Who? I have never seen an actual test where there was a significant difference at the same speed. A few guys on the Hatteras owners Forum tried it. I once had the need to do this test myself on a chartered Mainship 430 with Floscans over the course of 120 miles when one engine wouldn't start. I don't have the stats anymore, but it was basically a push, at some speeds slightly better with two.
Improvement how? In fuel efficiency? My results, and those of others was a push overall in actual consumption. with the twins, as you got closer to hull speed, actually outperforming (Cat 3116 in this case). Think of it this way, it essentially takes a certain amount of HP to drive the boat a given speed.And a certain amount of fuel to generate that horsepower. In addition, the single engine operation on a set of twins now requires rudder to maintain course, causing the single to have to "crab" the boat forward. This is likely what caused the twins to outperform at higher speeds.
I'd say hull form , distance between the props and the prop configuration itself are the biggest differentials, and why a variety of different tests yield different results. Some transmissions do not allow freewheeling, but require the shaft to be locked with the engine off, so there is another possible factor.
So I would never generalize that one out of two engines is better than two.
You said you'd never seen a test where there was a significant difference in efficiency at the same speed. I cited two tests that were documented in considerable detail here on T-F that netted in the range of 10-15% (in fuel efficiency). While that's not a large improvement....it's not always a "push". Obviously, the results depend on many factors (add rudder size/efficiency and engine configuration to your list).
One Vs Two
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eyschulman
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Note first two sentences above. While I do own a boat with twins I also own two with singles and in the past have cruised and lived aboard a full displacement trawler with single motor with a very fuel efficient drive train. Actually the boats I have owned numbering over 20 have been single to twin in a ratio of 10/1. So I appreciate both sides of the twin single arguments. What I have pointed out is that you can have a boat with twins and still have good fuel burn numbers even better than some if not many of the boats thought of on this site as trawlers and therefore fuel efficient. There are many factors that influence a boats fuel burn and what I point out is that the single twin option is not the major factor. Many point out that twins have more drag and I wonder if that big unusually wide keel and rudder that has to offset prop side thrust on a single is drag free. The extra weight of twins will effect fuel burn but all in all on a practical basis I agree with Tony Fleming the fuel burn difference if it exists is not enough to discourage the choice of twins.
psneeld
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Parasitic/skin drag drops way off the slower you go...thus the whole argument starts to fall apart unless specific speeds...in fact everything concerned....are addressed.
Even hull shape starts to become less important the slower you go...like the post in another thread that sowed the effort to move a planning hull at very slow speeds isn't much different than a full displacement.
So wasted motion, wasted friction, prop inefficiencies, etc etc...CAN, but not NECESSARILY can add up to make equal footing (efficiency) very difficult.
Flemmings wouldn't be as popular as a 8-9 knot (only) boat...and the price puts it out of the "worried about fuel costs crowd" unless they are cruising around the world every year.
Even hull shape starts to become less important the slower you go...like the post in another thread that sowed the effort to move a planning hull at very slow speeds isn't much different than a full displacement.
So wasted motion, wasted friction, prop inefficiencies, etc etc...CAN, but not NECESSARILY can add up to make equal footing (efficiency) very difficult.
Flemmings wouldn't be as popular as a 8-9 knot (only) boat...and the price puts it out of the "worried about fuel costs crowd" unless they are cruising around the world every year.
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Well put ps
As our twin 34' Tolly planning hull does near 3 nmpg at 5.5 to 6 knots on one engine and about 2.5 nmpg at 7 knots on two engines (7.58 knots is math calced "hull speed")... that suffices for me regarding efficient cruising.
When I want/need to get some place due to time schedule I can cruise her at 16 to 17 knots (or even a bit above) on full plane with approx 1 nmpg consumption. Also, Tolly's hard chine, quick return hull shape makes for considerable comfort in seas as well as wakes while running or at anchor. We appreciate its hull design's hard return much more than high-degree rolling back and forth of a round bottom. Also, with ability for nearly instant higher speed adjustments our Tolly's nimble ability to deal with tall wakes of oncoming or passing big-fast boats is greatly increased compared to displacement hulls that do not enable so much immediate hull position alterations on tall wake waves.
