Engine Efficiency

FlyWright said:

The more safely and efficient I can operate the boat, the more time I can enjoy operating it. It's all part of the equation of boating.

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Flyright

I agree completely with the above statement, however my point is once again, high or optimum engine efficiency and gph are not necessarily related, one must do the bsfc calculation.

I betcha my Et is better than yours. At 7.8 knots I consume 4.7 gph dragging about 55,000 to 60,000 lbs. Nothng close to Delfin though, he is the TF Et champ - size matters!

I'd like to see some efficiency in moorage rates.

I'd have to run about 50 hrs a week to come close to my moorage rates and I'm at the cheapest joint around.

Fly I can see that knowing what your'e doing as in how much fuel you have, all the logistics about where your'e going and where there is fuel and can you afford it and what makes a boat efficient and all the other boat "lore" that makes the boating experience fun and engaging is "part of the equation" re the boating experience as aptly put by you but obsessively dwelling on fuel consumption takes away from the experience in enjoyment as I see it.


I see you again Tom and size does matter. Pile up all the enjoyable hours of boating and compare it to how much you spend on boating. I'll bet my small size would deliver a good score. Yup .. size matters. The smaller the boat the more ya boat. Heard that plenty.

Delfin said:

Large container ships must have Et numbers that are quite high then.

I may be missing something, but based on the CAT 3306 Performance Data chart for prop demand hp and fuel consumption at 1250 rpm(verified by the fuel consumption gauge), plus our speed , we move 130,000 pounds through the water at 7.2 knots using 50 hp, which I guess gives Delfin an Et of 57.4.

Have I made a mistake?

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Moving a large weight slowly is very efficient......

No mistake that I can see. Your FNv at that speed and displacement is 0.6.....If you look at the graph in post #12, go across the bottom to .6 and run up to 57.4 you'll see Delfin lies directly on the dotted 1975 line.....

Tad Roberts said:

Moving a large weight slowly is very efficient......

No mistake that I can see. Your FNv at that speed and displacement is 0.6.....If you look at the graph in post #12, go across the bottom to .6 and run up to 57.4 you'll see Delfin lies directly on the dotted 1975 line.....

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Thanks Tad. I can use these calcs with the Admiral. I am not becoming fatter and slower, I am becoming more efficient....

Sweet.

I'm not comparing my efficiency, speed, or Et to other boats, but am interested in operating the one boat I own at the proper balance of speed, efficiency and safety to maximize my enjoyment. Everything is a balance and in my case, the speed difference between efficient cruise 7.4 and my previously normal cruise of 8 kts is not significant.

I also measure efficiency in MPG and am satisfied knowing that 2.78 MPG is achievable at a practical speed in my boat. I'm not anxious over the fuel costs, but I am interested in saving where I can, within reason. Obviously sunchasers's remark about not boating at all would result in max efficiency and safety (no fuel consumed/slip fees and no chance of a boating accident or failure), but throws out the baby with the bathwater.

Eric makes a good point that cutting slip fees makes a bigger impact on the overall cost of boating. That's something I'm also looking at, too, but also for reasons like reducing the enroute time to fishing waters and allow better access to new areas.

Eric, I am not now and never have been "obsessively dwelling on fuel consumption." I merely posted the results of nearly 100 hours of testing various power settings to find what feels like the right balance to me.

FlyWright said:

I have been tracking different power settings on my 34 Californian with twin Perkins 4.236 engines over the past year or so. I have run 30-40 hours between refuelings at the same power setting to provide a good sampling for each setting.

I seem to have found the sweet spot I am comfortable with for now, a good compromise between efficiency, speed and noise. If I slow to 7 or 6.5 kts, I'll likely save more fuel and even eclipse 3 mpg but the speed feels too slow for me to endure for a 30 hour test period.

