One Vs Two

If you start with a twin and make it a single, sure it can be as efficient.

Start with a single and it would be danged hard to make it as efficient as a twin.

Start with any premise and get to a conclusion...but it is not always true in reverse.

The reason for going to Diesel instead of Gas is the gas runs out of HP at a certain size.

To me the single diesel makes the most sense , until more HP is required to make the boat perform as desired.

Since 10- 300+HP diesels are off the shelf , cheap and reliable , the folks that need more than 300-400, hp will be looking for twins.

For a displacement boat of 100,000 lbs , well under 50 Tons , as single , probably a 6 cylinder truck sourced marinization should be fine.

No turbo, no intercooler would be wisest if offshore is contemplated.

Mechanical injection is finally catching up to the Air Police rules , so it also would be ideal for offshore.

Repairable is a big part of reliable.

eyschulman said:

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.

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markpierce said:

Fuel burn is more a matter of behavior (fast versus slow) rather than the number of engines.

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Well put both you guys... For newbie boaters seeking to purchase a post see my post #36. As an old song says - "It ain't the meat it's the motion hat makes my baby want ta rock!" Pun intended!

Any examples of a boat there the twin engine version has the same engine as the single? Or boats currently out there that even offer that option? The most recent one I can think of (which isn't saying much) was the Mainship 390 circa 2000-ish. The charter club I used to belong to had a single Cat 375hp version, and a twin with smaller Yanmars, which if I recall correctly were about 200hp. You see this more commonly on outboard boats, where the boat is available with, say a single 350 or twin 225s.

The Great Harbors are examples of modern FD boats where they decided to go with two small engines, the classic Hatteras FD LRCs also used two much smaller engines than their SD motor yacht sisters of the same size. So I am curious for examples of grossly over powered, twin engine FD boats.

A few years ago I was considering a KK 52. The boat is offered with twins JD 4045s or a single JD 6068. Sea trial data for both combinations showed (foggy memory) a 5 to 10% varying advantage to the single dependent upon cruising speed. The twin layout has the twin keels making it a better tracker in some eyes. Not to mention get home capability is enhanced. Both versions have TransPac range. More recent data from KK is available if one has an in with their sales team.

caltexflanc said:

Any examples of a boat there the twin engine version has the same engine as the single? .

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Sure. All the Grand Banks models that were offered as single or twins almost always used the same engines in each version. For example, our 1973 GB36, one of the first batch of GB36s made in fiberglass, is a twin with two FL120s. The single engine version of the same boat from the same time period uses one FL120. The same was true of the earlier wood models of the GB36.

The 1991 GB36 we chartered before buying our own boat is a single with a Cummins 220 hp diesel. The twin engine version of the GB36 from that same time period has two Cummins 220 hp diesels.

The same can be said of the GB42 which from it's introduction in wood was offered in single and twin engine versions. Initially the engine used was typically the FL120. As customer demand for more power grew, so did the engines. From the FL120 GB moved to the FL135 and on into Cats and Cummins, etc.

By the early or mid 1980s (I think) GB42s were almost always ordered as twin-engine boats so it's very rare to find-- or maybe impossible to find if they didn't make any-- single engine GB42s in the later years of its production.

Grand Banks boats could be ordered with whatever engine(s) a buyer or distributor wanted (up to a point). So a good number of GBs have been built with engines other than the factory's standard power. But the standard factory offerings of single and twin engine models used the same engine in each version.

When you wrotte

BandB said:

You're comparing two very different boats. Different shape hulls, different lengths, different widths. I assume different waterlines and yours is longer and therefore has a faster displacement speed. Then don't even know the type engines or vintage and that could be another factor. Definitely an apples and oranges comparison.

I will agree that in some situations twins get nearly the same fuel consumption but in others they consume more.

