Antifouling experiment

[mm5aho]

This experiment came about due to laziness, not scientific curiosity.
Contender was pulled out of the water yesterday for the winter. I was keen to see what the bottom was like, given what I did last winter out of the water.
I've always wondered why people take off surplus antifouling, some back to gelcoat every year, then apply fresh AF.
Some say the smoother finish helps with speed.
So last year I set to with a scraper and took the majority of the decades of surplus AF off the starboard side. But it was hard work, so I didn't do the other side. I then applied fresh coat of AF as normal.

On hoisting the boat, the difference in growth was noticeable. In no case was it severe, but there was certainly more on the Stbd side (where I'd removed the old stuff) than the port, where it'd been just another layer on top of the many. In other words cleaning the old AF had a negative effect on the AF performance.

I didn't notice any tendency to veer to starboard during the year.

So my quandary now is, do I do the other side to match? Or just revert to leaving the old AF in place?

[Silkie]

Can you be sure that the effect was solely due to the antifoul? You say that the difference was noticeable but not severe and perhaps there is a difference every year which you've not previously noticed because you had no reason to suspect one. Few boats will get symmetrical exposure to sunlight for instance.

Having said that, I stripped the entire hull back to GRP last winter (after a 10 year build-up) before applying one coat of primer and one of Cruiser Uno and thought that the fouling was slightly worse than usual by the end of the season but of course there are variations between years as well.

[BlowingOldBoots]

A neighbour at Largs Yacht haven rubbed down his old antifouling every winter and relaunched. He said he would do the same next winter if after rubbing down it was still sound. So he got three seasons out of one application just by rubbing back. He rubbed back with a wet green meanie or two.

[mm5aho]

Can you be sure that the effect was solely due to the antifoul?....

Can't be absolutely certain, but I can say that I have not seen a difference previously and would have seen that much of a difference.

The biggest difference I've ever noted from "normal" is primary summer location. Far less growth when left at Rhu between trips than at Dunstaffnage.

[wully]

Far less growth when left at Rhu between trips than at Dunstaffnage.

j

That'll be the radio activity in the Gareloch....

[Storyline]

This is the sort of thread I like - where the best solution is the one which involves the least work !

[pagoda]

This is the sort of thread I like - where the best solution is the one which involves the least work !

is that scraping off all the old anti foul or just adding a new coat?

big difference

[mm5aho]

Maybe the extra drag caused by old layers of AF was counteracted by the increased growth on the smoother side, such that i didn't sail round in circles?

Question is: what should I do this winter. Complete the removal, or just revert to the easy way of slapping on another coat?