Having goten tired of scraping goo off my Dyer dinghy's bottom, and realizing that metallic copper inhibits marine growth, I made my own bottom paint for less than $30. (Not as simple as just buying some bottom paint, but a lot more fun and interesting).
Since putting copper powder INTO a paint covers most of the copper with the paint binder, I tried a different approach. First, I sanded off the very old bottom paint and painted it with clear 2-part epoxy, slightly thinned.
Then, while the epoxy was just starting to cure, I sifted a very, very fine copper powder ($20 from ebay) onto the epoxy. This left the exposed surface of the dinghy as pure copper. I did the same with an acrylic panel, so I wouldn't have to pull the dinghy whenever I got curious.
I hung the acrylic panel from the dock near my boat, and have put dated photos into an album, Pictures by tanksalotct - Photobucket
The most interesting aspect of this is the "windows" that are clear. I didn't paint the windows area with epoxy, so after sifting/curing, I just brushed off the copper powder. In most of the bottom paint test panel photos I've seen in Practical Sailor, the unpainted areas between paints are covered with growth. If this isn't some sort of anomaly, then that would mean the areas of the dinghy that are scraped through regular use would have minimal growth.
I'll be updating the photobucket album as time goes by, and this Fall, I'll pull the dinghy and see what the bottom looks like. The best part of this, to me, is that as long as the copper doesn't slough off, the bottom paint should be permanent. Time will tell.