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Old 22-10-2014, 17:23   #31
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Re: Watermaker Intake

Dsanduril said:
"So, the builders may not be cheap, they just run the numbers and do the design. "

thanks for that observation here are some details based on your suggestion:

5 foot run to pump with one 90 bend and internal roughness of .012

the following thru-hull sizes at 2' below the surface with no pump suction calculated:

3/4" 6 GPM
1" 11 GPM
2" 57 GPM

the following thru-hull sizes at 2' below the surface with 10' of pump suction calculated:

3/4" 14 GPM
1" 28 GPM
2" 139 GPM

So I guess a 1" thru-hull could flow the 15 GPM my Yanmar needs plus the 3 GPM my Spectra feed pumps need with about 35% reserve capacity for flow.

And, a 3/4" thru-hull with the suction of the raw water impeller can flow twice the 7 GPM required by a 3-cylinder Yanmar.

The Spectra feed pump can self prime against a 4' head so I suppose they create a 4' head of suction?

My Yanmar engine rebuild manual specifies a raw water suction head of 1.66 meters or about 5.5 feet and I'll assume that is the same for all Yanmar fresh water cooled diesels. That changes the calculations above to:

the following thru-hull sizes at 2' below the surface with 5.5 feet of pump suction calculated:

3/4" 11 GPM
1" 22 GPM
2" 110 GPM

The 3/4" flow is still 57% above the max flow needed for a 3-cylinder Yanmar and the 1" flow is 46% more than needed for a 4JH2E.

Additionally, the 1" flow is 22% greater than needed for a 4JH2E (at max RPM) and two Spectra feed pumps.

Just beating my dead horse!
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Old 22-10-2014, 17:37   #32
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Re: Watermaker Intake

Quote:
Originally Posted by TacomaSailor View Post
the following thru-hull sizes at 2' below the surface with no pump suction calculated:

3/4" 6 GPM
1" 11 GPM
2" 57 GPM

the following thru-hull sizes at 2' below the surface with 10' of pump suction calculated:

3/4" 14 GPM
1" 28 GPM
2" 139 GPM
Not so fast, that's only 1/3 of the story.
Now go take a look at the different pump's rated flow rate, which of course mi amigos is for a flooded head and open discharge, as published in their specs. From real life testing the rated flow rate of a pump can easily drop in 1/2 once you put suction head and discharge pressure on it. You will need to add that loss into the equation as well, along with the typical dirty raw water strainer (and water maker prefilters) and sha-zam the next thing you know something is getting starved for flow. Maybe those idiots weren't.
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Old 22-10-2014, 17:48   #33
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Re: Watermaker Intake

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Originally Posted by SV THIRD DAY View Post
Not so fast, that's only 1/3 of the story.
Now go take a look at the different pump's rated flow rate, which of course mi amigos is for a flooded head and open discharge, as published in their specs. From real life testing the rated flow rate of a pump can easily drop in 1/2 once you put suction head and discharge pressure on it. You will need to add that loss into the equation as well, along with the typical dirty raw water strainer (and water maker prefilters) and sha-zam the next thing you know something is getting starved for flow. Maybe those idiots weren't.
Absolutely! It's why watermaker manufacturers and vendors specify a separate thruhull and why Tacoma's probably works fine. In the first case no one want to do all the work/engineering (and you truly can't rely on most customers - even professionals - to do it) so it's much easier to specify a separate feed. And in Tacoma's case either by design or luck (since I have no knowledge of how it went together) the relatively giant (by comparison with what most of us see in most boats) thruhull can adequately feed both until the cows come home.
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Old 22-10-2014, 19:28   #34
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Re: Watermaker Intake

I've no doubt everything TacomaSailor is saying is true. I have a neighbor across the street I always use as an example. He has a 74 Chevy Vega he bought new with 200 plus thousand miles on it and it still runs fine. I think some guys are just blessed with good Karma. What Rich has been saying above I agree with totally. I have been down this road many times. Tacoma is correct in saying that his older manual does not require a dedicated thru hull. But we have learned a lot since we were producing the 380C model Spectra. The Cape Horn Extreme330 is basically the new and improved 380C. I assure you on page 6 of the Cape Horn manual it requires a mandated 1/2" to 3/4" dedicated thru hull. What we have to remember is that every boat is different and that there are many models and sizes of watermakers. The 380C is based on a dual diaphram feed pump. Just move to either a Catalina300 or NewPort400 unit and the feed pump is entirely different. Both of these systems use a boost pump because of the feed pump design where the 380C does not require a boost pump as the feed pumps are able to draw their own vacuum. You can mount a 380C feed pump up to 36" above the waterline and it will still draw sufficiently enough to operate properly. Place an older Catalina 300 feed pump 36" above the waterline and you'll be ordering a new pump in short order. So many times it's apples and oranges to compare my watermaker with yours. As Rich has said very well, we want our customers to be happy with their watermakers. It is our job to continually improve not only the systems themselves but learn and change to newer ideas when it comes to the installation of our products. We really won't steer you wrong, it's in our best interest as well to make sure our systems are installed with the best practice possible. Practices learned in the trenches of hard won and many time expensive experience. Our salesmen our our front line guys and we bend over backwards to treat them as best we can, because we know our best salesman are our customers.
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Old 22-10-2014, 19:46   #35
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Re: Watermaker Intake

