Tom Hunter wrote:
I have a composite boat built in 1971 that had no holding tank up until a
week ago. The hull is carvel construction sheethed in fiberglass and is
2-3" thick. The boat is an 1850s design with internal ballast of concrete
and pig iron ( a boat with a concrete floor) and about 2 feet of freeboard.
She is 30' LWL, 9 tons with just over 700 square feet of sail.

The hodling tank is located amidships on the port side. The problem is
where to run the vent line? If it goes through the hull it will be
amidships and because of the low freeboard it will end up submerged quite
often. If I run it to the bow or stern it gets to be a very long line. I
thought about running it straight up to the cabin top with a filter on it
but that does not seem like a good idea either.

It's not...and neither is a long line to the bow or stern.

I do wish you'd asked questions before you selected the tank location,
'cuz that's not where I'd have recommended you put it. Since you're
still trying to figure out where to put the vent thru-hull, I'm assuming
you haven't used it yet...and also that it's an "off-the-shelf"
rectangular tank. If both the above are true, can you return it and
start over? It may mean you'll have add some length to the head
discharge hose, but one inline union isn't a disaster.

If you can...where's the head located in the cabin...forward or aft?
That'll tell me the best place for the tank.

--
Peggie
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Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://69.20.93.241/store/customer/p...40&cat=&page=1