Seacocks and thruhulls.

http://www.pbase.com/mainecruising/seacock_primer
http://www.pbase.com/mainecruising/replacing_thruhulls
http://www.diybob.com/diySeacock.htm

I am in the process of changing all my seacocks and thruhulls just because I feel this is the weakest and most dangerous factor in our boats safety. Other that the sailing skills of the wife and I:)

I just learned through research that the thruhull fittings are made with a straight thread and the valves that are being sold have tapered threads. The two do not make a good combination. I have only bought the thruhulls and have not looked at the valves being sold at the chandleries yet. Here to hoping that they have straight threads.

What you see here is the bronze thru-hull, being held in place with duct tape from the outside. I had to use a Dremmel to cut out the old fitting and clear more fiberglass out of the way.

I have made a 1/2" plywood backing plate, slightly larger in diameter than the base of the seacock. My wife 'painted' the backing plate with resin to seal it from water. The next phase is to make resin thickened to the consistency of peanut butter and mount it to the uneven hull, insuring it is perpendicular to the thru-hull. By perpendicular I mean the plate and thru-hull threads have to be 90 degrees from each other in order to get the best seal between the backing plate and the base of the seacock.

When the backing plate is cured in place, I will remove the thru-hull fitting and put a bead of Silkaflex in the groove in its base to seal it. Then I insert it in the hole in the hull then have my wife spin on the seacock, (also after putting a bead of Silkflex on its base), ensuring the handle has clearance to open and close with obstruction.

I will then tighten the whole system from the outside. There is no obvious way to grab and tighten the thru-hull without a special tool, a tapered plug wrench with two slots milled in its sited to match the two tabs INSIDE the thru-hull. Cost is approximately $50.

Now, as I am a cheap bastard, I made my own from a 9/16 deep socket and cut a slot in the end.

Socket was an old find at a yard sale (less than $10 for the set). The benefit of the store bought one is that as its tapered it will fit multiple sized thru-hulls while mine is only good for that one size (FYI, its a 3/4" fitting).