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Old 01-04-2012, 22:07   #1
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How Big/many does a thru hull need to be?

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?
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Old 01-04-2012, 23:32   #2
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Re: How Big/many does a thru hull need to be?

Well I'll answer one part. I would not run the galley drain that far. You'll have some cooking grease /oils going down the drain. Over time they would coat the inside wall of the hose. Add food bits and clogging and slow draining would be an issue. Any dips in the hose would only exasperate that problem
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Old 02-04-2012, 00:14   #3
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Re: How Big/many does a thru hull need to be?

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Originally Posted by sailorchic34 View Post
Well I'll answer one part. I would not run the galley drain that far. You'll have some cooking grease /oils going down the drain. Over time they would coat the inside wall of the hose. Add food bits and clogging and slow draining would be an issue. Any dips in the hose would only exasperate that problem
yeah, that seemed like a bad idea but thought I'd ask. Same with the head drain with hair/toothpaste I guess.
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Old 02-04-2012, 05:16   #4
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Re: How Big/many does a thru hull need to be?

Only 9!

Has the boat sank in the past that you want to go to all this trouble? Nothing wrong with having thur valve/fittings if checked once in a while, they are only under a couple of PSI. If it was so much better to combine all of them don't you think the builders would do so to save a few dollars?
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Old 02-04-2012, 05:26   #5
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Re: How Big/many does a thru hull need to be?

Quote:
Originally Posted by xymotic
... would a single 3/4" intake be enough to service an anchor wash-down, both sinks and possibly a watermaker?...
... is a 3/4" waste discharge big enough if the waste is run through a macerator?
I wouldn’t combine a watermaker with anything that could starve it (occasionally).
Depending on the macerator, you'll probably require a 1.5" discharge.
http://www.dometic.com/80316ecc-ee81...52148def.fodoc
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Old 02-04-2012, 08:20   #6
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Re: How Big/many does a thru hull need to be?

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Only 9!

Has the boat sank in the past that you want to go to all this trouble? Nothing wrong with having thur valve/fittings if checked once in a while, they are only under a couple of PSI. If it was so much better to combine all of them don't you think the builders would do so to save a few dollars?
Just in my immediate acquaintances I know of three big yachts that have sunk because of thru-hull issues. Must surely be one of the most common reasons for sinking from what I hear and read of other peoples boats. A brief search through recent CF will surely confirm this. Source of water ingress is often hard to track down by the time the flooding is noted - maybe hard to think clearly at the time, not clearly known or marked, no procedures to follow.

Cannot do much about cockpit drains and sensors and the engine needs its own intake BUT can work on the rest. Clearly an advantage to be able to track water ingress quickly. While I respect the issues about galley waste I think that can be managed. By the bye, water ingress through the galley sink outlet was cause of one of my personally known sinkings - boat had layed over on side with low tide and the incoming tide allowed enough water in to keep the boat low in the water and etc. Did not so much sink as simply not get up I guess - still very painful and enormously costly.


For my own yacht I have;
2 engine inlets - one port and one starboard.
2 sensors - sounder, speed
2 keel cooling - inlet and outlet
1 combined blackwater and gray water outlet (above water line usually but ...)
1 3" combined inlet
1 3" combined outlet
All bilge outlets at deck level midline

Which leaves me with the 9 of the OP - could cut off three engine related but that brings other issues. All in the engine compartment.
I think it is worthwhile reducing your risks. Not to say it will be cheaper - probably not but will sleep happier.
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Old 02-04-2012, 12:21   #7
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Re: How Big/many does a thru hull need to be?

For sensors one can use a combined one and on some boats the sounder sensor can be mounted inboard (no hole). In the gps era one can go without the speedo ... (yes, I know the opinions). So, simply, the sensor holes can be limited.

Can engine intake be run of the cockpit drain? Can the sink outlet be run thru the other cockpit drain? NOT?

Can the galley tap be run off the cockpit drain? Can the toilet and the galley share the same intake? NOT?

;-)

Can a 'chest' system be mounted with a single seacock and many outlets? NOT?

OK. I think there are many ways to reduce the number, but as long as the installation and the seacocks are sound there should be no problems with ("too") many seacocks.

PS It is a good idea to make all seacocks are in easily accessible places!

b.
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Old 02-04-2012, 12:34   #8
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Re: How Big/many does a thru hull need to be?

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Must surely be one of the most common reasons for sinking from what I hear and read of other peoples boats.

Biggest cause of boats sinking that have not hit something is .............. owners!

I bet more boats sink in a slip due to potabe water hook-ups to the dock than due to a leak suddenly happening from a hull valve connection. On my last boat I once found a though filling that had completely corroded and all that was holding it in was caulking, but it still wasn't leaking. Which is why you need to check them
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Old 07-04-2012, 23:51   #9
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Re: How Big/many does a thru hull need to be?

Thanks for the input people.

I probably could combine the galley drain with one of the cockpit drains, but it would be a 'scary' project to do so. The PO could not weld, and he bought a bunch of marelon obviously intending to switch at some point. I think I like the totally flush outside/re-enforced pipe inside idea myself though.

Thinking of a combined black/grey output is interesting, but then that implies a pump for all of the grey, right? Not sure I like that idea, I've replaced a LOT of shower sumps and they weren't even used that much.





And yeah, once a thruhull is submerged, it seems like it would be VERY hard to tell if it was the source. I'd just like as few as possible.
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Old 08-04-2012, 01:55   #10
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Re: How Big/many does a thru hull need to be?

One very large inlet into a chest should do the trick for engine, galley, washdown, and head.
Cockpit and cooling water/exhaust can go out the transom.
There are transom mounted speedo/deptho sensors.
I agree that head and galley outlets can not reasonably run very far, promotes serious odors if nothing else.

Bare minimum sounds like 3 thru-hulls below the waterline.

For the cockpit and exhaust drains out the transom, I would put rubber flaps over the outlets to minimize waves forcing water in. The exhaust would get a seacock regardless of the fact that it is above the waterline and has the flap, spend long enough going down wind and the slow ingress of water around the flap will slowly fill the water trap and backup into the engine.
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Old 08-04-2012, 03:46   #11
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Re: How Big/many does a thru hull need to be?

Something about seachests.. Through hulls on passagemakers ??? - Boat Design Forums
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Old 08-04-2012, 03:49   #12
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Re: How Big/many does a thru hull need to be?

I like the idea of having all intakes on the opposite side of the keel from the head discharge!
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Old 08-04-2012, 04:16   #13
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Re: How Big/many does a thru hull need to be?

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I like the idea of having all intakes on the opposite side of the keel from the head discharge!
Or certainly upstream, the idea of the sink down stream of the heads discharge is interesting.

Our galley and heads sink, plus the shower drain all discharge just above the waterline which I guess cuts down the risk.

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Old 08-04-2012, 05:02   #14
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In oder to eliminate submerged thru-hull fittings, stand-pipes should be considered. All our submerged discharge is done with standpipes which means there are no thru-hull fittings nor valves for that anymore.

ciao!
Nick.
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Old 08-04-2012, 07:41   #15
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Quote:
Originally Posted by s/v Jedi
In oder to eliminate submerged thru-hull fittings, stand-pipes should be considered. All our submerged discharge is done with standpipes which means there are no thru-hull fittings nor valves for that anymore.

ciao!
Nick.
And if the standpipe snaps off???

Dave
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