I have all Marlon thru-hulls on my Freedom 40/40 and have never had any
problems. And there are no bonding issues to worry about. Freedom also
states that you don't have to worry about the thru-hulls blowing out in
the case of a lightening strike, but I don't know how real that is.
Just something to ponder.

-- Geoff

Glenn Ashmore wrote in
news:gDuDb.5356$JD6.2598@lakeread04:



Doug Dotson wrote:

I don't trust plastic below the waterline. Marelon is
plenty strong but bronze is stronger. I have to install
a few more thru-hulls this spring. I guess I'll have to
do some thinking about it.

I had the same worry before I decided so I tried (as my compulsive
engineer personality requires) to analyze the threat. Corrosion is
not a problem. The main threats of marelon vs bronze are breakage
because of the lower ultimate strength and dimensional stability.
Dimensional stability results in sticking so routine exercising the
valve and lubrication are definitely in order. That is a good idea
for bronze also because chrome on bronze balls can flake and jam and
stainless balls can suffer crevasse corrosion between the seals. That
leaves the strength to be tested. I see 3 potential forces acting on
a flange mounted throughhull. The water pressure from outside for
which the flanges are far over designed, the bending force of the hose
and fittings but the fittings are much weaker than the throughuull and
potential impacts. Side impacts would be the big worry.

I tried to visualize what would cause a significant side impact on a
throughhull, probably in a knock down or roll over and came up with a
battery breaking loose, an anchor stowed loose in the bilge. So I
found an old used Forespar 1 1/2" seacock on ebay, mounted it on a
piece of 1/4" steel plate and whacked it on the side with a 5 lb
sledge. First blow had no effect. Second blow produced a small
crack about 1" long leading from the valve stem. Third blow broke a
bolt flange and lengthened the crack some but it was still well
attached to the throughhull. I have beaten enough bronze castings to
pieces to fit in my crucible furnace that I don't believe a bronze
throughhull would have held up but a little better.