thru hull replacement

I took out my flush head thru hulls in my E-27 and want to replace them and the gate valves with new bronze thru hulls and proper seacocks. My dilemma is that the engine feed is a 1/2" thru hull and I can't find a 1/2" seacock. If I go to a 3/4" flush head thru hull, is there a proper tool to cut the indentation or chamfer in the hull? Does this indentation need to be gelcoated before installing the thru hull?
The original indentations look as if they were molded in the hull as they are gelcoated the same as the rest of the hull. What has everyone done in replacing their !/2" engine cooling thru hull and not wanting to use a gate or ball valve?

Thank You
Jerry Griffith
E-27 Valhalla

I would suggest replacing them with Marelon instead of Bronze. It would give you one less thing to have to worry about in terms of corrosion. Forespar - http://www.forespar.com - has them.....

Thanks,
//sse

Adios Marelon - I have had it with those Forespar Marelon thru hulls. I have just replaced my third head thru hull in seven years for a total cost of $750 in yard bills not including the most recent replacement (had to have the boat hauled once). No matter what I do, that particular valve freezes and the handle breaks. However, the remaining seven Marelon valves in the boat still function! The new valve is one of the Forespar OEM valves featured in the Projects section of this site. It too is Marelon, but at least it can be disassembled. However, they are very hard to get. My yard was told by Forespar that it could not buy one even though it is a J Boat dealer and the valves are OEM on J Boats. The yard finally had to get it from TPI, which makes J Boats.

3/4 inch is more of a modern "standard" for head intakes and intakes on small diesels. Note that the flow through the intake is slower when you go up a bit in size. This is good because there is a little less chance of slurping up floating gunk in the flow of water going by...


So far, my five Forespar "OEM" style valves have been in a couple of years and all work like new. You can see my engine valve with a picture elsewhere in this forum. I like the way the valve can be used as a flushing source to put antifreeze thru the raw side of the coolling system. As far as the old chamfer in the hull, my installation avoided the whole issue -- the backing plate was epoxied in, and then the valve body was screwed down on the threaded thru-hull piece, all bedded in epoxy. Then the part of the thru-hull sticking out was ground off flush. Simple and strong. The valve can still be rebuilt, if ever needed, from inside, even while afloat. With the base epoxied to the backing plate, the whole assembly is bullit proof. See my photo in this forum, dated 10-19-02.
Drop me a message if you have questions and I will try to answer them. (And, yes I think bronze stuff is also just fine -- I wanted to avoid electrolysis problems.)

Best,
Loren

There are a couple ways to do it. One way is to use a hole
saw and then fake the bevel with a die grinder turning
a burr bit, if you don't get it perfect no problem, use plenty
of 5200 to bed it. Another way which is more refined is
to bore the hole to the correct depth and diameter with
a forstner bit, back fill with thickened epoxy and then
insert the through hull and do up the nut. Coat the
bronze with wax or mold release and take it out when
the epoxy kicks-then bed it normally.

Incidentally, I don't care for Marelon through hulls no
matter what anybody says- and they are not used on
any of my father's big boat designs, if that tells you
anything.

Martin King

PS To center your bit in the old hole, use a tapered plug
cut down somewhat with the center pilot hole bored in a
drill press.