Hi - need to rebed all my Stanchions on an old Hunter 33, and am looking for best material to make my own gaskets. This one is tough - the Stanchion bases mount to the towrail (corroded through) and then have a bend down to make them flush to the deck. Suggestions ?
Are your stanchions the same as in the attached picture (from my 1980 Hunter 36)? I went through the process several years ago of removing them to get at the aluminum vs stainless galvanic corrosion to the toe rail underneath the stanchion bases. If yours are the same, I presume that you are asking how to water-proof the two bolts that go into the deck. If like mine, the good news is that these go through only 1/4" sold fiberglass, not through the cored area. So even if leaking, the deck structure isn't damaged. I used good quality marine caulking -- but don't remember which. No leaking so far.
As suggested, yes, I think Butyl would be a better alternative. My suggestion would be to put the screws first all the way through the stanchion base with base in your hand -- not installed. Then wrap the underside around the screws with butyl tape. Then insert the screws/stanchion into the deck holes in a manner that the screws stay all the way against the stanchion as you insert. This will ensure that the butyl is in place to compress around the screws at the stanchion base underside into the hole/gap. Then do the two screws into the vertical toe rail after.
Another way that I might be tempted to try for the next time is to cut little squares from thin sheet rubber that can be purchased at hardware store plumbing departments. Drill a small hole in the center of the squares. Then with the screw already through the stanchion "milk" the squares up along the underside of the screw until it is up firm against the underside of the stanchion base. Then install the screws into the deck. When the nut from below is tightened, this DIY rubber gasket should compress tight around the screw and into the hole. If also done with butyl or caulk, should be leak-proof. After a few days, re-tighten. The rubber gasket would have to be quite thin say 1/8" or the elevation might be too high to along the toe rail screws to match the holes.