Flow Sensor for Sea Water Cooling

[Ralph Johnstone]

Of the many variables on our H310, the one thing I can always rely on is that one of the crew will forget to open the cooling water thru hull and then start the engine. Tried all of the usual tricks like wrapping the key around the thru hull handle, warning notice above the starter, and other etceteras, but it still happens.

I have found a flow switch from Defender Marine which will alarm when the sea water flow drops below 1.5 USGPM .......... so far so good. Now, after looking through the "Yanmar Service Manual", I find that the sea water pump on a Yanmar 2GM20F will put through 1600 liters/hr. with an engine RPM of 3600 RPM. This delivery capacity, I imagine, is with a total discharge head of zero feet as no discharge head is mentioned. With frictional head, velocity head, potential head, and the head on my beer, the capacity is somewhat less. If the rawater pump behaves like a positive displacement pump at lower RPM's, it would seem that with an engine idle speed of 800 RPM, the flow should be somewhat less than 1.5 USGPM and will set off false alarms with the flow switch.

Casting the theoretical mumbo jumbo aside, has anyone installed an "Aqualarm Cooling Water Flow Detector " on a Yanmar 2GM 20F and were they assailed with false alarms at idle speed ?
Thanks for any ideas on this problem.

Best regards,
s/v Island Hunter

 

[Ross]

I just look over the stern at the exhaust port. If I have water coming out everything is cool. If not I kill the engine and find out why no water. Doesn't cost anything.

 

[tommays]

I am fairly sure if you put a 1 gallon bucket in you exhaust water flow it fill up pretty quick as 1.5 GPM is not much water

I have found a water pressure gauge to be much better as it gives you a baseline on a healthy system


Tommays

 

[Maine Sail]

It think most use.

I think most boaters just use their ears, eyes and the temp gauge. With good flow you'll get used to the sound of the wet exhaust and eventually you'll be able to discern even small flow restrictions as the exhaust note & "splash" rhythm changes with less water flowing through.

Also the exhaust will look different and usually some white steam will be more present when you have restricted flow.

Personally I'd be very cautious inserting anything into the raw water intake line at least before the siphon break. If it cracks or fails it could be a potential boat sinking event. Also many flow sensors use a paddle wheel type, or flapper type of sensing device, though some are smarter and don't, but if it does it could likely get clogged with small debris/weeds even after the strainer.

Pay attention to your ears. I find they are my best and most accurate indicator of limited flow. I usually catch clogging of the strainer well before the temp gauge does..

Considering that device is made of CPVC I would definitely not install it before the strainer and would install it after the siphon break only..

 

[Ross]

Re: It think most use.

I was running the engine at the dock one day several years ago when my impeller failed. The exhaust got LOUD very quickly. My friend on the next oier said she heard it change. I showed her the impeller pieces and her first question was "did you get all of the pieces?"

 

[Maine Sail]

Ross...

Spending the $15.00-18.00 annually, and the five minutes (less than one oil change) to change your impeller should avoid this type of failure..

The point I think Ross was making is that your ears can alert you to changes in the water flow via exhaust note and water splash rhythm and it will save you $60.00+ dollars...


So.... Did you get all the pieces??

 

[Salish Sea Cruiser]

Re: It think most use.

I have had my seacock clogged on three occasions while charging my batteries at anchor; once by a fish and twice with weed. Twice I heard the sound difference and once the temp alarm went off on me. This bothers me, because the exhaust is very hot by the time the fresh water cooling water alarm goes off.

I bought one of these flow detectors, but for the reasons stated by others, I have never installed it. I don't have a strainer over the intaake through hull. I am going to install one when I hall this winter. If your interested in my flow detector, let me know.

 

[Ross]

Spending the $15.00-18.00 annually, and the five minutes (less than one oil change) to change your impeller should avoid this type of failure..

The point I think Ross was making is that your ears can alert you to changes in the water flow via exhaust note and water splash rhythm and it will save you $60.00+ dollars...


So.... Did you get all the pieces??

Oh yeah! I reassembled it just to be sure. And replaced it with a new one.
I believe in periodic maintanance. That was an original impeller and the engine had been warehoused for several years before I put it in the boat.

 

[Ralph Johnstone]

Thanks one and all for your replies.

Of course, the one thing I neglected to mention is the most important thing ......... the exhaust is under water. The exhaust is so quiet you cannot tell the engine is running if you're not on the boat. I can sneak up on submarines undetected it's so quiet. Unfortunately, you just cannot tell if cooling water is in there with the exhaust. I do have an engine temperature gauge but this takes time to register if some fool has left the cooling water thru hull closed.

And so ......................... my reason for wanting a foolproof method of detecting flow.

Thanks again all.