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"twins get nealy"

for example our boat :
- at 8,3 nds on one engine need 1,46 lt per nm
- at 8 nds on two engine need 1,14 lt per nm

It depends also of the type of engine (for example some new engines at 1500rpm needs 0,185 lt per hp and some at 1500rpm needs 0,155 lt per hp) and at witch rpm each engine need to "produce" the needed hp.
I am not clear !? It is normal ...I am French !!.

example of our consumption :

- sur un moteur à 1400 t/mn : 6,6 nds et consommation de 0,61 lt au mille.
- sur un moteur à 1500 t/mn : 7 nds et consommation de 0,81 lt au mille.
- sur un moteur à 1600 t/mn : 7,4 nds et consommation de 0,92 lt au mille.
- sur un moteur à 1800 t/mn : 8,3 nds et consommation de 1,46 lt au mille.
- sur deux moteurs à 1780 t/mn : 8 nds et consommation de 1,14 lt au mille.
- sur deux moteurs à 1850 t/mn : 9,80 nds et consommation de 1,78 lt au mille.


If (for the next boat !!) we decide to have just one engine we will chose an engine able to produce enough power at the best point of consumption (for Perkins or Deutz around 1500 rpm) to reach our "normal" cruising speed.

At this time twins of half the power may be (re the cost of the engines) a cheaper route as the emissions requirements may be different. One can buy simple non-turbocharged mechanical engines like the 40hp Mitsu I bought for Willy. At what point on the HP scale does one run out of Mechanical engines available? I would guess about 60hp. So this would probably only apply to 32 or 34' boats.

Those afraid of modern technology could save money and enjoy the advantages of a twin engined boat. The more expensive option of twin engines is very popular and it seems to me the buyers wouldn't buy twins if they didn't think they were better. Buyers have thus voted that twins are better.

But almost always twins come w more power and because of that aren't comparable re the twins v/s single question. Most of the trawlers of the 70s came w double the power of the singles. You then get into a more or less power question .. not twin v/s single.

manyboats said:

At this time twins of half the power may be (re the cost of the engines) a cheaper route as the emissions requirements may be different. .

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I heard this is about to change with less than 60 KWH genset manufacturers stockpiling this year's builds as Tier 4 kicks in at year end.

manyboats said:

At this time twins of half the power may be (re the cost of the engines) a cheaper route as the emissions requirements may be different. One can buy simple non-turbocharged mechanical engines like the 40hp Mitsu I bought for Willy. At what point on the HP scale does one run out of Mechanical engines available? I would guess about 60hp. So this would probably only apply to 32 or 34' boats.

....

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You can't put a non Tier III compliant engine in a new boat, so for us, using an mechanical engine in a US documented boat, is not possible. I would LOVE for someone to prove me wrong!

The Gardner 6LXB runs 127HP or 150HP. The 8LXB has 153HP and 176HP. I saw two refurbished Gardners in a boat yard in China, I think they were 8LXBs, and they sure were nice looking. I know a guy putting a 6LXB in his new boat but he will not be US documented.

Later,
Dan

dannc said:

You can't put a non Tier III compliant engine in a new boat, so for us, using an mechanical engine in a US documented boat, is not possible. I would LOVE for someone to prove me wrong!

The Gardner 6LXB runs 127HP or 150HP. The 8LXB has 153HP and 176HP. I saw two refurbished Gardners in a boat yard in China, I think they were 8LXBs, and they sure were nice looking. I know a guy putting a 6LXB in his new boat but he will not be US documented.

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Doesn't prove you wrong but this guy put a rebuilt 78hp Gardner 5LW in a 2010 custom built tug in Canada:

2010 Custom Tug Trawler Power Boat For Sale - www.yachtworld.com

I would be scared to death on a parts failure.

Donsan said:

Doesn't prove you wrong but this guy put a rebuilt 78hp Gardner 5LW in a 2010 custom built tug in Canada:

2010 Custom Tug Trawler Power Boat For Sale - www.yachtworld.com

I would be scared to death on a parts failure.

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2010 was five years ago, to state the obvious, and I surely don't know the regulations in Canada five years ago, I can barely comprehend what the US EPA mandates for today.

Parts failure per say does not bother me, but parts availability would be a question. My understanding is that Gardners were very reliable engines which really does not matter for us since we can't use the engine.

From a fuel burn perspective, the 6LXB and the JD 4045 TFM Tier III engines, at 40% load, would burn 2.5 GPH and 3.2 GPH. The JD 4045 TFM Tier II engine burns 2.7 GPH at 40%. The Gardner is doing this around 1100 RPM vs 1800-1900 in the JD 4045s. The JDs have a turbo where as the Gardner does not.

A replacement ECU for the 4045 is $2,250 to $3,270 with the higher price being on Amazon. :lol: What does Amazon NOT sell? Hmmm, EBAY has one for $940 that is supposed to be new....

