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Old 02-06-2013, 06:14 AM   #741
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Originally Posted by bfloyd4445 View Post
If my memory serves me correctly over 20% of the fuel the engine burns is turned into heat that is removed via sea water and wasted.
Pretty close. Here is a CAT heat balance for a modern marine engine.



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Old 02-06-2013, 06:16 AM   #742
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Greetings,
CAT heat balance?
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Old 02-06-2013, 06:29 AM   #743
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Here's a real cat heat balance ...
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Old 02-06-2013, 05:29 PM   #744
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So if you have a typical twin engine trawler the amount of wasted heat/fuel is not 38% but more like 25%.

Twenty % heat loss sounds very small. Are you sure it's that small. These internal combustion engines are called "heat engines" as they basically turn heat energy into mechanical energy.

And not to be forgotten is the fact that gas engines and diesel engines are very close to equal in efficiency at WOT.

That's what i said. Diesel engines were about 38% efficient in converting fuel to usable hp, approximately 20% more is lost in the form of heat. That's 58% leaving 42% for other losses such as friction, blow by, engine efficiency due to design and age, and of course the stoichiometric ratio is 14.5:1 and since fuel air mixture must be slightly richer than what is actually needed there is a very small % that goes out the exhaust. If the mixture is lean the result is less hp and more engine wear due to lack of lubrication. Diesel fuel is an oil and engine designs must take this into consideration if they are to meet EPA standards and consumer demands.

So, 38+20+42= 100% of fuel

So, the best we can expect is that 38% or 38 cents out of every fuel dollar spent will end up pushing our boat. I do not claim to be an expert in this area but i have been involved in some engine testing in the past and these are numbers from memory, perhaps some of our readers would have more precise numbers? I think the society of mechanical engineers in 1977 published an abstract in which they claim about 4% friction loss just from the engine. Since today's designs are basically the same i think that figure is likely still accurate still leaving another 38% loss for all other things like belts pumps transmission etc.

It sure would be nice if we could eliminate some of these losses. There is one engine design i read about that is an 2 cylinder but four pistons. I think this is a link to the company planning on marketing this more efficient diesel engine design http://www.ecomotors.com/ecomotors-internationals-opposed-piston-opposed-cylinder-engine-promises-revolutionize-commercial-ve

here is a link to another design planned for use in helicopters and a good video.

http://www.engineeringtv.com/video/Opposed-Piston-Opposed-Cylinder
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Old 02-06-2013, 05:43 PM   #745
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... and of course the stoichiometric ratio is 14.5:1 and since fuel air mixture must be slightly richer than what is actually needed there is a very small % that goes out the exhaust. If the mixture is lean the result is less hp and more engine wear due to lack of lubrication.
WTF?

You are joking, right?
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Old 02-06-2013, 06:07 PM   #746
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Floyd,

Diesel engines fuel mixture is about 60-1 at idle, 14-1 at WOT and anywhere in-between in-between. I think you're thinking of gas engines.

I reread your post and see where I went astray. I thought that only about 30% of the fuel went to moving the boat but it looks like I'm mistaken.

For people w old 35 to 44' boats w twin 380 cu in engines the road to economy and less heat loss is smaller engines or "a" smaller engine. And of course better hull shapes aft.

In your example Rick it looks like there has been no account for piston friction, bearing friction, gear friction ect. It would seem to me "mechanical work energy" would be output energy .... the power to turn the propeller shaft. Surely they need to separate the mechanical energy of frictional parts and what's left to power the boat .. or whatever.
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Old 02-06-2013, 06:20 PM   #747
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The captain of the cruise ship Norwegian Star told me 70% of the ship's power went toward propulsion while 30% went toward "life support" such as lighting, heating/cooling, cooking, sewage processing, water making, etcetera.

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Old 02-06-2013, 08:12 PM   #748
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WTF?

You are joking, right?
Do you think that engine efficiency in regards to your pocket book is a joke? I'm not rich so i like to keep my engines operating at maximim efficiency as much as possible. If the air fuel ratio is not correct it can lead engine damage and if rich a waste of expensive fuel and possible engine damage. Neither of these is a joke. Both result in the expendature of $$ that would be better spent on beer
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Old 02-06-2013, 08:15 PM   #749
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Greetings,
Mr. markpierce. OK, 70% to power and 30% to life support. That's all well and good but what about the 346.7 Kw (aprox.) generated by the 3467 souls on board assuming aprox. 100w per body and given off as heat? Just look at all that steam in front of Miguel! Did Capt. Harstrom take THAT into account? And what about the excess methane generated on Taco night in the La Cucina restaurant? An awful lot to consider...
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Old 02-06-2013, 08:36 PM   #750
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Floyd,

Diesel engines fuel mixture is about 60-1 at idle, 14-1 at WOT and anywhere in-between in-between. I think you're thinking of gas engines.

I reread your post and see where I went astray. I thought that only about 30% of the fuel went to moving the boat but it looks like I'm mistaken.

For people w old 35 to 44' boats w twin 380 cu in engines the road to economy and less heat loss is smaller engines or "a" smaller engine. And of course better hull shapes aft.

