as dennis said, run the boat again with the current prop. get WOT numbers (in both directions to eliminate current and wind) with the tabs fully retracted and adjusting trim to achieve the highest RPM. make sure you are around you normal load when you do this. that will be your accurate...
that would work, but that goes back to being painstakingly slow. maybe if it was really bad, the juice would be worth the squeeze, but mine cleans pretty quick and easy with spray and a brush on a pole
how are you going to ensure you dont get any on the gelcoat? it seems that it would be painstakingly slow going through and being OCD about where you get the product and where you dont.
ive had pretty good luck just using regular mildew spray, scrub with a soft brush, and rinse right away.
by sea or land?
if by sea, try Will with Captains Coach. he does yacht delivery professionally (as well as training). As a bonus, he documents everything on a youtube channel so you would get to see the journey as well.