1966 MFG Rebuild

Pmt133

Senior Chief Petty Officer
Joined
Jan 6, 2022
Messages
679
It was 90 F when I foamed my hull. I had the heater blasting the hull surface to also help. I feel I actually got good expansion. I waited for that reason. I also heated the buckets of foam parts to help as well and worked in small batches.
 

demarko210

Senior Chief Petty Officer
Joined
Jan 2, 2015
Messages
652
Remember that foam expansion is a direct correlation to the air & surface temperature of the cavity you are filling. You can do all the math you want, but if it's not above the foam manufacturer's recommended temperature for maximum expansion, your yield can be much less (like 50-60% of what you are expecting to get). Ask me how I know. 😂
We are not foaming this winter just a discussion on the processes of ways it can be done and sealed inside the boat. Hell I am hesitant to do glass work this winter. The math works as I said, if I make a cavity to hold X amount of volume and it only swells to 50% then I have only covered 50% of my volume. Simple;)
My goal is to meet a total volume of foam in the boat where I have created compartments.
 
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demarko210

Senior Chief Petty Officer
Joined
Jan 2, 2015
Messages
652
It was 90 F when I foamed my hull. I had the heater blasting the hull surface to also help. I feel I actually got good expansion. I waited for that reason. I also heated the buckets of foam parts to help as well and worked in small batches.
What was the outside air temp?
 

Pmt133

Senior Chief Petty Officer
Joined
Jan 6, 2022
Messages
679
What was the outside air temp?
90F. I used the heater to get everything above that temperature for good measure. I was cooking that day lol. It was sometime in July when I did it. Maybe 110F total?

I also ran the math based on US composites expansion rate and my measurements of cavity size for my order. The single big kit was enough by my math, but I got extra for good measure. I have ~2400lbs of buoyancy added.
 

Ptr.Torch

Cadet
Joined
Dec 23, 2024
Messages
25
= EDIT CUT =
900 boat weight * 1.5 = 1350 lbs buoyancy
1350 buoyancy / 60 lb per cubic foot = 22.5 cubic feet of foam estimated. (2lb foam)
=EDIT CUT =
?? Where do you get the 60 lb per cubic foot figure? That seems a bit too high to me. Flotation is (I'm probably preaching to the choir) based on the weight of water being displaced. ... did my research ... OIC! Web says 1 cubic ft of water is 62.4 lbs. Foam that weighs 2 lbs.. leaves 60 lbs for flotation. Got it.
Once I add some 1708 on the inside gunnel and I feel it is stiff enough I may not enclose the gunnels. So that will reduce the foam. if that is the case I will section off parts of the casting deck below to hold foam. Also build 2 foam boxes above the deck that will set on both sides of the bilge.

As long as I feel I have enough, I am good.
Quick Est. // If your boat is 8 ft wide, and 16 ft long (divide the tapperd forward section by half) so roughly 13 feet length wise, (doing the math) looks like you need about 3" of foam under your deck. That should be doable! (thumbs up)
 

demarko210

Senior Chief Petty Officer
Joined
Jan 2, 2015
Messages
652
Quick Est. // If your boat is 8 ft wide, and 16 ft long (divide the tapperd forward section by half) so roughly 13 feet length wise, (doing the math) looks like you need about 3" of foam under your deck. That should be doable! (thumbs up)
61.5" or 71.5" is the beam 16' 1" center line. My center stringers I cut to 3" and the others are 2" in height. Might need to fill the stringers also will see.
 
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MikeSchinlaub

Petty Officer 2nd Class
Joined
Jan 14, 2025
Messages
110
When I use two part foam, I cut 1" holes in the floor, spaced maybe 2 ft apart, along each individual cavity. Mix it about a quart at a time and pour in, starting at the lowest point. I'll crank the trailer's jack all the way up so everything runs back. One cup at a time for each section, give it a few minutes to expand before doing the next one. When it's up to the bottom of the hole, move forward. Once you get to the last hole, you'll want to be a bit more cautious, since it doesn't have a big cavity to expand in anymore. Guesstimate maybe 3 gallons total, so 1.5 for each part. Any of the math is beyond my brainpower.
 
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