Electricity and Water

[kesey]

Congrats to all the contributors to this thread. It is one of the most informative I've ever read.

There is a good article, by Don Casey, on Watermakers here:
http://www.sailnet.com/collections/articles/index.cfm?articleid=caseyd0079 &tfr=fp

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[Anonymous]

The Sailnet article about watermakers by Don Casey is riddled with holes when you look at it carefully. Rather than try to pull the whole article apart let me concentrate on his calculations for the cost of generating the electricity needed to run the watermaker.

Firstly, let’s look at the example he gives – a 3 gallon per hour machine drawing 8A. Modern watermakers are around three times as efficient – e.g. the Schenker 30M12 produces 35l/hr at 100w (about 8A). That’s around 9.25 US gallons – a factor of thee times better than the performance the article is working on.

The article then goes on to calculate the cost of fuel used in running a 25/50 hp yacht main engine and assumes that this will take 120 US galls per year based on running the engine for an hour a day to make the water. The article states this as $300. But this is a very odd way of looking at it. Assuming that the main engine was the source of power rather than a genset, one would ensure that a 100A alternator was fitted with a smart charger, giving a genuine 100A output. Only 8A of that 100A would go to running the watermaker, the other 92A would be charging the batteries and/or running other 12V equipment. In addition the engine would normally be heating a calorifier for domestic hot water. How else would the vessel get domestic hot water? A gas water heater? A dedicated diesel water heater? Or a genset providing 240V? All of these cost money to run as well.

Suppose you go for a 240V genset. A genset will use around 1.0l to 1.5l per hour and provide at least 4kW at that consumption. Let us assume a smart charger of 100A. So, during a one hour session (which is a sensible round number), the batteries get a gross charge of (100-8) Ah, or 96Ah gross. Of course with inefficiencies of the chemical conversion and resistive losses, the actual Ah you can retrieve from the batteries will be rather less, but that is inherent with batteries and has nothing to do with watermakers or gensets. You will still have plenty of AC power to heat the domestic hot water with an immersion heater (you can get 1500W and 2200W heaters), a kettle (2500W), a hairdryer (1500W), a washing machine (peak demand around 2200W but only when the heater is on), and all the electric bits that need charging from the mains, such as laptops. Not all at the same time, of course, up to the maximum output of the genset at that time and if you fit an ammeter you can get to learn what the different things draw and switch them on as appropriate. It isn’t difficult on a boat because you’re so close to everything. We did it for years and you soon get into the swing of it. You could fit a fancy load-shedding system if you felt inclined.

So the true extra cost of running the watermaker during the time that you would have run the generator anyway is almost zero. If you leave out the capital cost of the device and the repairs and consumables then you get 35l of water per hour for almost nothing. To replace the charge needed to run fridges and the other domestic loads, most people need around 120 to 150 Ah per day. Say two hours charging with a 100A charger so you will be running the genset for two hours a day in any case. That means you will get 70l of clean fresh water per day at an incremental cost of almost nothing. The genset will burn around 2 litres per day – around five days to the UK gallon of diesel. The fuel requirement is utterly trivial compared with the other costs of living – it is a drop in the ocean, if you’ll forgive the pun!


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[Anonymous]

HaraldS - Have you ever considered plumbing your genset's closed cooling system in such a way that either the genset or the main engine can heat the calorifier? That would make use of the waste heat from the genset and provide a greater power surplus - or simply reduce the fuel consumption.

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[HaraldS]

Thought yes; done no. Neither the yard nor I could find a fitting calorifier that would allow for two independant heat exchangers. In theory one could blend the two fresh water cooling systems of generator and main engine, but I really hestitated to do that. So then the choice was engine or generator, and with the engine it was much easier to fit, than to the generator in the sound proof box with a complicated cooling system that also cools electric generator. Would need to give it a lot of thought with respect to side effects like galvanic coupling, back pressure etc.

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[Ric]

Lemain, regarding your concerns about running a watermaker, I think HaraldS answer is sensible. If you are happy to swim in the water, then it will be ok for the watermaker. For the huge majority of typical anchorages in the Med, you will be able to safely use a watermaker. I would never use it in a marina (but then you have no need as you have shore-water virtually everywhere in the Western med these days), and only rarely would I avoid it in some anchorages - usually just those with a lot of motorboats.


Oil and diesel are deadly for watermakers because it can get through to the membrane and ruin it. And the danger is not just from oil and diesel floating on the surface - there is always some hydrocarbons disolved in the water in heavily polluted waters eg in a marina and these can be enough to be dangerous.

Even out at sea you can have your watermaker ruined by an oil slick if you are desperately unlucky. I once even read about one that had sucked in some whale excrement and was ruined by it.

However, don't let these issues put you off getting a watermaker. They are just something to be aware of and take sensible proportions. The advantages of a watermaker greatly outweigh the downsides.

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[Ric]

Lemain, about the 43DS, I think it is a very good choice. A few years ago when it was first launched, Voile et Voiliers magazine did a back to back test on a 43DS, a Jeanneau 43 Sun Odyssey, and a Jenneau 43 Sun Fast, all of which are built on exactly the same hull. Amazingly, the 43DS was the fastest!

I know speed may not be a crucial decision factor for you, but nevertheless if you choose a 43DS you will be getting a boat which is fun and satisfying to sail.

I suggest you also have a look at the new 49DS, launched at Paris boat show a few months ago, but not yet on the Jeanneau site. It is a really beautiful boat. Take a look at the pics of the 54DS on the Jeanneau site to get an idea of what it looks like.

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[Anonymous]

Ric - That's the second time someone has strongly suggested that I look at the 49DS. The problem is that with all the equipment I want I am stretching my budget to the limit if I go for a brand new boat rather than a new used boat. If there are any used ones on the market then that would be different. They say that it has become a buyer's market, and with interest rates on the turn, who knows?

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