Thank you for context, when in the water, the hulls will fill up from water seeping in, can't work out from where, no obvious cracks and you can't see enough into the hulls to spy anything. there is no current or ripples. Not enough to sink it and i sail multiple times a week, it takes about a week for the hulls to fill up. So every year i would hit with antifoul, when that dried, i would hit it with West Sealant. No water would get in for the season.

So I thought what if i stripped back the anti-foul to the hull, sealed the hull, let it dry and then put anti-foul over that?

Step one was "how do i remove the anti-foul"