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Old 01-14-2019, 08:59 AM   #1
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Mainship 430 twin engine

I have been told I could run just one engine at a time to reduce where and tear. Is this possible without incurring any damage?
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Old 01-14-2019, 09:03 AM   #2
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The drag of the running gear would decrease performance. I would also look at whether you can free wheel your transmission, or whether you would need to lock it off. A locked off prop is going to create a lot of drag.

You're going to put a lot of load on one engine in order to avoid 'wear and tear'. These engines are designed to run for thousands of hours. I'd run the boat the way it was designed to run.
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Old 01-14-2019, 09:08 AM   #3
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Thanks, looks like more research is needed.
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Old 01-14-2019, 09:19 AM   #4
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Originally Posted by Captains Quest View Post
I have been told I could run just one engine at a time to reduce where and tear. Is this possible without incurring any damage?
The best way to eliminate wear and tear is to religiously keep up with the book maintenance, read up on engine specific issues on boatdiesel, and run just below hull speed (1600 RPM ?).

What engines and hours do you have?
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Old 01-14-2019, 10:14 AM   #5
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I have attached a pdf of a graph of the fuel consumption for two different twin engine boats both with one engine or two operating. Bob Lowe, a former boat yard owner prepared the Alaskan data. The graph shows little difference in fuel consumption.

The only advantage and it is minor is reduced maintenance due to one engine not running. The disadvantage is that you load the running engine more which increases wear which is the opposite of your throught.

My advice is: forgetaboutit.

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File Type: pdf Fuel economy graph- one engine vs two.pdf (53.4 KB, 20 views)
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Old 01-14-2019, 11:03 AM   #6
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We used to charter a 430 in Northern California frequently. Many happy memories. Had a failure of the neutral switch once up in the Delta by Rio Vista. Continued the multi day trip up to Sacramento and back to Alameda on one engine. The boat had Floscans, so I was able to do a little comparison both from memory, and then double checked on the next charter. For any given speed, I didn't find much difference at all, don't recall specifics, as that was 16 or 17 years ago. I might find notes in our log book if I can find it when I am back home in 10 days. Engines were Caterpillar 3116.
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Old 01-14-2019, 01:20 PM   #7
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The engines on this boat are Catapiller 3116s
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Old 01-15-2019, 06:04 AM   #8
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The manual on my MS 400 says that, when being towed, do not allow the transmission to free wheel. Damage may occur to the transmission.
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Old 01-15-2019, 09:19 AM   #9
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First realize that your speed must be reduced in order to steer and not overload the one engine.

second various transmissions have differing requirements for freewheeling or not. Most will do it at slower speeds for limited distances. measuring tranny temps helps as does alternating engines every several hours. Some boats docked in strong currents sometimes freewheel a lot. The trans maker is the best source of an answer for your specific model. Experiments on sailboats have shown that freewheeling prop creates more drag than a locked prop.

Third you will save minimal fuel at the lowest speeds.


fourth rotating parts engine wear for properly set up and run boats is not significant and they will outlive you is properly maintained.


If you want long life engines slow down.
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Old 01-15-2019, 10:16 AM   #10
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Since we’re ex-sailboaters our normal speed is around eight knots. We figure anything above that is a bonus
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Old 01-15-2019, 10:40 AM   #11
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If the boat is propped right there is no danger of overloading either engine. If you have pss or tides shaft seals make sure you have an isolator so that the running engine doesn’t pump seawater into the non running engine. If you have twin disk gears you can fill the non running gear to the gills and monitor the temps. Lastly you can lock down the prop shaft and the drag is not as bad as people think.
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Old 01-15-2019, 10:55 AM   #12
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If the boat is propped right there is no danger of overloading either engine.

I assume you mean that there is no danger of overloading either engine while running on one. Not true.


Being propped right means that the engine(s) will reach rated rpms at wot or better. If you take a twin engine boat that is propped right running on two engines, then it will run at less than rated rpms at wot because it takes more power than one engine can produce to hit rated rpms. So it is overloaded.


Is it a problem? Probably not as long as you keep the rpms down to less than 60% of rated rpms which is what it should take to reach hull speed with one engine.


David
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