12v versus 240v versus engine driven watermaker

Puggy

Puggy

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hello all,

I am thinking about fitting a watermaker and I am looking at the options. What i am struggling with it what is the best power source for the pressure pump. I have a 90hp main engine with 2 x 90ah alternators through a smart charge regulator system, a 4kw genny, 60a shore charger and 600ah of domestic batteries with a 2500w inverter.

My default position was a 240v pump being driven off the genny as required. But my very experienced live aboard father in law is adamant that I should have a engine driven compressor as you always end up running the main engine for a couple of hours a day (which is true).

Views?

Thanks

Puggy.
 
We never needed to run the engine? we had plenty of electric from a towed gen when sailing and a wind gen when anchored. We found there was always plenty of cheap water available, but this was the Caribbean and the Atlantic coast of Europe, it may be different in other areas, but there were not many cruisers we met using water makers. One on a Santacruz 70 had an engine driven unit the argument being that it had a large compressor which would produce lots of water quickly as there was more hp.
 
How much water do you want to make per hour? We also never run our engine to charge the batteries as we use towed and wind generation as required plus 330w of solar. We make water when needed but have a very small unit which produces just 5 litres per hour, consuming 4amps at 12 volts from our house batteries. 3-4 hours a day is ample to meet our needs and at our present latitude power is never a problem. We do fill up when a cheap source of good water is available but like the freedom that comes with making our own.
 
OP says he has a 4Kw genny. Does that mean a properly installed diesel generator that is reasinably quiet? In which case why would he always end up running the main engine a few hours perday? If not for moving the boat. If he has a decent generator then that would be the best power source for water maker. If not then as his father says run the water pump for the water maker off the main engine. Or if he has a diesel generator can he run the water maker off the generator engine? good luck olewill
 
I just changed to a 12v motor driven HP pump.
I can charge the batteries from Main Engine, Generator or shore power through the charger or solar.
That gives me power options and redundancy in case of failure.
Previously had a 380v 3 phase generator and pump motor, never again! -they came with the boat.
 
General theory. It is best to avoid power conversion wherever possible. You have a source of rotary power (the engine) and need rotary power (the pump).
Next best, if an electric pump is really desireable, the generator is more suited to producing electricity than the main engine.
But, as Chalker says a 12V pump offers more options.
 
William_H said:
OP says he has a 4Kw genny. Does that mean a properly installed diesel generator that is reasinably quiet?
Click to expand...

Yes it is a proper Paguro genny. I was hoping not to be reliant on the main engine and make use of the genny.

What about a 12v system - is the loading too much for alternator/invertor scenario from the main engine?
 
I think the first question to be answered by the OP is how much water does he want to make in a day? How many hours is he prepared to run the water maker to make that much water? That will tell him how much energy he will need to produce in order to make the water: ie if electrically driven, how many amp hours, if engine driven, how many hours of engine running.

Once he knows how much energy he will need, he can start making decisions on how to produce it. However, given the setup described with a built in generator, my option would be for an electrically driven system, either 240 volts driving directly by the generator or 12 volts driven via the 12 volt system. I presume that the generator can be used for battery charging as well as the twin 90 amp engine alternators, so for flexibility perhaps a 12 volt system would be best.

Also bear in mind that for an engine driven pump it will mean connecting pipe work between the pump and the membrane system, rather than a neat box unit system that an electrically driven system could provide. It may be that that would be an advantage but still worth factoring in.
 
What about one of these:

dessalator AC DC Duo 60 to 75 lph watermaker. Runs off both 12v (32a) and 240v (4a).

Can run from:
- 240v genny 4a 750W draw
- shore power
- existing 60amp shore charger on DC (not sure you would ever need to do this)
- inverter (wouldn't have thought there would be need for this either)
- main engine: with a total of 180a theoretical maximum battery power there is plenty of power when motoring, even at reduced revs,
- solar power: DC motor consumes 370w. Start up loads can be absorbed by the batteries and solar can either run it or just reduce speed of flattening the batteries. Remember a total of 600ah main services batteries available. Would need some decent panels, but people often report 400w of solar generation when in the med?

Provides for every scenario.
No mucking about with a third mounting bracket on the main engine.

