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Old 04-28-2015, 07:17 AM   #61
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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.
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Old 04-28-2015, 07:49 AM   #62
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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.
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Old 04-28-2015, 07:59 AM   #63
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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.
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Fuel burn is more a matter of behavior (fast versus slow) rather than the number of engines.
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!
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Old 04-28-2015, 10:10 AM   #64
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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.
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Old 04-28-2015, 11:14 AM   #65
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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.
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Old 04-28-2015, 07:23 PM   #66
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Any examples of a boat there the twin engine version has the same engine as the single? .
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.
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Old 05-02-2015, 07:25 AM   #67
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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.

"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 1400 t/mn : 6,6 nds et consommation de 0,61 lt au mille.
- sur un moteur 1500 t/mn : 7 nds et consommation de 0,81 lt au mille.
- sur un moteur 1600 t/mn : 7,4 nds et consommation de 0,92 lt au mille.
- sur un moteur 1800 t/mn : 8,3 nds et consommation de 1,46 lt au mille.
- sur deux moteurs 1780 t/mn : 8 nds et consommation de 1,14 lt au mille.
- sur deux moteurs 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.
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Old 05-02-2015, 10:46 AM   #68
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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.
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Old 05-02-2015, 11:09 AM   #69
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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. .
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.
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Old 05-02-2015, 11:09 AM   #70
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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.

....
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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Old 05-02-2015, 11:33 AM   #71
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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.
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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Old 05-02-2015, 01:53 PM   #72
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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.
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. What does Amazon NOT sell? Hmmm, EBAY has one for $940 that is supposed to be new....

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Old 05-02-2015, 06:10 PM   #73
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How much is one for ANY Gardner
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Old 05-02-2015, 09:28 PM   #74
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How much is one for ANY Gardner
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.

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.

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Old 05-02-2015, 10:00 PM   #75
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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.
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Old 05-02-2015, 11:56 PM   #76
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The reason for going to Diesel instead of Gas is the gas runs out of HP at a certain size.
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.
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Old 05-03-2015, 10:26 AM   #77
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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.
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Old 05-03-2015, 11:25 AM   #78
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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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Old 05-03-2015, 12:14 PM   #79
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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.
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.
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Old 05-05-2015, 06:22 AM   #80
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"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.
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