Cavities

Micky

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Quick question.
We all know what the little or large blisters are on a boat hull when the boat is pulled out the water = Osmosis.

I'm working on a boat, it's about 1983 model, that has lots of very small cavities, about 2-3mm deep and 2-3mm across. There are quite a few of them spread out around the hull below the water line.
Odd ones here and there, and in some areas there are as many as a dozen all close together.
Looks like someone has taken a pot shot with a 12 bore.

Anyone got any ideas what these are, or what might have caused them.
 

William_H

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You need to grind the cavities out carefully to determine how deep they are. My first thought was that they may be holes in a large buiuld up of antifouling paint. if so it is a good reason to take the paint off. (or just ignore it)
However if it is down to the f/g substrate then you should grind down and give it several coats of epoxy after allowing it to dry. good luck olewill
 

oldsaltoz

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G'day Micky,

If this is a fishing boat then take more care with hooks...

Only messing with your mind. It sounds like the gel coat has too mach hardener mixed with it and has boiled, not uncommon in older boats and very common above the water line in any area that is not easy to spray into like the combing around the cockpit, small holes start to appear after a little wear, I suspect you have done some sanding and exposed the voids.

Easy to fix, first you must clean them out, a ball on a dremel tool will do a good job and not take too long, wipe with lots of Acetone, allow to dry (30 minutes) and apply a mix of closed cell micro balloons and epoxy resin with a flexible plastic ruler. Make sure you drag the ruler and mix over the area in all directions, it should give a smooth finish and need very little sanding.

As Epoxy is not UV stable you will also need to some paint to protect it; if it's all below the water line, a light sanding and antifouling should be OK.

Avagoodweekend......
 

Micky

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Thanks for the replies chaps.

Yep, oldsaltoz. I reckon your bang on with your info. These voids are in the gel coat.
What you say, is exactly what happened.
As i started sanding the bottom, they appeared.
They are clean and dry, actually they look like chips in the rim of a beer glass, all about 2-3mm deep.

Have now sanded off all the old Anti-fouling and filled most of them as i went along.

Thanks for the feedback.
 

Erre

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[ QUOTE ]
Quick question.

Looks like someone has taken a pot shot with a 12 bore.

Anyone got any ideas what these are, or what might have caused them.

[/ QUOTE ]

You might have hit the nail on the head. I heard about one vessel on the Essex Blackwater that a punt gunner had used to check the spread pattern of his punt gun (3/4lb lead shot!).
 

Avocet

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[ QUOTE ]

...
As Epoxy is not UV stable you will also need to some paint to protect it...
Avagoodweekend......

[/ QUOTE ]

Hmmm! That's a thought!

Sorry to hijack the thread but what are your thoughts Oldsalt, on my "little project" from this point of view? I'm about half way through it but as you know, I started last year so some of the first areas have been exposed to UV for over a year now! (OK, Cumbrian UV, so not the sort that we see a great deal of)!
 

oldsaltoz

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UV damage does not need sunlight, just light is enough. 12 months is not a problem, a very light sanding will remove the damaged surface and you will be sanding prior to painting so no problem.

On Deck in Oz epoxy will start changing colour in 6 to 8 months.

PS. I almost e-mailed you a couple of weeks age to see how you are progressing, you must be getting close to to the fun bit, overhead fairing with a torture board at arms length.

Avagoodweekend......
 

Avocet

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Ha HA!

OK, 2 years then?!

By all means feel free to e-mail. If your address hasn't changed I might e-mail you a couple of photos!

The "good" news is that I've started from the bottom and worked upwards so the "upside-down" fairing and flatting is pretty much done. I've been sanding each "stripe" as I've gone so it's also fairly smooth under the stern counter already. Well, I say "smooth", a blind man on a galloping horse wouldn't see the lumps! - (as long as he didn't brush against it and cut himself on it as he went past)!

Seriously, it's "40-grit" smooth at present but there are bits of old gelcoat in between the stripes which I plan to take out later - just to remind me where the surface used to be! Last weekend my router died on me but to my pleasant surprise, it was one with a 2 year warranty so I'm just awaiting a replacement. As you've probably seen on the news June has been something of a wet month here in the UK!
 
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