Here's what I have found on my 2800 RPM (WOT) engines:

2350 RPM (84%), 8.0 kts, 3.70 gph, 2.16 mpg
2100 RPM (75%), 7.6 kts, 2.79 gph, 2.72 mpg
2000 RPM (71%), 7.4 kts, 2.66 gph, 2.78 mpg

I'm sure these numbers would pale in comparison to single engine boats, especially the new technology diesels, but I'm happy with this level of efficiency from a pair of old school 1977 85 hp Perkins naturals.

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I have not takent he time to write my numbers down, but I have been keeping track in my head. It turns ou that I am getting very similar numbers to yours. I run at 1800 rpm forn long hauls (over a couple of hours) and for jaunts less then an hour or two I run at 2000 rpm. If i figured out the difference in cost/time savings I am sure it would be negligable. So mostly I just try to enjoy the journey. (i run the engines slower when on long runs so the noise isnt so loud... noise is the biggest factor for me)

My next project is to redo the insulation for better noise management...

We can't really figure ours out bc we also have diesel heat and a generator. Over the past almost three years we average six gallons per hour but that does not account for the heater and generator. I can't remember if matt said we've spent four thousand or six thousand on diesel since we bought the boat. He has it all on a spreadsheet.

markpierce said:

At my normal cruising speed of 6.3 knots at 1800 RPM, I'm getting 85% of the JD's 80 horsepower consuming about 1.7 gallons an hour.

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I thought that boat had a propeller at the end of the shaft ...

Unless you have changed it to wheels or some kind of cable drive it should be putting out about 30 hp.

PG,

How'ed you arrive at 6gph? Sounds about right though.

Mark I think you stepped in it.

manyboats said:

Mark I think you stepped in it.

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That's OK with me. (I looked at the wrong power curve.) I enjoy giving RickB a "lift."

markpierce said:

At my normal cruising speed of 6.3 knots at 1800 RPM, I'm getting 85% of the JD's 80 horsepower consuming about 1.7 gallons an hour.

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You may be running at 85% of rated RPM, that doesn't mean 85% of rated HP.
Wide open throttle for me is 1650 rpm with 150 hp using close to 7.5 gph at 11 kts.
At 1400 rpm I use 2.75 gph at 8 kts. My guess is that is around 60 hp.
A small throttle decrease can mean a large fuel savings.

By the way, that's 3 mpg for 87 tons. I was surprised I did that well with a Detroit 6-71.

manyboats said:

PG,

How'ed you arrive at 6gph? Sounds about right though.

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Uh... I leave the math to my honey pie and his spreadsheets. He plugged the fuel consumption and hours into his spreadsheet and told me the gph and $$ we've spent on diesel. I just say "yes dear". Isn't that what the admiral is supposed to do?

markpierce said:

That's OK with me. (I looked at the wrong power curve.)

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No, your repeated posting of those figures in numerous threads since you bought that boat indicates that you don't know how to read the performance graphs for a marine engine. If you didn't post in threads like this it wouldn't matter, most people don't but they don't pretend to either.

Normally it wouldn't matter one iota to anyone and I could care less how much you know or don't but when you choose to post in a thread titled "engine efficiency" that is read by a few thousand readers, it is not unreasonable to hope that what you post as factual information is at least close to reality.

If you are interested in efficiency and posted to contribute or question published or observed data then perhaps it should not surprise you when you repeatedly claim your engine is somewhere around twice as efficient as the most efficient marine engines on the planet, that that claim should attract some attention.

RickB said:

No, your repeated posting of those figures in numerous threads since you bought that boat indicates that you don't know how to read the performance graphs for a marine engine. .

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Interesting... as I don't know how to determine the efficiency of my engine but would like to. What parameters do you need to determine the efficiency or do you just read it off the engine spec sheet?

SeaHorse II said:

Interesting... as I don't know how to determine the efficiency of my engine but would like to. What parameters do you need to determine the efficiency or do you just read it off the engine spec sheet?

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The spec sheet will tell you the amount of fuel burned to produce a given amount of power as determined by operating that engine in a test cell. Period.

