Flow meter on raw water intake, Genny

[TJM]

I am applying some Engineering logic to "what can go wrong" on a Northern Lights 6kW Genny. Raw water cooling flow is not easily visual, except for discharge out the side.
I have replaced my black 3/4" ID feed hose from the impeller driven water pump to the heat exchanger with a thick wall clear hose. The hose being clear is a visual aid that I have sea water flow to the genny. I thought about placing a flowmeter in line with that feed line. The ball type meter so no moving parts like the paddle wheel type,
What are your thoughts ?

 

[Gdavid]

I don't know of a clear hose, even reinforced that a surveyor would endorse. Your generator has sending unit on the exhaust manifold/heat exchanger that is wired to interrupt the fuel supply if it exceeds the temp limit. You could tie into this circuit with a relay to sound an alarm as well or install a second sending unit to power an alarm independently. This seems like a more straightforward approach than a flow meter on the intake.

 

[High Wire]

If you have one of those newer water separator exhaust mufflers with an underwater water discharge, it’s very difficult to see flow.
A flow meter is a little exotic for seawater use. I believe Aqua Alarm has a check valve with magnetic switch to show open or closed.

 

[O C Diver]

If you have a strainer inside the boat with a removable lid and basket, add a couple of small floating plastic objects such as a kid's ball or fishing bobber. The water usually enters the strainer from the top and goes down through the basket. The floating objects will dance up and down with the flow of water. As the RPM and thus flow is constant, you should be able to spot reduced flow quickly.

Ted

 

[mvweebles]

I went a different route - I want to know when exhaust temps get too high for any reason. Borel Manufacturing (HERE) makes a nifty alarm that's easy to run and reliable. Triggers at 165F if I recall. They will make a panel for however many engines you have, and certainly two helms.

Peter

 

[Mac2]

Aqua alarm makes multiple sensors for your engine. One is a sensor on the raw water intake that sounds an alarm if the water stops flowing. You have to cut the hose to install it inline. I installed every sensor possible on my last boat (single engine). Very straightforward and the alarm is so loud you don’t need to run wires all the way to the helm.

 

[Stout]

On our Onan gen, there is a pressure switch on the discharge side of the pump. It shuts the gen down immediately when no pressure. It has saved us a couple of times when seaweed has plugged the through hull and when the impeller decides to shed its blades. We are down to a 60 hour replacement on the impeller. Our NL gen on our last boat had the same issue with impeller over about 60-70 hours. We only use Sherwood impellers from Fisheries Supply.

 

[slowgoesit]

If you have a strainer inside the boat with a removable lid and basket, add a couple of small floating plastic objects such as a kid's ball or fishing bobber. The water usually enters the strainer from the top and goes down through the basket. The floating objects will dance up and down with the flow of water. As the RPM and thus flow is constant, you should be able to spot reduced flow quickly.

Ted

Ted, that's brilliant! I've seen it done before, but forgot all about it. . .

 

[High Wire]

On our Onan gen, there is a pressure switch on the discharge side of the pump. It shuts the gen down immediately when no pressure. It has saved us a couple of times when seaweed has plugged the through hull and when the impeller decides to shed its blades. We are down to a 60 hour replacement on the impeller. Our NL gen on our last boat had the same issue with impeller over about 60-70 hours. We only use Sherwood impellers from Fisheries Supply.

60-70 hours? Something is seriously wrong there!

 

[Mac2]

On our Onan gen, there is a pressure switch on the discharge side of the pump. It shuts the gen down immediately when no pressure. It has saved us a couple of times when seaweed has plugged the through hull and when the impeller decides to shed its blades. We are down to a 60 hour replacement on the impeller. Our NL gen on our last boat had the same issue with impeller over about 60-70 hours. We only use Sherwood impellers from Fisheries Supply.

Have you tried the blue impellers? There supposed to be able to run dry for an extended period. They have them at Seattle Marine Supply. I haven’t tried them yet due to having numerous spares, but I can’t see how they could be worse. 60-70 hours is ridiculous-especially for a generator with such a good reputation.
Something to think about-my last boat (Manatee) would roll in big waves and suck air through the raw water intake and shut down. I installed a clam shell (scoop) intake strainer to force water into the raw water intake. This solved the problem for me. My boat only went 7 knots, so I was not that worried about forcing water past the impeller into the engine. This could be problematic on a faster boat.