In your example Rick it looks like there has been no account for piston friction, bearing friction, gear friction ect. It would seem to me "mechanical work energy" would be output energy .... the power to turn the propeller shaft. Surely they need to separate the mechanical energy of frictional parts and what's left to power the boat .. or whatever.
I think i may have forgotten to define what stoichiometric is.
Stoichiometric is the ratio of one reactent to another reactant in a chemical reaction. The optimum ratio of fuel to air is called the stochiometric ratio and for gas its 14.7:1 and diesel it is 14.5:1.Any other ratio inside the cylinder will result in less than optimum results.
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Old 02-06-2013, 09:32 PM   #751
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Then of course their is the hugh maintenence cost savings of the single over the twin.
This is a significant misperception. We know people with GB36 singles and when they have told us their annual engine maintenance costs they are not much different than ours. In fact, unless there is a significant repair project--- replacing engine mounts, exhaust systems, etc.---- the difference in service/maintenance cost between our acquaintances with single GB36s and our boat in a typical year amounts to an engine's worth of extra oil (12 quarts in the case of an FL120), an additional oil filter, and additional fuel filter elements. So a couple hundred dollars at best.
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Old 02-06-2013, 09:48 PM   #752
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This is a significant misperception. We know people with GB36 singles and when they have told us their annual engine maintenance costs they are not much different than ours. In fact, unless there is a significant repair project--- replacing engine mounts, exhaust systems, etc.---- the difference in service/maintenance cost between our acquaintances with single GB36s and our boat in a typical year amounts to an engine's worth of extra oil (12 quarts in the case of an FL120), an additional oil filter, and additional fuel filter elements. So a couple hundred dollars at best.
I agree 100% It only gets expensive when you need to rebuild two transmission, two props or two engines. The moral of the story is survey older boats very carefully and expect possible repairs. Better to buy boats with good histories or new!
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Old 02-06-2013, 09:52 PM   #753
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I think i may have forgotten to define what stoichiometric is.
Stoichiometric is the ratio of one reactent to another reactant in a chemical reaction. The optimum ratio of fuel to air is called the stochiometric ratio and for gas its 14.7:1 and diesel it is 14.5:1.Any other ratio inside the cylinder will result in less than optimum results.
Ummmm no. Your stochiometry is right, but that is not how a disel burns. The efficiency of a diesel comes from that fact that it burns lean as it a diffusion flame pattern, and also because it is is not mixed as it enters the combustion chamber. It is slow to burn, with excess oxygen. This is the main reason diesels have more torque as well, as it is a burn rather than an explosion.
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Old 02-06-2013, 10:07 PM   #754
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This is a significant misperception. We know people with GB36 singles and when they have told us their annual engine maintenance costs they are not much different than ours. In fact, unless there is a significant repair project--- replacing engine mounts, exhaust systems, etc.---- the difference in service/maintenance cost between our acquaintances with single GB36s and our boat in a typical year amounts to an engine's worth of extra oil (12 quarts in the case of an FL120), an additional oil filter, and additional fuel filter elements. So a couple hundred dollars at best.
oh gee golly, My error, huge is not appropiate. I should have stated twice as much as a single. What comes to mind are repairs like oil coolers heat exchangers exhaust manafolds etc but the fact of the matter is that modern marine engines are pretty darn forgiving and can really take a beating before repairs are needed. We know this must be fact because teins are very popular and we have already established they are less likely to be fully maintained than single engine boats..............
Marin, your absolutely right
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Old 02-06-2013, 10:18 PM   #755
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It's true that if one owns a twin for a long period of time there will be twice the expense of bigger ticket items like oil and transmission heat exchangers, water pumps or at least their impellers, perhaps fuel lift pumps, having alternators overhauled, and so forth.

So in that respect the statement "twice the cost of maintaining a single" can be a significant number at times. But components like these are not crapping out and needing replacement on any sort of frequent basis.

So from an annual perspective, the cost difference between operating one engine or two is pretty insignificant as I described earlier.

How insignificant over time will depend greatly on the age and condition of the boat in question, as well as how it was operated and maintained by previous owners, and how it is operated and maintained by you.
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Old 02-06-2013, 10:22 PM   #756
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In your example Rick it looks like there has been no account for piston friction, bearing friction, gear friction ect. It would seem to me "mechanical work energy" would be output energy .... the power to turn the propeller shaft. Surely they need to separate the mechanical energy of frictional parts and what's left to power the boat .. or whatever.
The portion labeled "mechanical work energy" includes internal friction, pumping losses and all the other mechanical losses.

There is much more to the subject than heat losses.
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Old 02-06-2013, 10:26 PM   #757
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Any other ratio inside the cylinder will result in less than optimum results.
What utter nonsense. Stoichiometric means that there is sufficient fuel to consume all the oxygen. No fuel is wasted and no excess oxygen is "wasted" just to carry heat away.

You are stuck in a spark ignition engine loop. The discussion is about diesels.
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Old 02-06-2013, 10:30 PM   #758
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The captain of the cruise ship Norwegian Star told me 70% of the ship's power went toward propulsion while 30% went toward "life support" such as lighting, heating/cooling, cooking, sewage processing, water making, etcetera.

I think his numbers are incorrect. Life support would have to include energy used to run the main engines since without them there is no life support. If he is referring to creature comforts his 30% may be correct. 70% for engine systems friction drag losses and actual prop
HP may even be in the ball park. Interesting thought. thanks
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Old 02-06-2013, 10:33 PM   #759
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What utter nonsense. Stoichiometric means that there is sufficient fuel to consume all the oxygen. No fuel is wasted and no excess oxygen is "wasted" just to carry heat away.

You are stuck in a spark ignition engine loop. The discussion is about diesels.
Rick, I thought I stated it was the optimum ratio of the two reactants fuel and air? Isnt that the same thing you said?
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Old 02-06-2013, 11:48 PM   #760
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I started a new thread on mixture and would like some input as there's much that I don't understand.
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