The numbers Mark posted are just the numbers supplied by JD on sheet 2 of the engine specific data sheet for his engine. Those figures may or may not have any association with the reality of that engine installed in his boat. The power figure he supplied is so far off that it should be obvious to anyone reading the data sheet in order to calculate boat performance or to share information about engine efficiency, hence my post.


You can use that sheet to estimate boat performance based on a theoretical propeller that absorbs the engine's rated output at its maximum rated rpm. What you do from there is most likely purely subjective or based on empirical data obtained during use or by recommendation of an expert or experienced user of the same boat and engine.


My take on it is that engine efficiency is only one small part of a much larger system which includes useage and subjective performance goals. You can have the highest possible fuel efficiency in terms of Brake Specific Fuel Consumption but put that engine in a poorly designed hull or use an efficient engine in an efficient hull in a manner for which it was not designed and can not perform then system efficiency is moot.

Do you want the greatest distance over the ground for the least fuel? The least time? The most weight carried? The best ride? What do you want from your boat?

Walt I wonder why you are interested in fuel efficiency?

I suspect your'e just interested in talking about it. Like me. If any of us were seriously interested in significantly more fuel efficiency we'd need to get different boats .. including me.

Engine efficiency is easy to determine as sunchaser and Rick point out but not very meaningful because the other part of the picture is the boat and totally accurate numbers are not possible as there are too many variables.

One way to come very close however is to accurately measure fuel consumption at a given speed and use the charts to determine how much hp is produced. But the numbers are only good for WOT at rated rpm. There are other charts that come closer but none will be "dead nuts". You can't isolate the resistance of the hull. Too many unmeasurable variations. But by just looking up numbers we can come close ... closer than we actually need.

RickB said:

...
The numbers Mark posted are just the numbers supplied by JD ...

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Regardless, the engine burns 4 GPH at full throttle (2400 RPM), and less than half that at 6.3 knots (1800 RPM).

My boat 40hp 2gph WOT 1 gal hr cruise.

Same speed half the power and half the burn.

manyboats said:

Walt I wonder why you are interested in fuel efficiency?

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It's an interesting subject although efficiency is almost at the bottom of my list. I simply wanted to know how it is arrived at.

Dirk Peters said:

You may be running at 85% of rated RPM, that doesn't mean 85% of rated HP.
Wide open throttle for me is 1650 rpm with 150 hp using close to 7.5 gph at 11 kts.
At 1400 rpm I use 2.75 gph at 8 kts. My guess is that is around 60 hp.
A small throttle decrease can mean a large fuel savings.

By the way, that's 3 mpg for 87 tons. I was surprised I did that well with a Detroit 6-71.

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Nice to see a real world user of marine diesel fuel reporting in. I often marvel at how fuel efficient tugs are, say vs a 1/3 the weight yacht. The recent edition of PM has a good article on the ATW N40 and how it accomplished its very fuel efficient task

Tom to me it's strange that anybody would think of Tugs as fuel efficient. Engines way way too large, very excessive weight and large wetted surface.

Perhaps if you looked at it from a power per ton requirement they wouldn't look so good.

Why do you suppose Dirk's boat is fuel efficient? He says "A small throttle decrease can mean a large fuel savings." Indeed but most all of that difference comes from the difference in hull resistance not engine efficiency.

I'm jealous of anybody w a DD. Dirk isn't the rated rpm of a 6-71 2300?

Wonder of the fuel consumption of this near-Coot-sized tug equipped with azipod.

Some of us LOVE fuel efficiency and could care less about engine efficiency...oh no...what is what???? Rick seems to get it.

It doesn't matter one little bit what your engine burns or what your flo scan says...it matters what you actually burn on your trip.

Some here will argue till they are blue in the face (and I'm sure they look just as comical when replying) that you can't or shouldn't as it's worthless to plan around tidal currents. Some will say...hey..it's just money and a small fraction of my boating budget..."who cares?" Well for some of us fuel can be a BIG chunk because we USE our boats a lot every year. Some will discuss how it doesn't matter because you don't have a FULL displacement boat yet at certain speeds ANY hull form gets realistically close to the efficiency of "full displacement" designs....cough....cough.