Seems quite conflicted opinions to this post.

To me it's pure Physics-you have a hole,you can suck X through it at Y.You divert as needed or if improperly calculated you're fubar.

All pumps,with quite few exceptions PUSH (head) with much more ease than suction side.

So,present company experience aside-it really just boils down to doing the calculations required correctly to avoid "problems" and/or turn valves using one through hole. Additionally,your pump sizing specs must be accurate.

I will say though-additional through hole makes happy without deeper thinking.
Lol



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Old 22-10-2014, 20:22   #36
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Re: Watermaker Intake

We are really down into the weeds here but it is interesting.

A prior response said:

"Now go take a look at the different pump's rated flow rate, which of course mi amigos is for a flooded head and open discharge, as published in their specs. From real life testing the rated flow rate of a pump can easily drop in 1/2 once you put suction head and discharge pressure on it."

My Spectra manual says to measure the combined discharge of the product water and the bypass water. They give required volumes for three different feed water temperatures and voltage measured at the feed pump.

Their maximum flow values are at 14.4V and 90 degree seawater. The measured values should be 2.7 GPM bypass and 0.3 GPM product for a total feed value of 3 GPM.

I took that value as the required feed water needed to meet the factory specifications and saw no need to worry about "flooded heads" or "open discharge."

Why do I need to consider the other considerations if the maximum required feed is 3 GPM? That is real life and is exactly what I measure when I tune up my system.

Another example provided to me by a civil engineer who manages a very large municipal water system and has lived with pumps and flow considerations for over 30 years.

A fire hydrant can connect (T) to three different fire engines. Each engine is pulling water from it at a different suction value and is flowing a different output. As long as the total suction pressure does not exceed the wall strength of the main and the total flow does not exceed that which is provided by the main pressure and diameter, and hydrant stand pipe diameter - there is no problem with three very different pumps drawing from the same source (thru-hull).

Yanmar and Spectra provided very specific flow requirements and the hydraulic calculations of flow is pretty straight forward so here I am with one thru-hull.

My professional career was measuring things and I began that career in oil refinery operations. I consulted with several civil engineers (including the one shown above) about the need for a dedicated watermaker thru-hull. My calculations and all those of the engineers showed that one more thru-hull was not necessary because Caliber installed a really big one for just the use we are discussing here.

The easy answer is "DEDICATED THRU-HULL" but it is not necessarily the best technical answer.


My contention is that there is nothing inherently wrong with a shared water maker source (thru-hull) as long as the source can provide an adequate flow to all users.
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Old 22-10-2014, 20:49   #37
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Re: Watermaker Intake

Quote:
Originally Posted by TacomaSailor View Post
My contention is that there is nothing inherently wrong with a shared water maker source (thru-hull) as long as the source can provide an adequate flow to all users.
And who will do this calculation and determine "adequate flow" for each and every boat based on their specific installation location, head lift, inlet line run, model of water maker, and hull speed? This is why you keep the engineers out of the sales department...asking a client to do or worry about this would freak way to many out when all they were looking for is a "go/no go" answer so they could go cruising.

I refer people to chapter and verse of our manual all the time only to get a response back,
"Manual, never read it. I just looked at the photo on the front cover and followed it".

And they are on year two of their Circumnavigation folks. All cruisers are not techy nerd engineers like us.

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Old 22-10-2014, 22:23   #38
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Re: Watermaker Intake

Tacoma, you consulted several engineers about dedicated thru hulls for watermakers? God bless you man, I'm sure there's a Freudian term for that.
But you do realize that the original manual for your watermaker was written by several "Engineers" and that the more modern manual was written pretty much by the same "Engineers"

Mostly with a lot of input and guidance by us mere mortals in the field.
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