Watermaker sizing

Talbot

Talbot

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Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
 
Talbot said:
Fitting a watermaker and trying to size it for my needs...

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...

Some approximate numbers which others may add to or challenge:

We use about 30 litres of water a day when in full-on holiday mode and not trying to conserve it. With a washing machine that would increase, to double? But equally it might halve if on passage or if swimming more (and so taking fewer showers). The Katadyne site reckons that 25 litres per hour will do a large mediterranean charter yacht with up to a dozen people on board - I don't believe this however!

Running the watermaker for a couple of hours every few days seems reasonable, so watermaking capacity per hour = daily usage could be a good starting point.

Watermakers use about 1Ah at 12V for 1 litre of water, some a bit less (they claim), many a bit more. Call it 50 litres you use daily (for a bloke on his own? Seems a bit high). That's 600 Whr per day, so ok for your panels even allowing for only moderate efficiency and limited sunlight hours.

So the real restriction is battery bank: the draw could be 60A x 3 hrs = 180Ahr; albeit only once every 3 or 4 days but represents a chunk of depletion unless your battery bank is huge, or you'd have to be making water every day which could become a chore I imagine.

The last point is that they produce a lot less than the rated amount when the water is colder than 25C, at 15C maybe only 40% of nominal output.

For what it's worth, I think 25 - 30 litres nominal capacity per hour is enough for us, sailing 2 handed.
 
Hi we have the Shenka water maker 30. Excellent piece of kit. Ours works of the batteries. We have a wind jenny and solar panel. Pickled now for the winter.
Have used it extensively for 5 years with no problems at all
Peter
 
Talbot said:
Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...

Always better to go for the biggest one that fits the space.
Better to have more than you need, one day you may have 6 or 8 on board.
 
we have a 240v echo tec 60 litre an hour device, we run it off a 4KVA genny for at least 2 hours a day to fully recharge the batteries and to give it something to do we also run the water maker and the water heater, hair dryer, washing machine (40watts - yes only 40watts). This means we have around 120 litres per day to wash us, the clothes and the boat.

My advice for what its worth is to fit the biggest one you can and use lots of water - water makers like to be used.
 
Talbot said:
Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...

I allow 12.5 litres/day per person, which over 12 years works out pretty accurately. That includes daily shower, cooking and washing-up (the latter is the biggest variable consumption). You can find out the washing machine cycle use from it's spec-sheet, water-use has been EC-mandatory for several years.

You'll be struggling to work any reverse-osmosis watermaker on PV panel input alone - I have 328 watts which is enough for normal use but won't begin to cover a watermaker. However most people only use theirs when running the engine and, in the Med, you'll have plenty of opportunity for that. If you must, you'll have to use a generator unit (but one with more than a trickle-charge DC output)
 
charles_reed said:
You'll be struggling to work any reverse-osmosis watermaker on PV panel input alone - I have 328 watts which is enough for normal use but won't begin to cover a watermaker. However most people only use theirs when running the engine and, in the Med, you'll have plenty of opportunity for that. If you must, you'll have to use a generator unit (but one with more than a trickle-charge DC output)
Click to expand...

Start-up current is always a problem, and rarely quoted in the specifications. However, the solar plus the battery pack should cope with that initial surge, and then a 555 watt solar ought to be able to cope with a 240w drain. On a bad day I can always use the generator to provide the power, (4KW) so cloudy days can be coped with.
 
Talbot said:
Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...


We have a Schenker 30 on board, which we would not wish to be without. In practice we achieve about 25 l/hr but as the unit only consumes 8 A/hr we can afford to run it for 3 hours/day, which our solar power (280 Watt) is well able to sustain. However, we are in the Med' where there is ample fuel (unbroken sunshine) with which to feed the solar panels. In my experience solar panels need direct, unadulterated sunshine to remain effective. A clound across the face of the Sun, even in the Med', can reduce their potential output of the panels by more than 75%. But, regardless of the source of electricity I would still elect for a Schenker. Particularly as support from the UK agent (Jim MacDonald of Mactra) has always been outstanding.

