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Running on one engine

GAS engine, transmission and generator repair and maintenance discussion forum.
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nolacarver
Scurvy Dog
Scurvy Dog
Posts: 19
Joined: October 6th, 2013, 6:49 pm
Vessel Info: 1979 33' carver
New Orleans, LA

Running on one engine

Postby nolacarver » October 9th, 2014, 4:14 pm

Does anyone have an opinion about slow speed cruising on one engine for economical purpose ? I heard some say it is bad for the dead gear box . thanks for any advice!

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Lyndon670
Admiral
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Joined: July 29th, 2013, 11:35 pm
Vessel Info: 2000 Carver 506
Volvo TAMD74EDC
Location: Georgian Bay
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Re: Running on one engine

Postby Lyndon670 » October 10th, 2014, 11:04 am

First off, it will not damage your opposing transmission. There is no connection between the engine and the transmission while in neutral - and as it is neutral, the shafts can spin "freely". Think of a motor home towing a car, or when you are coming into dock and have one engine in neutral and the opposing in gear.

As for the economy - not so much. Our hulls are planning hulls. They are designed to run efficiently while on plane - where most of the boat is above the surface. If you look at a single engine trawler, it has a large, high torque Diesel engine that bumps along at a low speed where it creates the most torque. Torque is what moves your boat. Trawlers are designed like a sailboat hull, either displacement or semi displacement. They are most effecient while in the water - below the surface.

Also, single engine boats have the engine and transmission, fuel tanks etc running the centerline if the vessel. Twins are mounted on each side, along with the accessories.

It's not a matter of "I get 8 knots in my boat with both engines running at 1200rpm, so I can go much farther if I shut one engine off". If you can get 8kts on twins at 1200 (example), it might take 1500 to get 8kts on one engine in your boat. Further to that, your boat will always try to turn to the direction of the motor that isn't running, so you will always be correcting the helm. With only one engine running, you will loose manouverability. You will drain one tank quicker than the opposite tank, causing stability issues.

At the end of the day, any of the boats in this forum that are badged "Carver" - are designed to run the way they came off the assembly line. If economy is your concern, run both engines as low RPM as is practical for you, or get her up on plane and pull the throttles back until you find the sweet spot - where she is barely on plane and the RPMS are lower.

Or stay at the dock and enjoy some cocktails - that's when boats are most economical!
Lyndon,
2000 Carver 506
FOXY JOE
Volvo 7.4TAMD
Queens Cove Marina
Georgian Bay, Ontario
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nolacarver
Scurvy Dog
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Posts: 19
Joined: October 6th, 2013, 6:49 pm
Vessel Info: 1979 33' carver
New Orleans, LA

Re: Running on one engine

Postby nolacarver » October 13th, 2014, 3:37 pm

Thanks for the reply. Not sure that coktails dockside with my crew is the most economical option. LOL..
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crquisto
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Vessel Info: 2000 Carver 406 Aft Cabin, twin 7.4 gas Mercruisers - Flyboy II
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Re: Running on one engine

Postby crquisto » October 14th, 2014, 2:54 pm

I've been told that the transmission is not a problem, but that there's is no cooling water to the driveshaft bearing if the engine is not running, so with the prop freewheeling, you'll damage your bearing. All good points by Lyndon670, but this might be an even bigger consideration. Any more inputs?
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Lyndon670
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Volvo TAMD74EDC
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Re: Running on one engine

Postby Lyndon670 » October 14th, 2014, 6:13 pm

A good point, but since it is not under load from the transmission, it won't be spinning anywhere near the speed of the opposing loaded prop. I could see this being a concern if the shaft RPM was high, but it won't be. There will be only drag turning that prop and it won't even be close to the speed of the opposite.

There is no such thing as a free lunch when it comes to boating. If the difference in running on 1 engine vs 2 engines is enough to think about, boating isn't for you. I spend $2000/year on diesel fuel on my 506 and use it every weekend. I spent the same on gas on my Silverton before my Carver. If fuel went up an extra $1000 and I couldn't afford it - then I can't afford it now and should sell.

Boats cost a ton to maintain, depreciate like a rock, drink fuel (power boats) like there is no shortage, and cost a pile to keep moored in a marina. I wise old boater once told me that if I can stomach standing in my shower and ripping up $20 bills as the water soaks through my clothes, then I will enjoy boating. If not - buy a motorhome.
Lyndon,
2000 Carver 506
FOXY JOE
Volvo 7.4TAMD
Queens Cove Marina
Georgian Bay, Ontario

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