What am I missing about this?

http://www.advanceyacht.co.uk/products/watermakers/ac-dc-duo/dessalator-d60-duo.html

Puggy
 
Partly depends what size w/maker you get. If its output is so small that it takes 3 hours to make the water you need, you'll regret having it run off main engine, when you have a genset.

I don't know how water makers deal with the variable RPM of the main engine. If you have to rev the main engine hard for several hours to make your daily water then that will be terrible.

I've had 2 boats (sisterships) with w/maker. First looked ok on paper (140 litres/hour) but in the salty med it made more like 120 and with lots of people on the boat it needed too much running. Second boat I specced 280 litres and that's great. So whatever size you think you need, think about doubling it!

In relation to the above, you might think you're gonna run the genset at anchor 3 hours a day so the w/maker needs to make your daily water in that time. But w/makers are noisy, and you'd prefer life on board if you run it 1.5 hours/day even if the genset runs for 3 hours/day

I would forget shorepower running. If you have shorepower you have a hosepipe. Depending on where you are, you may not want to suck marina water into your w/maker either, although the makers do say the system will take out e coli
 
Agree with jfm above. However, he has a large leccy capacity mobo.

I, however, have a raggy and I installed a dual voltage 24VDC/220VAC Dessalator Duo 100 water maker. Has a big DC pump and a big AC pump. With 960Ah house battery capacity and 540W solar array, I can run it for a while on DC mode. The real production capacity is closer to 140 l/hr than the suggested 100 l/hr stated by the manufacturer.

If there is doubt "Galarneau" will give enough rays to offset the demand, then we fire up the genset and also wash clothes while its running...

Boat is setup for a circumnavigation so there are many duplicate/alternate solutions aboard.
 
So, looking at all the posts (and thank you all for your advice) and doing further research, I am planning to go for the Dessalator 60lph duo 12v/240v unit and the slightly larger 6000 Paguro 6kw genny. This will allow me to run the watermaker in all the different scenarios, and as I am installing some AC in my boat, give me plenty of capacity to run everything simultaneously. The 6kw unit is a two cylinder unit and I have space to fit it comfortably, and is £500 more than the 4kw single cylinder unit.

Puggy
 
If it was me... I would go for the larger capacity DUO 100... just a bit more dosh but much more capacity.

You must consider a noise enclosure if you go for a 3000 rpm genset. Mine is an Onan with a 3 cyl Kubota motor. It is very silent; it runs at 1500 rpm. (I once forgot to turn it off leaving the boat...)

GL
 
We have a 4.5kva generator and a 120 l/hr watermaker. We have spoken to many people on our trip about watermakers. It is surprising how many people have problems with their watermakers. On our previous Atlantic circuit we had a small 12v watermaker that made only 5l/hr. It was a nightmare for leaking and causing numerous failures. Lesson learnt and we now have the most reliable set up I could find. This is a 1.5kw 240v motor driving a CAT pump with two membranes in series. These pumps are noisy but bullet proof. We never have leaks and the system works like a dream. Should the generator fail we can run the pump off the 3kw inverter and we run the main engine so the alternator is helping to keep up with the electrical demand. With the 420w of solar and the towed turbine we are not too far below the power needs of the watermaker motor. The 800 amp hour battery bank copes as a buffer very well. We had this scenario crossing the Atlantic when our ageing genny killed an injector.
The other benefit of a generator run watermaker is we can turn the electric immersion heater on at the same time as making water so when we are on a washing day we make the hot water at the same time. It usually takes about 100litres to do a full wash. Getting laundry done here in the Caribbean is expensive as they are mostly service washes.
The generator on its own with the immersion on gives us a tank of hot water for a couple of showers when you get back from the bar with 10 mins of generator run time.
Using the generator over the last 11 months since we left UK we have done less than 100hrs on it but made something like 10,000 litres of water
 
GEEM has a good point. Water makers are a PITA if they are not well made. The Dessalator unit is used by Amel and has been their sole WM offer for the last 25 years. They are a proven piece of kit! Though the engine driven unit referred by GEEM seems up to the task too.

It is a fabulous luxury not to dinghy to a laundry facility, wait, .... get raped on price, when washing becomes a must. :-) Like GEEM, we also have a big house bank and a large solar array. Genset sees little use.
 
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