Later,
Dan

How much is one for ANY Gardner

kulas44 said:

How much is one for ANY Gardner

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I do believe that the answer would be .....

$0.



Flip side, why is there always a flip side with boats, is that the Gardner appears to be twice as much money as the JD!!!!!! You can buy lots of ECUs, injectors and fuel for that much money. :lol:

Back to the original question, to determine if a single or twin engine is cheaper to run, you would have to compare the same hull with engines from the same generation so to speak. Engines from a different time could change the results one way or the other.

Later,
Dan

If you want a tank engine, look for a rebuilt Deutz 6 cylinder engine. Normally aspirated, and reliable beyond cummins, cat, and JD. The last one I rebuilt ran for 30 years - 50,000 hours at 2100 rpm pulling an irrigation pump. Two of those in a trawler would be perfect.

FF said:

The reason for going to Diesel instead of Gas is the gas runs out of HP at a certain size.

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Ff

I don't think you meant what you said.

If all the cars in the U.S. were diesel, instead of gasoline, we'd probably reduce consumption 20% with a like decrease in green house gases, etc.

Just don't tell the greenies, as it would burst their preconceived notions.

The lower the rpms, the greater the efficiency of diesel over gas, maxing out at idle, with an advantage that is close to 1 unit of diesel to 100 units of gas.

About the kk52 the numbers I've seen also reflect about a 10% increase in the twin versus single. Which seems about right.

Wxx3,
I think you're thinking only of fuel consumed .. not efficiency. Efficiency is fuel consumed v/s power produced. The max surely dosn't happen at an idle.

I would think the most fuel efficient engine for boats we think of as trawlers would be a small turbocharged engine doing it's work (cruising) at about 3500rpm.

I think we are both right. Efficiencies can be based on many different factors.
Yes, I am talking about fuel consumed, but at idle, a gasoline engine is still terribly inefficient for the power produced and the amount of fuel consumed.

Now, why do you say a turbocharged engine?

Turbo charging exists to increase the amount of power produced over the same rpm range of a non-aspirated engine.

Clearly, for vehicles on land, cars, trucks, etc, a turbo allows the engine to produce more power, yet, act like a small engine a low rpm's that land vehicles spend so much time doing.

A boat is different, since the loads are in a smaller range.

I did not want a turbo engine, solely based on complexity and cost to repair.

If the powers to be really wanted to save energy, a diesel-electric, much like a locomotive, would be best especially for cars and trucks. A hybrid based on a small diesel running constantly, using electric motor connected batteries for increased demand.

Wxx3 said:

I think we are both right. Efficiencies can be based on many different factors.
Yes, I am talking about fuel consumed, but at idle, a gasoline engine is still terribly inefficient for the power produced and the amount of fuel consumed.

Now, why do you say a turbocharged engine?

Turbo charging exists to increase the amount of power produced over the same rpm range of a non-aspirated engine.

Clearly, for vehicles on land, cars, trucks, etc, a turbo allows the engine to produce more power, yet, act like a small engine a low rpm's that land vehicles spend so much time doing.

A boat is different, since the loads are in a smaller range.

I did not want a turbo engine, solely based on complexity and cost to repair.

If the powers to be really wanted to save energy, a diesel-electric, much like a locomotive, would be best especially for cars and trucks. A hybrid based on a small diesel running constantly, using electric motor connected batteries for increased demand.

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Is there a better factor than brake mean specific fuel consumption for measuring diesel or gas engine efficiencies?

Diesel electric locomotives are indeed wonderful, especially for the traction component so incremental loads can be applied. Diesel electric and trolley systems in very large off highway trucks have not proven cost effective. The powers that be have voted, decades ago in fact.

"Is there a better factor than brake mean specific fuel consumption for measuring diesel or gas engine efficiencies?"

To make comparisons or predict a boats performance there is nothing better.

Except BMEP is not given for the majority of engines , till you get up with the big stuff.

All our boats would be more efficient if the NA had this info , and a realistic expectation of the vessels use.

FF said:

"
Except BMEP is not given for the majority of engines , till you get up with the big stuff..

