Watermaker Intake

[AndytheSailor]

Thanks for the video link SV Third Day, I get the point he made, about 32 times, ha ha, but point made. You have all been most helpful.

[monte]

I don't think it's been mentioned but most manufacturers I have come across recommend a forward facing scoop type through hull fitting. Also set it up as low as possible as many water makers require uphill pipe runs to the motors and filters. Elbow fittings on the through hull are not recommended..

[SV THIRD DAY]

Originally Posted by TacomaSailor

What am I missing here?

I am not disputing the recommendations of the experts but I am wondering when this absolute prohibition on a watermaker sharing a through-hull with another system became the official Spectra policy.

I'll let Tellie comment about Spectra specifics. But even with your years of cruising and time spent with a spectra installer in Mexico, you are still seeing a very small sample size of water maker installations, users, and most importantly trouble shooting calls and warranty claims. Every warranty claim and field failure is something that all good companies analyze and try to track down what they think was the root cause. Was it our gear that failed? Was it our installation instructions that were not clear? Was it the client not following our instructions? Was it just bad luck? I can’t speak for Spectra, but it is this failure analysis that brings me to the conclusion that using a T-fitting on a water maker inlet through hull is a bad idea and perhaps Spectra as well.

You did a smart installation with everything below the water line but how typical of an installation is yours? My experience tells me not so much. The more common water maker installation will be above the water line and have way more plumbing run than a sober engineer would like, but it’s a boat…we make compromises. So as a manufacturer that is not always working with the ideal installation location (and usually way too many 90-deg elbows in the inlet plumbing line installed by the client) we are forced to design and execute installation instructions so that they will work in as many situations as possible.

It’s not in our interest to put restrictions on how water maker can be installed because the more restrictions we put on clients, then the less clients we have. So we have an incentive to say, “sure…it’s all good…no problemo Amigo”. But here’s what I know from taking the calls. The No 1 problem in water maker trouble shooting is getting enough flow to the high pressure pump, so when I see my minimum size 1/2” through hull also being used by another device at the same time that means I have less flow available for the water maker and more headaches like the risk of air bubbles etc.

Bottom line I guess to answer your “what am I missing” question. I guess at the end of the day it boils down to two things:

1. Trouble shooting experience with a much larger sample size to learn from.

2. Being financially responsible for the installation instructions we put in the manual and advice we give clients.

(While No 2 will tend to make you more conservative, it also weeds out the BS advice pretty quickly when they go out of business....remember the www.DIYWatermaker.com fiasco. I get DIY clients with failed water makers calling me asking for help)

[delmarrey]

Originally Posted by TacomaSailor

In 2002 - 2004 I worked closely with the Spectra representative (factory trained) in the Sea of Cortez as we installed and repaired many Spectra systems. He never expressed any concern about the Tee off the diesel raw water strainer. I don't recall seeing any problems in the dozen or so boats I worked on with that arrangement.


Question:
a 2" thruhull can flow somewhere between 60 and 115 gpm (later estimate by Evans Stargazer) when two feet below the water surface. The 4JH2E Yanmar needs 16 GPM for cooling water (based on my factory rebuild manual) and the Spectra needs a little over 3 GPM of feedwater so why is the tee a problem if there is at least three times that amount of water available?

The Yanmar impeller pulls less than 1/3 of the available water to it and the two Spectra feed pumps are below the waterline so water will flow, by gravity, to those feed pump intakes. The water that is not pulled to the Yanmar impeller will naturally flow downhill from the Groco to the feedwater pumps 3' below it.

What am I missing here?

I am not disputing the recommendations of the experts but I am wondering when this absolute prohibition on a watermaker sharing a through-hull with another system became the official Spectra policy.

It is in my 2012 Spectra instructions that a dedicated thruhull is required with a forward facing scoop strainer, when, I don't know but it's there!

But just as I sepected, you do have an over size thruhull (2"), which is uncommon amoung most boater. That's bigger then some exhausts on sailboats.

The problem I see is air bubbles and restriction of flow. If one is willing to do other then what the instructions recommend then they should assume the responsibility of failures.


