However, my quick-and-dirty solution to the annual "missed-a-spot"
problem with ablative paint is alternating between having blue and red
below the waterline. Makes it pretty obvious, either color looks OK on
a white hull, and I try not to sail upside down anyway.

We use a wear indicator on our ablative bottom paint. The bottom is
first painted black and then covered with blue to go with the white hull
and red boot stripe. (I grew up in New England and that was a traditional
paint scheme.) We run until a large percentage of black is showing
through and then go for a haulout and do it all over again. The boat is in
the south and we boat year round.

Leanne
S/V Fundy