For a self-contained, capable, and very reasonable purchase price as well as a low maintenance cost boat… it is my and my wife’s considered opinions that Tollycraft 34' tri cabin fits the (our) bill!
Happy Boating Daze! - Art
Nomad Willy
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I know where you're going Tom and probably like most I suspect. Looking at the Hobbs and taking note of fuel purchaseses in gallons. I think most everybody does that thinking their non-cruising time is inconsequential. But it's usually not ... IMO.
But also in Art's case his boat is light (comparatively) and has a rather narrow beam at the WL. So his boat is somewhat ideal for what he is doing.
But also in Art's case his boat is light (comparatively) and has a rather narrow beam at the WL. So his boat is somewhat ideal for what he is doing.
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For me the conventional wisdom on the whole 1 vs 2 engine passage maker was driven by Beebe. After I crossed to the dark side from sailboats he became my reference and consequently I wanted no part of any twin engine boat. Well now having owned one for 2 1/2 years, and having done the same trips on a single engine version of my boat I've concluded that 2 engines are a luxury and I'm willing to pay for that. For me the small difference in fuel efficiency with regards to maximum range between fuelings are more than offset by the advantages of twin keels twin rudders twin hydraulic pumps and propulsion redundancy. Last month when a dock master in the Bahamas guided us to a slip that was a little shallower than normal with the spring tides we ran aground 20' into the slip. As the tide rose we attached lines and pulled her in and then secured her for 2 days. No worries about heeling over for four hours each low tide cycle.
Via iPhone.
Via iPhone.
What is odd about the new JD Tier III 4045 spec sheet is that it is not in the same format as previous versions. I have spec sheets for a couple of the older engines and they are consistent in format. The Tier III is the odd ball, in more ways that one. In the grand scheme of things, loosing the precision is not really that important, just slightly frustrating/questionable.
Seeing a new engine that is less fuel efficient as the older engine is frustrating. I wonder if these engines can be tweaked to improve fuel burn after installation....
Later,
Dan
Ski in NC
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Seeing a new engine that is less fuel efficient as the older engine is frustrating. I wonder if these engines can be tweaked to improve fuel burn after installation....
Later,
Dan
I've pondered that too. Nice thing about CR is EVERYTHING regarding fuel injection parameters is in the ECM. Timing, flow rate, multiple injections, whatever. So a "tuner" like in the trucks can get in there and fiddle with fuel map. Or find a ECM for a third world export engine, those "might" be optimized for burn and not emissions.
Can't see much of an environmental benefit to minimizing NOx and yet increasing CO2. Seems absurd on its face.
ranger58sb
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Another generalization that often isn't true in saying older engines get better economy than new. On larger engines Common Rail has changed things dramatically. MTU's, MAN's and CAT's are generally more fuel efficient today than they were in the past. The fact is engines evolve and there may be one change, even due to regulation, that lowers efficiency while there are others improving it. The manufacturers learn to deal with the changes.
Weren't Catalytic Converters supposed to ruin fuel efficiency on cars? In a vacuum they might have hurt it but manufacturers don't operate that way.
It's like outboards. In spite of the negatives, 4 strokes are generally more efficient than 2 strokes. But then, you have Evinrude E-Tec and it probably is the most efficient outboard today.
I hear the praises of old engines, but I'll take the new ones.
Weren't Catalytic Converters supposed to ruin fuel efficiency on cars? In a vacuum they might have hurt it but manufacturers don't operate that way.
It's like outboards. In spite of the negatives, 4 strokes are generally more efficient than 2 strokes. But then, you have Evinrude E-Tec and it probably is the most efficient outboard today.
I hear the praises of old engines, but I'll take the new ones.
