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Old 02-04-2013, 08:11 PM   #701
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Again, you have not defined economical. Money? Time? Purchase price? Ownership cost? Resale value?

Go to the archives and search out the stuff Eric has written about using two small engines in a displacement boat vs one larger engine. If it's done right-- and this includes the hull design--- two small engines can give a sufficient amout of power PLUS you get the advantage of a twin in terms of get-home and maneuverability, and you'll get this for either the same or perhaps even less fuel burn than the single engine version, given the engines that are usually put in these kinds of boats.

A theoretical example he's cited is putting two small engines in a GB36 vs one single FL120 (or Cummins 210 or whatever). As long as the speed desired is below hull speed, the two small engines will most likely be more efficient in terms of fuel use than the one larger engine yet you'll get the benefit of twin-engine maneuverability and redundancy.
economy: thrifty and efficient use of material resources : frugality in expenditures; also: an instance or a means of economizing : saving

as defined by websters. while websters dictionary may not be right i think that in this case they are the expert and I am the novice.

as for your two small engine example. Marin, it doesn't hold water. Two small engines are still turning twice as much machinery as one with the resultant friction losses requiring the expenditure of extra fuel. Fuel that a single would use to cruise more NM. In a nutshell. Granted that properly sized and engineered a twin can come close to the same fuel efficiency as a single, but, even Eric will agree, twins will require twice the expense of a single for maintenance as well as the extra fuel cost even if slight. oh, and then i forgot to mention the increased cost of a twin vs. single in regards to wear and tear. Guess what that would be Marin?....choices are, are they the same, or twice as much, or a cost greater than twice as much to reflect the extra load of engine systems not perfectly synchronized

Bottom line is you don't get something for nothing.

The only advantage of twins is maneuverability, and based upon what posters have indicated a greater get home ability if one engine fails. ..chuckle.....that is funny cause the truth is if you have a single how would you know that the other engine you have that broke down wasn't the one that's not there? With a twin they are both making noise in the engine room so when the noise lessons one knows a twin has died. Big letters Marin NOT ONE PERSON HAS MENTIONED ANY MAJOR ENGINE COMPONENT FAILURE ONLY MINOR THING LIKE STARTERS BELTS HOSES......all things one can easily replace if the spares are on board. and if not, its toonie time

i talk too much
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Old 02-04-2013, 08:13 PM   #702
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I've had both and underway I would prefer one. Near hard objects (docks) the twins will make you look like a stud!! I think the answer lies in how often are you docking and in what conditions. I was a demigod at docks in my single. Now I'm a God
....good point in a humorous way
thank you sir
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Old 02-04-2013, 08:16 PM   #703
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So, why don't automobile manufacturers put two engines in each automobile rather than one to increase efficiency?
That's a totally apples and oranges comparison. Automobile engines are not working or are hardly working most of the time. Some of them even have cylinders that "go offline" when the load is low So there is nothing to be gained economically by putting a second engine in a car because you don't even need the bulk of the output of the one engine most of the time.

Marine engines are "going uphill" all the time.

You don't maneuver a car with the engines and directional thrust, you turn the wheels. You don't need a get home engine in a car because if the engine craps out you go off to the side of the road and call a tow. The road and the wind aren't going to carry you into potential danger as you sit there.

So there would be no advantage I can think of to putting two smaller engines into a car instead of one properly sized engine for a whole lot of reasons including cost, complexity, etc.

A twin engine GB36 does not burn twice the fuel of a single engine GB36 assuming the same type of engine in each. And, for a cruise speed less than hull speed, it doesn't take much power to push the boat along. So while this sort of thing is not my forte I would not be surprised if Eric could demonstrate that putting a couple of 25-30 hp engines in a GB36 would move the boat at an efficient less-than-hull-speed cruise while together burning less fuel than the FL120 or Cummins 210 that is the typical engine used in these boats for both single and twin-engine versions moving the boat along at the same speed.
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Old 02-04-2013, 08:18 PM   #704
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I don't believe that (yet). So, why don't automobile manufacturers put two engines in each automobile rather than one to increase efficiency? (Batteries and electric motors are not engines, so don't come from there, please.)
Delta logic, can't be beat. Thanks Mark
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Old 02-04-2013, 08:28 PM   #705
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That's a totally apples and oranges comparison. Automobile engines are not working or are hardly working most of the time. Some of them even have cylinders that "go offline" when the load is low So there is nothing to be gained economically by putting a second engine in a car because you don't even need the bulk of the output of the one engine most of the time.

