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Old 26-09-2008, 18:52   #1
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Anyone know the raw water thru hull shape?

This is going to sound a bit odd, but..

I have a raw water cooled Yanmar engine.

Where the sea cock comes through into the engine compartment it seems to be embedded in a larger circular possibly plastic, composite or fibreglass plug, which is about 4 1/2 - 5" in diameter



http://www.internetmark.com/images/thruhullplug.jpg - if the above doesn't work..

There is a small hairline crack around the circumference, which has always been there, but I wanted to router out a small V, and fill it with some west system just to smooth it out (don't like cracks in my boat).

Does anyone have experience of the shape of this plug as it goes through the hull?

I don't want to suddenly be up to my ears in water if when I start routing it pops into the boat!!

TIA
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Old 26-09-2008, 21:51   #2
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It looks like a patch job of some kind but it's hard to tell from the picture.

I wouldn't grind on it while it's in the water but you could fiberglass over it until your next haul out, which should be soon to find out what the real story is.
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Old 27-09-2008, 11:15   #3
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Can you tell us anything about the slightly larger square (7 1/2") surrounding the circle?
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Old 27-09-2008, 11:55   #4
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As I am an amateur boat detective I'd say there was a square piece of plywood under the original valve. It looks like someone used a large hole saw to remove a portion of the wood to put in a new valve that required no backing or standoff. In the process they cut into the fiberglass then wound up scraping all the wood off. If want a quick fix I would invest in a shorthaul at a marina say before everyone goes to lunch. I an about an hour or so you could lightly sand the circumference of the circle and put a patch on it. Then go back in the water. That would be a quick fix.

The right thing to do would be to haul, remove the valve and investigate the area in question.
I wouldn't sand or cut or in anyway open that area while you are in the water.
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Old 27-09-2008, 12:46   #5
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Does the boat have a cored hull? I think today's Hunter's only core the hull sides but in your era there might have been core below the waterline.

If so, the plug was probably put in at manufacture to avoid the risk of water getting into the core where the sea cock penetrates the hull. This is good practice and it would make sense to use a completely rot proof material such as fiberglass or plastic. It's good that there's no sign of water staining.

The larger rectangular area might just be a taped-off area that wasn't painted (so caulking would stick better). It's hard to tape a circle. If it is wood, poke at it to see if there's any rot.

If the above guess is right, the circular plug is bonded to the inside of the fiberglass skin and the hole through the skin is just the size of the sea cock pipe. This is strong and good construction. There's no need to reinforce the edge. It would have been better if the seacock was flanged and bolted through the hull.

If the joint isn't getting larger or leaking, I really wouldn't worry about it. When the boat is next out of the water, you could sand off a little bottom paint to see if the circle is on the outside of the hull too - this is very unlikely - and very bad.

If the hull is cored, it never hurts to drill some small shallow holes in the area (don't pierce the outer skin) and see if the drill comes out wet. If so, seek expert help. If dry, fill the holes with epoxy and go sailing.

Carl
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Old 28-09-2008, 15:42   #6
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Quote:
Originally Posted by CarlF View Post
Does the boat have a cored hull? I think today's Hunter's only core the hull sides but in your era there might have been core below the waterline.

If so, the plug was probably put in at manufacture to avoid the risk of water getting into the core where the sea cock penetrates the hull. This is good practice and it would make sense to use a completely rot proof material such as fiberglass or plastic. It's good that there's no sign of water staining.
Thanks Carl

You were right!

After much research and comparisons with other boats and then Hunter owners, it turns out that the actual engine compartment base is about 2 inches above the thru-hull exit into the water, and the circle is just a cover for a 'well' beneath where there is the wood, tightening ring, etc.

The square area around it was where there was originally some kind of 'filler' or paint or something, and I guess over the years vibration from the engine had caused that small crack.

So I can now feel safe just caulking that crack to stop water seeping below (very rare water gets in there). I won't west system it as this would restrict access if the thru hull ever needs to be replaced.

Thanks again all, you're the best
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