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tim79mc
06-05-2012, 08:53 AM
Hi all,

I took the bow foam out of my MC as part of my effort in repairing the floor and stringers. The foam was waterlogged in the bottom few inches and I found delamination starting under the foam. The trapped water was also starting to smell rotten.

A few questions

- how much foam do I need to replace for floatation requirements?
- Is the front foam structural in any way? I intend to keep the bow area open for storage and put foam under the floor throughout the boat.
- what foam have people found success in using? I would like to use sheet foam that I can cut to shape and place in between the stringers, under the floor. I would like to have some PVC piping hold the foam off the hull so water can drain.

Any advise greatly appreciated!!

thatsmrmastercraft
06-05-2012, 11:32 AM
You are going to need to get with someone who really knows what they are doing to ensure you have sufficient flotation in your boat. I would like to do the same thing to my '77, but haven't made the effort to find out the details on replacement flotation. Good luck.

gid
06-05-2012, 12:51 PM
Spray it with closed cell foam? I have been thinking of pulling the floors up in my 72' to install foam as there is none in the boat.

madcityskier
06-05-2012, 04:33 PM
Use expanding spray foam, and then cut it off flush with the stringers. It'll also help to minimize flex in the new floor.

thatsmrmastercraft
06-05-2012, 04:42 PM
Finding foam is no problem. Calculating how much foam to provide sufficient flotation is the key. If you don't have enough flotation, you may as well have none.

Shipwreck is the only place that I can think of that might have the answer. http://www.shipwreckboats.com/

amber 6
06-06-2012, 05:08 AM
Please advise what is meant by provide sufficient floatation.

How does adding foam to the space between the hull and floor change the floatation or do you mean in the event of it turning over? I have read that some people have not replaced the foam on their rebuilds.

tim79mc
06-07-2012, 12:16 AM
I turned on my engineer's hat and did some estimates on how much foam I need. I came up with 18 cubic feet in addition to what is already in the gunnels. I got this by estimating weights of steel and fiberglass and looking at densities. The result compares with a guesstimate of the amount of foam I removed from the bow.

I can get 18 cu feet with 10' x 1' x 1/2' for the outer stringer area plus another 2' x 5' x 8" section under the floor in the bow. I'm convinced that if I foamed under the whole floor, there is more than enough flotation.

My concern is that the "closed cell foam" that I removed from the boat was water logged. I don't want foam touching the hull. any suggestions for how to accomplish that goal?

tim79mc
06-07-2012, 12:27 AM
I found a USCG compliant foam at http://www.shopmaninc.com/foam.html

It clearly states 95-98% closed cell - the foam will waterlogged if exposed to water. This matches the performance of the original bow foam- when water gets into the bilge area and under the foam, capillary action will wick the water under the foam and begin to accumulate. Not what I'm looking for...

tim79mc
06-07-2012, 12:29 AM
I found a USCG compliant foam at http://www.shopmaninc.com/foam.html

It clearly states 95-98% closed cell - the foam will waterlogged if exposed to water. This matches the performance of the original bow foam- when water gets into the bilge area and under the foam, capillary action will wick the water under the foam and begin to accumulate. Not what I'm looking for...

Take a look at my restoration thread to see why I don't want foam touching the hull - look at the bow area pics.

http://www.mastercraft.com/teamtalk/showthread.php?t=47981