Log impeller and leaks

[blackbeard]

.. in this case, NASA though the problem might not be confined to any one manufacturer.
Problem is, there is a very slight leak somewhere and the area inside the boat near the impeller is therefore damp. When to boat was on a swinging mooring it seemed to be worse when there was a bit of a rough sea running through the moorings during an onshore blow; the boat now has a sheltered pontoon mooring and the problem is less, though still present, and I suspect most evident after beating into a bit of a sea. Some years ago I discussed this with NASA who kindly sent me (free of charge!) some new O rings which seemed to solve the problem for a while, but it eventually returned.
In practical terms, it's not much of a problem in that the quantity of water involved is small, it only needs clearing up once in a while and is never more than a cupful. More annoying than serious, except that I cannot use the forepeak locker for anything that might be damaged by damp.

So: anyone else had this problem; and, Any ideas what might be causing it? and on how to fix it? I should add that I cannot see any fault (crack etc) in the log housing and it seems to be (as far as I can see) fairly well embedded in the hull.

And: going on from this: seems that one sure fire way of solving the problem would be to remove the impeller and its housing and restore the hull to its original unpierced state. Then I wouldn't have a log, but do I need one, given that I have GPS? After all, the original reason for having a log was to enable an estimated position, and in any case I have a fairly good idea of how fast the boat is going ... what I think I don't need is yet another below-waterline hole in my boat ...

 

[pvb]

If the log housing is properly sealed into the hull, it can only be an O-ring problem. The trouble is (as I discovered recently) there are squillions of different sizes of O-rings and you need exactly the right size to prevent leaks. I'd sold my boat and, with about a week before the buyer was due to take it away, I found the log was leaking. I can't tell you how many O-rings I bought before I got the right size, but it was well in to double figures.

 

[PuffTheMagicDragon]

It helps to lubricate the O-rings with a smear of Vaseline from time to time, according to the manual of my Nexus triducer (Airmar).

 

[Corribee Boy]

I found a slight damp area around the log impellor backing pad, shortly after launching. It wasn't coming down from the top of the thread so I assumed it was creeping around the hull flange. I'd had the impellor out recently and nothing about the tube worried me - until I decided to turn the backing nut to slacken it and put some sealant in it. Luckily I was parked on a sandbank because it the tube sheared off as I backed the nut off by hand.

I hadn't studied the tube, and I'm not sure the fault would have been visible from inside the tube without the use of a dentist's mirror or something, but my point is, failures in the tube can and do occur!

 

[RumPunch]

Are you sure it's the impeller housing ? My reason in wondering is I had a weep from a keel bolt, and it only happened when to boat was being buffetted. Obviously the pendulum effect of the kee trying to move was causing the leak - didn't happen when moored up on the marina or moving in still waters.

 

[alahol2]

I believe the NASA log housing can be damaged by some types of sealant, ie making it brittle. Their installation instructions say it should be filleted in with GRP filler. The OP should check by giving the housing a 'wobble', preferably when aground/out of the water.

 

[Corribee Boy]

Yes, as far as I'm aware my tube was the original from 1984, but it was certainly brittle. If you opt to try this while dried out on a sandbank, make sure you've got all components and tools to hand before the tide returns!