brake drums cannot be resurfaced - there are rules against this. so when a brake drum wears out they have to junk it. they weight about 100 pounds apiece. we get them for free. you can chain them together and drop them overboard. other end of the chain goes to some large floating object (large enough to float the chain).

we use them here in central florida to anchor boats in our unofficial mooring field. there is a 36 foot cruiser and a 41 foot out island moored to six brake drums each. the 36 footer has been there for two years. i would guess that two or three brake drums would do for you...