As for a Mex tech, need I say more........

[TacomaSailor]

"As for a Mex tech, need I say more........"

Gringo Tech - Retired commercial pilot and A&P certification

[Terra Nova]

It is very bad tech to share an engine intake with anything. And it is a disservice to others to recommend this type of installation.

[TacomaSailor]

Originally Posted by Terra Nova

It is very bad tech to share an engine intake with anything. And it is a disservice to others to recommend this type of installation.

WHY? HOW?

Can you offer a technical explanation of why it is so wrong?

- from a hydraulics (water flow) perspective
- from a flow control perspective

If the total available flow is three to six times the required sum of all the flows and each flow line has a control valve - what is the problem?

I was very specific in my description of what works on my boat with my diesel. I did not recommend my setup to anyone here. I just said it had been problem free for 14 years as had an identical setup on another larger cruising sailboat.

Please provide details not just "because that is the way it is"

A seachest is a highly recommended option for minimizing the number of thru-hulls in a boat. That is certainly a shared flow system. So, what is different in the case of a large thru-hull (mini-seachest) plumbed to multiple water uses, each with a control valve.

Additionally, my diesel cooling water (fresh water/antifreeze) is shared between an ARDIC diesel heater (with a integral water pump) and an Isotherm hot water tank. That shared system is the only possible way to connect the various systems and uses shared flow thru multiple pumps.

A third observation is that the Spectra 380c has two feed pumps that Y or T off the line connected to the thru-hull. If that is the design provided by Spectra - then why is it not OK to Y or T off the line connected to the thru-hull prior to the Y or T that goes to the feed pumps? The two situations seem identical.

I am not trying to be contentious here - I am trying to learn what it is that I mis-understand about shared water flow systems.

"it is a disservice to others to recommend this type of installation."

I recommended nothing to anyone - I carefully and clearly stated that I was describing the setup on my boat and my friends larger cruiser - both of which have been problem free for 14-years.

Obviously, based on 14-years and thousands of hours operation, there are some situations where a shared thru-hull is a cost effective and reasonable implementation.

[Terra Nova]

TS--nothing I say will convince you to modify your installation. Hopefully, though, others will see that you have simply been very lucky, so far.

[jkleins]

Originally Posted by Terra Nova

TS--nothing I say will convince you to modify your installation. Hopefully, though, others will see that you have simply been very lucky, so far.

Why would we if you can't even offer a rational explanation of why. While I agree that the engine is one of those things in a boat that you don't want to mess with I am not seeing how it is bad if the flow is adequate. The sea chest example is one I have not been able to reconcile myself in looking at that concept so if you have a good explanation I would certainly welcome knowing why one (a seachest) is great and the other (a large through-hull with multiple outlets) is prohibited.

Jim

[Dsanduril]

I wasn't going to wade into this one, but I'm with Tacoma. A poorly engineered system is just a poorly engineered system. Most boaters probably have something like a 3/4" seacock and that is barely enough to feed the engine its cooling water. Since that is what most watermaker vendors see, it's easier to use a blanket statement in the manual that says "thou shalt use a separate seacock and thruhull" than to say "the feed water pump requires a flow of X at a net positive suction pressure of y, you must design the intake system hydraulics to provide these conditions".

Tacoma describes a system that can provide at least as much suction pressure and flow to the feed pump as any standalone 1/2" or 3/4" thruhull installed in the same location, probably more, even when his engine is running. Personally I'd prefer that the manual provide the flows and suction pressure requirements rather than the blanket statements, but that would then require people to think.

[SV THIRD DAY]

WADR if you don't recognize the difference detween sharing a sea chest compared to a 1/2" or 3/4" through hull then in my view you are just arguing for the sake of argument and for a little slow day entertainment. Nothing wrong with that, heck that is what internet chat rooms are for. The problem is when you give the impression that a guy can share his standard 3/4" engine cooling water through hull with a water maker. I know you were specific in your boat layout and 2" through hull but that's not how the internet works for most people looking for answers. They will take your "it worked for me" comment and then ignore your below water line install and 2" through hull, which is Not the norm at all...not in the 20 to 30 or so water maker clients that I help through their installations per month.

