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Old 02-25-2016, 11:40 AM   #1
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Running Generator While Under Way

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
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Old 02-25-2016, 11:51 AM   #2
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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.
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Old 02-25-2016, 12:46 PM   #3
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Yes. There are times when I run the genset to top everything off (refrigeration, house batteries, etc.) before entering an otherwise quiet anchorage.
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Old 02-25-2016, 12:49 PM   #4
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Many vessels start it before their main and leave it running till plugged in....or longer if having to anchor/moor away from power.
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Old 02-25-2016, 12:54 PM   #5
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I believe they are designed to run while underway....Good luck on your solar....
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Old 02-25-2016, 01:06 PM   #6
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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.
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Old 02-25-2016, 01:09 PM   #7
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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.
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Old 02-25-2016, 01:58 PM   #8
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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.
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Old 02-25-2016, 03:06 PM   #9
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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.
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Old 02-25-2016, 03:15 PM   #10
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Quote:
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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.
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Old 02-25-2016, 03:17 PM   #11
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If there is a problem, you'll never hear it until you stop the mains.
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Old 02-25-2016, 03:27 PM   #12
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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.
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Old 02-25-2016, 03:38 PM   #13
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We run our generators nearly all the time we're underway. HVAC, Freezers and Refrigerator, Washer and Dryer, Watermaker, Thrusters.
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Old 02-25-2016, 04:07 PM   #14
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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.
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Old 02-25-2016, 04:15 PM   #15
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Quote:
Originally Posted by wyoboater View Post
Gennys with very low hours compared to the engines be a scarey thing.
Why?
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Old 02-25-2016, 04:33 PM   #16
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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.
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Old 02-25-2016, 04:55 PM   #17
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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.
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Old 02-25-2016, 05:17 PM   #18
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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.
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Old 02-25-2016, 05:52 PM   #19
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Common to run genny while underway here especially in summer to keep the boat cool.
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Old 02-25-2016, 06:10 PM   #20
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Quote:
Originally Posted by Gull View Post
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
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