Electric raw water pump?

[FPNC]

A medium sized water pump">raw water pump will pump over 30 liters a minute at WOT. That's 8 gallons a minute or more. Larger pumps will pull more water than some utility water systems can supply.

Most of this water is used to cool the engine. The actual exhaust cooling could get by with much less.

The water that leaves your heat exchanger may have a delta of only 10°. This is why it takes a lot of water to cool the engine. Particularly in tropical waters.

What electric pump are you looking at which can supply that much water flow with head pressure calculate in?

[Markusm]

It can be done with propulsion engines. I worked for 10 years on a long range sport fishing boat that had marinated Cummins tractor engines that used water from our (electric 220v 3 phase) bait system to cool the main engines. The boat was originally designed to be keel cooled, but weld cracking problems (presumed to be from the temperature differential of seawater and coolant in an aluminum boat) required a re-design. The solution (which worked for 60,000+ hrs), were separate heat exchangers. As has been noted, the flow rate in a propulsion engine varies based on RPM, but as long as it is sufficiently sized, the thermostat will maintain coolant temperature. Keel cooling in steel fishing boats is very common and there is no control of the surrounding sea water.

I'd still be a little reluctant to set the boat up this way. It does introduce a couple of other potential ways to fail (if you lose all or part of the electric system), you lose your main engine. If there is no other way to do it, it will probably work, but its kind of a kludge.

[Colonel Bob]

Originally Posted by neelie

I’m thinking of replacing the belt driven raw water pump with an electric pump.

Is this a dumb idea? Has anyone done this !

The reason why I’d like to do this is because the belt driven one is all but inaccessible if the engine is hot because I have to lean over the engine to change belt or impeller.

With electric, I can mount it somewhere convenient.

My Jeanneau 42DS has an ENTEC 4.2kw genset in the port locker. I discovered that the previous owner had removed the impeller for raw water and installed a small Johnson electric pump powered by the genset output. Seems to work well, water pressure builds as soon as the genset is running and stops when it shuts down, so no excess raw water in the loop.

[sv Stella Maris]

Our boat has used an oversized electric raw water pump for our Genset's 2 liter Kubuto Marine Diesel. Vane pump never needs maintenance, provides correct flow for engine's maximum power output (excess water simply passes through), no impellers to fail. Uses house a/c power. Very happy with the system (many years old...)

I would not use this for my primary propulsion engine as a standalone. Maybe if I ran two in parallel, but then the complication overcomes the appeal. Impellers speak to other aspects of the system concerning flow obstruction, not merely impeller health...important industry diagnostic feedback...

Simple, Strong, Safe.

[deblen]

Originally Posted by neelie

Jeez… no need to be so enthusiastic agreeing with me.

OK… the impellers never get to fail, I change them every year regardless. And even on a cold engine it’s a job for a dwarf contortionist with a universal joint between wrist and elbow.

This is why I got to thinking about arranging a more maintainable solution.

The rubber impeller is the weak link in the chain of engine reliability - bits break off and clog up the heat exchanger, if for any reason the pump body is dry the impeller will self destruct.

Suggest you install a "raw water" type filter in the hose that feeds raw water from pump output to heat exchanger inlet-to catch rubber,etc bits.A plastic filter works fine.
Cheers/Len


Example:https://www.marineoutfitters.ca/inde...e=752324006045

[Cynara]

Don't fix things that are not broken.

Does that belt only works the water pump.

You can dail/anchor until it cools down

[rocks]

We have been using two Davies Craig pumps for 6 years. Have not had a problem
https://daviescraig.com.au/electric-water-pumps

[kubota]

use 2 float switches in waterlift muffler.
when upper one trips on, turn off electric raw water pump mosfet. .
when lower one trips off, turn it back on.
if neither is tripped, send a sys failure alarm.

a simple pwm circuit will let you adjust average flow to match engine at your nominal operating conditions
to avoid excess cycling.

whole setup done in less than a weekend.

i find electric diaphragm pumps far more reliable and serviceable than engine driven impeller pumps.
soft bronze parts and bearings wear out not just impeller. at $400 apiece and $200 for a rebuild kit with a spare i am $1000 down before i left the dock. i can keep 2 hi q electric spares for half that price.
rebuilt my johnson on engine impeller pump at $200 and a days work 4 times in the time
my electric pumps have run without rebuild with similar hours.
your mileage may vary.

[JAFO]

Originally Posted by neelie

And even on a cold engine it’s a job for a dwarf contortionist with a universal joint between wrist and elbow.

This is why I got to thinking about arranging a more maintainable solution.

I'd be asking myself if there's any way I can cut an access hatch into a panel, so I can get at it more directly.

[davegeorge44]

I had a boat some time back that had been rigged with an electric raw water pump. We had an incident where we ran over a line in the water that stalled the engine. The pump kept pumping and the engine filled up with sea water. Had to remove the injectors and turn the engine over with the starter motor. Blew water all over the engine room. If you do go the electric pump route, make sure that can't happen to you.

[kubota]

that's why the sensors in the waterlift. .
and u r done. water keeps flowing in and not evacuated
regardless of reason and pump stops.

even without electric raw water it can save you if cooling underflows due to any reason or exhaust leak or back siphon causes overflow which can ruin your engine.

kinda like having a alternator disconnect protect on your battery switch. you can live without the protection,
but when it goes wrong its kinda not good.

[RaymondR]

Originally Posted by davegeorge44

I had a boat some time back that had been rigged with an electric raw water pump. We had an incident where we ran over a line in the water that stalled the engine. The pump kept pumping and the engine filled up with sea water. Had to remove the injectors and turn the engine over with the starter motor. Blew water all over the engine room. If you do go the electric pump route, make sure that can't happen to you.

If you wire the pump through a relay as I suggested as soon as the engine stops and the oil light goes on the pump stops.

[capt jgw]

I ran my old Albin AD2 that way for a season. Obsolete engine with a gear driven proprietary raw water pump for which there were no parts available. I hooked up my spare potable water pump till I found a new pump I could retrofit. It worked fine, but the chance of over supplying and flooding the engine was present. A couple years later the head gasket failed and I had to repower the boat.

[capt jgw]

Originally Posted by Searles

If the s/w pump is well below the W/L use a belt drive centrifugal self primimg pump ,no more rubber impellers ,or use the globe dry run type ,⚓️⛵️

Your mileage may vary but I tried three different Globe impellers on three different engines. None of them would pump water. The pumps all worked fine with the black rubber impellers. I won't buy Globe again.

[billcrowley]

Neelie - if you are having trouble fetching rubber impeller parts out of the heat exchanger, consider adding a second raw water strainer between the raw water pump and the heat exchanger to trap these pieces and make them easily retrievable.