 

[firehoser75]

TJM,
I installed 2 additional alarms on both main engine and generator. The Aqualarm flow alarm (alarms instantly if water flow stops - in time to "save" the impeller) and a Borel exhaust hose alarm. Both of these alarms saved me from potential issues and proved to be well worth it (for me).
The flow alarm sounded instantly when my generator (when at anchor) sucked in a small fish that totally stopped water flow. I was able to shut down the gennie before any damage occurred to the impeller. I tried many ways to remove said fish, but finally had to go for a swim and used a metal rod from below to "break up" the fish, resolving the issue.

The exhaust alarm on the main engine sounded to inform me of an exhaust hose overheat (no overheat anywhere else as confirmed using an IR thermometer). The cause was a failing exhaust elbow, that from the exterior looked brand new. At that time, my exhaust system setup (like many, many others) was poorly designed and was of the type that Tony Athens (from sbmar.com) calls "doomed to fail". If I had not had this alarm, I could have suffered a very expensive problem like saltwater ingress into the turbo or even the engine via the turbo and exhaust manifold. Other than looking via disassembly, I would not have known there was an issue without this alarm!!!
On the scale of boat expenses, these alarms are cheap insurance. I have no affiliation with any of the mentioned products or sbmar.com, just a happy customer.
Hope this info helps (anyone reading not just OP)

 

[Comodave]

I went a different route - I want to know when exhaust temps get too high for any reason. Borel Manufacturing (HERE) makes a nifty alarm that's easy to run and reliable. Triggers at 165F if I recall. They will make a panel for however many engines you have, and certainly two helms.

Peter
View attachment 136929

+1 on these. I have put them on my last 2 boats.

 

[Stout]

“ Have you tried the blue impellers? There supposed to be able to run dry for an extended period. They have them at Seattle Marine Supply. I haven’t tried them yet due to having numerous spares, but I can’t see how they could be worse. 60-70 hours is ridiculous-especially for a generator with such a good reputation.
Something to think about-my last boat (Manatee) would roll in big waves and suck air through the raw water intake and shut down. I installed a clam shell (scoop) intake strainer to force water into the raw water intake. This solved the problem for me. My boat only went 7 knots, so I was not that worried about forcing water past the impeller into the engine. This could be problematic on a faster boat.”

Mac, I have not tried them, are they the silicone units? I thought I had read the the silicone impellers spun off the shaft inserts. The intake on our boat is over 2’ below the waterline so I don’t think we have ever drawn in any air, even off the coast of WA in following seas.
I think it is because the pump housing is so small. I have replaced the pump assembly also, but at 50hrs I pulled the pump to check the impeller and the blades were starting to crack at the root and the round ends. Luckily it is only about a 20 minute job to R&R the impeller.

 

[Greg QS]

On our Onan gen, there is a pressure switch on the discharge side of the pump. It shuts the gen down immediately when no pressure. It has saved us a couple of times when seaweed has plugged the through hull and when the impeller decides to shed its blades. We are down to a 60 hour replacement on the impeller. Our NL gen on our last boat had the same issue with impeller over about 60-70 hours. We only use Sherwood impellers from Fisheries Supply.

?? woah

I have 2 nl gensets, Had a cummings in a previous boat. 2 year replacement cycle minimum 400 hrs on either . Time is normally the killer not run time.

You better disassemble your pump. You have a restriction. , a bad cam, or bad pressure plate or a discharge restriction.

 

[Greg QS]

I remember I had some issues on an old lister peeter genset spinning out the brass from the rubber. Wound up being a clogged exhaust manifold . It created to much back pressure and the rubber would cut loose from the brass. Never overheated untill brass would cut loose. Took me some time to figure out.

 

[Arc]

On our Onan gen, there is a pressure switch on the discharge side of the pump. It shuts the gen down immediately when no pressure. It has saved us a couple of times when seaweed has plugged the through hull and when the impeller decides to shed its blades. We are down to a 60 hour replacement on the impeller. Our NL gen on our last boat had the same issue with impeller over about 60-70 hours. We only use Sherwood impellers from Fisheries Supply.

There is no way 60 hrs life is right. That’s 1 week of use

 

[Jay N]

For WESTERLY's 5kw NL, a problem arose after about 5 years of ownership. Started needing to replace raw water impellers at 90 hours, then 57 hours, then 25 hours. The generator never shut down due to overheat, but was manually shut down whenever the exhaust produced a hollow sound.


