Sea Strainer Flow Meters

I've been reading up on all the posts and I see that having a functioning sea strainer is very important. Are there not any kind of flow meters you can install on your sea strainer inlet hoses that would alert you to any possible issues like blockages or decrease in flow? Just wondering for the future boat purchase.

I will be interested to here the responses. Personally, I've often wondered if a vacuum gauge would work instead of a paddle wheel. I use them on my Racor fuel separators and would think they would accomplish the same thing (clogging filter increased vacuum) on a raw water system.

Ted

I've seen people use a pressure gauge after the raw water pump to show intake restrictions or a weak impeller.

I have a fuel flow meter installed on my Boston Whaler Revenge. I only use it for final trim on the motor but I'm guessing i could use one as a flow meter for water intake as well some day. Just dreaming of a big boat future.

Discharge pressure switch after raw water pump

Our 2008 vintage Cummins 9kw generator has a barb tee on the discharge of the raw water pump. There is a pressure switch mounted on the tee that is wired into the control for the gen. It shuts the gen down very quickly if no pressure. Have had it work when the the intake to strainer plugged and when an impeller failed (not related to first shutdown). I would think one could set this up on a main engine to sound an alarm?

$30 temp gauge or the more expensive $90 dollar version with a probe on exhaust elbow quickly alerts you to reduced flow

Set temp to 10 degrees above normal elbow temp.

Cheap version, been working fine since 2018 and alarm goes off well before an auto shutdown event
https://www.trawlerforum.com/forums/s6/cheap-engine-temp-alarm-38822.html

More expensive dual probe version

https://www.trawlerforum.com/forums/showpost.php?p=928744&postcount=16

floater said:

I've been reading up on all the posts and I see that having a functioning sea strainer is very important. Are there not any kind of flow meters you can install on your sea strainer inlet hoses that would alert you to any possible issues like blockages or decrease in flow? Just wondering for the future boat purchase.

Click to expand...

I like the aqua alarm system. Its not necessarily a 'meter', it is a 'flow switch' and if there is not flow, an alarm goes off. If you combine it with the exhaust temp alarm which goes off if the wet exhaust temperature gets too high, you are covered twice.



https://aqualarm.net/cooling-water-flow-c-2/?zenid=c638630735f00fa4a51fbe6fbc941ae8

I see the exhaust temp setting for Aqualarm's sensor that is mounted to exterior of wet exhaust is 200-degrees. I seem to recall a prior thread where 165-degrees. Is 200-degrees an acceptable temp? I agree with bligh - nice setup to have both alarms in an dedicated panel setup. Looks like it isn't too pricey either.

Peter

Exhaust gas sensor is my choice

My Borel exhaust temp alarm is set for 176F. It has test wires at the band wrapped around the exhaust hose which can be touched together to test the alarm.

Aqualarm raw water flow detector/alarm.

The benefit of these alarms is that they go off instantaneously the water stops flowing. Wouldn't be without one.

By the time an overheat alarm goes off, it may be too late for your impeller.

boatpoker said:

Aqualarm raw water flow detector/alarm.

The benefit of these alarms is that they go off instantaneously the water stops flowing. Wouldn't be without one.

By the time an overheat alarm goes off, it may be too late for your impeller.

Click to expand...

My impeller is getting changed regardless.

mvweebles said:

I see the exhaust temp setting for Aqualarm's sensor that is mounted to exterior of wet exhaust is 200-degrees. I seem to recall a prior thread where 165-degrees. Is 200-degrees an acceptable temp? I agree with bligh - nice setup to have both alarms in an dedicated panel setup. Looks like it isn't too pricey either.

Peter

Click to expand...

The high temperature cutoff on the water injecting elbow on my generator trips at 230 F.

Aqhalarm is the way to go. Don't try to reinvent the wheel!!!

boatpoker said:

Aqualarm raw water flow detector/alarm.

The benefit of these alarms is that they go off instantaneously the water stops flowing. Wouldn't be without one.

By the time an overheat alarm goes off, it may be too late for your impeller.

Click to expand...

But if the water is slowed/reduced those water flow alarms don't go off
But if the water is slowed/reduced the exhaust elbow will get hotter so the temp alarm I linked to will go off.

Impeller is saved as it still had water in the system albeit reduced flow.

Had ours go off last year, temp on engine was still at around 82c, slightly higher than normal but elbow had got over 50c setting off alarm, still had plenty of water flow just not as much as we should.

I just bought an Aqua Alarm after my neighbor had to shut down an overheating engine while crossing the shipping lanes (shortly after making a prudent call to slow down and let a tanker pass vs throttling up to pass in front). When his port engine shut down he lost his electronic engine controls leaving him dead in the water.

