On Sun, 28 Oct 2007 12:12:54 -0400, HK wrote:

The most annoying stains I seem to encounter on the hull are
those left behind by the tannin in the water.

Yes. There is also a reaction that takes place between salt water and
air which leaves a tannin like stain even when the water is clear. The
only way to avoid it is lots of wax on the hull.