Marine engines are "going uphill" all the time.

You don't maneuver a car with the engines and directional thrust, you turn the wheels. You don't need a get home engine in a car because if the engine craps out you go off to the side of the road and call a tow. The road and the wind aren't going to carry you into potential danger as you sit there.

So there would be no advantage I can think of to putting two smaller engines into a car instead of one properly sized engine for a whole lot of reasons including cost, complexity, etc.

A twin engine GB36 does not burn twice the fuel of a single engine GB36 assuming the same type of engine in each. And, for a cruise speed less than hull speed, it doesn't take much power to push the boat along. So while this sort of thing is not my forte I would not be surprised if Eric could demonstrate that putting a couple of 25-30 hp engines in a GB36 would move the boat at an efficient less-than-hull-speed cruise while together burning less fuel than the FL120 or Cummins 210 that is the typical engine used in these boats for both single and twin-engine versions moving the boat along at the same speed.

your explanation is not supported by common sense The exstra cost of twins is not limited to just fuel, the fact is all other costs are twice as much with fuel being just a little bit more. That no one not even you can refute.
rest my case.
Ok gang what the verdict?
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Old 02-04-2013, 08:32 PM   #706
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However, this is a new question
No. It is NOT a new question...
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Old 02-04-2013, 08:36 PM   #707
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Greetings,
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Old 02-04-2013, 09:11 PM   #708
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Big letters Marin NOT ONE PERSON HAS MENTIONED ANY MAJOR ENGINE COMPONENT FAILURE ONLY MINOR THING LIKE STARTERS BELTS HOSES......all things one can easily replace if the spares are on board. and if not, its toonie time
All three of our precautionary shutdowns were caused by situations that could not be remedied on-the-spot. And two of them were totally removed from and had nothing to do with the engine itself. In each case we came home on the other engine. Had we had a single, each case would have required a tow to port.

And you have blown this "twins cost more to operate, service and maintain than singles" business way out of proportion in my opinion. In our case, servicing means 12 additional quarts of oil and another filter. In the overall scheme of the cost of boating, that's not even an additional cost worth considering. It's virtually free.

Our two engines burn not that much more than the same boat with one of the same engines because to go the same speed the single engine has to work harder, thus burning more fuel. But even if it was, the cost of fuel compared to the overall cost of boating is also damn near free, even at $4 a gallon.

True, you have two sets of parts wearing out instead of just one, but they don't all wear out together so it's not like you're presented with this huge bill every x-years. And the really big expenses---- new engine mounts, new exhaust systems, new shafts, bearings, etc.---- don't come around very often. Maybe never depending on the condition of the boat when you buy it and how long you keep it.

So based on our 14 years of having the boat we have now, I just don't see the cost difference between one and two engines as being a big deal. Moorage, insurance, ground power, the boat's systems--- plumbing, electrical, electronic--- and overall maintenance costs--- paint, brightwork, tools. new lines, dinghy motor tuneups, haulouts, bottom paint, etc., etc. etc,--- far outstrip over time the service and maintenance costs of the engines. Compared to all that, the additional cost of running a second engine is negligable.

Reasons favoring a single---more engine room space, easier service and maintenance access, more protected prop and rudder, quieter, less vibration, simpler electrical system, lower purchase price (usually)--- are far more significant in terms of deciding between one and the other than the cost difference between running one and running two in my (and my wife's who keeps the books) opinion.
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Old 02-04-2013, 09:30 PM   #709
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Obviously: Two engines are better than one for acceleration, maneuvering and take-off/landing (i.e. docking). Ask any bird.

