Which Watermaker To Choose

[foggysail]

SV--

Yours was an interesting post. I enjoyed reading it. No problems following your math and assumptions with the exception of the pressure that Dave (Goboating) raised for the 1st membrane to get almost 21% product. If that is the case and your membranes show no discomfort, DOW might be overly conservative with its ratings for better reliability/life. Or just maybe to enhance the sale of greater number of membranes by recommending operation with a lower product yield/membrane.

Foggy

[ka4wja]

1) Uh yes Therapy, I'm fully aware of this....But....

Originally Posted by Therapy

By the way, did you know that if your salinity probe goes you can go into your MPC unit and tell it to ignore it and then you can use the watermaker like before with the MPC controlling all the rest of the functions?

Well, not quite ALL of the other functions....
And, that is exactly what I wrote (I think), and what you quoted...

But, for clarification, should you "bypass salinity probe", the automatic divert valve does not function, and you should use your external/manual diverter valve to direct product water either overboard or to bilge, until a low enough TDS level is reached....(and you can determine this either by using an external, handheld meter, or by "tasting" the product. or by just waiting a few minutes after starting the watermaker in manual mode, before sending the product water to your tanks...)

While this may not seem to be a big deal.....if your raw water isn't "clean" ocean water, but rather "questionable" harbor water or "agri-run-off" water from river mouths, etc. then it CAN be a big deal, and simply allowing product water directly into your tanks from first start-up is not a good idea....









2) Here again are examples that what works for one, doesn't always work for others....

Originally Posted by Therapy

Our boat had 60 gal total capacity in two 30 gal tanks. We went through one tank every 2 1/2 - 3 days. That is 5 hours of run time not counting start up and flush after. I found that a long time (for me). I would go with more capacity next time.

My other issue was the water I was floating in clogged the filters a lot faster than I cared for. Having to go "away" for a whole day (there - 5hours of watermaking - and back) was no fun either. Though it could have been called a fishing trip I guess.

Maybe I just stopped in crappy-water places.

a) I, myself, have always experienced a slightly higher than spec'd fresh water production from my Spectra Ventura MPC-5000, and find I can fill a 28 gal tank in about 4 hours and a 32 gal tank in about 4.5 hours (+/- a few minutes).....
But depending on water temps, salinity, voltage at the pumps, thru-hull and filter flows, etc. your mileage may vary....YMMV


b) I DO understand the filter clogging issue!!!
I was frustrated the very first day I used my new Spectra (the day after the installation was complete), as the pre-filters clogged in just 4 hours!!!
Oh boy, was I pissed.....

But Dick Murray came by that next day, and showed me what the problem was.....the crappy water I was floating in!!!!
And, once I realized what he was showing me, I felt really stupid!!!
But, he gave me a whole additional box of filters (24 in all) for free, and told me to use the watermaker here at the dock for a few days/weeks to see how I liked it (and if I didn't like it, he'd give me my money back!), and then sail out into clean water (just 1.5 miles to the inlet) and use it there for a while......
Well, in the ocean I can go a year without changing a filter....but here at my own dock, I can go about one afternoon!!!
So, I DO understand!!!




3) BTW, just to be clear, I have NO connection to any watermaker manufacturer/dealer (other than being a satisfied Spectra owner and customer of Dick Murray / Murray Marine).....
And, while we've already established that like Rich and Tellie, I'm no expert, I do have opinions based on experiences and education....

So, just to be clear, in my opinion, the two best watermaker companies around (for those of us on mid-sized cruising sailboats) are:
a) Spectra (Tellie's fav)
Spectra Watermakers - The World's Most Efficient Marine and Land Watermakers and Desalinators

b) Cruise RO Water and Power (Rich's company)
Cruise RO Water and Power

Although they both are RO watermaker manufactures, they make very different products, that approach things in a different way....
Which one is "best"??? That depends on what YOUR application is, etc...
Read my post above (#158)




Fair winds...

John
s/v Annie Laurie

[SV THIRD DAY]

Originally Posted by goboatingnow

13gph/76gph = 17%. Seems very odd. I see where the 76 comes from but the 13 seems to be picked along with the 20( in the previous equation) to magically arrive at the desired output.

Dave

No problem Dave...I'm so close to the numbers and info that sometimes I assume things that I shouldn't when giving an answer. The 20GPH production at 68degs F from membrane one along with the 13GPH from membrane two in a dual membrane system plumbed in series isn't theoritical data derived to make the numbers look pretty. This is the real life field testing data from sea water. The reason you don't typically see these numbers talked about by RO Manufactures is because, honestly, they don't want you to really know or understand what's going on! After all, once the rocket science myth of water makers is taken away, how can they justify the high prices of having something special?

To Review the Numbers:
The 96GPH and 76GPH is just the real life math when you turn the high pressure pump flow rate of 1.6GPM into GPH. 96GPH goes into Membrane one. 96GPH less what membrane one takes away as fresh product water (20GPH) goes into Membrane two, so 96GPH-20GPH = 76GPH. The rest is just plugging in the actual real life numbers and seeing what the recovery rate is...no magic or fudging numbers. 20% for membrane one and 17% for
membrane two at 800SI.

