Pelagic,
I applaud your energy system considerations.....and if looking for watermaker choices...have a look at my post here....
http://www.cruisersforum.com/forums/...ml#post1106384
1) I have experience with PM towed-water-generators and small alternator-based prop-shaft generators.....
a) The towed-water-gen (Hamilton Ferris) is my curret set-up and I like it very much for those cloudy days on
passage.....but my 520 watts of solar /
MPPT controllers do most of my energy genration on-board....
I get about 1.2 - 1.5 amps per knot of boat speed from 3kts - 7kts...and a bit more (2amps/kt) above 7 kts.....
In heavy seas when at boat speeds 8 - 9 kts, it does break free from the front of one swell before digging into the next.....so power output becomes limited....although Hamilton Ferris does make some nice
bronze weights that are supposed to solve the problem, I haven't used them (yet)......
Since My solar keeps me well supplied with power, I usually deploy my water-gen only on cloudy days on
passage, and then usually at boat speeds above 4 kts...but it DOES
work VERY well!!!
See an article/photos of my set-up here...
Towed-Water-Generator
b) Back in the 1970's we had a small (35-amp Motorola)
alternator w/ its simple
regulator attached to the outside of the case, spinning from a larger pulley on the prop shaft......which back them was called a "sailing generator".....
It produced about 1.5 to 2 amps per knot of boat speed undersail.....and a bit more as we sailed near
hull speed (8.5 kts).....took it off the boat 20,000+ miles and many years later....
(note this back in the day of
radar draing 18-20 amps at 12vdc...plus
refrigeration, etc...and solar was pretty expensive as well, so got our "green energy" anyway we could....)
{And, a
funny note....I still own this exact Motorola alternator, as it is mounted on the front of a 400+ hp Chevy V-8 engine in a '23-T Rodster (Hot Rod) I built years ago...}
2) Depending on "where" and "how" you are sailing/cruising, the
advice / recommendations will vary....
But, for "most" cruising in the tropics or temperate latitudes, between 30* N and 30* S (as well as summertime up thru 40* latitude), adding as much UNSHADED solar as you can fit, before wind-gen or water-gen is my usual advice as well as most of us who've done so!!!
In cases where there will be shade on the panels, it is best to figure daily energy output conservatively, and make calculations based oin the total amount of solar (in watts) that will be unshaded for most of the day's highest production hours (+/- 3 hours from local noon).....
Note that depending on your exact layout and what shading you have, this number may be taken from panels in one central group....or different panels (such as some on one side working well before noon and others on the other side of the vessel working well after noon)
{as an example, if you had 600 watts total, and in the moring you had 200 watts on one side shaded, and in the afternoon had 200 watts on the other side of the vessel shaded....you should figure daily average energy generation form the array based on approx 400 watts....and whatever extra output you get is just an added luxury...}
As for calculating that energy generation for planning purposes....
Depending on "where" and "when" you're sailing/cruising, the values do change....but for the most popular areas within 30* of the equator, you can calculate a daily average over an entire years...(having higher production in summertime with higher sun angles and lower production in witer with lower sun angles)
Based on your 24 volt system, and using
MPPT controllers, you can take the total amount of unshaded solar (in watts) X 20% = average daily A/H's generated by the solar array....
{Using the above example of a 600 watt array, with an average of 400 watts unshaded for the highest producing hours, that gives you 400 x 20% = 80 amp / hours generated per day.....
Have a look at an article/photos of my solar set-up here....
Solar Panels
3) For my article/photos on my watermaker choice and installation have a look here....
Watermaker
4) In a nutshell, I recommend a large solar array....or at least the largest you fit without substantial shading.....
BEFORE spending much time/effort on water-powered generators....
Only after going the solar
route, then look into the water-gens...
Fair winds and sunny skies....
John
s/v Annie Laurie