wind vane on Laura Dekker's Guppy

[prv]

If the seacock was installed upside down with the threaded part uppermost I could use a boot similar to the mast to seal against water quite effectively. Round bar with a diameter slightly less than the seacock through hull may squeak a bit

I see what you mean. The difference between the mast and a tiller shaft is that the mast doesn't rotate, but a conical boot (with a top hole slightly smaller than the shaft, in its unstretched state) would probably work as a crude lip seal and do the job. Not how I'd do it, but if you have limited time, facilities, and budget then it seems workable. Might need a bit of timber packing or GRP buildup to get the angle right if your shaft doesn't arrive at exactly 90 degrees to the deck.

With a brass or bronze through-hull and a bit of white grease I don't think it should squeak. As I said before, our upper bearing (and the lower one for that matter) is a simple metal tube in which the shaft is a close fit, it's lightly greased and silent.

Pete