I don't have the bandwidth right now to multiquote or respond to many postings, so I am going to try to catch many points in one post.
My debate points on higher/lower capacity units have mostly defined low capacity as <3gph. I cannot see how these make any sense at all. The 8-12gph DC systems fill a much more usable middle ground (we have been cruising 4+ years with a 6gph system). However, I have found that these systems do not make sense for full time cruising in the tropics with no marina visits UNLESS they are an energy recovery system (and that means Spectra/Schenker). I have purposefully set these aside in my points because their price
makes no sense. If one is buying
new, it still makes sense to me to get a 20-30gph AC system for half the price
of a 8-12gph DC system.
The issue regarding output and power is the terminal voltage, not the battery
batteries make no difference here because their voltages are the same as any other battery
type - regardless of how long they hold that under-spec'd voltage. You will still need a running charging
source to meet output specs because these units are spec'd at 13.8V.
There is no way to make a DC system more efficient other than buying
an energy recovery unit. I am assuming proper wiring
I agree that if one has sufficient solar/wind, one can run a lower output DC system for long periods of time. However, this isn't really practical unless one has an energy recovery system. These are VERY expensive and another debate altogether. It really is about amps per gallon, but the price wall makes the decision complicated. If money
is no object and one has enough wind/solar to provide daily energy PLUS water
(and you know this is true from actual experience with your usage and systems and not a paper calculation), then I agree that a Spectra/Schenker makes sense.
A larger capacity DC system either uses as much, or more, energy as a higher capacity AC system or, if an energy recovery one, costs as much as a moon landing. And at this size it will be less energy efficient because you will be trying to charge the battery at the same time as pulling 100 amps out of it instead of simply running it directly off the AC of the generator
. It will be a rare boat indeed that can supply enough solar/wind to power a 1000gpd system, let alone meet daily energy demands - energy recovery or not.
, etc adds complication and mucho cost. Nothing wrong with that, but cost has been one of the major debate points of this thread, and many people I meet with these systems are constantly fighting them and jumping over the automated parts
to keep them running. If you are leaving your boat for a long time (many months), it makes more sense to simply pickle the membrane. If you are only leaving for a couple of weeks at a time, a single
good freshwater flush will last that long.
I disagree that the smaller systems have reduced operating and capital costs. The facts are easy on the capital costs - the larger AC units are the same price, or less expensive, than the smaller DC units. The AC units all use common parts
found anywhere in the world. The membranes are standard sized and easily ordered inexpensively. Go ahead and price a membrane from Village Marine
or PUR. Then price a HP pump from any maker of your choice. Then see about getting that HP pump repaired in Columbia
. Now do the same for a standard sized Filmtec membrane and a common CAT or General HP pump. Operating costs in terms of $/gallon may or may not be reduced depending on how it is operated and how much cost went into the alternate energy systems running it. An AC system run off an inverter
while motoring is essentially free since you needed to motor
anyway. However, even dedicating a Honda generator
to a watermaker
is less upfront cost than a large wind/solar array.
It is not just polluted anchorages
that are a problem. Try running your watermaker
in beautiful Thompson Bay Long Island Bahamas
. Or almost any other bay on Long Island Bahamas
. These are fantastic cruising grounds, but they are full of silt and your filters will completely plug
within 20 minutes. Same at Crooked and Aklins. We are often anchored behind beautiful reefs
with excellent snorkeling and fishing
during tradewind season where the sand is washing
over so much that the filters clog fast. We are also often anchored in beautiful fun places in the summer months when the algae and microscopic jellyfish (hydras?) are thick and will clog your filters in no time. Now let me tell you about anchoring
near mouths of rivers that provide excellent exploring and wildlife. Guess what happens there...?
In other words, we too leave polluted anchorages
as fast as we can, but regularly encounter excellent cruising grounds that we wish to spend time in that are not amenable to making water
. In these areas, we are finding our 6gh system to be a pain.
In tropic waters, the system cannot set more than 3 days without flushing
To summarize my opinion and experiences, the <3gph systems make no sense at all. The 8-12gph DC systems make some sense depending on your water needs, your cruising grounds, energy usage and supply, and if they are a Spectra/Schenker make much more sense if you ignore the cost of these units. 20-30gph AC systems make the most sense for those who wish to use live and use water comfortably, cruise
in tropic climates, do not have a military-sized budget
, have a generator of some sorts (even a suitcase Honda) and an appropriately sized inverter
coupled with a reasonable alternator