Fuel usage: "new" vs "old" diesel engines

Regarding "new" vs "old" diesel engine fuel burns.

I find it difficult to understand why some new, modern, state of the art engines burn twice as much (or more) fuel than my Gardner 8LXB, designed, I believe, in the 1950's, and built in 1978 burns.

Granted, my engine produces (from one source) 20% to 40% more pollution than the newer engines per gallon consumed, but if mine is consuming less than HALF the fuel for the same work (miles made good through the water), and the new design is 20% to 40% less polluting, but burns over twice the fuel per mile made good through water . . . . . isn't the new, modern, sophisticated, common rail, secret spy ring engine actually polluting MORE than my old engine?!?

Mechanical: 1978 Gardner 8LXB with 36" Hundestat CPP
Boat: 1982 Robert Beebe designed 50' Passagemaker
Normal cruising weight: 75,000 to 90,000 lbs, depending on fuel/water on board.
Normal cruise: 7.5kts, 1300 rpm, pyrometer (EGT) 430(ish) deg F. Typical 120v load.

Fuel burn: 2.4 gph measured, which gives me 3.125 nm/gal.

And I'm not even taking into account the pollution and expense of drilling, refining, and transporting that extra fuel in order to run the boat with a modern engine the same number of miles over the ground . . .

And I didn't factor in that my engine is also running a hydraulic pump that is running the hydraulic motor that turns my 12kw 120v generator . . . . so if I have a need for LOTS of 120 power, there is no need to start another diesel engine to provide the hyd pressure/flow.

Just thinking out loud . . . .

The old Gardners are pretty efficient compared to a lot of other diesels. It also helps that your propulsion package (including the CPP) and hull are all well matched for efficiency. In general, once you get past the old Detroits, newer diesels haven't gained all that much efficiency compared to older ones. Maybe 10-15 percent at best. But the newer stuff often scales better, so efficiency doesn't change as much with RPM or load.

I'd expect that a well selected modern package could at least match your existing setup, but I'm not sure you could do a whole lot better. Most of the highest efficiency modern engines are just bigger and more powerful than your boat needs.

slowgoesit said:

I find it difficult to understand why some new, modern, state of the art engines burn twice as much (or more) fuel than my Gardner 8LXB, designed, I believe, in the 1950's, and built in 1978 burns.

Click to expand...

What new, modern, state of the art engines are you comparing to yours?

In what boats?

-Chris

Clean air diesels run a richer combustion mixture to promote
more efficient combustion than their older counterparts.
Thus, they pollute less but burn more fuel doing so.

We have observed this 1st hand on several of our tugs that
have had older mechanical diesels replaced with their new
equivalent electronic sibling.

All of the above is true. In addition, the Gardner operates at low rpms, so it has low parasitic loads. Also I suspect the piston and rings were designed for minimum friction but ignore fuel and exhaust leakage past the rings.

David

It's really hard to compare boats relative to fuel burn. You can have two identical boats withe the exact same engine / transmission package, but different pitch props can require the RPM to be different enough to effect fuel economy. Obviously I'm wandering off in the weeds here. To me, the tell all is how many HP per gallon the engine generates in the peak part of the torque curve. Most fuel efficient diesels in our size range are generating around 20 HP per gallon in the peak of the torque curve. After that, it's a question of whether you can get the speed you want in that peak torque area.

Ted

I think the underlying assumption is incorrect, namely that a Garner is twice is efficient as a modern day engine. If I remember correctly a Gardner consumes around 190-200 g/kw-h of output power (bsfc). My 2017 Scania consumes the same. For similar size/output engines, I just haven't seen huge variation in efficiency of the engine itself.


And comparing one boat with a Gardner to another boat with something else is a nearly impossible task since there are so many different variables. It's comparing apples to gorillas. Even accurately measuring fuel consumption is highly problematic.


Engines on their own are well characterized, and with some searching, data that is often published. BSFC is an apples to apples comparison between two engines. A Gardner is quite good, but definitely not 2x anything, let alone any current build.

ranger58sb said:

What new, modern, state of the art engines are you comparing to yours?

In what boats?

-Chris

Click to expand...

Chris, thanks for your input. I looked at various engines, not boat specific, since I'm looking at HP output for engines at different RPM's, but even that is problematic with a CPP, since I can do 1300 rpm for instance at flat pitch (equivalent to being in neutral with a boat without CPP). or 1300 rpm at a pitch to push our boat 7.5 kts at about 430 deg F Pyrometer (EGT). Comparing manufacturer HP output at various RPM's without CPP, and associated fuel burn listed is what I looked at.

My intent is not to get down in the weeds of minutia with this, so if that is what you are after, you're barking up the wrong tree! This thread was just a casual observation regarding newer vs older engines. For instance in our GB36, re-engined with a Cummins 6BTA, fuel consumption was about 4.5 gph at 7.5kts, using around 80 to 100 hp.

