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Old 08-04-2012, 06:59   #16
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Originally Posted by xymotic
I recently hauled my new-to-me boat. She has 9 underwater thru-hulls.

2 are straight thru pipes for the cockpit drains.

3 are transducers.

Near the head, there were three with the head discharge about 1' upstream of the sink intake, and one capped off.

#8 is the engine intake.

#9 is the galley drain.

So I'm thinking of how I want to approach this. I think I can live with the head discharge being close to the sink intake, if they were reversed.

would a single 3/4" intake be enough to service an anchor wash-down, both sinks and possibly a watermaker? (I won't have a genny, but this is a total refit so anything else I might want seawater for?)

Would it be dumb to route the galley drain forward to the head, or vice-versa?

is a 3/4" waste discharge big enough if the waste is run through a macerator?
For what its worth... The only below-the-waterline penetrations a boat should have are only what is minimally required.

For me, it is only the raw water intake and exhaust output that sits below the waterline. All sink drains sit above-the-waterline. My head has a dedicated fresh water supply. And when I'm offshore and in discharge-legal areas, my head drains directly into the water via a thru hull that sits 2 inches above the water.

I would re-evaluate whether you need that many penetrations below the waterline. The fewer there are, the less likely you are to take on water in the event of a failure.

Ed & Lindsey - Sacramento, CA
1977 Bayliner Victoria "Astral Blue"
MMSI #: 338127697
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Old 08-04-2012, 07:12   #17
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Re: How Big/many does a thru hull need to be?

Originally Posted by goboatingnow View Post
And if the standpipe snaps off???

And what if the hull falls apart? come on, let's assume properly constructed vessels and systems or it just becomes useless discussing anything. Standpipes don't snap off, they are laminated or welded into the hull, you can make it as strong as you want or as the naval architect calculated.


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