URGENT:Can I fill the pylons with"great stuff"foam and cut??

I've used the two part expanding foam from US Composites before. It's good stuff- easy to work with. But unless the area you're trying to fill is fairly well sealed, it is likely that it will run out of the openings. It starts out pretty thin and takes about 30 to 60 seconds to start expanding and once it starts, you really can't pour any more 'cause it goes pretty quick. Temperature has a big effect on it's viscosity and pot life.

As far as the foam breaking the pylon, I'd say it's a non-issue. It'll just continue to expand towards the area of least resistance which would be the top opening.

I do question whether it's really necessary or a good idea to fill the entire pylon with foam. I believe they come stock with just a plug in the top. You might be better off making a plate that matches the inside profile of the pylon to slide into the pylon 6 or 8 inches and then fill the pylon with foam from there up. Another issue that they talk about with these expanding foams is that filling long tubes can be a problem because if you have to do multiple pours (which you probably will) the foam that ends up on the sidewalls of the tube begins to grow inward and constrict the opening for future pours (this stuff is really sticky).

As for the vent tubes, as I stated before, as long as you keep the plugs out when not using the boat, you won't have an issue (and even if you do forget to pop the plugs every now and then, it shouldn't be a problem). The vents are really only necessary for extreme temperature or elevation changes.

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Ok sounds good. I was under the impression that the whole pylon usually has the foam plug. Ill make some sort of blockage to keep it from going all the way down the pylon. Thanks!