I haven't used Ultima but Hydrocoat is far, far softer and more ablative than anything I have used, and that includes ACP50 and CPP Plus. Fouling was the least with ACP50, CPP Plus was OK, and Hydrocoat was the worst. I think they may have stopped making ACP50 for some reason. My comparison was when I tried scrubbing the waterline while swimming around the boat and I quickly stopped because I went right through two coats of the Hydrocoat with almost no effort. Plus, when I hauled out the paint was severely scraped and just plain gone in areas where I bumped up against the mooring ball, etc. Despite all that it wasn't terrible, so I might stick with it for the ease of application--I don't feel sick from the fumes afterwords, which is nice.