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Re: [PSUBS-MAILIST] through hulls



I have only one mechanical thru-hull on my boat, for the drop weight release screw. I am using a 1 inch stainless shaft with two "O" ring glands cut into it. This shaft fits within a 1 inch ID---2-1/2 inch OD sleeve welded into the hull bottom. This sleeve is 3/4 inches thick. The sleeve has pipe threads cut into the top so a 2-1/2 inch ball valve threads down onto it. The 1 inch release pin has a 3/4 X 3/4 inch square end on top. To release the drop weight, a socket is placed down through the open ball valve and the release screw is rotated until the drop weight drops off. The pin stays in the welded sleeve. The ball valve is then closed again.
I opted for this method because a hydraulic system seemed unreliable as a means to hold the heavy drop weight/carriage assembly if I hit rocks or some other hard object with the sub bottom.
It seems to me that cutting the "O" ring grooves into the shaft is not only a lot simpler than cutting them into the sleeve interior, but as this shaft is removable, it will be easier to replace this part where no cutting and/or welding will be needed. I don't have K boat drawings. If the pin and sleeve are made of 316 stainless, they should last a long time, but the "O" ring glands are a place that may need attention sometimes. Maintenance like cleaning, polishing, replacing the "O" rings, should be done quite regularly. Even rinsing with fresh water after diving. My thoughts have always been.....any kind of attachment on a sub operated in salt water should be designed for quick dis-assembly for cleaning and maintenance, and as many parts as possible should be removable without cutting or welding in case of wear or damage.
The "block V " seals have a good track record, and seem like a sound alternative. I think they are more forgiving than "O" rings as far as close tolerance and alignment.
Frank D.