Running Generator While Under Way

[Montenido]

Hi folks,
I have a pretty dumb question, but I could not find it in any of the searches. Is it acceptable to run your genny while under way? I have twin Cat 3208s with small alternators, so the alternators will top off the start batteries, but probably not the house bank for shorter trips.

If I run the genny while moving from one spot to another I will arrive with everything topped up I would expect. I'm just wondering if there are any downsides to running while under way.

I'm still working on a solar set up, but have yet to pull the trigger.

Thanks in advance, and please be kind .

Cheers, Bill

 

[drb1025]

Yes, if you want to run AC/heat, top off batteries, heat the water, cook on your electric stove, etc. I run mine while underway usually when I need heat from the reverse cycle units.

 

[Giggitoni]

Yes. There are times when I run the genset to top everything off (refrigeration, house batteries, etc.) before entering an otherwise quiet anchorage.

 

[psneeld]

Many vessels start it before their main and leave it running till plugged in....or longer if having to anchor/moor away from power.

 

[Alaskan Sea-Duction]

I believe they are designed to run while underway....Good luck on your solar....

 

[ulysses]

On single handed prolonged journeys I will run a gen usually twice in a 24 Hr. period (alternating gen sets) for about 45 minutes each run. This usually tops off all battery banks, maintains refrigerator, heats water and such.

 

[Ski in NC]

No harm in running it underway, that is completely normal use. It is better for it to at least occasionally run at 50-80% load, not good for it to run light load like batt charging all the time.

 

[wyoboater]

I like to allow my batts to run things for awhile.........constantly topping them off isn't good for them, but, when they get below 50% or so (or if I want a/c) I'll fire up the genny whether underway or not. That's what they're designed to do..........And, as previously posted, running the genny under load is good for it. Genny's with very low hours compared to the engines be a scarey thing.

 

[Gull]

Caution

One note of caution:
You should first check what style of strainer is installed on the genset raw water intake.
Most should be a flat plate style strainer, but I have heard of a scoop type also being installed.
If you have a scoop type strainer which faces forward, the forward velocity of the vessel will cause the raw water to enter the system under pressure which can force water into places it shouldn't be..
I'm not sure how common this is, but it's worth checking before starting up the genset at 7 knots.

 

[rwidman]

One note of caution:
You should first check what style of strainer is installed on the genset raw water intake.
Most should be a flat plate style strainer, but I have heard of a scoop type also being installed.
If you have a scoop type strainer which faces forward, the forward velocity of the vessel will cause the raw water to enter the system under pressure which can force water into places it shouldn't be..
I'm not sure how common this is, but it's worth checking before starting up the genset at 7 knots.

I had that discussion with the marina manager just recently. Not about my boat, but about a friend's boat. He maintained that the scoop should face forward, my argument was that it shouldn't for the reason you mention.

 

[High Wire]

If there is a problem, you'll never hear it until you stop the mains.

 

[Gull]

Fortunately I have a flat plate strainer - I would probably replace a scoop with a flat plate irrespective of the direction the scoop was facing. I wonder about the efficiency of the water pump pulling in raw water with a rear facing scoop.

 

[BandB]

We run our generators nearly all the time we're underway. HVAC, Freezers and Refrigerator, Washer and Dryer, Watermaker, Thrusters.

 

[psneeld]

actually if you did have a forward facing scoop strainer...running the genset would be better than not...the forced water (if greater flow than the pump was pushing) would be blown out with the exhaust rather than back filling the cylinders.


But correct...gensets generally don't have scoop strainers...mine is just an open thruhull to seacock...not external strainer at all.

 

[sunchaser]

Gennys with very low hours compared to the engines be a scarey thing.

Why?

 

[psneeld]

gross generalization but I can relate.....


many friends take pride in how few hours they have on their gensets but assure me they will start and run fine because they start them up every month to circulate the oil.


Like so many things in boating...there are just so many that really don't get it.

 

[sunchaser]

gross generalization but I can relate....

Our genset has about 1/4 the hours of the mains. We don't sit at anchor running the thing 24/7. Normally we are cruising 6 to 12 hours per day with on engine alternators more than able to keep the batteries charged while we are motoring along.

When anchoring for the night, we run a bit less than an hour for downtime activities and same in morning to top off batteries and hoist anchor. Our deficit is about 250 daily amp hours at 12V. With about 160 amps of max charging capacity 1.5 to 2 hours of genset run time is normally all we need.


