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Old 02-03-2020, 08:38   #1
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Watermaker seawater heating & supply

My boat came with a custom installed watermaker with an engine driven HP pump and a membrane which produces 120lph. I have only used it once, during the sea trials to ensure it worked, which it did. Now, 8 months later, I am rebuilding the complex engine cooling system and trying to clean things up and ensure that I can maintain/repair anything that might go wrong.

Because seawater around here is only about 5-6C, and doesn't get much above 12C in some places even in summer, the previous owner, who owned a commercial watermaker business, had the input of the watermaker fed through engine heat exchangers to pre-heat the seawater, and also to provide some feed pressure to the HP pump using the engine water pump">raw water pump. (there is a gauge for monitor this, and a needle valve to adjust the amount of flow diverted to the water maker).

This part I understand, and am prepared to monitor as needed. The part which concerns me is that the supply water for the membrane is seawater which has been through heat exchangers (two copper coolant/seawater units, and a Groco bronze oil cooler) and therefore have the potential to introduce contaminants (oil, coolant) into the watermaker loop, which could affect water quality, and damage the membrane.

I have read a lengthy thread here about the reasons not to use shared through-hulls for watermakers (although mine is different in that the seawater source is at pressure after the raw water pump), but my question is more related to the issue of potential contamination of the seawater source due to the coolant and oil heat exchangers. I am interested in hearing some feedback on this, and if any others have encountered systems like this, or alternatives for warming the seawater intake to the WM. The previous owner and designer of the system stated that the membrane is more efficient if the intake water can be 20C or above, so I could forego the pre-heating of the seawater if I can accept a lower WM output rate.

As an aside, in that other thread (https://www.cruisersforum.com/forums...ke-135029.html) flow rates for Yanmar engines were quoted, which I found interesting, as the Jabsco raw water pump I have is rated at 7.5GPM, yet my engine is probably equivalent to a 4cyl Yanmar (VW 1.6L diesel, 50hp) in terms of cooling needs. The engine still runs strong after 20+ years and >4k hours since a rebuild, and temperature rarely exceeds 180F. This may be due partly to the engine being oversized for the boat, so it doesn't work all that hard unless I am cruising near hull speed. I just found that interesting, and would be curious if those Yanmars suggesting 16GPM flow actually use a 16GPM raw water pump? The output from my exhaust always seems to be a lot higher flow than most boats of a similar size.
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Old 02-03-2020, 08:50   #2
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Re: Watermaker seawater heating & supply

Do you see yourself staying in the PMW, or going south in the future? That might have a bearing on the issue.

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Old 02-03-2020, 08:58   #3
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Re: Watermaker seawater heating & supply

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Do you see yourself staying in the PMW, or going south in the future? That might have a bearing on the issue.

Pete
Good question. We definitely want to go south in future, but we're not sure if this is the right boat; probably not. We are considering keeping this boat for local cruising, and searching for a boat in California or Mexico to go south with, since we will still spend summers in BC, and don't want to be without a boat while at home (and sailing north each spring is a long haul).

So I guess that comes back to the question of watermakers and seawater temperature - do others in colder water just accept slower rates, or do they heat the water somehow?
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Old 02-03-2020, 15:22   #4
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Re: Watermaker seawater heating & supply

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We are considering keeping this boat for local cruising, and searching for a boat in California or Mexico to go south with,
If looking for a boat in Mexico, hard to beat the value in this one. Mot mine, but know the boat and it is the finest of its breed.

https://sites.google.com/view/svloom...baforsale/home
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Old 02-03-2020, 16:01   #5
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Re: Watermaker seawater heating & supply

Membranes are rated at 77F about 25C. I'm in the PNW and make water between the Columbia River and Alaska. I pre-heat my water using electric water heater screw in elements in a 1.25" pipe, since I run the generator anyway to make water. I did have the HP pump on an engine, but it caused light load problems (engine screaming but only needing about 5hp) so went to an electric motor driving the pump.
I doubt the heat exchangers used to heat the water is an issue if kept in good repair. You could add a Y and another heat exchanger before the others that is just for heating the membrane water. At 5C, you'll get about half the rated output. So about 15 gph. Max temp for Filmtec membranes is 113 F about 45C, I'd worry about that. Most HP pumps just need low pressure water, so the RW pump output is probably fine as long as the engine temps are normal.
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Old 02-03-2020, 16:21   #6
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Re: Watermaker seawater heating & supply

It's a risk. The downside is not likely, but if it happens it is really serious. We can argue all day if the risk is worth taking or not, but the benefit of heating the watermaker feed is small. Ethylene glycol is a pretty potent poison, and has a lot of nasty effects even well below lethal dosages.

