I have, Like many of us, Looked everywhere for the answer to hull problems.
I have an uncle who works maintaining an air fleet for marathon oil and he gave me THE Answer!!! It's an aluminum tape used for sealing seams and some other temp repairs on aircraft. it comes in a variety of thicknesses and is the deal! Last season my father and I took out our 21SC on a weekend trip, first day in we hit an underwater snag while reaching to close to the shoreline. we patched it with 2 layers of the tape (large patch over small like a glass repair) and To be honest I probably wont bother to patch it this summer. IT IS THAT GOOD! well now I'm putting a 3" stripe down the keels on my 16 and the bottom of our 18's dagger-boards an I expect great things! it comes in a variety of thicknesses from 2mil foil to 4mm (the Thickest I've yet heard of) My roll says IdealTape Co. Lowell MA
on it. The adhesive probably varies between brands and intended uses so I don't know about the chimney tape sold at sears and such. But from What I've seen This is The Answer to our prayers. i Imagine it will take a while to wear through 2+mm of AL.
here is a picture of what it looks likehttp://www.componentforce.com/userfiles/image/categories/aluminiumtape165c_lg.jpg
I have almost a full 150' of this stuff so I won't be buying another roll anytime soon, but go out there and see what works...I really think this might just be the ticket! And Regardless of whether or not it's a good keel protector, It is a great patch! I keep 2 4x4" squares on all the boats just in case.