Well, tradition, you know?
I have to agree with Bob about coating the bottom as a water sealer. But since (my refinished brightwork) has only been on the boat for about a month now, I can't really prove that it helps. On the otherhand, it is a very small incremental increase in work compared to removing and stripping wood. #M4200 shicks to it just fine. Speaking of stripping varnish, the first mate used a heat gun and scraper to good effect, and all I had to do was a little sanding to prep the wood. We didn't bleach out anything, and the finished job looks pretty good. We used Epifanes varnish, not Cetol, but that is really a judgement call on how dark or yellow shaded you want the wood. West marine really rips you off for Epifanes, so I suggest looking at Jamestown or Hamilton Marine as a supply source. Dan Casey's book on refinishing is very good, it does a good description of the process of flowing on varnish and then tipping it back to level it out. One thing he didn't mention is using very light brush pressure on the final coats, pressing too hard forces air bubbles and foam out of the brush onto the varish surface. Rebecca Whitmann's Brightwork Companion has a real good description of the pro's and cons of oiling teak vs. varnish, as well as many suggestions for those who are just getting started. We used her book to get a good idea of what varnishing was all about (she has very good advice on materials), and Don Casey's book for some down to earth suggestions about technique.