Bottom paint chipping off - just how much speed are we losing?

[Andrew Means]

So we had the Wino Country Safari out on blocks to get it buffed (something that we hadn't done since we've owned it) and I had a chance to look at the hull. The paint is chipping off in big chunks in places, probably a 1/16th of an inch thick. I've heard of 'barrier coats', and chipping as a result of them being applied, but I don't really know anything more than that.

The good news is that the fiberglass is in great shape, and we'll be in for some sanding come springtime so we can get the bottom painted. In the meantime I'm curious how much speed we will gain when we paint the hull. Have any of you had to paint a hull with paint chipping off like ours? What kind of speed advantage did you get when you painted?

 

[Frank Langer]

It could be that the paint that is chipping off is part of a barrier coat, but it could also be an accumulation of layers of bottom paint. I have seen boat hulls with years of bottom paint applied layer on layer until it got quite thick, and eventually began to chip off. There are varying opinions whether it is best to remove this by sanding, or by scraping. A recent thread spoke of using a sharpened truck spring to get a good curve over a broad area as an effective tool for this purpose.

While I suspect that every boat will be a bit different as to effect of uneven hull on speed, I would hazard a reasonable guess that chipping paint could result in a loss of about 1/2 knot compared to a smooth bottom. If the bottom is burnished like some racers do, I think that would gain at least a full knot over an uneven bottom. A fouled hull due to algae growth and barnacles would slow the boat down quite a bit more--I recall one liveaboard who rarely sailed, but ventured forth one day and could only reach a max speed of 2 knots under power due to a fouled bottom.

I'll be interested in what others think on this.

Frank

 

[mherrcat]

That is what my hull looked like when I first had the bottom painted in January 2009. The flaking and chipping will show up even more when the bottom has a few days to dry out. I had the yard take all that accumulated paint off and apply an epoxy barrier coat before putting on the final coats of bottom paint.

This is the best pic I could find of the "before" condition. You can see in the top of the picture where the paint had chipped previously and whoever did the last bottom painting didn't even bother to sand it down:

 

[Andrew Means]

How much did it cost to have the yard strip it all off for ya, if you don't mind me asking?

 

[mherrcat]

They were running a bottom painting special at the time and I believe the price for the normal bottom painting was about $1,150 which was only to sand and apply bottom paint over the existing paint. The additional labor and material to remove all the old paint and apply the epoxy barrier coat was, I believe, $1,000. So about $2,150 total. (This is based on what I recall their original estimate being.)

I looked at the invoice and it's kind of hard to tell since I had other major work (shaft coupling, cutless bearing, steering quadrant, rudder work) done at the same time and then had a big fight with them due to work they did without consulting me first. So the final invoice has a lot of stuff discounted.

 

[rwthomas1]

If the layers of paint are chipping/falling off the boat, speed loss is the least of your worries, loosing your newly applied antifouling and the resulting growth is a larger problem. I have two words for you "soda blasting" I did a down to glass sanding, scraping, etc. bottom job on my boat by myself. It really, really sucks. I will never do it again. Look into having a contractor "sandblast" the bottom with baking soda. Its very common here in the Northeast, its envirofriendly if that turns your screws, and it won't hurt the fiberglass one bit. The finished surface is ready to be barrier coated after a washdown. Barrier coating is easy, if you can apply antifouling paint, you can handle barrier coating. RT

 

[mherrcat]

...losing your newly applied antifouling and the resulting growth is a larger problem.

I agree. At some point you are going to have to remove years of accumulated paint.