Rudder blisters

[knotatwork2]

Hello
My 1987 Hunter 23's rudder has some blisters on it. It has never been painted. I need some guidance on what steps to do please. Should I sand it down ,with what grade sandpaper and if I do, what do you seal it with, then paint it with anti fouling paint. My boat has vc 17 painted on the bottom, I was hoping to use that on the rudder also. Thank you.
Ken

 

[Crazy Dave Condon]

can you post some photos and I would suggest posting in the small boat section where most for your size boat goes. A lot depends on what is on the rudder. I will comment when I see what you are talking about. Is there any water in the rudder and if so, drill a couple of small holes in the bottom to allow water to drain out and allow two months standing up in a dry warm place to allow the moisture inside that rudder to dry out.

 

[Terry Cox]

Hi Ken, if the blisters are dime size and only a few of them, not to worry. Once the boat is on the hard I usually pop them with my finger, let them dry out, scrape and sand to fair and then cover the rudder with at least two coats of bottom paint.

If the blisters are much larger then you need to open them up, dry them out, scrape and sand to fair any soft material, fill with epoxy if necessary then cover with bottom paint.

Pictures of your situation would help.

 

[DianaOfBurlington]

'Professional' fix for this

Grind 'em out with a 3" angle grinder, like to the shape of a small saucer. Fill with some polyester/vinylester filler, like Evercoat 27 (cheaper), or else the blue-green 3M stuff (expensive). If it's deeper (voids showing after you make a saucer out of it), start with a tab of fiberglass mat and then the filler(s). Then sand fair, continue to scuff up all the gelcoat for basic adhesion, and paint it with epoxy before adding barrier coating and your choice of paint. It won't be a problem again for another 25 years.

The main thing is the painting-over with epoxy, which is what barrier-coating manufacturers recommend over repairs using filler before the application of the barrier coat. I learned this the hard way (read that: reading the manual after starting the job). :naughty:

 

[knotatwork2]

Hello,
I have small blisters, the gelcoat chipped off the end of rudder, no water inside. What should I do to correct this. I want to paint the rudder with vc17 ,which is what on the bottom of my boat now.
Thanks, Ken

 

[Crazy Dave Condon]

I would dremel those even though numerous, fill in with two part expoxy to include the area where gel coat missing, sand smooth and refill if necessary and sand. Coat with barrier coat and the bottom paint. It did not look as if the bottom of the rudder blade has split unless it has which you will need to advise.

Find out which bottom paint works well for your area is the best advice on that.

 

[DianaOfBurlington]

Blisters vs cracks (att'n: Ken and Terry)

What I said about grinding them out especially applies to Ken's problem. If they're gelcoat cracks (spiderwebs), that's *different* from blisters.

There's only two reasons I can think of for cracked gelcoat: stress and air bubbles. Stress can do funny things-- I had tons of it in the hull right under where the shrouds attached to the toerail. No mystery there. Oilcanning (repetitive 'b-doinking') of wide, flimsy sections of hull-- above the v-berth, aft of the quarter berths-- will show the same thing. These need to be done with a Dremel and filled with epoxy (second choice: polyester/vinylester product) and appropriate filler. 'Draw' the tool along the line, as far as it goes. If you hit it once, a little, and you see no crack just below the surface, leave it alone. Otherwise dig them out till you see no remainder of the crack (usually into the greenish resin-- the gelcoat is microscopically thin on most of our older boats by now).

Airbubbles look like blisters; but they don't show up for the same reasons. Airbubbles are typically caused by the factory peons applying too much gelcoat with too little brushing and daubing (such as with a fast, wide sweep of the gun), so that a thin skin of gelcoat gets into the outer skin of a corner (like along the top of the hull, under the toerail, along the bow, edges of the rudder) but more of it forms a kind of bubble over which the first layer of fiberglass goes, so that it's never noticed. When the boat comes out of the mold, the outer layer of gelcoat appears to be a sound skin. But it will crack and admit water, if only just into that bubble. I found a lot of these in Diana's topsides under the toerail. They may look like thin cracks; but you hit it with the tip of the pointy stone on the Dremel and it gives way to a veritable cave in there. I had one on the transom, looking like the tiniest little line, but I hit it and-- I do not make this up-- it was 5/16" deep and about 7/8" across in there. Really I wonder if it had ever really been leaking at all. But it's filled now with epoxy (and glass fibers).

As for blisters, they're caused by one of two things: pinhole cracks admitting water from the outside, or, worse, osmosis from the inside of the hull (which typically is not gelcoated-- it should be). These look like what Ken has on the side of the rudder blade. I would be careful to check if the foam core is not wet or rotting-- grind these out with the 3" wheel as I said earlier and see what's inside there. Definitely fill these with 'glass patches, not mere filler putty.

As to what Terry said, I made the utterly stupid mistake of painting barrier coating over what I *assumed* were only minor stress cracks in the bottom. Fast-forward a whole winter: the cracks were coming through the barrier coat. This is not good. Had to grind down all the barrier coat in those spots and address the Dremel to those areas, which I should have done the previous season. This is why many of Diana's recent pics show bald spots in the grey Pettit Protect on her bottom. As soon as the season breaks I will have these done (again).

So don't let these go. If you see cracks in paint or gelcoat, especially if they're under the waterline, FIX THEM NOW. That is all. :naughty:

 

[DianaOfBurlington]

Ken's rudder edge

Ken, do I see an outside flange around that rudder blade-- like the two halves are dimpled outside? Is that how they made that thing? Heinous.

I would grind that whole thing off, to take the half-a-knot's gain and the more delicate steering ability, and 'glass over the whole leading edge and re-fair it. Why not? --you have it on the bench now. All it is is work.

Then again I am the idiot who actually researched NACA airfoil sections to reshape the lead of his keel (and the rudder blade); but then I was aghast at how badly the factory had shaped both of these, as I will be if I find that what I fear about your rudder is actually what the factory did.