Alternating Engines while Underway

“Not all boats are the same”
Indeed I may not even be a trawler guy if that was the case.

What would make this “run one of two” practice better or even possibly good would be a boat designed for that. A slight change may be a vast improvement and that’s positioning the propellers inbd quite close to C/L. May require angling the shafts and engines a bit to have good servicing space. With so many boats now having thrusters twins w the props well appart is’t necessary.

I've got a bunch of dives on this one. Its got 4 prime mover diesels and just 2 shafts. Think of the efficiency experiments one could run... before it sank.

Was a much better dive in the late '80s, before the weather deck collapsed into the ER.

Commercial fishermen having reliable diesels is based on reputations made when diesels were much simpler. Usually 100% mechanical, no circuit boards, electronic sensors and so on. Most current and new fishing boats are built with twins, especially those operating in remote dangerous waters. Almost all engines used commercially are heavy duty rated and can operate at light or heavy load without much, if any affect on engine life. Unlike small diesels.
My Detroit Diesels are 70 years old, overhauled once at 65 years. A previous owner cruised every year Canada to Mexico at 300 rpm over rated hp.

I get better economy with both at low rpm than one unless at trolling speed.

We use two engines when needed, otherwise I travel using only one engine running between 1750-1850RPM. On our return trip, I just reverse the engines used. This RPM moves our boat at about 7K, now that is impressive when I consider we didn’t move much faster than 5K with our sailboat.

The up side is enormous. First the engine wear is greatly reduced because of reduced hours couple with reduced load when operating. Of course this is also reflected in our fuel consumption. At 2800RPM with both engines pushing the boat to about 12K our fuel burn is around 0.4 MPG. At 1800 with one engine fuel economy jumps to 1.5MPG. OK, under this condition our speed is slower than what most others travel at. That matters not, we are not racing anybody and find half the fun is just getting there.

Nomad Willy said:

If you’re engine’s too big why not downsize. Two smaller engines or for the out of the box crowd how bout one small engine on one side and a bigger engine w the prop closser inbd giving colse to asymmetrical thrust w both engines running.
Just say’in .. Just think’in.

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The cost of change-over can be prohibitive.

Many (most?) folks -- especially those who've bought from the secondary (i.e., used) market -- are faced with running whatever engine(s) came in the boat. Removing fully-functioning engine(s) X to replace with engine(s) Y or Z or whatever can be fairly expensive.

For either little gain, or only significant gain over a really major length of time.

-Chris

diver dave said:

I've got a bunch of dives on this one. Its got 4 prime mover diesels and just 2 shafts. Think of the efficiency experiments one could run... before it sank.



Was a much better dive in the late '80s, before the weather deck collapsed into the ER.

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Okay that’s just gratuitous. Also, I loved it.

Proper frog kick. Proper stages. Hey, I see two vastly different cultures represented, given the gear configuration and you guys obviously get along. Impressive. Nice to see the dark period of the mid 90’s bearing fruit after all those that we lost.

Videos like this are superb.

Easy when there is no current. I’ve since broke down my doubles and just do side mount now. Tougher in wrecks but makes more caves doable and much easier ground handling.

ranger42c said:

The cost of change-over can be prohibitive.

Many (most?) folks -- especially those who've bought from the secondary (i.e., used) market -- are faced with running whatever engine(s) came in the boat. Removing fully-functioning engine(s) X to replace with engine(s) Y or Z or whatever can be fairly expensive.

For either little gain, or only significant gain over a really major length of time.

-Chris

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Hey Chris I was talking about building new boats designed to run single or twin. Relatively small changes in design could vastly improve running on one engine when you have two.

Of course if you found the right boat say a twin w bad engines but was a very nice boat presumably you’d get it really cheap.

Twins are alive and well whether planing or displacement M/V. In fact this is where the market is if one looks around. As we cruise Alaska the best guess I have is 19 out of 20 recreational M/V are twins.

BTW, the best example of running a twin engine boat as a single is a Nordhavn. Yup that well engineered smaller diesel provides a great example of shutting down an engine. Many Nordhavns though have and are being built with same size twins and no get home. Ditto the larger Krogens.

None of this means you can’t shut an engine down and ghost along to save a few bucks per day. But most twins are set up with alternators and electric that require both engines to be running.

I had an interesting talk with a commercial fisherman yesterday. On his Delta he had a genset that matched his main for HP draw. The genset runs hydraulics, freezer compressor as well as the high KW lights. Point being, there are many ways to provide power for a vessel. For the serious minded two or more forms of power generation are the rule. Yes, sails provide power too.

Last but not least, gosh there are lots of triple outboards around.

I guess. It depends. If you are running your boat at slower displacement speeds than what it was designed for. Likely your Motors are not getting up to preferred operating operating temperature. Possibly leading to glazed cylinder walls. Running one motor at the same speed you would run your twins would put more load on that motor. Likely making the motor healthier. Probably not much difference in fuel consumption

Most diesels like to run at about 80% load. If I had time and just on a leisurely transit I would rather one one engine to keep some load on than two at a very low load each. In the ‘80s my two screw US Navy Destroyer frequently went in “trail shaft” mode to conserve fuel if we were not in a rush. Eco speed (most economical speed) has been the way of the commercial world for many years now. So yes, it’s horses for courses, but if all the right aspects of the operation are there it is a perfectly reasonable operating mode.