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Saturday, April 13, 2013

Water Makers

Having a good water maker is an import component of a cruising boat.  In various parts of the world, shore-side water is of questionable quality, very expensive, or not available at all.

Poor quality water is probably the worst scenario.  Top up you tank with it, and not only have you taken on bad water, but you have contaminated all the rest of the water you had before.  Now you are really stuck.

Cost is another issue.  A water maker isn't cheap to install, and isn't cheap to operate, but it's cheaper than buying water in some areas.

And then of course there is the luxury of having plenty of water and not having to worry about it.  I like that.  It's great not having to ration water when you are on a long voyage, be able to shower as much as you want, and do laundry as much as needed.  The trap, however, is that you also need to have a plan if the water maker fails.  The trick is to keep the tank topped up, or at least know what minimum amount you need to reach an external source on rationed consumption.  For example, if you can get by on 15 gal per day and have a 20 day voyage, you don't want to let your tank get below 300 gal.

I thought the water maker selection for N6062 would be easy, but not so.  The N60 includes a standard "option" for a 600 gal per day Village Marine water maker, and most Nordhavns are equipped with that or a similar model.  That sounds like a well worn, well proven path, so I just checked off the box next to the option.

Our current boat has a Spectra water maker.  I selected that one for two primary reasons.

First it's DC powered which means we can run it while the boat is underway without the generator.  Water makers like clear, clean salt water to work on.  That's abundant out in open water, and scarce in harbors and anchorages.  As a result, the best time to make water is while you are out in open water and have the engine running providing a source of power.

Second, the Spectra comes with a automatic control and flushing system.  The control system operates all the pumps and valves, monitors the salinity level of the produced water, dumps it overboard until the salinity drops below a certain level, then produces clean fresh water for as long as you tell it to.  When it's done, it automatically flushes the system with fresh water from your tank.  This is an important step to prevent the growth of biologic matter in the sea water still in the system, and extend the life of the expensive filter membrane.

In fact, the fresh water flushing is so important that you are supposed to do it once a week if the maker is not used, and the spectra does this automatically as well.  After you make water, it kicks into this maintenance mode where it counts down the days, does a flush for a few minutes, then starts counting down all over again.  It really takes the hassle of of owning and operating a water maker, and is particularly useful if you are away from the boat for more than a few days, which we typically are.  Last summer, we were up in the New York and Canadian rivers for nearly 2 months and the water maker just took care of itself until we returned to salt water and were ready to put it back to work.

All this background is a log way of saying that this auto flush feature was the full extend of my due diligence on the Village Marine unit supplied in the Nordhavn, and sure enough, it has such a feature.  Well, sort of, it turns out.

As I searched around on the net reading about people's experiences, and talking to Village Marine owners, I came across a few serious gotchas.

The biggest is that the Village Marine is an AC powered system.  At first I didn't think this mattered.  It's a much higher capacity system that the Spectra that I currently have, so I figured I'd just run the generator, make water, do laundry, etc.  Because the maker can crank out a bunch of water is a short time, the generator run time would be limited.  And I figured that if we are leaving the boat for an extended time in a marina, it would be on shore power so the flush process would continue to work.

But the part I overlooked is that the whole control system is AC powered, and when AC power is interrupted, the control system forgets what it's doing and needs to be restarted.  That means that while cruising, when AC power is coming and going all the time, the system will keep resetting to zero, completely defeating the countdown and auto flush feature.  So even though it has an auto flush feature, in practice I'd have to count down the days myself and manually start a flush when needed.  That sucks.  And the same problem exists while on shore power.  Anytime the power blinks, which is regularly in a marina, the auto flush feature would stop.  In essence, the Village Marine does not have auto flush, even though it's listed as a feature.  It simply doesn't work in any useful way.  The only way to make it work would be on a boat that has 24x7 generator power (not me), or to install a dedicated inverter just to power the water maker.

So, back to the drawing board on water makers.  I know the Spectra product and know it works in a sensible way.  One of the great misconceptions about water makers is the mistaken belief that DC water makers are very low output, and that you need an AC unit to make water in any reasonable quantity.  It is true that many DC units are very low power and very low production rate, designed for use on sail boats where power is scarce.  And it is also true that very large water makers for mega yachts and cruise liners require so much power that AC makes the most sense.  But in the range required for anything is the 40' to 100' range, there are DC models that match the performance of the AC models in every way.  And in many cases, their overall efficiency in terms of kwh consumed per gallon of water produced is much better.  For example, the standard issue Village Marine used by Nordhaven is either 600 or 800 gallons per day output.  Spectra offers a DC model in three flavors of 360, 720, and 1000 gal per day.  Seems the same to me.

So, after some haggling over price, I've deleted the Village Marine and replaced it with a Spectra Newport Mk II 1000 gallon per day DC powered water maker.  That will meet our needs much better than the Village Marine.

2 comments:

cedric.rhoads said...

Kick ass analysis as usual PH. Very useful as well. How's the rest of the design work going?

Peter Hayden said...

It's going well, thanks. The current challenge is a diesel heating system. It should be easy, but for a variety of reasons, it's not. It will get a dedicated posting once there are a fewer balls in the air. I also owe a post on the build progress at South Coast. They are moving really fast.