You don't seem to like the answer of "why" that's been given now a few times: experience shows problems and since the water maker companies are on the warranty hook for those problem we want to minimize risks....that's what warnings and recommendations are for.

Now if you called and asked me if your sea chest would work, I would say yes. I would even say that a 2" single through hull should work also...but manuals are not written for the exceptions to the general rules...they written for the norm.

Of course clients are free to ignore our recommendations, its their boat, they are the captain, and as my wife reminds me all the time, I'm just a Cruising/live aboard Bozo. But if your HP pump gets damaged by cavitations caused by lack of inlet sea water flow or an air bubble that gets sucked back in through your other shared device plumbing and then ruptures the membrane, don't expect me as a manufacturer to pay for your wanting to ignore the warnings, that just seems fair right.....but in the real world it will still be my fault....

[TacomaSailor]

ThirdDay,

I appreciate your concern and, having written a lot of technical manuals, the problems with writing instructions that cover all circumstances.

I was pretty specific that my comments applied to only my boat and situation.

"The problem is when you give the impression that a guy can share his standard 3/4" engine cooling water through hull with a water maker."

I guess I am naive or have not looked at enough raw water intakes!

My calculations show that a 3/4" thru-hull 2' below the waterline can only flow 6 GPM which is less than 40% of the needed flow for my Yanmar 4JH2E and even a 1" thru-hull can only flow 12 GPM which is still only 75% of what is needed for my Yanmar.

Even a Yanmar 3GM (3-cylinder) requires over 7 GPM of raw water thru the heat exchanger. Who installs a thru-hull that can just barely flow the minimum water needed for effective cooling? Don't boat builders plan for small blockages and flow restrictions and provide at least 25% more potential flow than is absolutely necessary?

Call me "shocked" at the cheapness of sailboat builders!

[Terra Nova]

Originally Posted by TacomaSailor

...Don't boat builders plan for small blockages and flow restrictions and provide at least 25% more potential flow than is absolutely necessary?...

Yes, but then some boat owners just T off of them for other purpose.

[SV THIRD DAY]

Originally Posted by TacomaSailor

. Who installs a thru-hull that can just barely flow the minimum water needed for effective cooling? Don't boat builders plan for small blockages and flow restrictions and provide at least 25% more potential flow than is absolutely necessary?

Call me "shocked" at the cheapness of sailboat builders!

I'm shocked on a daily basis Amigo...and it's why the CYA approach is taken in manuals and in giving advice. The raw water cooling for my 120Hp Ford Lehman through hull for example, 1/2". My 8KW genset....1/2". My galley sea water foot pump (as if I need one of those with a 30GPH water maker ) is 3/4" what's up with that?

[Dsanduril]

Originally Posted by TacomaSailor

...

I guess I am naive or have not looked at enough raw water intakes!

My calculations show that a 3/4" thru-hull 2' below the waterline can only flow 6 GPM which is less than 40% of the needed flow for my Yanmar 4JH2E and even a 1" thru-hull can only flow 12 GPM which is still only 75% of what is needed for my Yanmar.

Even a Yanmar 3GM (3-cylinder) requires over 7 GPM of raw water thru the heat exchanger. Who installs a thru-hull that can just barely flow the minimum water needed for effective cooling? Don't boat builders plan for small blockages and flow restrictions and provide at least 25% more potential flow than is absolutely necessary?

Call me "shocked" at the cheapness of sailboat builders!

Your calculations are based on free flow of water from the depth you specify to atmospheric pressure on the inside. Most engine cooling pumps are the rubber impeller type and thus can provide significant suction lift. The pretty standard Johnson impeller pumps, for instance, have a rated suction lift of 3m (~10 feet), so re-run your calculation with the equivalent of the thruhull at 12 feet (2' actual + 10' suction) and see what number you come up with. So, the builders may not be cheap, they just run the numbers and do the design. With these pumps there is no need for positive suction head.