Kunzig said:
Often it is best to check with the locals, the boats that have been around awhile - they will know what works the best in that area......
Here's another vote for seeing what other folks in your area / water conditions are using. Here in the Lower Chesapeake Bay with warm / hot water temps and plenty of sunshine, I like to use Interlux Micron Extra. If I lived and sailed in Maine, I would have a completey different choice.
The other boaters in your area will have decided what works in your area. You will probably not get a consensus on a particular choice. You will get several opinions / options. Then pick one of the locally recommended paints, based on what you want to pay, how often you haul, paint color availability, et cetera.
Over the years, many boaters pick a particular brand for whatever reason that seems valid to them. Myself, although I have also used paints from Woolsey, and Pettit, I have decided that I like using Interlux paints the best. Nothing really wrong with the others, I like Interlux the same way some folks drink Pepsi, and some drink Coke. It's a brand loyalty thing.
Whatever brand you go with, you need to get the best surface preparation for the longest lasting, best effective paint job. First step is to use acetone (or similar) to remove all the mold release wax that will be on a new rudder. Then you need to sand the surface you want to paint to roughen it up to "hold" the paint better. (Or instead of sanding, there are various products that accomplish the "sanding" by chemical etching. Interlux's is their Fiberglass No Sand.)
Next step is the recommended primer, and then, finally your chosen bottom paint. If you choose an ablative (many reasons to do so, a few not to), lots of folks will make the first coat a different color than the last one or two. This way you can see when the top coats have "polished" off and it is time to re-coat.
I would also suggest that, once you pick a brand of bottom paint, you follow that manufacturers suggestions for cleaners, primers, et cetera - I would not mix Company A's primer with Company B's bottom paint. It may work out OK, but do you really want to do that particular "science project"?
Interlux has a painting guide on their website that is loaded with lots of good tips / info. Other manufacturers may also have info posted but I am not familiar with the others. You can find it at
http://www.yachtpaint.com/LiteratureCen ... sa-eng.pdf. Whether you decide on Interlux or another company, there is lots of good info in their guide.