Ive just found this thread, which partly answers a question I wanted to put:

The boat has just been pulled out for the winter and I have noticed that the prop shaft nut is loose. It is castellated, and six months ago was wired on using thick galvanised wire, which has now corroded away.

Clearly that was the wrong method. Should I use a stainless steel cotter pin ? Or Monel, or bronze? The shaft is stainless, the prop and nut bronze.

If the tightest I can get the nut does not coincide with the single hole, should I use a longer lever, or back it off, or drill a new hole in the nut or shaft?