He noticed the gauge but never heard an alarm. Smoke (coolant) filled the ER) in the moment it appear to be smoke, he called Mayday and the CG got him back to our marina.

His decision to slow down and let the tanker pass probably saved his life. The fact that he noticed the temp and took quick action saved his engine.

Cheap insurance to monitor water flow and exhaust temp (and fire, high water, oil and engine temp).

Simi 60 said:

But if the water is slowed/reduced those water flow alarms don't go off

Click to expand...

Incorrect. I have used Aqualarm for three decades and tested at various flow rates. They most definitley will sound an alarm at some point of reduced flow (before it becomes critical). When the flow is reduced enough to let the gate fluctuate, they will activate. I have used them on an HT6-354 Perkins, a Volvo TAMD 60B and a Westerebeke 55A, the best $100 I've spent.

boatpoker said:

Incorrect. I have used Aqualarm for three decades and tested at various flow rates. They most definitley will sound an alarm at some point of reduce flow

Click to expand...

OK, my misunderstanding, its just that you and the manufacturer said......

You

The benefit of these alarms is that they go off instantaneously the water stops flowing.

Click to expand...

Manufacturer

It activates an immediate alarm (not included) upon loss of raw water

Click to expand...

I mistook stops and loss of raw water to mean that.
Reduced flow would have been a better way for me to understand.

"I seem to recall a prior thread where 165-degrees. Is 200-degrees an acceptable temp?"

The use of 165F for a sea water discharge is so salt will not come out of solution and slowly plug the operation. 200F is fine warning for circulating coolant.

165F for sea water is good temperature to stay below in coolers and heat exchangers too.

I have a new set of Aqua Alarm exhaust bands in my hands. One for engine and one for generator. Temp is 200 degrees. Also have Aqua Alarm high water switch. All connected to a panel with fire alarm bell. To be installed this winter. Had them on my previous boat. Great system, great company support, and reasonable price.

I agree completely with the members recommending a combination of flow alarm and exhaust hose over temp alarm. I use the Aqualarm flow alarm with a Borel exhaust temp alarm, all connected to an Aqualarm alarm panel. I chose the Borel alarm because it has a lower alarm temperature setpoint than the Aqualarm.

I had the Borel alarm go off in the first season after my install. It took a while to track the problem, but it turned out to be the beginning of a failure (rust through) of my exhaust elbow. The hose was over 200 degrees in spots, when normal would be close to 100. Without that alarm, I would not have known about the elbow failure until damage was done (eg. melted hose), and I could have had raw water enter my turbo and/or engine!! All other engine temps were well within parameters.

That alarm saved my bacon
I periodically test my flow alarm by slowly closing my through hull. The alarm always sounds well before the valve is totally closed.

The flow alarm sounds to indicated an impeller issue, a closed thru hull, or something blocking the thru hull (I had a small fish get stuck in my generator's thru hull one time and my alarm went off right away), allowing for swift action saving the impeller (unless that is the issue). The exhaust overtemp alarm will be the first "early" warning of an impending overheat including a blown hose past the pump that the flow alarm would miss.

I went with exhaust temp sensor, as I feel it needs zero maintenance. If you were doing pressure, you would want an adjustable differential pressure switch piped before sea strainer and right where raw water injects into exhaust elbow. The more devices measured, the more differential, giving you more accuracy and including all components of the system. Just a thought

I put in a Borel alarm system. It has 3 exhaust sensors, 2 high water alarms and 2 Water in Fuel (WIF) alarms for the main engine Racors. Very easy install and uses no power unless there is an alarm condition.

I have just bought 2 dual alarm Engine Guard units, made in Australia, Fitting next week, for water temp and on the exhaust elbows. I was jolted into doing it as two acquaintances with same engines as mine both destroyed their 6BTAs thru water loss, within a few weeks of each other, don't know full story yet but bill was in the range of $60,000 , at a cost of $230 cheap insurance methinks.

floater said:

I've been reading up on all the posts and I see that having a functioning sea strainer is very important. Are there not any kind of flow meters you can install on your sea strainer inlet hoses that would alert you to any possible issues like blockages or decrease in flow? Just wondering for the future boat purchase.

Click to expand...

I personally believe better than any guage would be to check the strainer every day before you run the motor or generator

Yes, of course. I always check before starting and look for good flow immediately after starting. But... while underway I've sucked a plastic bag, a bunch of sea weed even had a fish get stuck in the intake.

Cartouche said:

I personally believe better than any guage would be to check the strainer every day before you run the motor or generator

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