Bottom paint - 2 coats or 3? Or even 4? 5? Why not 6?

[Ralph Johnstone]

Any way I typically get 5 years out of bottom paint before hauling and repainting.

Your hull bottom looks identical to mine before pressure washing. Just a light coating of slime which washes right off. And yet you use a completely different bottom paint. You've obviously found "your" perfect bottom paint for your area.

The big difference here is that a few of us stop long enough to closely inspect their hulls at each haul out and are willing to NOT go along with the manufacturer's advertising crew which tells us "MUST APPLY OUR BOTTOM PAINT EVERY YEAR OR BARNACLES WILL CONSUME YOUR HULL."

It all comes down to common sense, "No barnacles after one year, it's a waste of time and money to add another coat ." If you've got barnacles after one year, you probably don't have the best bottom paint for your area.

We've found ours most likely due to pure luck. Researching this would be enough to drive one bonkers.

 

[Barnacle Bill]

First of all, it depends on where you sail and what the water is like. Someone mentioned Trinidad. That is a great paint for heavy salt water flouling, but certainly not for fresh water.
There are two basic types of antifouling paints. Single season and multi-season. Multi-seasons are usually referred to as ablative. These types of paints work like a bar of soap. The paint and toxicant leaks away at the same rate, eventually leaving a bare hull when it is all gone. So, like a bar of soap, it keeps cleaning your hands until the soap is gone. Often a good time to repaint is when you start seeing bare hull showing through.
Single season paints are usually a copper oxide based biocide. They are single season paints because when they dry a chemical change takes place rendering them not so effective anymore. And the toxicant leaches away from the paint. Therefore, when you see a single season paint on the hull, you cannot assume there's any toxicant left. Therefore, single season paints are required to recoat each year, if you pull the boat for the winter. And because of that chemical change, they are not recommended for trailerable boats that are pulled out and put in several times over a summer.
With multi-season paints, the toxicant and paint leaches away leaving a bare hull - hence no eventual build up.
Since single season paints are recoated annually, there will be a build up of paint which eventually will get so thick it needs to be removed and the process started over. But.....
Single season paints are great paints for boats left in the water over long periods of time. Such as those boats not pulled for winter storage. And usually they are more suited for salt water environments than ablative paints, which usually don't have the same intensity of toxicants, but there may be a few as technology is getting better.
So, since multi season paints last a longer period of time, that is because you put on more coats than a single season paint.
Usually the manufacturer recommends 3 coats for multi-season paints and two for single season paints.
Read the label.
What you don't want is the marina to come up with a high pressure sprayer and blow all the multi-season paint off your hull when you pull out in the fall. That's your hard-earned money down the drain. There usually is some sort of slim on every boat in the fall, and so a light cleaning to rid that from your hull is required.
If, by chance you are one who used single season paints and you have applied a fresh coat of paint and for some reason you had to pull your boat so the hull dries, then, knowing you have lots of toxicants in the paint, you can lightly burnish or sand the surface to open up the pores (so to speak), to re invigorate the application before you launch.

Hope this helps.