

 

Thoughts?

 

thanks,

Hugh

 

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Hugh, 

Having worked with polyurethane expanding foam before I wouldn't use it for what you're describing because I can see it being a big messy pita with lots of shaping needed afterwards. Have you considered building the removable box out of regular old 2" blue insulation foam? You can cut and shape it easily and it can be glassed. It is maybe a bit softer than polyurethane foam but not much. You could laminate a 4mm ply top and bottom to keep it getting dinged up and then glass it. 

 

You would want 2 lb expanding foam otherwise it would be just as much weight as if you built it from 4mm plywood which might also be a good option. On a Spindrift 10 nesting the corner seat boxes as designed are about 1.6 cubic feet of volume and have a surface area of about 9 square feet. I think the boxes would end up about 6 lbs each if made from 4mm plywood (with some stiffeners on the top). 

-Alan 

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Thanks for the response. I was thinking I could mold the expanding foam in place. Basically put a lengthwise dam between the aft seats and the thwart cover everything with wax paper and then let the expanding foam mold itself to the curves of the hull. The thought was  the only shaping I would have to do would be get the top of the foam blocks flat.

 

From the little research I've done I was thinking 4lb foam would be needed for the strength. Do you think 2lb foam would be strong enough to sit on?

 

I hadn't though about plywood boxes. Trying to build a box that would match the contours of the hull would be beyond my ability.

 

Blue foam would be easier to work than plywood but would still take some artistry to get it to fit.

 

Thanks,

Hugh

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With dams you're probably right that it wouldn't be too bad. I think 2lb foam would be strong enough if you put a 4mm plywood seat top on it to spread the load and glassed all the sides. You'll probably also want to recess some other bits of plywood here and there for attaching whatever fastening system you devise. 

 

4lb foam is still going to be pretty soft certainly soft enough to put a fingernail into pretty easily and dent with firm pressure from a finger so I would put a thin ply top on it regardless which will give the top a lot of stiffness. More than you could get with the same weight if you just put glass on the top. I think you'll just have to give it a go. 

 

 

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Thanks again, I'll order some 2lb foam and will let you know how it goes.

 

 

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Pourable foam tends to leave voids and absorb moisture without some additional protection. Also anything less than 5 pound foam will need a fair bit of reinforcement to be stiff enough to use for you application, rivalling (as Alan mentioned) a lightweight plywood box. 2 pound foam will do, but instead of waxed paper, I'd use thin plastic sheeting, even a plastic bag, to line the enclosed area, before you pour in the foam. I've found waxed paper can contaminate surfaces (exothermic adhesives, melt the wax), which will drive you nuts in finishing or subsequent epoxy applications. This will keep the foam from actually sticking to the space, the foam does stick to it (plastic), though not all that well, good enough to keep moisture out of it. I do this with foam filled buoyancy chambers. I use a spray adhesive (3M-77 or similar) and stick the plastic into the area. If it's to be removable, a very light ducting, just enough to make it stay put. Line the area, with some generous overlaps in those areas, then pour. The plastic will come out with the foam if desired, which can be handy too.

 

Once you're poured and have trimmed the ooze out, a few layers of heavy combo fabric will make it stiff enough to tolerate sitting on it. Don't go too light on the skin or you'll have butt cheek dents in short order. I like the 4 mm plywood option better as less work, lighter weight and least costly in materials, myself. On a CS-17 build I did a while back, rather than have the aft bulkhead and aft deck, I elected to make a removable seat across the transom. It would have been easy enough to have simply glued a hunk of foam under it, to serve as you've suggested, though this CS-17 had more than enough buoyancy in chambers to accommodate a fully crewed and swamped boat.

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Thanks for the tips. I've already placed the order for the 2lb foam so i'll plan on using a plywood top.

 

 

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