Seacock handle turns freely but valve doesn't close

[Bowdrie]

Originally Posted by CarinaPDX

Another thought: I would consider taping a bit of split tubing onto the bottom of the valve such that as the valve nears the thruhull the water spurting out the side would be deflected back against the hull. That would have avoided that cold shower...Greg

Haha, now if we could get all boat builders to place the seacocks in such a position/place where the poor unfortunate tasked with such a job can easily work on the seacock with BOTH hands in an unrestricted manner.
I would first unscrew the valve to the point where only a thread or two were still engaged.
Then whilst holding the plug/cork in one hand take the last turn(s) to free the valve and within a second or so the plug/cork was in the thru hull.
After cleaning/drying the thru hull threads and applying whatever thread sealant was desired, reverse the procedure.
Hold the valve as close to the thru hull as you can, just tilted away enough to "pull the plug", and once again, a quick flip of the wrist and you're screwing the new valve on.
Really, unless working conditions are poor the amount of water ingress is quite small.
Of course, if you're hanging in a bilge with someone preventing you from falling in headfirst, and you can only work with one hand you might have to be a bit more ingenious, like rig-up a little something to hold your plug/cork and the new valve close-to-hand.

[eroc]

this reply is relative a similar issue with marlon seacocks by Forespar, the smaller sizes have very small square drive shafts which can easily shear off, leaving the valve in whatever position it was and a significant problem. Some forespar valves have bodies separate from the through hull attachment which can be replaced from the inside, no problem - just do a little dive and cork the outside and proceed. Others are a 2 piece body with the bottom forming the
hull attachment , impossible to remove without a haul out. Ran into this situation last year on a 1994 C&C.
Marlon valves with similar design are still available but with enough change that the top portion of the valve simply would not fit the bottom , however the guts of the valve are the same, so it is a matter of unscrewing the top of the valve body, removing the broken ball , and using the internal components of a new valve including the seats and all the o rings, taking great care in the correct positioning of the o-rings ( determined when taking the new valve apart)