saving fuel

[Capt Ratty]

What would be wrong with running on one engine for an hour, then switching to the other eng for an hour. Slow speed, maybe 8 knots. Fuel savings?
Longer eng life? No harm to trans?
41' TC with 6v/53. Typically burns 1 gal. per mile with both engines @ 8 knots.

Thanks

 

[REBrueckner]

Lots of posts on this topice....fuel savings ARE minimal or non existent...

 

[67hat34c]

once i finish hooking up flow scan to gps then I will try it. I would doubt there is any savings however due to prop dragging. I know that on Freebird we ran at 10mph on one engine and got unbelievable economy. However the prop on the dead engine was removed.

Still cant believe how little fuel we burned in 32 hours of running that 1271 N at 1400 rpms. Never calculated the burn but we never switched tanks and if i remember right we only burned mabe half to 3/4 of the tank we were drawing from. Will have to ask the Bird about that.

 

[mix]

What would be wrong with running on one engine for an hour, then switching to the other eng for an hour. Slow speed, maybe 8 knots. Fuel savings?
Longer eng life? No harm to trans?
41' TC with 6v/53. Typically burns 1 gal. per mile with both engines @ 8 knots.

Thanks

I think the trany that isn't running has to be stopped by some means from turning-or will harm it. We did this several times on my friend's 45' Hatt-when he lost an eng. -and had to get home on one.Mix

 

[fishin Hatt]

Yes you have to stop the shaft from turning !!! The engine runs the lube pump for the trans. If it spins from water friction it could damage your trans. check your trans manual it should show "Come home screws" on trans. which will stop he shaft from turning.

 

[Canuck Dennis]

On my 43 dc with 6-71 n's, we ran on two at 9-10kts burned about 15 gph, ran on one and burned 7 gph at 7.5 to 8kts, smooth waters.

With twin disc tranny's one can run 2-4 hrs on 506 models, then start engine to re-lube. then shut down or use that engine and shut down the other, prop drag when free wheeling is minimal.

On the twin disc 514 models, 8 hrs is max on one engine before re-lubeing etc.

DM

 

[Canuck Dennis]

On my 43 dc with 6-71 n's, we ran on two at 9-10kts burned about 15 gph, ran on one and burned 7 gph at 7.5 to 8kts, smooth waters.

With twin disc tranny's one can run 2-4 hrs on 506 models, then start engine to re-lube. then shut down or use that engine and shut down the other, prop drag when free wheeling is minimal.

On the twin disc 514 models, 8 hrs is max on one engine before re-lubeing etc.

DM

 

[Capt Ratty]

Well, we got conflicting reports on this. I would think at slow speed of 8 knots, there would not be enough wash to heat up the trans. I will check to see what tranny I do have. At any rate it sounds like it may be worth a try. I will like to here the results of a flow meter.

Thanks to everyone responding.

 

[REBrueckner]

Capt Ratty..before you risk your trannies, and undergo the hassels, read prior threads on this topic...Some posts have actual NMPG with one engine, with two engines, with freewheeling and with prop locked via flo scan data. If you really want to save fuel, run slower. Allisons cannot be freewheeled; Warner Velvet can be, but I'd never do it.

 

[krush]

Well, we got conflicting reports on this. I would think at slow speed of 8 knots, there would not be enough wash to heat up the trans. I will check to see what tranny I do have. At any rate it sounds like it may be worth a try. I will like to here the results of a flow meter.

Thanks to everyone responding.

The problem is that the transmissions are not splash lubricated like a car manual transmission (or an outdrive on an I/O). The bearings requires the pump to pump the oil around and get oil to the bearings. The same is true of almost ALL automatic transmissions in cars...though some old cars and benz's had pumps on the output shafts and you could push start them.

if you install a small auxilary pump, and it wouldn't take much, to circulate fluid to keep the bearing lubed then you could free-wheel all day.

 

[Pascal]

"On my 43 dc with 6-71 n's, we ran on two at 9-10kts burned about 15 gph, ran on one and burned 7 gph at 7.5 to 8kts, smooth waters."

this is not a fair comparison becasue the fuel burn between 7.5 to 8 kts and 9 to 10 kts is VERY different, especially on a 43 where hull speed is closer to 8 kts. Even between 9 and 10 knots, your fuel burn will go up by at least 20% vs 10% speed increase.

if you compare the exact same speeds, you will see that the differences are minimal, if any.

and as discussed MANY times, most transmissions require locking up the shaft unless you want to burn the bearings.

also, if you're going to try to push the boat over 7.5 kts on one engine, your'e going to have push that engine harder and maybe on the edge of overloading it.

it's no big deal to run on one engine if you have to otherwise, dont' bother.

 

[Capt Ratty]

Ok, we don't want to break anything.
How long can I run at 8 knots, 1500 RPM, and not load up the engines.
Just blow them out for 10 minutes before getting to port?

 

[Pascal]

Naturals or Turbos? as long as they are running at normal temp, it's no problem... 1500 is warm enough for my 8V71Ns

 

[Capt Ratty]

Yes, they are naturals and run at operating temps.

Thanks for all your help.

 

[fishin Hatt]

Capt Ratty..before you risk your trannies, and undergo the hassels, read prior threads on this topic...Some posts have actual NMPG with one engine, with two engines, with freewheeling and with prop locked via flo scan data. If you really want to save fuel, run slower. Allisons cannot be freewheeled; Warner Velvet can be, but I'd never do it.

I'd like to read those posts about this topic......Anyone know where to find them???

 

[REBrueckner]

I searched but could not find the thread(s) but I KNOW at least ONE is here because I remember posting my own results...and seeing basically the same results from others...as well as flow scan data from one poster...and a discussion of freewheeling efficiency vs shaft/prop lock efficiency to which I contributed....One issue was how to lock a shaft so in an emergency it can be quickly unlocked....but the overall result was that running one one engine produced no measureable improvement in NMPG.