Bottom paint, the good and the bad

D

Don and Brenda

New member
I have never owned a boat with bottom paint, is this a good thing to look for? I plan on storing the boat on the trailer with the exception of some long trip on the inside passage. Is this something I willl need to refresh every few years and is the boats performance down graded?
 
Don and Brenda,

There are far more experienced people to answer this question than I, but I'll give it a shot.

I guess the first question to answer is, why do people paint the bottom of their boats?

It is my understanding that there are two reasons.

1. Fiberglass and wood absorb water over time if left in water for extended periods of time. Before vinylester, fiberglass boats would get blisters under the waterline where water was absorbed into the fiberglass. Newer boats don't suffer from this problem much any more, but some people still apply epoxy (yes the glue) to the bottom of the boat to build a barrier between the fiberglass and the water.

2. To prevent animal and plant growth on the bottom of a boat. If left in the water for extended periods (which in some locations may be a short as a week or two) aquatic life attaches to anything left in the water. This aquatic life builds up and greatly affects the performance of a boat both in MPG/GPH or handling.

So the next question is, will this boat be in the water long enough for these two issues to affect it?

Many boats that sit mostly on trailers and in dry storage do not have their bottoms painted, because their time in the water is limited and most aquatic growth 'slime' can be washed off. Since they don't spend much time in the water, they don't need the protection of the epoxy coat either.

The Pacific North West (PNW) does not have the growth rate of aquatic life attaching to hulls as say the South East (Florida) or the South (Texas), so you have a little more lee way when it comes to deciding on bottom paint or not.

Even the best bottom paint only last ~ 2 years. The old paints which contained a lot of copper are being discontinued if not made outright illegal. Newer bottom paints are designed to slough-off and take the aquatic life with it. As a result they only last a year or two before they remove themselves.

You need to think about how long you'll be in the water with the boat when you do your inside passage trips. That will answer your question.

I hope I've helped.
 
Our CD22 was in the waters of WA and BC for 2-3 weeks at a time with little growth problem. After a two-month Alaska cruise, it took a lot more elbow grease to clean her up, but still no great problem.

Our current 26-footer was pretty much the same until we started traveling slower (6.5 knots) most of the time - then growth became a major issue.

We cleaned her up really well, including countless hours scraping off the little glue circles left by the barnacles. Applied a two coats of sandless primer and three of Pettit Hydrocoat, and excellent water-based ablative bottom paint. She has three summers in AK on that paint with great results, and seems to be in fine shape for at least one more.

If the boat's performance is downgraded, it is only very slightly. On the whole I would say it's better, because she doesn't pick up much growth to slow her down along the way on a long cruise.
 
To clarify one small point, bottom paint does not offer any sort of water intrusion resistance, it only helps prevent bottom growth from forming on the hull. Only epoxy or other resins prevent water intrusion.

Even a very small bit of slime or bottom growth can dramatically affect the performance and fuel consumption of a boat. I once lost 10mph and 1000rpm from wide open throttle due to slime on the bottom (not on Napoleon of course - I take good care of her!). However, at the end of last season I was running 2 knots slower for the same cruise power and it was due to some bottom growth.

In my opinion you should have bottom paint if running in salt water for more than 2-3 days at a time.

I get two seasons out of a bottom paint job, and you should do a touch up in between the full paint job. For a touch up, take a block of sand paper and scuff up any bare spots, wipe clean, then apply paint over that area.

Bottom paint will reduce performance slightly but not nearly as much as growth. From anecdotal experience, Bob without bottom paint can get 50mph out of his Tomcat and I can get 46.5 for example. (We have the same props, same engines, though slightly different weighting).
 
When "keeping" my previous boats "in the water" in FL, 24hrs/day/yr, they had to have bottom anti-fouling paint (my preference is Copper Sulfate). Barnacle instrusion was absolute without antifouling bottom paint. Additionally, as has been mentioned, it will reduce slime.

Currently, I'm keeping my 25' Cruiser on the trailer and launching instead. I do make 3-5 day runs - keeping the boat in the salt water during these periods, but I am meticulous about cleaning the bottom when I pull Antibody out after these extended periods.

In particular, in FL, where the water temperatures are much higher, the rate of barnacle intrusion is very high without employment of an antifouling bottom paint.

Not sure if Coppper Sulfate is even allowed in antifouling bottom paints any longer.

None-the-less, if you keep her in the water, you should use antifouling bottom paint always, IMO.
 
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