Sure, lower the PSI below 800 and you make less water and have a lower recovery rate, but why would you want to make less water for the same power just to worry about some arbitrary Recovery Rate number that wasn't made to apply to marine water makers but rather land based 24hr/day systems anyway? On the boat where power is king, you want to make as much water as possible as fast as possible, knowing that your membranes will be fine at 20% recovery. This thinking is harder to justify when you sell replacement RO Membranes (as other do) for $399, $500 or even $1400! A $1400 or $700 RO Membrane had better last, so you baby them and give up fresh water production to do it. But when you stop playing the proprietary parts game and sell a Dow SW30-2540 for $187. I don't care as much if my membranes last 6yrs or 7yrs because I would have made a LOT more water during those 6yrs, saving in equipment running wear and tear etc. It's a design philosophy that some agree with and others think is crazy, that's totally fine.

Here's some PSI vs Production data for the SeaMaker 30 water maker taken in the San Diego Bay at 68degs. (33,500 TDS, 68-degs, 1.6GPM Hp Pump, two DOW SW30-2540 membranes)
PSI 700 = 28 GPH
PSI 750 = 32 GPH
PSI 800 = 33 GPH
PsI 850 = 34 GPH

So if you make more water at 900PSI than 800PSI, why Rich don't you advice your customers to run at 900PSI?
And
If you are making 33 GPH at 800PSI, why do you call your SM30 a 30 GPH water maker and not a 33GPH?

Well some water makers DO in fact run at 900psi, we are happy at 800PSI to let the Honda 2000 run the water maker AND a battery charger at the same time (30A-12v) while not bumping up the recovery rate quite as much. But after saying that, on my personal boat when I'm not running the battery charger while making water, I DO run at 900psi at times, especially when I've drained my 450gals of water sharing it with folks in the anchorage without a water maker

As for why 30GPH and not 33GPH...easy...I'm out floating in the anchorage with other cruiser that have my water maker and I don't want negative calls over the VHF radio complaining that I shorted them 0.0275GPH.

Rich
SV THIRD DAY
Next to the Diesel Heater at anchor in Port San Luis, CA
Plotting my return to Warn Sunny Mexico!

[goboatingnow]

Originally Posted by foggysail

SV--

Yours was an interesting post. I enjoyed reading it. No problems following your math and assumptions with the exception of the pressure that Dave (Goboating) raised for the 1st membrane to get almost 21% product. If that is the case and your membranes show no discomfort, DOW might be overly conservative with its ratings for better reliability/life. Or just maybe to enhance the sale of greater number of membranes by recommending operation with a lower product yield/membrane.

Foggy

I still don't understand foggy , Dows permeate flow figures are maximums the recovery rate is between 8% and 15% ( at lower product flow,) it is of course possible to get out the stated GPH of product flow, but not at the stated input flows.

Dows membranes have a recovery factor of approx 0.57 ( litres/minute ) per bar so its more then possible at 800 psi to get the output. But not given the stated input flows. The poster stated the system pressure was 800 psi which is within the operating range of the membrane, so I still don't see how the membranes " are being pushed "

You did the original maths are you saying your wrong.

I've not seen recovery rates anything like what's stated here from Filmtec membranes.

Confused.

Dave

[goboatingnow]

I stand corrected, if these are actual flows measured then Dows spec sheets are way off. I wish I had my DIY water maker notes , I lost them in a house move ! I can't remember seeing 20% recovery rates
are these the low energy membranes by any chance

It's very strange because permeate flow rate is related to pressure ( more correctly pressure above the osmotic pressure in the vessel ) I could understand going over the pressure spec to get better rates. But Dow themselves publish test data at 800 psi. Why would a manufacturer understate the membrane performance within its spec limits. ( is it down to water temperature ??)

Dave

[ChuckSK]

I just ran Rich's numbers through ROSA and the results were almost identical to his claims. So ROSA matches reality and vice versa.

Dow wants a minimum flow through the membranes to keep them flushed. With the price of membranes below $200 it does make sense to run them with less flow even if it reduces their life somewhat.

If I didn't already have a watermaker I sure would consider Rich's.

Chuck

[goboatingnow]

Ok I think I now remember. Dow state 8% at high flow with 15% at lower flows. I've never seen a graph of recovery rate versus flow but it must not be constant. Since the GPH is only really a little above the minimum required , it must be that the recovery rate is actually in the 20% range for that small a flow rate. ( I've never seen this stated anywhere )

The max feed rate for that membrane is 6GPM , it must be that closer to minimum flow rate the recovery is above the stated figures. ( which makes sense as theoretically at 800 psi and zero flow the recovery is 100 %)

I wonder what happens at below the minimum flow rate ( or very close to it) shouldn't recovery rates further increase , allowing even lower energy requirements. I know that would put the second membrane under the min flow rate specs . But I wonder how hard a limit is that ( to carry off the salt buildup )

Jeepers I should build another one.