That turtle simply needs bigger twins, more rpm, and a smaller body!
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Old 02-04-2013, 09:47 PM   #710
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Greetings,
Mr. Art. Hmmmm....interesting point...So what you're saying is TWINS are more maneuverable...
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Old 02-04-2013, 10:12 PM   #711
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Greetings,
Mr. MM. In reference to your post #692...
  1. Cephalopods (cuttlefish, squid, octopus and nautilus) have three hearts, two that pump blood to the gills and one that pumps blood round the rest of the body. Their blood is blue.
  2. Earthworms have multiple hearts, one in each segment of their body.
  3. And the hagfish (a slimy sea creature looking like a cross between an eel and a slug) has four hearts, two brains, a skull but no backbone. I would never question Gaia's wisdom.
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Old 02-04-2013, 10:56 PM   #712
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RTF---And while the Cephalopods have three engines, they have eight or ten drive systems and that makes them amazingly maneuverable. No crashing into docks and looking stupid with these guys.

And the hagfish which apparently has four engines, two plotters, a radar and no keel is obviously far better suited for a life at sea than some silly twin-engine Grand Banks with a half-wit at the wheel.
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Old 02-04-2013, 11:13 PM   #713
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Greetings,
Oh Mr. Marin. Now you're just being silly...
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Old 02-04-2013, 11:40 PM   #714
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Greetings,
Mr. MM. In reference to your post #692...
  1. Cephalopods (cuttlefish, squid, octopus and nautilus) have three hearts, two that pump blood to the gills and one that pumps blood round the rest of the body. Their blood is blue.
  2. Earthworms have multiple hearts, one in each segment of their body.
  3. And the hagfish (a slimy sea creature looking like a cross between an eel and a slug) has four hearts, two brains, a skull but no backbone. I would never question Gaia's wisdom.
Mr. RT, Esquire,

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Old 02-05-2013, 01:03 AM   #715
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why don't automobile manufacturers put two engines in each automobile rather than one to increase efficiency?
Good Grief! Thread resuscitated!

Clearly auto makers are in error. If I had 2 engines I could walk the car sideways into tight parking spots, or enter my garage without doing violence to the power steering on full lock (Peugeots need a football field like space for a U turn).
Auto makers will have to invent "wheel wash",typical maneuvering speeds are not fast enough for four wheel drifting.
Long live the thread!
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Old 02-05-2013, 01:14 AM   #716
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Clearly auto makers are in error.
Imagine motorcycles with an engine powering each wheel!
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Old 02-05-2013, 01:15 AM   #717
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If one has two boats w 200hp one w 2 engines and one w one engine the difference in fuel efficiency will be very small and not worth talking about so why am I talking about it???????????????????????????????????????????????? ???

Seems obvious to me as the differences in all the variables are extremely small. With specific boats and engines either example could be most fuel efficient.

I'm sure a GB 36 w twin Yanmar 4JH 55hp engines would be more fuel efficient that a GB 36 w one FL120. And that's more efficient that a GB w 2 FL120s. Just the slightly better fuel efficiency of the Yanmars would make the Yanmar powered boat most efficient. Don't everybody buy your Yanmars at the same place and keep in mind that it may take 110 years to pay for a small part of the re-power cost.

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Old 02-05-2013, 03:06 AM   #718
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Good Grief! Thread resuscitated!

Clearly auto makers are in error. If I had 2 engines I could walk the car sideways into tight parking spots, or enter my garage without doing violence to the power steering on full lock (Peugeots need a football field like space for a U turn).
Auto makers will have to invent "wheel wash",typical maneuvering speeds are not fast enough for four wheel drifting.
Long live the thread!
3 point turn on an 8 lane highway ay Bruce? Haha :-D
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Old 02-05-2013, 07:00 AM   #719
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Even a 25% difference in efficiency is meaningless to a 200 hr a year slow boat owner.

3 GPH vs 4GPH WOW!
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Old 02-05-2013, 07:47 AM   #720
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I'm going to toss a new wrinkle in the subject. The often stated and presumed assumption is that twins mean more friction and mechanical loss due to the second set of running gear, etc. I'll buy that, it's a no brainer, but WAIT!!

What about the fact that most of our boats have the single engine running gear mounted behind a big old keel. Disturbed water!! Singles are running in clean water well away from the keel. Aha an efficiency gain. Do they cancel each other out? They may well.
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