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I have found that for engines made during the past decade that this information is readily available. I say this because during this period I have considered vessels powered by JD, Cat, Cummins and Perkins Sabre - all with prop curves and BSFC data readily available. Since all these guys make bigger engines it is likely an across the board decision and required for Tier XX certifications.

For older engines not so easy to find same.

Wxx3,
You wrote that the lower the rpm of a diesel the greater efficiency of a diesel compared to gasoline. Who cares about gas power in trawlers? But very true.

As for our diesel engines aren't they most efficient at about 2/3rds to 3/4 of rated rpm? With a typical propeller load of course.

And isn't a turbocharged engine most efficient w the turbo at medium boost? Turbo engines at near the top end aren't relatively efficient IMO but more efficient somewhere below high boost and max power but above the point where the turbo just starts working. Below that speed a turbo is like a dog dragging a broken leg.

It's a matter of how much heat is generated and how much heat is lost. Bigger engines at slower speeds (in our range of power) are much better at radiating (losing) heat and thus energy and efficiency.

These are the reasons I thought a small turbo diesel working at a load and rpm of about 2/3rds to 3/4 of rated rpm would be most efficient.

And if this is true the diesel and especially the turbo-diesel is ideally suited for our boats if operated two thirds load/rpm. A bigger heavier slower turning engine would weigh more and even it's extra weight would decrease it's efficiency. A 10% increase in boat weight = about a 10% increase in fuel burned.

A good rule of thumb is the most efficient rpm for a diesel is to find peak torque on the full load curve, and see what rpm that is. Then cruise at that rpm at part load.

For engines in the 5-8 liter range, it's usually around 1400-1700rpm.

High rpm engines, rated at 3000+ rpm usually do not have very good bsfc at higher rpm. At high rpm, pumping losses go way up.

Really big slow engines are not that good either. Too much friction and heat loss.

Turbos do not necessarily inprove efficiency. But they allow a smaller engine to make more power, and the smaller engine saves fuel by being lighter and having lower pumping and thermal losses from the smaller size.

If the exhaust driven turbine was coupled to the crank, that would improve efficiency. But the energy in pumping more air in is not captured as a net effect on the crank.

Best efficiency usually comes from picking a hp rating not at the top of the range for a given block, maybe a notch or two or three down. Match hp needed by boat to mid range, say 50-70% of what engine can develop at full. This also tends to lead to long engine service life.

Hard to do with small engines down in the under 100hp range, there just are not many options out there.

Ski I'm really getting into this post.

So the turbo dosn't ever (rpm or load wise) at some point produce more work per gallon of fuel? Just permits us to use smaller engines? That seems like a lot of money spent for a very little gain. I see smaller engines and less weight as a plus but most here view it the other way around.

Re pumping losses Yanmar's 55hp JH engine was rated at 3800rpm but it seems through advertising by other small engine manufacturers that low rpm was beneficial Yanmar suddenly changed the 55hp JH to 3000rpm. Same power .. just lower rpm. Seemed impossible to me.

Higher rpm has advantages. Like lower side loads on pistons against the cylinders. Less force is required w more strokes. And torsional vibration should be less as there are more strokes w less intensity.

I know some engines do have turbos connected to the crank .. DD?. But it's always a trade .. back pressure for X. If the trade is worth it .. it's justifiable.

"50% to 70%" .. I agree. Shooting for 60 to 65.

When I shopped for an engine for Willy I thought there were quite a few engines to select from. All mostly alike though except possibly Yanmar.

Ski in NC said:

A good rule of thumb is the most efficient rpm for a diesel is to find peak torque on the full load curve, and see what rpm that is. Then cruise at that rpm at part load.

For engines in the 5-8 liter range, it's usually around 1400-1700rpm.

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Hmmm.... Full load peak torque for our 6CTAs is indeed right at 1700 RPMs. Looks like fuel consumption (prop curve) at 1700 RPMs would be about 7 GPH, per engine. Don't have our speed tests file here, but I'll compare that as soon as I can. Seems to me, the hull is a pig at 1700 RPMs, though...

-Chris

1700 might be a happy spot for the engine, but might be horrible for the boat!!

My boat is ok but not great at 1700, but likes 1900-1950. Close enough for me.

Both engine AND boat must be happy with cruise rpm.