And if you roll in the additional or more frequent serving and maintenance that's needed on the old generation diesels, whatever advantage they may have in terms of fuel usage (if any) can disappear under the added cost of operating them in terms of labor, time, parts, etc.
READY2GO
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Maybe I am ill informed or biased (or both), but I would think the annual maintenance of a new diesel with all the new gadgets and aftercoolers and such would be considerably more than say an old Fl 120 or Perkins or such.
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Must be the dirty pictures.
Maybe you should just unblock it, Dauntlessatsea.wordpress.com
I don't change oil while underway. Period.
Simply no point.
With a range of 2500, that equates to a bit more then 400 hours. Easy Pesey.
400 continuous hours versus 200 hours of start, run, off, cool, sit, then repeat numerous times.
READY2GO
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I was thinking the normal oil change for a FL120 was 100 hours. That has always seemed too frequent to me but that is what I have done. I could understand 100 hours if it had a capacity of 6 quarts, but with 3 gallons it seems overkill.
psneeld
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it is....and there are those that will argue that...even me...
my engine oil analysis guy says going to 200 would be fine...but that's my engine and how it is being used...I have been at around 150 for the last 2 trips to/from Florida between changes.
like about every other topic here...it depends. 400 hours non stop is probably less hard on the engine and oil than 100 hours, 2 hours at a time with days or weeks between.
Ski in NC
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In analyzing actual dyno reports, the data simply do not support that. I have not done anything with MAN or MTU, but with Cummins and Cat, the newer emission rated engines are no better or slightly worse. But that varies with the models, and also the differences are fairly small.
I think the theory is based on the fact that the new generation engines don't need servicing and new parts and such nearly as often as the old engines. Sort of like new cars vs old cars.
And the oil change interval for an FL120 is called out in the operators manual as being 200 hours, not 100. Some people, including us, change the oil in their FL120s more frequently than 200 hours, but 200 is the interval called for by Lehman.
The oil change interval for the injection pump is 50 hours. But that takes only a few minutes to do and involves only about a half a quart of oil.
Wxx3
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Yes, the manufacturer learn to deal with the changes and you pay for it.
Let's have a little test. We'll make it multiple choice.
Which is the correct answer?
Modern engines are better than the older generation engines because:
A. they will last longer
B. they are less expensive to fix
C. they are less expensive to make
D. they have longer maintenance periods
E. All of the above
F. None of the above
I look forward to the results.
Now, to get back to single versus twin. It's real simple. If the ONLY concern is fuel efficiency, it is impossible to increase the parasitic losses and have the same fuel efficiency.
In other words, two is always less efficient than one.
As an aside that I'mn sure Marin will jump in on, if increasing engines could even keep the same efficiency, then why are are so many airlines flying us all over the place, with only two engines? Because it's safer and the airlines care so much about us?
markpierce
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Some (like myself) feel comfortable riding in either a single-engine automobile or boat, but not in a single-engine plane or a non-engine glider (done both). While others (like Marin) are NOT comfortable in a single-engine boat but are comfortable in a single-engine airplane or automobile. People are weird.
psneeld
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Though I know Marin has other reasons for preferring twins....your point is comical.
I love the luxury of twins...sure would relieve a bit of stress with my cruising plan...but just not in the cards for me at this point.
But spend enough time on TF and the point about people being weird is the all time most correct point made....for a lot of reasons.
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Nomad Willy
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The buyers of new boats want twins. They can afford it and buy twins. They have no problem paying for the boat or the fuel to run it.
Then .. Years later the boats are owned by folks that hardly have the money to maintain them and because most twin engined trawlers have a second engine the same size as the single engined boat. And of course the twins burn more fuel and people blame it on the fact that the boat is a twin. Whereas they really should be blaming the builder for selling boats w too little power or too much power. If you build a boat w X amount of power you need to change the hull design if you double the power assuming the boat was originally powered correctly it would be overpowered. Or the reverse of that. My boat is correctly powered and if you halved her power she'd definitely be underpowered. So underpowered I wouldn't want the boat. It's more clear cut w FD boats as they have a narrower range of required power. With SD boats and some hulls one could find a boat that for example needed about 150hp that may be powered by a 100hp engine or engines or 200hp engine or engines. But the same boat w 75hp or 250hp would not be properly powered.
