Join Date: Jun 2005
Location: New Orleans
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With a small enough boat, a stationary dock or float, a place on land or dock to lead a halyard to, and a quiet wake-free area, try careening the boat over with the halyard. this'll get the waterline area much higher up, and raise the keel on an angle to where it's closer and easier to scrub with a long-handled scrub brush from a dinghy. Scrub the mossy stuff, then wet-sand what you can reach, for smoothness. Heeling the boat in this way will enable you to sand and scrub "downward", which is much easier and less tiring than "upward".
Then reverse the whole process and do the other side.
Be careful. there will be lots of strain on the halyard, be sure it doesn't jump the sheave, and watch your dock lines and passing traffic carefully.
This isn't easy, and may not be physically possible on the bigger boats, but if you can work it, it's effective, and it's definitely cheap, costs no more than the wet-dry sandpaper.