Raw water pump - how about electric?

[QBhoy]

Flow rate isn't a concern actually, as the flow rate doesn't change. On mine, there's a pump that takes sea water and pumps it into the exhaust, and a separate pump that takes the sea water and flows it through a small heat exchanger, and then out of the exhaust. There's a thermostat which swaps power to the relevant pump, and is seamless. When the engine's operating at power, the power to each pump is swapped more frequently than when it's idling.
The relay's auto standard (rugged/available/cheap), the thermostat is also 'auto' quality, with the sensor being in the fresh water header tank.
Originally, the engine had a mechanical thermostat, which IS the work of the devil, designed to clog and fail by virtue of its operating temperature with salt water!
The heat exchanger is 22kW, with a thermal shock to the engine coolant being about 5°C depending on which cooling pump is running, with the temperature peaking to 35°C on the exhaust when the 'heat exchanger' pump is operating, otherwise it's at about 19°C when the exhaust cooling only pump is running.
The exhaust temperature alarm is set at 50°C, which then lights up an LED, and gives an audible alarm.
Having warm salt water running through an engine is one that's suitable for the manufacturer, not the user. I'm aware that many engines are already fresh water cooled, but I didn't have that option, as to rig a 2nd mechanical pump for the fresh water engine coolant was far more complicated for me.

Flow rate it definitely a concern, I’d think !

 

[vas]

+1 on QBhoy above.
Pretty sure that engine idle at say 600rpm and working hard at 2.5k rpm will pump different quantities of water around (most likely 3-4X as much water...).
Are you sure that say geting the flow somewhere at the middle (just for the sake of argument!) will be enough to keep the engine at <80C when running hard? Going for full rpm/heavy load flow would mean that at idle speed you'll either keep the engine way too cool or have (as mentioned earlier) backpressure issues.

not to mention that a failed fuse or disconneccted cable or faulty alternator or broken pump, or or, will leave you with no cooling whatsoever and the exhaust flex hose will melt after a few mins filling the e/r with exhaust gasses.
OK the last can also happen with a broken belt or shaft of closed seacock.

 

[QBhoy]

+1 on QBhoy above.
Pretty sure that engine idle at say 600rpm and working hard at 2.5k rpm will pump different quantities of water around (most likely 3-4X as much water...).
Are you sure that say geting the flow somewhere at the middle (just for the sake of argument!) will be enough to keep the engine at <80C when running hard? Going for full rpm/heavy load flow would mean that at idle speed you'll either keep the engine way too cool or have (as mentioned earlier) backpressure issues.

not to mention that a failed fuse or disconneccted cable or faulty alternator or broken pump, or or, will leave you with no cooling whatsoever and the exhaust flex hose will melt after a few mins filling the e/r with exhaust gasses.
OK the last can also happen with a broken belt or shaft of closed seacock.

Agree. All depends on the pump too and t stat arrangement, if she has one. Just know that the arrangement I’m closely aware of on a lovely old delta ski boat. She has a 3.0 auto engine in her with an electric jabsco type pump. If she’s cruising or on low load..she runs very cool, even being set up fairly well. Speed controller now helps that and previously controlled by a variable valve flow. Seems to work…but it would be a worry in my head at least. Can also flood the engine with water if it’s turned on before the engine is running with exhaust pressure, as far as I remember.

 

[jamie N]

Both of these pumps operate at 6L/min. The flow rate doesn't vary through the exhaust: it's always 6L/min whether the engine is at idle or at full power, thus the flow rate isn't an issue. The exhaust won't be flooded at idle, experience has shown this. 6L/min with the engine under max power causes the heat exchanger pump to operate for about 10-20% of the time. That's 6-12 seconds a minute, as the cooling through the heat exchanger is effective, whereas at idle the heat exchanger pump operates for (maybe) 1% of the time. The engine temperature is maintained at the temperature set from the thermostat, which is a more interesting point for me, as it's finding the sweet spot between crystallisation, temperature and the flow rate through the heat exchanger to see how swiftly the crystallisation will become apparent, and of course the higher temperature desired for more efficient running.
The engine is circulating the same amount of water within itself as it's a closed circuit, so flow there isn't an issue. Flow rates only become an issue if one of these pumps fails, and cease to flow. If one of the diaphragm pumps fails, it's a 1 minute fix to either plug in the 'spare', or to change the plumbing to the pump through the heat exchanger, as these are simple screw fittings. If the engine impeller pump fails, then that's a real pain, as it'd take at least 30 minutes, as I've not made a blank and a diverter to swiftly hook up one of the diaphragm pumps, but most engines do have the same issue with impellers. My reason for the diaphragm pumps is to have a freshwater cooled engine, and it was the simplest and safest way of doing this.
The engine is always running before the seawater pump is running, so there's no opportunity for the engine to flood in that manner, which isn't uncommon on a conventionally cooled engine.
The pumps are always turned off either seconds before or after the engine is stopped.
It's a procedural thing, the same as fastening your flies after having a pee.

