Actually-
There is another way to do this - ala the Taipans- Sort of a long description but principle should be clear if you read through this! Cut out 2 of the foam pieces as you describe- Run a needle with strong, thin thread through middle of both pieces- tie thread around toothpick and snug up against one piece (the "bottom") of foam- make sure thread is long enough so it reaches from the hound (the attachment at the top of the mast where the shrouds attach) to the top of the mast- Now insert this piece of foam in the top of the mast- put a nice, thick bead of silicone on the top of this piece of foam- about 1/2" thick- near, but not necessarily touching, the mast inside wall- now shove this piece down the mast to the level of the hound (if you mark your "shover"- a small piece of PVC pipe or even your tiller extension will often work or the thread you will know when you are there). Put the thread through the other ("top") piece of foam and shove it down the mast, pulling the thread through as it slides down- You can put a bead of silicone on the bottom of this piece if you desire but if you put enough on the bottom piece this is not necessary. Now the object is to use the thread to keep the bottom piece from being pushed further down as you shove the top piece down against the bottom- thereby extruding the silicone sealant ("squishing it") out from between the two pieces against the inside of the mast and, voila, sealing it! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Kirt