Through-hull or engine water supply for watermaker?

[Karanga]

My current watermaker intake is not deep enough, and occasionally sucks a bit of air in choppy water (very not good!).

What is the collective expertise on the best solution?
1
Bore another through-hull, with all the attendent pros and cons of another hole under the waterline
2
Insert a T-piece into the raw water hose (via saildrive leg) for the engine cooling system

Thank you
Tim

[MikeHoncho]

I’m existing raw water thru-hole for the engine is right next to the sink drain. No bueno if yours is too.

[stormalong]

Place another through hull as low as possible. I had the same problem and that was my solution. If you have a keel sump put it there. Besides air you have the risk of drawing in oil. Oil sits on the surface, it will destroy your membrane.

[chrisr]

agree : do it right and fit a new through hull for the water maker

and while you are at it, i would bypass the water intakes in the sail drive legs and fit decent through hulls for cooling water intake. saildrives are notorious for slowly blocking up with shell etc and restricting the water flow. if you haven't had this happen yet, it just means that the time when it does is getting closer !

cheers,

[mvmojo]

I tee'd off the engine cooling water. Eliminated the need for a boost pump (and another thru-hull). Made thousands of gallons of water with no problems.

[Madehn]

My water maker specifically said to not share a thru hull. That said if I had to do the boat all over again I would have put in a good sized sea chest and taken everything from that. Too soon old to late wise.

[Tellie]

"Never" tap into any engine related raw water-cooling
lines for a watermaker input. As stated above, install a new and proper thru hull on the next haul out.

[Karanga]

Originally Posted by mvmojo

I tee'd off the engine cooling water. Eliminated the need for a boost pump (and another thru-hull). Made thousands of gallons of water with no problems.

This is the likely practical story, many times over.
Even though it would go against the grain of the purists.
Hence the original query...
Thank you all, for replying.

[GordMay]

Originally Posted by Tellie

"Never" tap into any engine related raw water-cooling
lines for a watermaker input. As stated above, install a new and proper thru hull on the next haul out.

Originally Posted by Karanga

This is the likely practical story, many times over.
Even though it would go against the grain of the purists.
Hence the original query...
Thank you all, for replying.

Indeed. Never take the advice of an industry expert - WTF do they know?
Thanks Tellie.

[fourlyons]

Can somebody explain the logic for not sharing a through hull between the engine and a water maker, as long as the through hull is sized for the combined flow?

How is this any different than using a seachest to supply multiple consumers? Or is it a bad idea to use a watermaker with a seachest?

Thanks

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[Fishspearit]

Originally Posted by fourlyons

Can somebody explain the logic for not sharing a through hull between the engine and a water maker, as long as the through hull is sized for the combined flow?

Do you mean if a larger through hull that is capable of handling the combined flow is installed, or do you mean if the through hull that is designed for only the engine is used?

If you never run the engine while running the watermaker you will probably never have a problem. If you run them at the same time you run the risk of depriving the engine of its designed water flow if you are pulling additional water through a through hull that was only designed for providing the engine with sufficient flow.

You MAY not ever have a problem with it, but you can expect people to give advice for 'best practices' on here, and 'best practice' is a lot different from 'you can get by' type of marine maintenance and repair. There's a million ways to do things wrong on a boat that still work for a while.

[fourlyons]

Originally Posted by Fishspearit

Do you mean if a larger through hull that is capable of handling the combined flow is installed, or do you mean if the through hull that is designed for only the engine is used?

If you never run the engine while running the watermaker you will probably never have a problem. If you run them at the same time you run the risk of depriving the engine of its designed water flow if you are pulling additional water through a through hull that was only designed for providing the engine with sufficient flow.

You MAY not ever have a problem with it, but you can expect people to give advice for 'best practices' on here, and 'best practice' is a lot different from 'you can get by' type of marine maintenance and repair. There's a million ways to do things wrong on a boat that still work for a while.

Thanks, but that is all obvious and you didn't address the core of my question.

Let me restate it.

If, for example, your engine and your watermaker require a total flow of 40 gpm at full flow, and your through hull is sized to flow 50 gpm, is there still an issue?

How is this any different than using a seachest?

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[Tin Tin]

If you T with two machines sucking from the same through hull, you may need to put in non return valves so the more powerful pump does not suck water from the other. So for example if your water maker is running and you switch off your engine, the water maker may suck out the water from your engine raw water cooling system because it will be easier to suck and potentially suck air depending on your set up. The water maker installation guide should specify through hull dimensions, I would be surprised if the engine through hull was designed to provide a lot more than the engine required. You could T off the head raw water inlet, much as that sounds disgusting.

[GordMay]

Originally Posted by fourlyons

... If, for example, your engine and your watermaker require a total flow of 40 gpm at full flow, and your through hull is sized to flow 50 gpm, is there still an issue? ...

I'd think not [a problem], but Tin Tin raises a good point [previous post].
A 2" I.D. through hull will deliver about 55 GPM [3300 GPH], assuming Low Pressure [<1.5 psi - 0.445 PSI for every 1 foot in depth], and about 6 Ft/sec flow velocity.

[Tellie]

It's not a matter of thru hull size and gpm flows. An engine raw water pump can certainly overpower the draw side of most watermakers. Many watermakers can suffer a draw down when the engine and watermaker are run at the same time. Even a slight draw down can affect proper operation and can damage many watermakers pumps. Many watermakers can suffer from a vacuum created on it's input line when the watermaker is not in use thus draining the watermaker of enough water that it can leave the membrane exposed to air. Sea chests and thru hulls are two different things. A sea chest creates it's own body or volume of water, whereas a thru hull does not. Smaller volume watermakers can temporarily share another intake thru hull like a salt water head intake if sized right, but it would be prudent to check with the manufacturer of your watermaker to get their input first because many watermaker manufacturers will void the warranty if you are tied into the engine. It is always a no no to share the engines cooling intakes with any other device on a boat. I don't know of one reputable watermaker company that does not require it's own dedicated thru hull. We have all been down this path many times. It's a lot cheaper to pull the boat and install a proper thru hull than to start pulling watermakers and engines.