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Old 09-02-2010, 14:14   #1
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Raw Water Manifold?

I am planning on putting A/C (reverse type) onto my boat. The frequent solution to raw water intake is punch a hole in the boat.

Several months ago I came across a picture/description in an "improve your boat" book, where the individual made a square box manifold. They increased the engine raw water intake and used the manifold to divert the water to several items (sink, watermaker, etc.). The thought being to limit the number of holes, even if they are larger.

Several questions:
1. Have you seen such a thing and have a reference? (this one had a clear viewing port so you could see that water was coming in through the valve.)
2. Is this a reasonable approach? I am trying to balance more holes agains fewer larger ones, so alternatives are welcome.
3. The reason I am posting here (instead of plumbing) is the engine currently uses that water so I want to protect it. Can I make the through hull larger, run it into a manifold as long as the run to the engine is still the same size?
4. Does the engine intake size matter, presuming it is at least the size of the current hose?
5. Is this overkill when a "T" without changing the size of the through-hull would work? How would I know I have sufficient volume for both the engine (Yanmar 3GM30F) and an A/C (undetermined), or watermaker, or...?

Thanks in advance.
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Old 09-02-2010, 14:19   #2
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I don't like running engines off of a shared intake. HVAC needs an intake that will be constantly wet. The pumps are not self priming.
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Old 09-02-2010, 17:41   #3
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What you are referring to is a 'Sea Chest', they are found on large commercial and military vessels and provide a 'Intake Reservoir' for raw water systems and work well on larger vessels due to their substantial size/capacity.

Sharing the engine intake water is sometimes done for engine driven refrigeration systems. This is the only time I would consider it as the engine and refrigeration is on the same water circuit.

However, I would not recommend what you are proposing, it seems a lot of work compared to installing a dedicated thru-hull, the pipe run for an AC system has to be on a constant rise from the intake thru-hull (probably fitted with a forward facing water scoop) to the discharge thru-hull with the pump in circuit below the waterline otherwise you will end up having to prime the pump everytime you need the AC. Further, it may be possible that the engine pump may try to pull water from the AC loop if there a slight restriction from the main thru-hull, then after this water is exhausted you are pulling air which will be easier for the pump than the water. You would be surprised how much some engine raw water pumps can flow at max. RPM's.
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Old 09-02-2010, 22:56   #4
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Manifold

Does this answer your question ?
Quote:
Originally Posted by Kefaa View Post
I am planning on putting A/C (reverse type) onto my boat. The frequent solution to raw water intake is punch a hole in the boat.


Several questions:
1. Have you seen such a thing and have a reference? (this one had a clear viewing port so you could see that water was coming in through the valve.)
Certainly, had on my own catamaran - Single large Marelon thruhull below the waterline >> Seacock >> Elbow >>> Manifold :: Seawater fills the Manifold >>> offtakes to engine, watermaker, aircondioner etc. The top cover of the manifold is held in watertight position by wingnuts.
To clean the manifold, close the seacock, open the manifold remove the strainer and clean.

2. Is this a reasonable approach? I am trying to balance more holes agains fewer larger ones, so alternatives are welcome.
Yes
3. The reason I am posting here (instead of plumbing) is the engine currently uses that water so I want to protect it. Can I make the through hull larger, run it into a manifold as long as the run to the engine is still the same size?
YES , make it bigger if you like
4. Does the engine intake size matter, presuming it is at least the size of the current hose? YES , make it bigger if you like
5. Is this overkill when a "T" without changing the size of the through-hull would work? How would I know I have sufficient volume for both the engine (Yanmar 3GM30F) and an A/C (undetermined), or watermaker, or...?
If you have 2 1/2" Thruhull it will deliver a lot of water
Thanks in advance.
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Old 14-04-2016, 08:42   #5
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Re: Raw Water Manifold?

I'f your looking for a raw water marine manifold check out this website www.acmgr.net they have a excellent line of manifolds.
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Old 15-04-2016, 02:52   #6
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Re: Raw Water Manifold?

Big boats and ships have shared intakes sometimes. A hold over from steam and condensers. Usually a large vertical pipe with other pipes and valves at 90. The main pipe has a valve at the bottom and the pipe often extends above the waterline with a removable top for cleaning. You see them in steel fishing boats, sometimes with a shared outlet on the opposite side of the keel. The main intake pipe on a battleship is about 6' across.
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