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[Bobg]

I sail in lake superior, the boat goes in the water in the spring, and comes out in the fall with virtually nothing on the hull, is bottom paint necessary, I used to put vc 17 on but was skoffed at by fellow boaters for spending the time and money, however, my dock mate says that without it the boat can take on water through the gel coat, not sure what that means, has anyone ever heard of that?

[Noah]

Yes, I suppose it would be possible, but you'd probably start to see blisters and when you popped them they would smell like vinegar/styrene. Are you sure you have bare gelcoat, not a barrier coat? If it is bare gelcoat do you wax the bottom? BTW- bottom paint alone on gelcoat won't stop the osmotic penetration. You will need a barrier coat first.

[Stu Jackson]

Bob,

I am often more than slightly amused by the inanity that comes from "fellow boaters" and "dock mates".

Neither of these guys know what they are talking about.

Sometimes when input comes in that is counter to traditional, well respected norms and means, methods and techniques of standard practice, it can be, uhm, staggering, frightening, indicative of stupidity, hard to believe...

It's like when someone says gravity isn't real, or down is up, etc.

You just stop and go:  WHAAAT?!?

Stuff, sometimes nasty stuff, WILL grow on the bottom of your boat, freshwater slower than saltwater.  I had a Catalina 22 that we left in a lake from Memorial Day to Labor Day for a few years.  ONLY because this lake had an "underwater car wash boat bottom cleaner" did I not put bottom paint on it.  We dry sailed it back on SF Bay.  Stuff DID grow on the bottom, and I cleaned it with a plastic scouring pad regularly during the season when I went swimming at anchor.  The bottom was GREEN even after the underwater boat wash.

Everyone I know who has a boat in the Great Lakes uses VC17 or the Micron equivalent.

Everyone I know who has a boat in saltwater uses effective bottom paint usually based on where they sail to select the appropriate material.

Bob, that's why they make this stuff.

I am simply gobsmacked at the BS you're being fed.

Tell ya what:  Stick a piece of fiberglass on a line off the end of your dock.  Check it every once in a while.  Come back in two months and let us know what it looks like.  That is what will be on the bottom of your boat, too.  You'll wonder why you can't reach hull speed at WOT.

Unless your water is so, so cold and your season is so, so short, it would be unusual to not use bottom paint.

And bottom paint alone does nothing regarding osmotic blistering, only a barrier coat does.

Good luck, but tooth fairies don't exist either.

[Bobg]

well the bottom of my boat without vc 17 is dark blue, so I suppose that is the barrier coat you are talking about, my season is from june to september, right now the temp of the water is 66 degrees, I didn't buy what my dock mate said about boat taking on water through the gel coat, but I am grasping at straws here as to why my boat has lost a knot after re pitching my prop from 9" to 10".  I can put a basket of beer down in my water for a month and it comes out like it went in, no discoloring. I will put vc 17 on the boat next spring and see what happens. its cheap enough,  OH well, september is just around the corner already

[KWKloeber]

Bob

Maybe the dock expert is referring to osmosis/blistering when there's no barrier coat?  Who knows?

When I hear dock talk that doesn't at first appear to make sense, I press them about it.  It usually reveals (1) they mean something valid but different and have trouble explaining it, (2) I have a brain freeze and they are right, (3) (pretty quickly) confirming that they have no idea what they're talking about (so don't try to change their mind,) or (4) they are only repeating other dock talk.

With the temps of Superior, I can believe the little-growth scenario.  It's somewhat similar on Ontario.

kk