Here is perhaps the most convincing reason that I have yet encountered to thru-bolt your flanged sea cocks....and implicitly another good reason never never to install one of those in-line valves in your boat in-lieu of a sea cock. If your boat is in a yard that alleges that in-line valves are sea cocks, you now have a reason to tell them why the two are different, and why you are sticking with Linn and Larry. The quote below is courtesy of Linn and Larry Pardee's marvelous web page:
http://www.landlpardey.com/Tips/Tips_2002_November.html
This post was dated Nov 2002:
Proper sea-cocks
"One of the jobs we have done at Mickey Mouse Marine this season, was to install a new marine toilet in a clients boat. We inspected the sea-cock and found it was, like many that are being used today, not connected in any way to the hull, with only the threaded portion of the thru-hull fitting connecting it to the boat. It was a sort of fortunate/unfortunate story. Unfortunately electrolysis had gotten to the thru-hull and it crumbled as we tightened the hose clamps because it was the only thing securing the sea-cock to the hull, if we pulled on the sea-cock handle to close it, that too would have broken loose. Fortunately the boat was dried out on our tidal grid and we could fix the situation before water poured in. But it reminded us again that this type of arrangement is potentially disastrous. Not only can electrolysis cause a failure, but a good whack from shifting gear could snap this connection. Check your sea-cocks to make sure they are bolted to the hull in such a way that should the thru hull fitting fail; you can still close the valve and keep water out. A very good and affordable proper sea-cock is made by Groco in the US."
Personally I am starting to see the wisdom in Ebb's desire to have no holes whatsoever below the static waterline.
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