Best regards,
Island Hunter

 

[Rob19574]

Aqualarm

I actually have and installed the Aqualarm on my Yanmar YSM12 (12 hp). It works when I start up the engine as the alarm goes off for a second until it senses flow. However - this past summer, I had a hose kink on me after I did work on the my engine and when replaced the gally assembly (which is located over my engine) I acidentlay pinched one of the cooling lines. Flow was restricted to a point to heat up the engine but the alarm did not go off...I noticed lack of water pumping out the exhaust and saw the engine temp gauge rising....shut everything down and fixed the problem without any damage to the engine. That said though I do not trust the Aqualarm and would recommend a few things:
- Listen to Mainesail about water pump maintenence
- install a water stainer
- install a engine-temp and water pressure gauge in easy view from the helm (mine is currently located against the cockpit wall near my feet and is hard to see at a simple glance so I am going to jump a second gauge off that one mounted somewhere much higher)

Good luck - Rob

 

[Ross]

I think I would put a "High Temperature" alarm in the exhaust hose. If it goes above 220 degrees F> then you have lost the cooling water.

 

[Salish Sea Cruiser]

Re: Aqualarm

Rob, I agree. That is exactly where I'm heading. I put the temp gauge in last winter and put it at my feet and I have to strain to read it. This winter I will move it up where I can see it.

 

[RAD]

High temp exhaust alarm

I have the same problem while under way that my exhaust is under water and having a center cockpit puts me a greater distance than most. I listen & hear while at the dock and even go look every time I start up but for piece of mind I installed a wet exhaust sensor

http://www.borelmfg.com/index.html

 

[Rich Stidger]

An external strainer will prevent nearly all clogs

For years I was plagued with seaweed clogs in my strainers. My genset strainer was particularly affected because at anchor lots of stuff just floats by waiting to be sucked in. When moving the chances are less to ingest stuff.

I agree that listening to the exhaust is a great indicator, but I have had my genset shut down because I am below and do not go topside EVERY time to checkand hear the exhaust. The reason could be bad weather, just out of bed and not fully dressed, or whatever. The auxillary exhaust is easy because you start it in the cockpit so you are in the right spot to see/hear the exhaust.

I contimplated installing external strainers for a couple years, but was concerned that the clog would simply move to the outside of the hull where it would be much harder to clear. Two years ago, I acted and installed external Groco strainers on all three of my engine and A/C thru-hulls.

Since then I have had NO blockages whatsoever and only a few strands of seaweed in my inside raw water strainers. This was a dramatic change from cleaning substantial quanities of weed out of my inside raw water strainers. These external strainers hinge open so you can clean out any barnicles that have taken residence in the thru-hull.

These aren't a substitue for regular impeller replacements, but it sure seems to eliminate the impeller failures due to a clog during the season.

 

[Monty Miller]

My solution

I mounted magnetic switches on the A/C and engine thruhull valves and placed two red leds in the companion way. When the leds are on it means the valves are closed. One could easily take this one more step by wiring the engine thruhull switch to the ignition with a buzzer. Turn the ignition on and if the valve is closed the alarm would go off.

 

[Bill O'Donovan]

Overkill

I would not trust the raw water lever to the crew any more than I would let them back the boat into the slip. Some things are the exclusive responsibility of the captain. But you've got an ingenious solution nonetheless.

 

[Maine Sail]

That's the right strainer!

Two years ago, I acted and installed external Groco strainers on all three of my engine and A/C thru-hulls.

Since then I have had NO blockages whatsoever and only a few strands of seaweed in my inside raw water strainers. This was a dramatic change from cleaning substantial quanities of weed out of my inside raw water strainers. These external strainers hinge open so you can clean out any barnicles that have taken residence in the thru-hull.

These aren't a substitue for regular impeller replacements, but it sure seems to eliminate the impeller failures due to a clog during the season.

Rich,

You installed the right strainer!! The hinge is 100% necessary, IMHO, as I have had strainers that are non-hinged become clogged with eel grass and then you have no way to get it out!

I took a different path, that is working well, and increased my intake diameter to 1" so everything actually gets to my internal strainer and I don't have to dive. So far so good. If I ever go back to an external strainer I'll use the hinged one from Groco too..

A good basic rule of thumb for external strainers:

1) Never face a scoop strainer forward when installed on an engine or generator. You can FLOOD the engine and fill it with water.

2) While you are better to face a scoop backwards you can create added vacuum to the intake and may shorten impeller life. I still find this better than a hydro-locked engine.

3) Use ROUND omni-directional type strainers, preferably with a hinge, on sailboats if you MUST use one. The round strainers will not force water into a non running engine and create no additional vacuum.

4) If you sail a catamaran or tri and have "scoops" and one engine goes down you should ALWAYS close the non-running seacock or you run a very high risk of flooding the non-operational engine.