This is one of those things...

The theoretical reasons for not putting a tapered thread ball valve on a
straight thread through hull are absolute and irrefutable. All the strain
is on just one or two threads. The stress is nearly infinite. The
electrical connections is through a very small amount of metal. It will
sink your boat. No question.

The practical experience and track record of doing this is also absolute and
irrefutable. It's been done for years. I've never heard of a boat sinking
because of it. The just retired yard guy I talked it over with a couple
years ago had been doing it for over 20 years without a problem.

A proper seacock is always better but I have a ball valve threaded onto an
old through hull in my boat. The through hull was rock solid and it was in
a place where nothing heavy could fall against it. The threads just deform
a small amount and pipe sealant does the rest. I would use a stick type
compound that will harden in this case instead of Teflon tape.

--
Roger Long