Single vs Twin: It's Baaaaack!

[markpierce]

My Perla is happy with our single engine. Strong, high railings are more relevant to her (as well as my) sense of safety.

 

[MurrayM]

Nature is the best at design, and although there may be species that double things up like eyeballs, lungs, or testicles, I don't believe there is one with two engines, or hearts.

Gotta go with the wisdom of Gaia on this one!

 

[bfloyd4445]

Chose wisely and the wife will support anything you chose to do. Go cheap and she'll be constantly worrying and asking "What happens if the engine breaks?"

Twins every time in my book.

...well said...
if she is prone to seasickness that may result in the purchase of the queen mary, if funds warrant..well maybe taking up a new hobby like soap operas may be the end result if she owns you.

currently with me it was boats or her, I chose boats and she is still there. She even boats on occasion. I had boats first she is second!

 

[bfloyd4445]

Nature is the best at design, and although there may be species that double things up like eyeballs, lungs, or testicles, I don't believe there is one with two engines, or hearts.

Gotta go with the wisdom of Gaia on this one!

i like your words Murry. Good point.

 

[Marin]

Marin, this issue is not regarding your wife it is regarding which ic a better choice in an economy cruser a twin or a single.

I'm afraid I'm going to have to say that if you do still not realize the totally personal reason for making the choice, but believe there is some "formula" for arriving at your answer, then it might be time for you to think about getting into another pastime.

Because you have to define economy, too. Is it more economical to have two engines and come home under your own power in the event of a problem than deal with the risk, expense, and hassle of coming home on a rope?

If you get a boat with two smaller engines there's every chance it will burn less fuel than a boat with one bigger engine. We burn 5-6 gph with two engines for 8 knots. Our good friend Carey with the lobsterboat burns 11-12 gph (IIRC) with one engine to get 13-15 knots.

Which boat is more economical? The one that burns 5-6 gph and takes for frickin' ever to get anywhere or the boat that burns twice that fuel and goes nearly twice as fast? What's more economically important to you--- time or money?

You're looking for an answer that nobody can give you because someone like Carey may think the economy of time is far more important to him than the economy of cost, while someone else may desire to keep their boating cost as low as possible and are willing to spend a lot more time getting places to do it. And in Carey's case, the economy of time is being realized with a single engine boat with a great big engine in it while in our case the economy of cost (which we don't care about) is being realized with a twin engine boat. So singles vs twins isn't even an economical argument, sometimes.

But I will give you my answer to your questions as to maneuverability and get home advantage giving the edge to a twin over a single being worth the (not that great) added expense. Absolutely, 100 percent, unqualified YES.

 

[bfloyd4445]

I'm afraid I'm going to have to say that if you do still not realize the totally personal reason for making the choice, but believe there is some "formula" for arriving at your answer, then it might be time for you to think about getting into another pastime.

Because you have to define economy, too. Is it more economical to have two engines and come home under your own power in the event of a problem than deal with the risk, expense, and hassle of coming home on a rope?

If you get a boat with two smaller engines there's every chance it will burn less fuel than a boat with one bigger engine. We burn 5-6 gph with two engines for 8 knots. Our good friend Carey with the lobsterboat burns 11-12 gph (IIRC) with one engine to get 13-15 knots.

Which boat is more economical? The one that burns 5-6 gph and takes for frickin' ever to get anywhere or the boat that burns twice that fuel and goes nearly twice as fast? What's more economically important to you--- time or money?

Your looking for an answer that nobody can give you because someone like Carey may think the economy of time is far more important to him than the economy of cost, while someone else may desire to keep their boating cost as low as possible and are willing to spend a lot more time getting places to do it. And in Carey's case, the economy of time is being realized with a single engine boat with a great big engine in it. So singles vs twins isn't even an economical argument, sometimes.

ok so we we qualify the original question by stateing at displacement speeds. We are not asking which is superior but which is more economical.
Marin, I'm just seeking to mine the vast experiance of our very knowledgeable forun members.

My thanks to everyone for taking the time to answer what at some times might seem like dumb questions

 

[Marin]

We are not asking which is superior but which is more economical.

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.

 

[BruceK]

My thanks to everyone for taking the time to answer what at some times might seem like dumb questions

Repetitive rather than dumb, I think.
Anyway,that post certainly sounds like closure of the thread. I wish.

 

[Daddyo]

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

 

[markpierce]

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.)

 

[bfloyd4445]

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

 

[bfloyd4445]

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

 

[Marin]

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.

 

[bfloyd4445]

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

 

[bfloyd4445]

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?

 

[CPseudonym]

However, this is a new question

No. It is NOT a new question...

 

[RT Firefly]

Greetings,
"It's Alive!!!" - YouTube

 

[Marin]

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.

 

[Art]

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!

 

[RT Firefly]

Greetings,
Mr. Art. Hmmmm....interesting point...So what you're saying is TWINS are more maneuverable...

 

[RT Firefly]

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.

 

[Marin]

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.

 

[RT Firefly]

Greetings,
Oh Mr. Marin. Now you're just being silly...

 

[MurrayM]

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,

I guess even Nature, once in a while, has to chuck spaghetti at the wall to see what sticks

 

[BruceK]

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!

 

[MurrayM]

Clearly auto makers are in error.

Imagine motorcycles with an engine powering each wheel!

 

[Nomad Willy]

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.

Keep on Trawl'in.

 

[Hendo78]

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

 

[FF]

Even a 25% difference in efficiency is meaningless to a 200 hr a year slow boat owner.

3 GPH vs 4GPH WOW!

 

[Daddyo]

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.