Valve trivia...
Morgan is right! Expecially having to dive under the boat and polish 'em....
I think that you mean "Bronze". Brass is a no-no on thruhulls and valves.
If you go the little "Search" label in the blue title bar on this page and enter words like seacock, or thru hull, or bronze, or marlon, you will find a wealth of prior commentary on this site. It's all good -- from many owners with good real-world experience -- even the ones that disagree with me.
There are some great pictures posted as well in prior threads. Remember that you can click and drag any picture off to your computer desktop for later printout and contemplation.
Something we can all agree on -- use a flanged ball-valve, secured to a backing plate that is glassed to the hull. Note that if you relocate a valve, it takes quite a few layers of cloth and roving to properly close the old hole, and you need to slope the adjacent layers of hull layup on both sides. Any competant shipwright should know this, but read the concise Gougeon Bros booklet on epoxy repairs for your own initial guidence.
One other note: underwater thruhulls should not be "nylon" or "brass" or "plastic"..... While you can source cheaper nylon/plastic thruhull fittings for above the water, the underwater parts should be Marlon (glass reinforced) or Bronze. Note two: if epoxied in, the Marlon fitting can be ground flush on the exterior like ours were.
Cheers,
Loren in PDX