The lethal dose in adult humans for ethylene glycol is about 100 ml (1/3 cup). Swallowing may cause nausea, vomiting or diarrhea. Excessive exposure may cause CNS effects, cardiopulmonary effects (metabolic acidosis), and kidney failure. Toxicity follows 3-stage progression. (1) involves central nervous system effects including paralysis of eye muscles, convulsions, and coma. Metabolic acidosis and cerebral swelling may also occur. (2) involves cardiopulmonary system with symptoms of hypertension, rapid heart beat, and possible cardiac failure. (3) involves severe kidney abnormalities including possible renal failure.


If your engine heat exchanger developed a leak and contaminated your water supply, how would you know?--before you died? Ethylene glycol doesn't have a nasty taste, if anything it is pleasantly sweet. Dogs LOVE it, many have been poisoned lapping up a puddle in a driveway.

I would never install a client's watermaker that way, because I wouldn't want to risk the lawsuit. If you really want to keep this set up, I would switch the engine to a non-toxic propylene glycol based coolant. But that's just me.
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Old 03-03-2020, 01:12   #7
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Re: Watermaker seawater heating & supply

Yeeeeah, not a big fan of this installation either. Surprised it was done by someone in the business. I agree with billkny on this one as well. Mixing the heat ex changer with the watermaker and it's lethal antifreeze is a big concern.
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Old 03-03-2020, 04:49   #8
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Re: Watermaker seawater heating & supply

The system sounds crazy

Seawater must be pre filtered before the hp pump

These delicate pre filters are normally the most maintenance intensive component in a water maker system

Sea strainer , sand filter, Micron filter .....hp pump

How is this system configured on your boat ?
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Old 03-03-2020, 05:05   #9
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Re: Watermaker seawater heating & supply

I may be missing something but why is it a concern to heat the water up in the first place? It’s cold yes but many people add ice to their water and anyway it will go into the tank to somewhat regulate as well. Just don’t see the purpose at all.... Personally I wouldn’t have any part of this setup.

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Old 03-03-2020, 07:16   #10
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Re: Watermaker seawater heating & supply

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The system sounds crazy

Seawater must be pre filtered before the hp pump

These delicate pre filters are normally the most maintenance intensive component in a water maker system

Sea strainer , sand filter, Micron filter .....hp pump

How is this system configured on your boat ?
Geez... forgot all about that part! Either there is no filter and the membranes are at serious risk, or there is a filter and a clogged filter potentially overheats the engine by throttling back the raw water flow.

Even if you think drinking antifreeze is a good idea, the filtration issue should talk you out of it.

Oh, and one more thing... if you divert a significant part of the engine raw water flow to the watermaker you risk overheating the exhaust system leading to melt down and maybe fire.

The more I think about this the less I like it.
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Old 03-03-2020, 07:37   #11
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Re: Watermaker seawater heating & supply

Tellie can correct me if I’m wrong, but I believe the upside to colder water is lower TDS, warm water gives you higher output, but higher TDS.

Many times here on this forum people discuss complex, difficult modifications for what would seem to be small improvements, often times a simpler and much easier solution would be to oversize something or simply accept longer operating times.
It’s usually batteries or similar.

Think of it this way, relabel your 120 Lph watermaker as 100 lph, remove all that complication and you’ll be fine, and or maybe you could add a second membrane if your pump is large enough to handle it to increase output if you really need the higher output.
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Old 03-03-2020, 07:43   #12
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Re: Watermaker seawater heating & supply

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I may be missing something but why is it a concern to heat the water up in the first place? It’s cold yes but many people add ice to their water and anyway it will go into the tank to somewhat regulate as well. Just don’t see the purpose at all.... Personally I wouldn’t have any part of this setup.

Greg
Cold water and or high salinity water significantly reduce the output of a watermaker. You can’t change the salinity, but it may be possible to heat the water.
I sort of doubt that, and my line of reasoning is on my 30 GPH water maker for instance, it has a 2.6 gallon per minute water flow, that is a huge, tremendous amount of water to heat, even by a few degrees.
For example it takes 1500W of electricity dumped into 11 gls of water for an entire hour to heat it, and that’s from 80f to start with.

It would take a pretty big motor, operating under a significant load, like say propelling the boat to generate enough waste heat to heat 2.6 GPM of water a significant amount I would think.
So now you have to be motoring to make water?
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Old 03-03-2020, 22:44   #13
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Re: Watermaker seawater heating & supply

At the 5C sea water temp he's talking about would half the output. He doesn't have to heat it to optimal, but 20 warmer would make a big difference. I make water in Alaska and heat the water with electricity to about 70F in the coldest water. It makes a big difference.
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