Sealing the bottom flange is only half the battle.
Sealing the top flange is equally important.
When sailing at speed, the water tends to "hydraulic" up into the well and if the top flange is leaking your boat will take water.
If the bottom flange is leaking, the hull will "take water" any time you sail. If the top flange is leaking, the boat will usually only take water on windy days.
In order to use Jeremy's "best method" it will be most effective if you turn the hull upside down when trying to seal the top flange.
The last "don't ask me how I know" bit of wisdom is that the most difficult area to seal, the narrowest area and the point at the rear of the trunk/flange, is usually the place where the leak is.
My 1988 Hobie 18 was flanged top and bottom. Tom Machette's 1992 Hobie 18 is only flanged at the top.
That was one of the very few changes in the Original Hobie 18 from 1978 to 2004, and in my opinion, it was a good one.
(Not counting the Magnum and the SX of course, which killed the class)
