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Old 29-03-2018, 13:14   #1
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Watermaker and generator on same thru hull

I am installing a watermaker on my Endeavourcat 30. I am trying to decide whether to cut a new hole in the hull. If there is a thread on this already, I apologize. I searched for a while and did not find an answer.

The watermaker will be installed in the same area as the generator which has a thru hull / seacock and strainer 15 feet away in one of the keels. It uses a 1/2 inch hose for cooling water.

My initial plan was to run a second water line and install a new thru hull and strainer for the water maker.

As I was planning for the second thruhull, i read a recommendation that one thruhull is better than two. This makes some sense since the two holes would need to be only a few inches apart. However, I am concerned that the water capacity would not be enough for both units. (It is a 110 watermaker, so I need to run the generator to use it.) Obviously, I could pull the existing seacock and replace it with a larger one, but I was hoping to do it on a short haul. I think getting the old one out is more likely to cause damage and turn into a major project

I am thinking that I can mitigate the problem to some degree by running two separate water lines and only sharing the thruhull.

I would like opinions on whether the single 1/2 inch thru hull will restrict the water flow enough to create a problem. The other consideration would be to use the existing strainer, or to tee the hose before the strainers.

I appreciate your opinions.
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Old 29-03-2018, 13:22   #2
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Re: Watermaker and generator on same thru hull

Install a second 3/4" thru-hull, with its own strainer.
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Old 29-03-2018, 13:44   #3
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Re: Watermaker and generator on same thru hull

If you don't want to do a haul out to install an additional through hull, you can install a hard "Y" valve on an existing though hull with a strainer, such as to a head, where you can ensure a clear flow to the watermaker. This would add one more step to preparing your watermaker to run, but limits the number of through hulls you need and/or a haul out just to add a through hull for the watermaker.

https://www.youtube.com/watch?time_c...&v=XURN_awplww
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Old 29-03-2018, 13:48   #4
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Re: Watermaker and generator on same thru hull

I would install another thru hull.
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Old 29-03-2018, 22:11   #5
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Re: Watermaker and generator on same thru hull

Install a T piece in the generator inlet downstream of the stopcock and run a flow test into a bucket with the generator running. If you get sufficient flow into the bucket to supply the water maker run them both off the same thru hull. Empirical beats theoretical in this sort of situation and it's good practice to minimize the number of thru hulls each of which has the potential to sink your boat.
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Old 29-03-2018, 22:20   #6
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Re: Watermaker and generator on same thru hull

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Old 29-03-2018, 22:43   #7
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Re: Watermaker and generator on same thru hull

Would there not be an issue with either the watermaker or the generator sucking water from each other and that be potentially dangerous/damaging to either? Genuine question, I have no experience of this kind of thing...
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Old 30-03-2018, 06:43   #8
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Re: Watermaker and generator on same thru hull

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Would there not be an issue with either the watermaker or the generator sucking water from each other and that be potentially dangerous/damaging to either? Genuine question, I have no experience of this kind of thing...
ABSOLUTELY
I would never share a generator and watermaker through hull that's just a disaster waiting to happen.
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Old 30-03-2018, 09:14   #9
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Re: Watermaker and generator on same thru hull

How far away is the generator exhaust? My generator spits out bits of oil on occasion and that could kill the watermaker. I'd be very worried about that. The ideal place is in the other hull I would think.
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Old 30-03-2018, 09:19   #10
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Re: Watermaker and generator on same thru hull

Rather than a separate thru-hull, consider tee'ing off your generator AFTER the heat exchanger but before the exhaust elbow and feeding the generator cooling water to your watermaker input. This serves two purposes. First, it eliminates the need for a separate boost pump for the watermaker high pressure pump since the water is already under pressure from the generator raw water pump. Second, since the water is heated somewhat, it improves the efficiency of the watermaker membrane allowing you to run it at lower pressure. (You want to adjust the pressure to meet the membrane product specs, not to get more product water than it's rated for.) If you want, you can plumb the watermaker brine discharge water back into the generator at the exhaust elbow, but generally the watermaker doesn't use enough water to worry about. I had a watermaker on my sailboat plumbed this way and it worked fine discharging the watermaker brine overboard rather than back into the exhaust manifold. Put a valve in the feed to the watermaker so you can shut the water to it off when you're running the genset but not the watermaker. Whether you run the discharge back into the exhaust elbow or not, don't put a valve on the watermaker discharge line, since that runs the risk of you forgetting to open it when you start up the watermaker and damaging the membrane and hoses due to too much pressure.
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Old 30-03-2018, 09:28   #11
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Re: Watermaker and generator on same thru hull

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Originally Posted by mvmojo View Post
Rather than a separate thru-hull, consider tee'ing off your generator AFTER the heat exchanger but before the exhaust elbow and feeding the generator cooling water to your watermaker input. This serves two purposes. First, it eliminates the need for a separate boost pump for the watermaker high pressure pump since the water is already under pressure from the generator raw water pump. Second, since the water is heated somewhat, it improves the efficiency of the watermaker membrane allowing you to run it at lower pressure. (You want to adjust the pressure to meet the membrane product specs, not to get more product water than it's rated for.) If you want, you can plumb the watermaker brine discharge water back into the generator at the exhaust elbow, but generally the watermaker doesn't use enough water to worry about. I had a watermaker on my sailboat plumbed this way and it worked fine discharging the watermaker brine overboard rather than back into the exhaust manifold. Put a valve in the feed to the watermaker so you can shut the water to it off when you're running the genset but not the watermaker. Whether you run the discharge back into the exhaust elbow or not, don't put a valve on the watermaker discharge line, since that runs the risk of you forgetting to open it when you start up the watermaker and damaging the membrane and hoses due to too much pressure.

DANGER....BAD BAD ADVICE....

There are so many bad things that can happen with this set-up I'm not going to get into them on Good Friday....but PLEASE don't do something like this unless you like drama and spending money on costly and needless repairs.

This is one of those "I read it on the internet" fiascos....
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Old 30-03-2018, 09:37   #12
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Re: Watermaker and generator on same thru hull

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ABSOLUTELY
I would never share a generator and watermaker through hull that's just a disaster waiting to happen.
Especially a non 12v watermaker that needs the genset running :-(
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Old 30-03-2018, 09:46   #13
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Re: Watermaker and generator on same thru hull

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Especially a non 12v watermaker that needs the genset running :-(
Not really...the advice would be the same for an AC or DC water maker or any device. Sharing a through hull with something that could cost you thousands of dollars if cooling water is lost is just crazy in my opinion. If you want to share a through hull, use a head intake, raw water wash down intake, or galley sea water intake. Those don't cost you mucho dierno when something goes bad...which on a cruising boat thing always do.


besides...most of the cruisers I know with 12v water makers have to run their generator anyway while making water.....
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Old 30-03-2018, 10:02   #14
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Re: Watermaker and generator on same thru hull

I think the real answer depends on the water demands of the two devices, and whether or not the thru-hull is large enough to achieve the flow-rate required. If you can't figure out the answers to those three things, then go with another thru-hull; as others have said that could paired with a low-use device such as an head inlet.
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Old 30-03-2018, 10:24   #15
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Re: Watermaker and generator on same thru hull

A properly installed thru hull should actually strengthen the hull in the immediate area. After that it's a matter of maintenance.
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