IMO a good example of being correctly powered would be a 36' trawler w single or twin options of about 150hp to about 200hp. Single 200, twin 75, single 150 or any other combination from 150hp to 200hp. Some people like faster boats and some prefer range or slower speed. But 100% variation is too much.
I agree w eyschulman that some twins are more fuel efficient than some singles and the the fact that they are twins has very little to do w their fuel efficiency. Assuming boats of the same total power are compared.
The above is my opinion only and some cost of building and other marketing considerations were not considered.
Then .. Years later the boats are owned by folks that hardly have the money to maintain them and because most twin engined trawlers have a second engine the same size as the single engined boat. And of course the twins burn more fuel and people blame it on the fact that the boat is a twin. Whereas they really should be blaming the builder for selling boats w too little power or too much power. If you build a boat w X amount of power you need to change the hull design if you double the power assuming the boat was originally powered correctly it would be overpowered. Or the reverse of that. My boat is correctly powered and if you halved her power she'd definitely be underpowered. So underpowered I wouldn't want the boat. It's more clear cut w FD boats as they have a narrower range of required power. With SD boats and some hulls one could find a boat that for example needed about 150hp that may be powered by a 100hp engine or engines or 200hp engine or engines. But the same boat w 75hp or 250hp would not be properly powered.
IMO a good example of being correctly powered would be a 36' trawler w single or twin options of about 150hp to about 200hp. Single 200, twin 75, single 150 or any other combination from 150hp to 200hp. Some people like faster boats and some prefer range or slower speed. But 100% variation is too much.
I agree w eyschulman that some twins are more fuel efficient than some singles and the the fact that they are twins has very little to do w their fuel efficiency. Assuming boats of the same total power are compared.
The above is my opinion only and some cost of building and other marketing considerations were not considered.
... if increasing engines could even keep the same efficiency, then why are are so many airlines flying us all over the place, with only two engines? Because it's safer and the airlines care so much about us?
In your poll, I'd pick "all of the above."
Airlines like twin engine airplanes because they are less expensive to operate than three and four engine airplanes. They are not "safer," although the newer generation engines, which go on both twins and four engine planes like the 747-8 and A380, have benefited greatly from technology advances in both efficiency and reliability.
(I put the term safer in quotes because it's actually not a term the industry, particularly the airframe and engine manufacturers, likes to use. The preferred term is "reliable.")
But the bottom line is that today's turbofans are powerful enough to fly large twins as far as you'd ever want to ride on one (a plane only has to be able to go halfway around the world, after that any range increase is somewhat pointless). And they are so reliable that two provide as much redundancy as three or four.
The rule for how many engines a commercial transport has to have is basically this: the plane has to be able to lose one engine at the most critical point during a full-gross-weight takeoff and continue the takeoff and climb to a safe altitude and fly on the remaining engine.
A four engine plane does not have four engines to make it safer, it has four engines so it can fly. And the same rule applies--- a four engine plane has to be able to lose one engine and continue the takeoff and climb on the remaining three. If it loses two engines out of the four, it's in a world of hurt.
Advantages to the airlines of twin engine planes are pretty far ranging--- fewer spares in inventory, shorter turnaround times, simpler (aka lighter) on-board systems, more efficient wing, reduced emissions, reduced maintenance costs.... the list goes on for a long time.
One parallel to our boats is that the fewer the number of engines on a plane the more work those engines have to do. So where the turbofan engines on a the four-engine 747-8 each generate a maximum of about 67,000 pounds of thrust, each turbofan on the twin-engine 777-300ER generates a maximum of 115,000 pounds of thrust.