Problem was that the raw water thru-hull valve was stuck in a partially closed position even though the handle was fully open. Turned out that the un-bonded valve was internally corroded, but with no outward appearance of corrosion. The need to replace impellers was simply a symptom of a restricted water supply.


As others have mentioned, there can be a restriction on the exhaust side as well that may well cause the same situation.

 

[Simi 60]

$30 temp alarm on exhaust elbow tells you if raw water has stopped
Probe is held onto elbow with electrical ties
Simple, cheap, effective.

 

[Comodave]

$30 temp alarm on exhaust elbow tells you if raw water has stopped
Probe is held onto elbow with electrical ties
Simple, cheap, effective.

That is exactly what the Borel alarm is.

 

[Simi 60]

That is exactly what the Borel alarm is.

Except not $30 (-;


The option I am talking of also has a number readout so you can visually see temp change before alarm goes off.
This can indicate say, 1 blade missing or slightly blocked filter

https://www.trawlerforum.com/forums/s6/cheap-engine-temp-alarm-38822.html

 

[Lepke]

When I check to verify an engines water flow, I feel the hose or pipe. It's always noticeably cooler.

 

[Portage_Bay]

When I check to verify an engines water flow, I feel the hose or pipe. It's always noticeably cooler.

As told to me by a mechanic for more experienced than I also your hand round the hose / pipe immediately after the water injection point. It should be a uniform temperature. Hot spots could indicate impending failure of the exhaust riser.

 

[TJM]

Wow, awesome response and advise. I looked at both alarms and will be purchasing them both this weekend once I confirm hose sizes. I will also place each system on my Lehmans for the same reason. THANK YOU

 

[Comodave]

Except not $30 (-;


The option I am talking of also has a number readout so you can visually see temp change before alarm goes off.
This can indicate say, 1 blade missing or slightly blocked filter

https://www.trawlerforum.com/forums/s6/cheap-engine-temp-alarm-38822.html

No but you can get WIF alarm and high water alarm for a very reasonable price.

 

[Simi 60]

The one I use on the main engine
Dual probe so one on exhaust elbow
And other on oil filter


https://engineguard.com.au/

 

[JadePanama]

$30 temp alarm on exhaust elbow tells you if raw water has stopped
Probe is held onto elbow with electrical ties
Simple, cheap, effective.

This is along the lines of what I added. We have a Maretron system, and I just added a temp module with temp probes attached along the raw water piping after the seawater pump. I have it set to alarm when temps rise above my safe threshold. added to both engines and both gens, and still had two open slots on the device to add 2 EGT sensors to the engines.

Not necessarily the simplest stand alone solution, but if you happen to have a system like Maretron in place, this is a super simple and relatively inexpensive addition and now flows into all my MFDs and Maretron system.

 

[Senojev]

Another Vote for the Blue Globe Impeller

Our Onan 9k genset on our NT 37 devoured Sherwood impellers in anywhere from 30 to 60 hours. One time in 10 hours! We thought it may be due to running dry until the pump primed but shutting the thruhull at the same time as shutting the gender down had no impact on impeller life. Cummins had no solution and I have heard other Onan owners in both NTs and other vessels have the same issue.

We changed to a blue Globe impeller five years ago and it has over 250 hours with no sign of any issues.

 

[MaDehn]

On my sailboat I have the aqua alarm. Works well and easy to add. Got tired of impellers and tied a 110 volt centrifugal pump to the generator output. When the generator runs long enough to produce power it starts pumping water. No muss no fuss. No impeller problems

 

[Steve DAntonio]

I went a different route - I want to know when exhaust temps get too high for any reason. Borel Manufacturing (HERE) makes a nifty alarm that's easy to run and reliable. Triggers at 165F if I recall. They will make a panel for however many engines you have, and certainly two helms.

Peter
View attachment 136929

I second this suggestion, these alarms are worth their weight in gold, you will get an alarm long before anything overheats, including the wet exhaust system itself, and it will sound before the genset's own auto-shutdown kicks in. You should have one on your engine(s) as well.

More here https://stevedmarineconsulting.com/onboard-alarms-part-i/

And here https://stevedmarineconsulting.com/wp-content/uploads/2014/03/ExhaustSystems170-FINAL.pdf

 

[backinblue]

There is no way 60 hrs life is right. That’s 1 week of use

It kind of depends. My generator does not get much use, and 60 hours could be 2 years worth. This season I'll try to run it more often whether I need to or not.