For serious cruisers with a well set up inverter, battery bank and charging system 1/4 ratio is not uncommon. For sit at anchor and watch TV 1: 1 is quite common. So much of this though relates to boat, style and equipment.

 

[Bay Pelican]

There are times on night crossings/ and or heavy fog when I have both radars, autopilot, navigation computer/monitor, and all the lights I have turned on that my batteries are not being topped up. Run the generator and charge the batteries. May be less of a requirement now that I have LEDs but haven't thought about it since the changeover.

 

[bayview]

Common to run genny while underway here especially in summer to keep the boat cool.

 

[O C Diver]

One note of caution:
You should first check what style of strainer is installed on the genset raw water intake.
Most should be a flat plate style strainer, but I have heard of a scoop type also being installed.
If you have a scoop type strainer which faces forward, the forward velocity of the vessel will cause the raw water to enter the system under pressure which can force water into places it shouldn't be..
I'm not sure how common this is, but it's worth checking before starting up the genset at 7 knots.

This is wrong. Water is incredible heavy. You would have to be going very fast to generate enough velocity pressure to lift the water up and over the anti-siphon break. Usually this break is 18"+ above sea level.

If there was any risk of this happening the tow boat captain would require you to close your engine seacock before he started towing you.

Ted

 

[markpierce]

You guys must have huge electrical draws if your engine's alternator isn't sufficient when underway, necessitating simultaneous use of the genset.

 

[BandB]

You guys must have huge electrical draws if your engine's alternator isn't sufficient when underway, necessitating simultaneous use of the genset.

Yes, we do.

 

[Capt.Bill11]

I had that discussion with the marina manager just recently. Not about my boat, but about a friend's boat. He maintained that the scoop should face forward, my argument was that it shouldn't for the reason you mention.

It depends on the type of "scoop" you both are talking about. There are those designed for engine use that can face forward while underway. And there are those that are not designed for engine use while underway and should only be used on say an air con raw water intake thruhull.

 

[bligh]

I just spoke with a friend who's #3 cylinder was seized on his genset. Turns out he was in some nasty weather and seawater worked its way up through the exhaust into his generator. I figured running his genset (or closing the seackocks) would have prevented this.

I'm a fair weather boater for the most part, but I think I would feel more secure if i ran my genset along with my main when the weather was got a little nautical. Im not afraid to put hours in my genny.

 

[capt jerry]

i dont think that the water can get by the raw water pump impellers that much with a front facing scoop when the genny is shut down.they are pretty tight aganist the housing unlessthey are worn out?

 

[psneeld]

yes water can get by an impellor.


front facing scoops for a genset are often considered a no no for planning vessels, maybe semi displacement vessels and probably no big deal on 8 knots and below displacement (but why take a chance)


Sunchaser....yep...4:1 is not out of line at all...probably the 20:1 main(s) to genny that raises some eyebrows....thought that's more along the lines we were talking when saying grossly different...

 

[Ski in NC]

You do not want a fwd facing scoop on a gennie. Water can and will push past the impeller. Aft facing scoop almost as bad as it can suck water from water lift muffler into exhaust manifold. Best no scoop and a siphon break.

Water getting into gennies paid for the construction of my boat. So trust me, it happens. And water won't get into it with it running. On some boats with marginally safe installs, I told them to run the gennie if underway whether they need it or not, at least the running engine keeps water out of itself.

Regarding hrs, I almost never run my gennie while underway, the ME alt and inverter do the job. But anchored out, gennie might run all night. Interesting that ME now has 2280hrs, gennie has 2040hrs, not too far apart considering they don't run together.

 

[MYTraveler]

Many vessels start it before their main and leave it running till plugged in....or longer if having to anchor/moor away from power.

Same here. It is important to adequately load your generator. Depending on your electrical demands relative to the output of your alternators, you may be better off running the genny only after the batteries have run down a bit.

 

[Hawgwash]

I run mine while underway usually when I need heat from the reverse cycle units.

Does your reverse cycle produce adequate heat here on the coast for winter cruising?

 

[drb1025]

Does your reverse cycle produce adequate heat here on the coast for winter cruising?

Yes, they produce good heat all winter. I was a little concerned about the water temps when I bought the boat, as the units become inefficient and stop working as water temp reaches around 40 degrees, but I have never had an issue. The water here is generally mid-40s in the winter. I was recently talking with a local boater that was getting ready for his fourth Alaska trip and his heat source was also reverse cycle. He said he has never had an issue with heat even in SE Alaska. That surprised me, although I am planning to install a Wallas diesel heater for a supplemental heat source before we make that trip.