I could go on for quite a bit....but after a long life of cruising boats, 3 liveaboards, and lots of commercial miles where economy mattered to someone...there are lots of tricks to keep your annual fuel bill down...how you do it is up to you....just referring to an engine graph and posting how great your engine is while a tropical rain forest grows on the bottom of your boat while underway serves no purpose other than to make you feel good.

manyboats said:

Tom to me it's strange that anybody would think of Tugs as fuel efficient. Engines way way too large, very excessive weight and large wetted surface.

Perhaps if you looked at it from a power per ton requirement they wouldn't look so good.

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If that tug were put in perspective it would look very different. When delivered it made 10 knots from a 100HP gasoline engine that directly turned a prop at 350 rpm. That engine weighed close to 6000 pounds.


Modern yachts don't do too badly. A moderate size (40 meters) boat that weighs 740,000 pounds can get better than 9 knots out of 20 gallons per hour and keep 20 people in luxury for about 21 days nonstop while traveling nearly 5000 nautical miles. I wouldn't call that inefficient.

You might look at it as it takes that yacht 11.6 gallons to transport each person onboard 223 miles per day in absolute comfort and luxury.

What does efficiency really mean when you are not hauling cargo and hoping to make a profit?

markpierce said:

Wonder of the fuel consumption of this near-Coot-sized tug equipped with azipod.

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For starters, it has a pair of DD8V71s turning 44" diameter props the old fashioned way.

It is the old Cates #20 built in 1969 and is just over 41' long. If you wound it up to its full bollard pull it would probably burn around 30 gallons per hour.

manyboats said:

Tom to me it's strange that anybody would think of Tugs as fuel efficient. Engines way way too large, very excessive weight and large wetted surface.

Perhaps if you looked at it from a power per ton requirement they wouldn't look so good.

Why do you suppose Dirk's boat is fuel efficient? He says "A small throttle decrease can mean a large fuel savings." Indeed but most all of that difference comes from the difference in hull resistance not engine efficiency.

I'm jealous of anybody w a DD. Dirk isn't the rated rpm of a 6-71 2300?

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My answer to that is "It depends"
DD 71's range from the ancient two valve head models to the turbo charged monsters.

Mine is an "N" with a lower speed blower and the smallest injectors they make.

As for the T.B. McClintic being a tug, it just looks that way. It was built in 1932 as a floating surgeons office. It's heavy but very streamlined. A 50" prop on a 4-1 gear helps keep the fuel bill low. I agree that hull resistance at a given speed is the primary factor overall efficiency.

sunchaser said:

Nice to see a real world user of marine diesel fuel reporting in.

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?? No more "real world" than all the other members of this forum who run toy boats with the same engines and displacement for the fun of it.

tugboat efficiency is measured by the amount of fuel consumed to develop a given bollard pull. If they aren't working hard they are just wasting a ton of fuel hauling around an engine far far larger than they need to move the boat from the dock to the job.

That is why the newest approach is to go hybrid and shut off the diesel except when they need the power.

Real world numbers Perkins 6.354:

Anacortes to Ketchikan 897 miles 180 gals
Ketchikan to Sitka 847 miles 183 gals

Needless to say we didn't go by the shortest route and between Ketchikan and Sitka and we bucked the tide and winds a couple of times. I generally tried to run between 1500 and 1600 RPM but really focused more on a SOG target so as to get to a place in time for the tide or to end the day at a decent hour. A couple of times I got into the throttle pretty deep for a couple of stretches in 5-6 foot following seas to maintain a little better control and then I was running in the 1800 to 1900 RPM range.

Tom

tpbrady said:

Real world numbers Perkins 6.354:

Anacortes to Ketchikan 897 miles 180 gals
Ketchikan to Sitka 847 miles 183 gals

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That is my idea of "efficiency" and a good return for the quantity of fuel burned on a boat large enough to provide a good standard of comfort.

How's about 8 inches per gallon?