Bottom Paint ?

[turkish6]

hello everyone.

So our first boat is out of the water. we did all our winterization (thanks to help from fellow board members) we then put our cover on (thanks to the guy before us who had a custom one made). now we are looking into the bottom paint. The yard gave it a good power wash when he hauled out and there is no slime or growth on the hull. We inspected the paint and in about 20 spots there are parts where the bottom paint is done and we see the original blue gelcoat underneath. When you scrap at that those bare spots the paint just comes off. If I keep going going eventually I get to spots that are harder to get off or don't come off at all. I don't see anysigns of blistering. My questions are as follows;

1. Why do we have bare spots. (is it because it was no prepared correctly)
2. What should we do about these bare spots.
3. Is it wise to invest the time to scrap the entire bottom and then put on a fresh coat of paint?
4. If I have to scrap the bottom is it ok to scrap now and paint in the spring.
5. Is it better to get off what I can then paint over it like that?

btw this is not race boat. just a family cruiser

[David M]

If the pressure washer did not remove the anti-fouling paint then it is probably not going to come off anytime soon.

Bottom paint does not need a primer but the surface you apply it to does need to be clean, dry and scruffed up with some 3M pads or some sandpaper.

Look carefully for blisters on the bare spots...especially near the waterline. Hopefully you will not have any.

There are two types of bottom paint..paint that ablates meaning it is designed to fall off over time exposing new anti-fouling agent and there is the harder bottom paint which is designed to remain very smooth. The latter is more appropriate for racing boats which don't mind sending a diver down frequently to clean a bottom which fouls at a higher rate.

It's okay if your bottom paint comes off easily if it was an ablative paint in the first place...this is normal.

If you feel the need to knock off excessively loose paint then get one of those very course scrub pads on a pole and wet sand down the loose stuff. In fact, do this anyway to assure a good surface for the new coat.

You can do this now and then apply a fresh coat in the spring.

Most people choose to roll on the paint which is cheaper but it also means the paint may not have been rolled on evenly leaving an occasional thin spot that has ablated to the point where there is no paint left.

If you want to spend the bucks, then you could have all the paint removed, the hull sprayed with an epoxy barrier coat like Interlux 2000 or Interlux 3000 and then have a bottom paint sprayed on. But since you are not racing, I would not bother.

Since you cannot get TBT anymore, look for a copper based paint. The higher the percentage of copper the better. Try not to go into shock when a gallon of copper bottom cost you over $150.

There are paints now which are not supposed to hurt marine life but from what I have seen they are not anywhere as effective as copper based paint. Nobody has found a clearly effective solution yet.

Another wise idea while you are hauled out...pull all your thru-hull valves and inspect them.

[fstbttms]

Originally Posted by David M

There are two types of bottom paint..paint that ablates meaning it is designed to fall off over time exposing new anti-fouling agent and there is the harder bottom paint which is designed to remain very smooth. The latter is more appropriate for racing boats which don't mind sending a diver down frequently to clean a bottom which fouls at a higher rate..

There are a lot more than two types of bottom paint but most people are familiar with the two most commonly used types; modified epoxies and ablatives. Generally speaking, neither is better or worse than the other as far as anti fouling performance goes; nor is one type more appropriate for racers than the other. There are many excellent examples of both types of products. And depending on how it is applied to the hull, any bottom paint can made very smooth (or rough).

Originally Posted by David M

Since you cannot get TBT anymore, look for a copper based paint. The higher the percentage of copper the better. Try not to go into shock when a gallon of copper bottom cost you over $150.

turkish6, you would do well to try to find out what kind of bottom paint the boat has on it now, as some anti foulings are not compatible with each other. The West Marine catalog & web site have an "Advisor" page with a primer on anti fouling and a paint compatibilty chart-

West Marine: West Advisor

Check it out. There is a lot of good information there.

[David M]

...or you can check with your boat yard manager. They are supposed to know this stuff. If they do you wrong then they are supposed to correct their mistakes at no cost to you.

[S/V Illusion]

Talk to the other boaters in your yard to see what the most popular paint is - different locations represent different conditions and no one bottom paint is universally effective in all locations. Depending upon what paint you choose, some are not effective if allowed to dry over a prolonged period, therefore, should not be applied now for a spring launch. Also, copper content is not a true indicator of efficacy. Of far greater import is the paint's ability to make fresh copper available which again is largely dependent on location as well as how often you actually use the boat. In other words, there is no "best" paint nor is there only one criteria by which a choice can be made. Having said that, ablative paints have one significant advantage over others - their ability to slough off with use preventing build-up over time thereby making maintenance much easier.