anybody crusing with one engine off?

H

houston water boy

New Member
Nov 5, 2012
11
kemah and galveston texas
Boat Info
2004 480 sedan
11ft boston whaler
Engines
cummins QSM 11
I have a 04 390 MY with 480CE cummins running thru ZF 280-1A transmissions. Trying to slow down in my seasoned age and keeping some of my money for more trips causes me to ask this question. Single engine appears to work fine, just don't know about the trans sitting in neutral and I imagine the prop is feewheeling, is that ok or not?
I know on my vehicles I tow behind motorhome only a few certain vehicles can be towed while trans in neutral.
This has turned out to be an incredible cruising boat as long as I keep it "trawler" speed )7-9knots) which is what what the real world seems to be crusing! However it still is a beast when ya gotta get somewhere.
:huh:
 
I have seen this question asked before with various answers. I would call or email the transmission manufacturer for their recommendation. Also if you have dripless shaft logs they should have the cross over cooling line to feed the idle shaft when in neutral.
 
The majority will tell you that running on one that slow will not net you very much more fuel economy since one engine is working harder than two just lugging along. With the cummins in that boat you are probably at 7-9 knots at about 1000 rpm? I'd just run both and save your transmissions and shaft logs without having to worry about explaining the Hour difference in motors when you go to sell it.
 
Cross over would only apply if he shuts the engine down that is in idle. If you keep the engine running the dripless shafts ,even if they are plumbed independently, will receive cooling and your trans will still circulate the oil to the trans cooler so no problems. If you want to shut it down (which I assume you would) and want to make sure your shaft log and trans receive no damage, you can lock the shaft from spinning in the ER.
 
My last boat had digital fuel flow meters, so I determined efficiency with one engine vs both engines spinning the props. That was a few years ago, but the bottom line was that one prop under power and the other free wheeling (blocking the prop would probably create more drag) was only marginally better.
 
Not sure how true... but I've read (maybe here) that running on one will place undue wear on the shaft bearings. It makes since to me with the constant strain while trying to keep the boat moving straight.
 
I have come in on fumes once on one engine, just bumped into gear, gennie off. The other engine was off and the transmission in gear. It was a slight problem to keep her straight but not insurmountable. The only reason I did it this way is because the engines are fueled from different tanks. Both engines at calculated hull speed will probably be most comforting overall.
 
I too would like to know the official answers to these questions. One of the considerations when cruising long hours and long distances is building huge hours on the engines. Shutting one down will cut that in half.
 
I don't agree John, it will mean more hours on the engine. If you travel 25 miles at 25 mph, you put on 1 hour on both engines. If you do that tip on one engine going7-8-9 mph, you will be OVER 2 total hours of engine use. (you will however probably save fuel)
 
The hull speed for our boats (44-45' at the waterline) is just under 9 knts. So with both engines on we can attain that at around 1000 or so rpm's. At those rpm's we are burning very few gph.
 
katricol said:
The hull speed for our boats (44-45' at the waterline) is just under 9 knts. So with both engines on we can attain that at around 1000 or so rpm's. At those rpm's we are burning very few gph.
Click to expand...

How does one calculate that? I would like to know for the days I just want to bore holes in the water for hours on end without worrying about the next gas stop!

TIA
 
I don't think the OP was looking to necessarily go the same speed with one engine as he would at idle with both. He may willing to give up some speed for efficiency. In my comparison I didn't attempt to have the boat travel at the same speed. It was slower (obviously) with the one engine at idle vs both, but still the numbers didn't support the idea that in a 100 mile stretch that the fuel bill would be all that much less with one engine only - it would just take that much longer to get there!
 
My hull speed is about 7.4kts, which I can get @900RPMs-1,000RPMs, obviously running on both engines in AVG conditions. Total fuel burn at those RPMs is 3.8GPH. I never tried to cruise on one engine in attempt to get the speed of 7.4kts due to similar question OP posted. I never took the time to find if my transmission can free wheel without internal damages. I'll try to get the answer and want to see how my boat will perform. One time when I was out fishing I trolled for some time using one engine to slow down my speed. I remember that my idle speed on one engine was around 3.5kts. If my memory serves me right, my normal idle speed on both engines is around 5-5.2kts.

The question whether you'll save a lot of fuel will most likely depend on the speed you're trying to achieve. IMO, as long as one keeps the working engine under or at 1000RPMs the saving might be there. I think John's point was that if the idea is to go slow then using one engine will save you half of the hours.

Regarding the difference in the engine hours it's very easily to manage by alternating the engines (go from point A to point B on port engine and comeback on stbd engine).

As far as I know cross over cooling will take care of the shaft on the side with the engine off. So, my only concern at this point is to know for sure what's the deal with transmissions when engine is off and the shaft is free wheeling.
 
We enjoy running slow 1200 RPM (cocktail speed) at 7 MPHand about 5 GPH. If we have bad weather on the horizon or late to the restaurantwe kick up to 3500 RPM, 27 MPH at 32 GPH.
When we are on the boat we are where we want to be so whyhurry?
 
When I go in my long fishing trips (200-300 mile round trip) I do the majority at hull speed which most conveniently is also ideal trolling speed. I basically double my fuel range and economy this way.
 
katricol said:
I don't agree John, it will mean more hours on the engine. If you travel 25 miles at 25 mph, you put on 1 hour on both engines. If you do that tip on one engine going7-8-9 mph, you will be OVER 2 total hours of engine use. (you will however probably save fuel)
Click to expand...

Now for the rest of the story: living near the big bend in Fl, we are limited as to where we can go when we cross the Gulf on plane. If we show down,w can go anywhere. On a direct path, we could save 1/2 the time and 90% of the fuel if we go slow. If we go on one engine at a time, we save 1/2 of the engine time at sailboat speeds, but straight lines.
 
I was told by the delivery captain you want to place a little load on my gas engines, specifically the transmissions. He said ideally 1500 rpm's for slower idle. I don't boat in a no wake zone and my engines are gas. He said it was harder on the transmissions than running at around 1000 rpms.
 
It takes "x" amout of btu's of energy to move "x" amout of wieght at given distance in a given time. Running with one engine off anything above displacement mode would not be worth it.
 
I agree with VinceR-we run both engines at the cocktail speed with auto pilot-whyhurry?
 
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