Dave

[foggysail]

DAve, back in my engineering management days, my guys presented me with a plaque with one of my often stated quotes to those young engineers. It read "you cannot ******** the circuit" meaning sweet words were never going to make poor design work properly.

As you noted in your last post, if the flows are actual, no matter what the spec says, it remains actual. Without pumping up ROSA, I doubt that kind of product resulted at 800psi. Also we know temperature has a great affect on product. And ROSA gives clear warning when you test an operating condition beyond Dow's recommended boundary conditions.

Foggy

[goboatingnow]

I don't a actually think the membrane is being pushed at all, not in the way we think We know that lower flows at a given pressure result in higher recovery rates. Ie the 8% is a snapshot. Dow state that upto 15% is the maximum , but maybe this is conservative, I'd love to see a graph of recovery versus low flow rates. It must be more then stated towards the bottom of the membrane feed flow rates.

I need to power up ROSA again

Dave

[foggysail]

Chuck-- you got your post in while I was typing--

[Pelagic]

I really appreciate the contributions and technical explanations of those involved in providing and studying yacht R/O systems as well as the layman’s perspective of user experience like John (Ka4wja) for elevating this discussion.

For those of us presently in the decision process, you guys really are the ‘fining agents’ in coming up with a practical brew!....

‘Water, water, every where, Nor any drop to drink.’

[SV THIRD DAY]

Originally Posted by goboatingnow

I've never seen a graph of recovery rate versus flow but it must not be constant.
Dave

And why would Dow publish one, considering the market for RO Membranes used in Boat RO systems doesn't even register in their overall RO Membrane market, it's a rounding error on the balance sheet. With no offense to any "engineers" out there, this is the classic case of giving an engineer a tech spec sheet on how Spaghetti is made and then not believing it can be stuffed with Cheese to make a Ravioli. The data and tech specs are simply for a different application, a continuous operating plant where O&M costs outweigh everything else. In those cases the 7% recovery rate rules the day and why on earth would you ever go above 10%??

Then you have another problem, why would this data and info be given out by the guys in the water maker industry to educate their customers? It's not generally talked about, because the less the customer understand and knows, the more they need the $800 membrane or their expensive systems. Saying these types of heresies doesn't make me "Mr Popular" in the water maker world, but as a Cruiser myself, I don't really care about getting invites to the right parties after the Annapolis Boat Show.

The testing data I gave was all taken at 68-degs with laboratory conditions and controls and is the average of 6 RO Membranes (since they all vary slightly in production). Some companies rate their outputs at 70 or even 80 to take advantage of the increased product water production that will occur as a function of molecular kinetics. We rated our units production at 68-degs, so in the warm waters of Mexico and the Carib, production will go up slightly, as will the Recovery rate of course.

As often happens when a bunch of techy guys are turned loose on an internet chat room, we could have taken this thread down a road most people don't care about, but hey...to us number cruncher types, it's as exciting as sneaking a peak at our Dad's Playboy back in the day.
Off this Weekend to Mexico for some affordable dental work....lets not even get started on THAT topic...ha ha ha.

Cheers

Rich
SV THIRD DAY

[wolfenzee]

Watermakers are one of those relatively new gizmos that a small percentage of boat owners can afford that are thought to be "essential". With more confidence than their reliability deserves. You should have large holding capacities, as many alternate ways of collecting and/r processing fresh water as well as bbe conservative in your usage...on land water is wasted at tremendous rate, you can get all the water you need and still be conservative (just act like you are on a boat)

[goboatingnow]

I powered up ROSA

Yes foggy its just related to feed flow. The curve of recovery rate versus feed flow is decidedly non linear. In fact at 0.7 GPM the recovery rate is 31% , where at 4GPM its 9%. !!!

Thanks Rich, interesting , just as an aside ROSA confirms what I thought, you aren't pushing the membranes at all, your calculations are within the design specs. What gives you the better power efficiency is to run the membranes at the lowest feed flow possible consistent with maintaining the minimum feed flow into the second membrane.

In fact it would be interesting to see the actual recovery rate would be going to the minimum recommended feed rate. ( or even below) I can't remember why I didnt see this before , but then again when I built my one , I didn't do a lot of math, merely used standard bits.

Dave

[goboatingnow]

Originally Posted by wolfenzee

Watermakers are one of those relatively new gizmos that a small percentage of boat owners can afford that are thought to be "essential". With more confidence than their reliability deserves. You should have large holding capacities, as many alternate ways of collecting and/r processing fresh water as well as bbe conservative in your usage...on land water is wasted at tremendous rate, you can get all the water you need and still be conservative (just act like you are on a boat)

Actually this isn't true. Water-maker technology is extremely simple and extremely reliable, ( nor is it new technology ) what's complicates things are

(A) manufacturers smoke and mirrors

(b) poor understanding of their operation and subsequent maintenance

(C) failure of ancillary control systems and the lack of knowledge or system design to revert to simple manual operation.

At its simplest , it's some pre filtration, a feed pump. A high pressure pump , a membrane in a pressure vessel and a valve or two. , all mechanical ,mostly plumbing

rich I agree totally re smoke and mirrors from major RO manufacturers , real case of white mans magic.

Dave