Just a rule of thumb. Real sea trial data are much better.

manyboats said:

Re pumping losses Yanmar's 55hp JH engine was rated at 3800rpm but it seems through advertising by other small engine manufacturers that low rpm was beneficial Yanmar suddenly changed the 55hp JH to 3000rpm. Same power .. just lower rpm. Seemed impossible to me.

"50% to 70%" .. I agree. Shooting for 60 to 65.

When I shopped for an engine for Willy I thought there were quite a few engines to select from. All mostly alike though except possibly Yanmar.

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Eric,

The 4JH3E was 2.0L - 56HP @ 3,800 RPM. The 4JH4E was increased to 2.2L with advertised power of 55HP @ 3,000 RPM and the current 4JH5E is 2.2L with advertised power of 53HP @ 3,000 RPM.

The factory recommends propping the 4JH3E to 3,900RPM and operating at 2,900RPM. This is 75% rated RPM and under 50% rated HP on the propeller power curve. It is also is at the lower end of the Specific Fuel Consumption curve. This actually looks pretty conservative.

It seems the smaller, higher-speed diesels are optimized for the speeds at which they operate.

As for the later engines having lower rated engine speeds, I'm sure the market demanded less noise. Direct injection Yanmars can be somewhat noisy, but are very smooth.

Ski,

As it turns out, 2,900 RPM is absolutely the sweetest for the engine and boat. The structural and shaft vibration just melt away. The sound even drops 2 dBA in the pilothouse.

The torque is beginning to fall off at that speed though.

Attached is a performance chart for the 4JH3E that demonstrates these numbers.

That's wonderful Larry.
Here my memory was not so good but generally speaking fairly correct.
It's interesting that the lowest fuel burn and highest torque are miles apart on the Yanmar.o It would seem that perhaps it varies a lot on what engine is being scrutinized. I've heard often that the power and torque usually or often comes at the (roughly) same engine speed. I think engine manufacturers tend to try to get the torque down low and the efficiency tends to run high.
Thanks very much for the excellent information. Our small engines don't get much attention here as the Perkins and Fords are so numerous.
Re what Ski presented I'm glad we don't have a turbocharger to deal w but if we did we could have a lighter and smaller engine.

Are we off topic yet?

manyboats said:

That's wonderful Larry.
Here my memory was not so good but generally speaking fairly correct.
It's interesting that the lowest fuel burn and highest torque are miles apart on the Yanmar.o It would seem that perhaps it varies a lot on what engine is being scrutinized. I've heard often that the power and torque usually or often comes at the (roughly) same engine speed. I think engine manufacturers tend to try to get the torque down low and the efficiency tends to run high.
Thanks very much for the excellent information. Our small engines don't get much attention here as the Perkins and Fords are so numerous.
Re what Ski presented I'm glad we don't have a turbocharger to deal w but if we did we could have a lighter and smaller engine.

Are we off topic yet?

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Ski is essentially correct, but I think you are missing the point about turbos.

Turbos work well in an application which requires a broad rpm range.

Our engines don't.

On the plane to Ireland.
Our engines don't

Gotta go

LarryM said:

Eric,

The 4JH3E was 2.0L - 56HP @ 3,800 RPM. The 4JH4E was increased to 2.2L with advertised power of 55HP @ 3,000 RPM and the current 4JH5E is 2.2L with advertised power of 53HP @ 3,000 RPM.

The factory recommends propping the 4JH3E to 3,900RPM and operating at 2,900RPM. This is 75% rated RPM and under 50% rated HP on the propeller power curve. It is also is at the lower end of the Specific Fuel Consumption curve. This actually looks pretty conservative.

It seems the smaller, higher-speed diesels are optimized for the speeds at which they operate.

As for the later engines having lower rated engine speeds, I'm sure the market demanded less noise. Direct injection Yanmars can be somewhat noisy, but are very smooth.

Ski,

As it turns out, 2,900 RPM is absolutely the sweetest for the engine and boat. The structural and shaft vibration just melt away. The sound even drops 2 dBA in the pilothouse.

The torque is beginning to fall off at that speed though.

Attached is a performance chart for the 4JH3E that demonstrates these numbers.

Click to expand...

The problem with the attached curves is the BSFC curve at the top is for full power all through the rpm range. Throttle on the stops throughout. Not realistic for a boat. A better curve would show bsfc along the prop load curve. That would be something we could use.