The photo says a 1000 things, one being the weed is just below the water line, I use this knowledge to maintaine Odysseus and only antifoul half a metre down, as below is just a slime. I actually only antifoul all the boat every 3 years.
My conditions are in and out of brakish water so it helps but even when in the solent I only did the whole boat every 2 years. Also I use Jotun seaforce 30, which has been withdrawn now so need to find another, but I have 10 lts left.
I am not racing any more, just a cruising way of life. So check it out next time you lift out.
Hope this helps
Odysseus
Bav 38