I always try and talk to our clients to understand the "why" of their purchase
decisions and then follow up with them to get some feedback and where's what I'm finding along with my thinking.
The SM20 (20GPH) and SM30 (30GPH) both use the same high pressure pump and motor
, a 1.0Hp motor
that uses 9.3A at 120v AC (motor can also run at 220v). So if you look at it from a Amp per gallon standpoint you are making 50% more water for the same power usage with the SM30. There is also some built in membrane redundancy in the SM30. If one of your two RO Membranes were to fail while out cruising, you can quite easily just run the water maker off of one RO Membrane and continue the cruise
with a 20 GPH water maker. The cost difference between the SM20 and SM30 is $855, so between the 50% production increase (or 50% less generator run time) and the redundancy it’s a compelling argument. Literally, the only difference between the SM20 and SM30 is the addition of this second RO Pressure Vessel and Membrane plumbed in series. The SM40 is the SM30 but with a larger pump and motor. Of course you can always upgrade from a SM20 to a SM30 at any point down the road for the same $855 price
difference, so there really isn’t a “risk” in starting out with the SM20 and we have folks make this upgrade all the time because well, salt water
is evil! But honestly, if you can afford the initial $855 upfront I think it makes the most sense, especially with a crew of 4!
The mindset of a 12v water maker is “energy efficiency” since you are trying to make water solely off or your battery
bank, so you live with less production per hour to help keep down the amp draw. With a 12v water maker, Amps/Gallon is a key yardstick of performance. But once you have the power of an AC Genset, sure you want efficiency, but it is no longer the governing criteria and Amps/Gallon of production water just isn't as important because you usually have power to spare while running the genset. With an AC 120v water maker, it just makes sense to make as much water as quickly as possible to minimize generator time or make more water to keep the tanks
full. There were times when we were hanging out in a chocolate water estuary where we didn’t make water, so once our 450 Gallons of tankage was gone, we would head
out of the estuary for the day to refill the water tanks and then head
back in at the end of the day. With a low output 12v water maker it would have been difficult to “catch back up” once the tanks were ran dry.
Spectra makes a great water maker and like us, has great customer service
, so I can't ding them at all, nore can I or anyone match their Amps/Gallon numbers! So for a boat without a generator and just a battery bank, I send those folks to Spectra and know they will be happy. Sure they will have less water, but that is the best match for their boat. I think once you make the decision to have a generator (or Honda
2000) then an AC 120v water maker like one of ours is the way to go. There isn't a "wrong way" to go in the 120v vs 12v water maker decision as long as you know the decision tree and strengths and weaknesses of each approach. You wouldn’t buy a 120v AC water maker with a 400AH battery bank and 300W of solar
without a generator, just as I don’t think it makes sense to buy a 12v 17GPH water maker if you have a ships genset that you run regularly and have a >20+ GPD water demand.
A possible knock on the 120v AC approach is that if your generator dies so does your water maker. Well maybe...but if you buy a unit that can't run from a 2000W inverter
powered by your alternator
and battery bank, you have a back-up powering source. This is why the SM30 is a better seller than the SM40, I think. Sure the SM40 makes more water per hour, but it also uses a 1.5Hp motor at 13.3A so that takes it out of the powering range of most inverter/alternator as a back-up for if the genset dies. I was explaining this to a cruiser last week and his response was, "Son, if my generator dies our air conditioning
is also out and we are heading back to the dock
anyway, so sell me that SM40"! As someone who spends the summers in the Sea of Cortez
in 110-deg heat without air conditioning
, I had to laugh, but it shows the differences people have in what they need that works for THEM. Sure some can live with a 500ml shower
every other day, but I can call you for a fact that we would not be on year 7 of full time living aboard
if I had to ever tell my wife and daughter to take shorter showers. Our love life would be a lot less without nice comfortable showers...hot stickey my friend means you don't get any...ha ha ha). What we do is run our Honda
2000 or 8K diesel
genset when at anchor to make water, but while underway motoring we flip on the 2000W inverter
to make water. This way we entered the anchorage with full tanks.
You can reach me 7 days a week pretty much whenever I’m awake for technical support/Customer service
, it’s the advantage of me being a live aboard cruiser, I’m always looking for an excuse to get out of a boat project
and talk cruising and water makers! Rich@cruiserowater.com