I have seen a lot of pictures showing foam poured into the hull compartments, always before the deck added/installed. Why is that the case. I have seen many production boats where the foam is added after the decks have been installed. It would seem a better way to make full contact between the foam and deck (would add a little more support) if the foam were added after the deck is installed.
I was considering installing the deck, leaving the edges unglassed to allow for any foam "expansion seeping", cutting two 1 inch holes in each chamber to allow for application, then after the foam is poured filling and glassing over the holes. Then as a final step glassing the edges of the deck to the sides.
Is there a reason why this is not typically done in this way?
I have been building an FS17 and as you might have guessed I am close to the point of installing the deck.
foam
- OrangeQuest
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Re: foam
Yes, you have to know the exact volume of the area you want to fill and then how the foam will react to the temperature and moisture and hope all goes well without busting everything open.
Production boats, the foam is sprayed in so all surfaces get foam on them first and the foam then spreads to the empty spaces and fills them in. And mixing is done as the foam is sprayed out. Need to put small batches in a compartment and see how the foam does, it's not just poured in a few areas, and it expands to all the other areas. And you don't want to mix a big batch to pour in a few holes because it will expand and block the opening before you finish pouring so you have big empty cavities with a lot of wasted foam.
Also, pour and walk away with touching it, you will pop the bubbles after it starts to expand. Once you fill a compartment and it hardens, sand, cut the tops to be level with the stringers and you still have the extra support and the foam. Roll a little neat epoxy on the top of the foam and you can stick the floor to it and seal the foam up at the same time.
Production boats, the foam is sprayed in so all surfaces get foam on them first and the foam then spreads to the empty spaces and fills them in. And mixing is done as the foam is sprayed out. Need to put small batches in a compartment and see how the foam does, it's not just poured in a few areas, and it expands to all the other areas. And you don't want to mix a big batch to pour in a few holes because it will expand and block the opening before you finish pouring so you have big empty cavities with a lot of wasted foam.
Also, pour and walk away with touching it, you will pop the bubbles after it starts to expand. Once you fill a compartment and it hardens, sand, cut the tops to be level with the stringers and you still have the extra support and the foam. Roll a little neat epoxy on the top of the foam and you can stick the floor to it and seal the foam up at the same time.
"that it isn't just an ordinary sort of boat. Sometimes it's a Boat, and sometimes it's more of an Accident. It all depends." "Depends on what?" "On whether I'm on the top of it or underneath it."
A. A. Milne
A. A. Milne
Re: foam
OQ is correct, plan for a little overflow or go back and add a little more to each compartment. Then saw or sand any extra off down to the top of the stringers. Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978
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Re: foam
All about risk. If you bulge your decks; do over.
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- Netpackrat
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Re: foam
I assume that the production boats where they pour the foam in after the fact, they have the benefit of experience building the same boat over and over. They have had ample opportunity to develop a consistent measuring and mixing technique, and know exactly how much foam they need to measure out and pour into a given compartment, based on prior experience. Amateurs with wildly varying degrees of experience, building one boat in their garage, not so much. And as pointed out by others, get it wrong after you have glued the decks down, you damage your structure and get to tear apart and re-do.
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