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Old 10-08-2017, 09:14 PM   #1
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Raw water flow meter

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Any suggestion for detecting seastrainer blockage and flow reduction to engine cooling circuits. I am planning a longer trip up northwest Australia and there is a ribbon weed that is prone to blocking sea strainer. Of course regular inspection with a clear lid is one option but would like some instrument that can measure flow so I can be on top of any issues before they turn into problems.

Real world Experiance rather then armchair opinions valued.

Thanks TF folks

Y
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Old 10-08-2017, 09:19 PM   #2
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I put a Borel Mfg system that has an exhaust temp sensor that will go off shortly if you have a loss of cooling water flow. You can configure it to have high water alarm and water in fuel. Simple to install. No interest in company, just happy customer.
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Old 10-09-2017, 12:16 AM   #3
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The PO installed raw water alarms on both mains. They are between the stainers and the raw water pump. Since they have never alarmed during operation I assume they would go off if there was a clogging of the strainer or the pump failed to draw enough water. When they alarm during the start up process they are loud enough to wake everyone.

My choice, if I was to re-do it, would have been to put it at the end of the cooling system, that way if a hose broke any where, the alarm would sound. Like right before the cooling water is injected into the exhaust. On other boats I have had hoses split, filling the bilge with salt water and the engine overheated before any other alarms went off, including the bilge alarms. I would rather know there was an issue before that point. I guess anything is better than nothing.

http://aqualarm.net/cooling-water-fl...7bfce6e8f55fa8
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Old 10-09-2017, 05:44 AM   #4
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Aqualarm makes a raw water flow sensor and alarm kit. But I prefer a temperature sensor on the exhaust hose like Balmar's. No moving parts- the Aqualarm can stick and high temperature is really what you want to avoid.

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Old 10-09-2017, 06:34 AM   #5
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Quote:
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I put a Borel Mfg system that has an exhaust temp sensor that will go off shortly if you have a loss of cooling water flow. You can configure it to have high water alarm and water in fuel. Simple to install. No interest in company, just happy customer.
Had a look at this. Unclear if this a suitable for 24 volt systems. What voltage do you run?
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Old 10-09-2017, 08:48 AM   #6
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Second Dave on this. A high temp switch on the wet exhaust is the most reliable protection for loss of sea water flow. I have found the flow switches to be prone to fouling, causing them to be unreliable. Many times powered up system with engine not started- and no alarm.
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Old 10-09-2017, 09:46 AM   #7
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Had a look at this. Unclear if this a suitable for 24 volt systems. What voltage do you run?
It runs fine, it is just a switch. I wired mine on a 24 volt boat in parallel to the existing temperature sensor.
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Old 10-09-2017, 11:23 AM   #8
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My boat is 12 volt. I had them make up high exhaust temp for both mains and the generator, two high water alarms and WIF for both main engines.
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Old 10-09-2017, 12:13 PM   #9
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Aqualarm has all sorts of exhaust monitoring kit, not just water flow.

Exhaust, Engine Monitors : AQUALARM, Warning Systems For Land And Sea
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Old 10-09-2017, 01:41 PM   #10
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We use the EGT as a way to detect cooling system irregularties.

If there is any problem, the EGT gauge seems to detect it first.
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Old 10-09-2017, 01:54 PM   #11
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We use the EGT as a way to detect cooling system irregularties.

If there is any problem, the EGT gauge seems to detect it first.
I'd agree that's the ideal method, but still highly recommend an alarm, especially if the helm duty is regularly circulated among perhaps less vigilant or experienced crew. Belt and suspenders approach, but it is an extremely expensive and potentially catastrophic event.
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Old 10-09-2017, 04:58 PM   #12
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At low power settings, egt will be below max even if engine has lost sea water flow. Can burn up the (supposed to be) wet exhaust before egt goes up by much.

I would not use egt to monitor for loss of sea water flow.
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Old 10-09-2017, 05:26 PM   #13
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Maretron has a raw water flow detection system so if you already have a NMEA2000 system then this is another option.
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Old 10-09-2017, 07:34 PM   #14
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At low power settings, egt will be below max even if engine has lost sea water flow. Can burn up the (supposed to be) wet exhaust before egt goes up by much.

I would not use egt to monitor for loss of sea water flow.
Ski, I respect your opinions on engine matters greatly; could you expand on this though? I don't understand how low EGT can burn up the wet exhaust flow.
And a gauge will tell you that it is running hotter than normal for a given RPM.

Thanks!
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Old 10-09-2017, 09:12 PM   #15
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IMO, one cannot have too many alarms on their main engines cooling systems!
I use a flow sensor and an exhaust elbow temp alarm.
They both test on startup, ungodly scream, but you wouldn't miss that like you might miss a subtle creep on the EGT gauge.
Wwestman, you are 100% correct about the location of the flow sensor.
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Old 10-09-2017, 09:34 PM   #16
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Based on this thread and what I have learned I have ordered the exhaust temp sensors and alarms for both mains and the gen set. And since the alarm had a forth position included a high water bilge alarm (which I had wanted anyway).
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Old 10-10-2017, 07:58 AM   #17
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Ski, I respect your opinions on engine matters greatly; could you expand on this though? I don't understand how low EGT can burn up the wet exhaust flow.
And a gauge will tell you that it is running hotter than normal for a given RPM.

Thanks!
I think we might be confusing two things: EGT is exhaust gas temp which is the hot dry exh gas coming out of the manifold or turbo exit. Most diesels at full power are around 900 to 1100F. HOT. At slow cruise like a trawler, EGT is around 400-600F. Many boats have EGT gauges (pyrometers) to display this temp on the helm. You can set an alarm on the pyro so if your engine normally runs at 700, you can pick setpoint at say 800 and it will beep if it goes up. But if you decide to run slower and EGT is now 500, things would have to go quite wrong to hit setpoint of 800.

Most of us when talking about exhaust temp alarms are discussing the wet exhaust. At engine exhaust outlet, sea water is injected into the flow to cool it. Wet exhaust temp after it is well mixed is usually something like 20-40F above sea water temp. Cools it from 900F to say 100-120F!! So we put the temp alarm switch somewhere downstream of the mixing point and pick a setpoint of say 150F. If something causes low sea water flow, this temp will rise quickly, usually quicker than engine coolant temp.

Also, since water flow switches have to be set to not alarm at dead low idle, their setpoint must be at a rather low flow. So if sea water flow drops significantly while at high power, the flow switch will not trip until flow is near zero. And at that low flow, wet exhaust components may already be cooked.
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Old 10-15-2017, 08:09 PM   #18
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Yes good info. I will only say that on a V engine, you need two monitor points. We were on an ocean passage when a passenger saw some smoke out back. Turned out to be one clogged riser and burning exhaust hose was the result. That could have been worse if that hose burned all the way through.
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Old 10-15-2017, 08:17 PM   #19
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That is why I like a system similar to the Borel Mfg system. It does not go into the water flow, just attaches to the outside of the exhaust hose. If the water flow stops, the exhaust will almost immediately get hotter and the alarm goes off. Does not matter if the engine is under load or at idle as to water flow. If you have a V engine, just add 4 sensors instead of 2. No connection to Borel, just a satisfied customer.
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Old 10-15-2017, 11:23 PM   #20
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Aqualarm also has outside strap attachments for wet exhaust that measure overtemp.
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