The Grand Banks we chartered before buying our own boat was a single. I was fine with it. I have no issues with single engine boats in terms of reliability or maneuvering. I am totally "comfortable" in a single engine boat.
However, I don't like them. And the reason I don't like them is operating them is dead boring to me. I like operating equipment, and the more complex that equipment is the better I like the challenge of learning and mastering its operation.
When we decided to buy our own boat we didn't care if it was a single or a twin. The boat we'd been chartering was a single, the canal boats we'd started running in England and Wales are singles, and this was all just fine.
As it turned out, the boat that best met our requirements and what we wanted to spend on a boat was a twin. I was a little apprehensive when we got it as I'd never run a twin engine boat before. A good friend--- the founder of Kenmore Air--- who had a twin engine, steel-hull deFever, told me in response to my expressing my apprehension to simply, "Go out and start using it. You'll figure it out just fine."
Which is what happened. And I also learned hat I REALLY liked operating a boat with multiple engines (our newest boat has three which is even more fun).
So my preference for multiple engines has nothing to do with being comfortable or feeling safer, it's because running a multi-engine boat is really cool.
The fact we don't have to come home on the end of an expensive rope if an engine has to be shut down is a great bonus, but it's not the reason I prefer multi-engine boats.
My wife, however, has stated that she is more confident in a boat with more than one engine under the floor. And a happy wife makes for a happy boating experience. But she has owned single engine planes and has never balked at the idea of flying into rough country in a single engine plane. Why she is fine with one engine in a plane but doesn't want one engine in a boat is something she's never been able to explain.
The reason we fly a single engine floatplane is that it's the only choice unless we want to cough up major, major bucks for a Twin Otter on floats. Floatplanes work best as high wing planes for reasons too numerous to go into here. Low wing planes have been put on floats from the Piper Aztec all the way up to the DC-3. But from a practical point of view, they aren't. So the world of floatplanes you can actually do something with like haul lots of stuff (as opposed to kit planes, ultralights, etc.) is pretty exclusively limited to single-engine, high-wing planes. Most multi-engine planes are low wing.
While I got a few hours flying a Cessna 310 in Hawaii, I never got a twin rating because I've never needed it for the flying I've been doing for the last four-plus decades. And even back in the 1970s, twin-engine planes were expensive to fly and even more expensive to own. I had a ball flying the 310 for the same reason I have a ball running multi-engine boats. But the need and the dollar justification have never been there.
I never got a helicopter rating for the same reason. I have one hour in a helicopter as part of a project for work many years ago. All I did was try to learn to hover a few feet off the ground. I have to say it is the hardest thing in terms of operating a piece of machinery I've ever done in my life. I'm sure I could have mastered it eventually, but I can tell you that anyone who thinks flying (manually) a helicopter is easy is full of crap. Sure, one can learn to fly one very, very proficiently. But in comparison to flying a helicopter, flying a fixed wing aircraft is like lying on a sofa taking a nap.
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markpierce
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Whether a twin or single wasn't in my criteria for the boat as going fast wasn't important. (I'm a former mono-hulled sailor.) It had to have a keel-protected propeller, rudder, and shaft. That's rare to find in a twin-engine boat. And then there is other criteria such as cost, decks, railings, visibility and so on. Besides, the low profile of the Coot wouldn't be practical for two engines.
eyschulman
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These treads can start getting a bit off track. To bring it back the point I am trying to get across is that a twin engine boat with the right design and build can be fuel efficient as good as most trawler types and better than some. I was not interested in beating the dead horse about which motor set up One or two is better since this is obviously a mater of choice and sometimes size of wallet. I have followed this fuel burn issue by reading the performance #s posted on sea trails(usually optimistic) and noting that many trawler and other single motor boats were not doing as well as (my not the dealer or builders optimistic #s ) for fuel burn. Potential boat buyers should not turn down a boat with twins on the assumption that fuel burn will be really bad that may not be the case at all.
markpierce
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Fuel burn is more a matter of behavior (fast versus slow) rather than the number of engines.
