One engine cruising (dragging prop)

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tundrarules
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One engine cruising (dragging prop)

Post by tundrarules »

When you guys cruise at low rpms, one engine off, do you put the dead engine transmission in neutral or leave it in gear so the prop doesn't spin? Not sure which is best.

Thanks


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1985 29 Sedan
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TinLizzy
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Re: One engine cruising (dragging prop)

Post by TinLizzy »

It is best to put it in gear. If not, the tranny turns the whole time and there is no water going through the cooler.
Rodney
1975 28 Express-Twin 350 Chevy's, SOLD
1990 32 Express--Twin Mercruiser 454 with Bravo I outdrives
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Busia
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Re: One engine cruising (dragging prop)

Post by Busia »

With the Borg Warner Velvet Drive, the manual says that there is no problem to run with one engine off and the transmission in neutral. Put the shifter in gear and I don't think much will happen without the engine running. You need the engine running to turn the hydraulic pump in the transmission to make hydraulic pressure to engage the clutch plates. The clutch plates clamp down and send power to the output.
BUSIA
located in Ketchikan, Alaska. Gods country
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EWRice
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Re: One engine cruising (dragging prop)

Post by EWRice »

As Busia said, it does not matter on a hydraulic transmission. If the input shaft is not being turned by the engine, the transmission defaults to full neutral. This is the case with all hydraulic transmissions, including automatic trans in cars and trucks.
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TinLizzy
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Re: One engine cruising (dragging prop)

Post by TinLizzy »

My bad! I stand corrected.
Rodney
1975 28 Express-Twin 350 Chevy's, SOLD
1990 32 Express--Twin Mercruiser 454 with Bravo I outdrives
Portage Canal Waterway-Upper Peninsula,Lake Superior
Aquaholic
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Re: One engine cruising (dragging prop)

Post by Aquaholic »

Interesting topic to me. Can I assume that the reason for doing this would be to reduce fuel usage? If so, does anyone have actual data / stats for how much or if this made ant significant difference with their boat? We are planning an approximately 800 mi month long trip this Summer and we plan to take our time cruising slowly. Is there an advantage to running on one motor at a time?
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Re: One engine cruising (dragging prop)

Post by EWRice »

I don't do it so much for fuel savings. I don't like idling my engines too much. V8 engines in boats have certain rpm ranges that are "sweet spots". 900-1500 seems to be the low sweet spot while 2800-3200 rpm is the high end sweet spot. Below that you run the risk of excessive wear from low cylinder temps. In between the low and high ranges you tend to build high cylinder pressures and high bearing loads. Above the high range and you are just pushing the design limits under load.

In my boat, running one engine at no wake speed keeps me up around 1000 rpm. The boat is much quieter, too. I would be willing to bet that one engine at 1000 rpm would use noticeably less fuel than two engines at 700 rpm, over an extended trip.

I would be curious to hear from people who have done this.
Muskegon Lake
1972 32' Express flybridge
"AL13"
Twin 318s
On board air & prime 920
1963 Thompson Super Sea Lancer
Graymarine 327
1961 Alumacraft 12'
'55 10hp Johnson
Fastjeff
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Re: One engine cruising (dragging prop)

Post by Fastjeff »

About the only way you stop that dead engine's prop from rotating would be with a mechanical lock of some kind, and that would cause wasteful drag. I ran one motor regularly at my previous marina (that had a 2 mile no wake zone). Better on gas, and the boat just sounds better. I relite the dead motor only when it was slip time.

Jeff
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bcassedy
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Re: One engine cruising (dragging prop)

Post by bcassedy »

EWRice wrote:I would be curious to hear from people who have done this.

EW ...

Don't have the info that you're looking for but, if you'd like, can get it for you in early May when we launch. Our boat's on the hard at Rivertowne Marina on the east side of Cincinnati. We'll be taking it downriver to our summer marina at Lighthouse Point Yacht Club in Aurora, In. Distance is 33.5 miles (MM 465.5 to MM 499). We can do half that trip on 1 engine and the remainder on 2, maintaining the same speed we normally cruise at (9MPH). We've got a Floscan on board and can determine the total gas usage for each leg of the trip and report back, if you'd like.

Bill
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barkleydave
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Re: One engine cruising (dragging prop)

Post by barkleydave »

Over many years I have played with 1 vs 2 engines.

If you are trolling for fish... by all means drop to one engine and idle only. You want your speed slow slow slow!

If you are trying to maintain 9 knots approx. then 2 is the best. Running on one engine much above idle is diminishing returns. Dragging a wheel increases drag as speed increases. You then have to counter your rudder to steer ahead which further increases drag. Fuel savings is minimal if any and the additional run time to your destination pretty much cancels out the 2-5 10th of a mpg savings.

Now I have done with it a twin with diesels.. and it works out better. Diesels have much more torque and low speed and turn larger wheels. I found with a twin trawler I could drop to one and still run at 6 knots (which is a slow cruise) and the mpg increased about 30 percent.



Also if cruising you will in most setups only be charging one of your battery banks.

This is only my opinion and your results may vary :)

safe boating,
dave
1987 Marinette 29 FB Sedan
Retired Boat Accident UL and USCG trained investigator
Retired USCG Captain
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