Mike
 
charles_reed said:
I allow 12.5 litres/day per person, which over 12 years works out pretty accurately. That includes daily shower, cooking and washing-up (the latter is the biggest variable consumption). You can find out the washing machine cycle use from it's spec-sheet, water-use has been EC-mandatory for several years.

You'll be struggling to work any reverse-osmosis watermaker on PV panel input alone - I have 328 watts which is enough for normal use but won't begin to cover a watermaker. However most people only use theirs when running the engine and, in the Med, you'll have plenty of opportunity for that. If you must, you'll have to use a generator unit (but one with more than a trickle-charge DC output)
Click to expand...

Your figure is spot on. We use 5 gallons per day for two people including quick shower each
 
We have a 90 L/Hr mains unit which produces plenty for six of us for extended cruising and two of us liveaboard, with washing machine.
 
In an earlier post I suggested that the right size of watermaker is one which makes in an hour about what you use in a day. Does anyone have a theory, or a different or better rule of thumb?

A huge one will take mean you have to use the generator and it will only be run infrequently, which may lead to fouling.
A tiny one will need to be run several hours a day, which would be noisy and might shorten its life.

Or is the optimum so wide it really doesn't matter?
 
Ideally you want to run the watermaker every three days. Any longer and you may need to consider pickling the membrane. Whether you run for 2 hours or 4 hours every three days will depend on use of water, size of watermaker and available source of power. You could run a smaller watermaker every day for 5 hours if you have limited power but having done this it is tiresome.
Our last watermaker was a katadyn. It made about a 5 litres per hour for about 5 amps at 12v. It was ok and I could run of 12v.
The watermaker I am currently assembling will make 15 to 20 gallons per hour off 240v via generator. It will be run through a VSD so I can slow the motor down and run through the 3000w inverter at reduced water output and current. With this set up I can run the main engine to create power through the alternator such that the watermaker can be de-rated and we won't drain the batteries. The VSD is also handy as it provides a soft start for the 1500w/240v motor.
 
geem said:
Your figure is spot on. We use 5 gallons per day for two people including quick shower each
Click to expand...
That's an interesting figure. I was reading a US couple who say that in the Bahamas they can use 4 gallons /daybeing careful.
That means with 80gallons onboard you could last 20days/three weeks b4 having to drink beer only!!
This would enable an Atlantic circuit without a watermaker. Altho an extra crewmember would mean setting off with 120gallons.
Would a few long distance types like to reveal their starting capacity?
Last year in the Med I was only carrying 65 gallons max with two onboard, it seemed plenty.
 
Figures vary widely. We use about 80 litres pp per day showering after swimming off the back end and a decent shower at the end of the day this includes washing up and use of the washing machine maybe twice a week. The water maker is rated at 160 l per hour and so gets put on two or three times a week when we charge the batteries and put the bread maker on. My advice purchase fit the biggest you can get in to the available space.
 
Talbot said:
Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...

No personal experience but have read many accounts of people wishing they had chosen larger.
 
Talbot said:
Fitting a watermaker and trying to size it for my needs - I recognise that that means different things for different people, but some opinions would help.

I will be single or double handed. I have 555 watts of solar, and a generator (but would prefer to use the available solar only for making water) I also have a washing machine.

I am looking at the Schenka smart 30 or 60 (30 or 60 litres per hour) and trying to decide on the right size?
Click to expand...

I can carry 900 litres water on board and considering a watermaker so this is an interesting thread for me. Whilst you can be economical with water I see you have a washing machine and the half load one I've got uses more water than a person/day and its no good shouting at it to use less!!. I've come to the conclusion to go for the biggest I can fit/afford and run it for less time than a smaller one. My key consideration was to have the capacity of the watermaker match the running time of the genny so that I got maximum use of the genny at around 75% load. I have been told that 12 or 24v motors are more expensive than AC ones and probably not as readily available worldwide.
Some companies offer double capacity for only <£200 more. Look at the specs of the HP pumps/motors.
 
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