 

[QBhoy]

Both of these pumps operate at 6L/min. The flow rate doesn't vary through the exhaust: it's always 6L/min whether the engine is at idle or at full power, thus the flow rate isn't an issue. The exhaust won't be flooded at idle, experience has shown this. 6L/min with the engine under max power causes the heat exchanger pump to operate for about 10-20% of the time. That's 6-12 seconds a minute, as the cooling through the heat exchanger is effective, whereas at idle the heat exchanger pump operates for (maybe) 1% of the time. The engine temperature is maintained at the temperature set from the thermostat, which is a more interesting point for me, as it's finding the sweet spot between crystallisation, temperature and the flow rate through the heat exchanger to see how swiftly the crystallisation will become apparent, and of course the higher temperature desired for more efficient running.
The engine is circulating the same amount of water within itself as it's a closed circuit, so flow there isn't an issue. Flow rates only become an issue if one of these pumps fails, and cease to flow. If one of the diaphragm pumps fails, it's a 1 minute fix to either plug in the 'spare', or to change the plumbing to the pump through the heat exchanger, as these are simple screw fittings. If the engine impeller pump fails, then that's a real pain, as it'd take at least 30 minutes, as I've not made a blank and a diverter to swiftly hook up one of the diaphragm pumps, but most engines do have the same issue with impellers. My reason for the diaphragm pumps is to have a freshwater cooled engine, and it was the simplest and safest way of doing this.
The engine is always running before the seawater pump is running, so there's no opportunity for the engine to flood in that manner, which isn't uncommon on a conventionally cooled engine.
The pumps are always turned off either seconds before or after the engine is stopped.
It's a procedural thing, the same as fastening your flies after having a pee.

That’s all relevant to your set up perhaps. Sounds like it’s a good set up and you know your stuff around it. But perhaps I and others were pondering over the set up in general that was asked around originally

 

[jamie N]

Yup, you're absolutely right there, in that it isn't necessarily transferrable or desirable, and of course it was quite a bit away from the OP's original enquiry!

 

[QBhoy]

Yup, you're absolutely right there, in that it isn't necessarily transferrable or desirable, and of course it was quite a bit away from the OP's original enquiry!

Yeah. But great to hear or read what you’ve stated. I always have time for that kind of thing. Always interested to read such things. All the best

 

[superheat6k]

Having learnt the hard way about flow monitoring, or rather the disaster than can occur when the seawater cooling fails, I am in the process of fitting both flow switches on the seawater inlet pipes to the pumps and exhaust temperature probes.

Both will be hooked up to a dedicated alarm alert panel.

When I seized the Cummins on my last boat either of these devices would have allowed me to act sufficiently early to save the engine.

The routinely installed fresh water temperature gauge and alarm is akin to a chocolate fire guard as by the time these go off your engine is likely about to or is already seized !

 

[Molteni]

Having learnt the hard way about flow monitoring, or rather the disaster than can occur when the seawater cooling fails, I am in the process of fitting both flow switches on the seawater inlet pipes to the pumps and exhaust temperature probes.
Both will be hooked up to a dedicated alarm alert panel.

I have also fitted both of these. The audible alarms are on the ceiling just inside the cabin. In the case of the seawater flow alarm, there a hugely bright Red LED on the instruments above the companionway.
The third alarm and LED is for oil pressure failure, far better than a rarely viewed oil pressure gauge!

The earlier you are aware of any issue, the better!

 

[emmalina]

A bimetalic strip on your exhaust elbow connected to a loud siren is very effective. A lot of gen-sets use this system to kill the engine if it overheats.

 

[Plum]

Having learnt the hard way about flow monitoring, or rather the disaster than can occur when the seawater cooling fails, I am in the process of fitting both flow switches on the seawater inlet pipes to the pumps and exhaust temperature probes.

Both will be hooked up to a dedicated alarm alert panel.

When I seized the Cummins on my last boat either of these devices would have allowed me to act sufficiently early to save the engine.

The routinely installed fresh water temperature gauge and alarm is akin to a chocolate fire guard as by the time these go off your engine is likely about to or is already seized !

what seawater flow switches are you fitting?

www.solocoastalsailing.co.uk

 

[jamie N]

I fitted this linking it to this.
Total cost under a fiver.

 

[ianc1200]

Thread drift, but this made me wonder whether could have an electric pump running white vinegar cleaning around the system for say 30 mins to clean out limescale & heat exchanger and oil cooler - end of season clean through.

 

[Plum]

Thread drift, but this made me wonder whether could have an electric pump running white vinegar cleaning around the system for say 30 mins to clean out limescale & heat exchanger and oil cooler - end of season clean through.

Yes, quite a normal thing to do but vinegar not so good. The best is Rydlyme RYDLYME Marine Biodegradable Descaler - RYDLYME Marine , which I have used, although expensive although some people report of good results with brick acid. Plenty of older postings on this subject, particularly in the mobo forum. Instructions are here, although could be used for any other descaling chemical. https://www.rydlymemarine.com/wp-content/uploads/2019/12/Inboard_intructions_0917.pdf

I used one of these pumps https://www.rydlymemarine.com/wp-content/uploads/2019/12/Inboard_intructions_0917.pdf , removed the seawater pump impeller and left the fluid circulating for 4 hours. Video here:

www.solocoastalsailing.co.uk

 

[Plum]

Thread drift, but this made me wonder whether could have an electric pump running white vinegar cleaning around the system for say 30 mins to clean out limescale & heat exchanger and oil cooler - end of season clean through.

if you have not already seen it:- Pro Flush alternative to Rydlyme

www.solocoastalsailing.co.uk