Just to make it clear, I'm NOT interested in doing a doctoral thesis thesis here, just casual conversation.

slowgoesit said:

Chris, thanks for your input. I looked at various engines, not boat specific, since I'm looking at HP output for engines at different RPM's, but even that is problematic with a CPP, since I can do 1300 rpm for instance at flat pitch (equivalent to being in neutral with a boat without CPP). or 1300 rpm at a pitch to push our boat 7.5 kts at about 430 deg F Pyrometer (EGT). Comparing manufacturer HP output at various RPM's without CPP, and associated fuel burn listed is what I looked at.

My intent is not to get down in the weeds of minutia with this, so if that is what you are after, you're barking up the wrong tree! This thread was just a casual observation regarding newer vs older engines. For instance in our GB36, re-engined with a Cummins 6BTA, fuel consumption was about 4.5 gph at 7.5kts, using around 80 to 100 hp.

Just to make it clear, I'm NOT interested in doing a doctoral thesis thesis here, just casual conversation.

Click to expand...

For the GB36, 7.5 kts was likely faster than an ideal speed. Your current boat has a longer waterline, so the fuel burn cliff starts at a higher speed. Plus, the flat transom SD hull GB was likely a slightly more draggy hull, although lighter weight would have offset some of that.

twistedtree said:

I think the underlying assumption is incorrect, namely that a Garner is twice is efficient as a modern day engine. If I remember correctly a Gardner consumes around 190-200 g/kw-h of output power (bsfc). My 2017 Scania consumes the same. For similar size/output engines, I just haven't seen huge variation in efficiency of the engine itself.

Click to expand...

Not sure why you think that "the underlying assumption is that a Gardner (not Garner) is twice is (sic) efficient." I never made that statement.
Fact is that I am getting 7.5 nm through the water, using 2.4 gallons/hour.

Interesting Fact: A similar Beebe designed boat, same hull, similar loading, with a Cummins 6BTA, 215hp version, at 7.5kts, he is burning 6.6 gph. You can draw whatever concussion from that you want, but both boats, side by side, same hull design, similar loading, etc, one goes 3.125 miles on one gallon of diesel, the other, 30 year newer design engine, goes 1.36 miles on one gallon of diesel . . . . . call it whatever it is, more efficient, whatever, just curious.

rslifkin said:

For the GB36, 7.5 kts was likely faster than an ideal speed. Your current boat has a longer waterline, so the fuel burn cliff starts at a higher speed. Plus, the flat transom SD hull GB was likely a slightly more draggy hull, although lighter weight would have offset some of that.

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I agree, not a perfect comparison, as my GB36 had a hull speed of 7.9 kts, and my Beebe's hull speed is calculated at 9.2 kts, but it IS a comparison of sorts.

I think you stepped on a hornets nest with this thread.. But love your boat, love the story of the trip and think its one of the nicest boats on the forum.. Enjoy!

slowgoesit said:

Not sure why you think that "the underlying assumption is that a Gardner (not Garner) is twice is (sic) efficient." I never made that statement.
Fact is that I am getting 7.5 nm through the water, using 2.4 gallons/hour.

Interesting Fact: A similar Beebe designed boat, same hull, similar loading, with a Cummins 6BTA, 215hp version, at 7.5kts, he is burning 6.6 gph. You can draw whatever concussion from that you want, but both boats, side by side, same hull design, similar loading, etc, one goes 3.125 miles on one gallon of diesel, the other, 30 year newer design engine, goes 1.36 miles on one gallon of diesel . . . . . call it whatever it is, more efficient, whatever, just curious.

Click to expand...

That seems really high for the Cummins. Maybe a gearing/pitch issue? I agree with the previous posts that efficiency spreads between older and newer diesels should be pretty minimal *all else equal*. It's also really hard to get all else equal in practice.

slowgoesit said:

Regarding "new" vs "old" diesel engine fuel burns.

I find it difficult to understand why some new, modern, state of the art engines burn twice as much (or more) fuel than my Gardner 8LXB, designed, I believe, in the 1950's, and built in 1978 burns.
. . .

Click to expand...

Wow, an 8lxb seems generous for a 50fter

Our sister from another father ship at 55ft has a 6lxb
They considered a 6lxb for ours @ 60ft during the rebuild but went nta855 Cummins instead
Friends with the 65 ft milkraft hull with a few feet extra beam have an 8lxb.

They report a similar fuel burn to ours @ 7.5 to 8kn

slowgoesit said:

Chris, thanks for your input. I looked at various engines, not boat specific, since I'm looking at HP output for engines at different RPM's, but even that is problematic with a CPP, since I can do 1300 rpm for instance at flat pitch (equivalent to being in neutral with a boat without CPP). or 1300 rpm at a pitch to push our boat 7.5 kts at about 430 deg F Pyrometer (EGT). Comparing manufacturer HP output at various RPM's without CPP, and associated fuel burn listed is what I looked at.

My intent is not to get down in the weeds of minutia with this, so if that is what you are after, you're barking up the wrong tree! This thread was just a casual observation regarding newer vs older engines.

Just to make it clear, I'm NOT interested in doing a doctoral thesis thesis here, just casual conversation.

Click to expand...

Not to worry. Intent behind my question was just to set up for a subsequent comment about apples to gorillas, different results from engines, boats (lengths, weights, hull shapes), gears, speeds, etc....

And then a further recognition that we don't always have control over selection: the available boat has whatever engine it has, repowering is expensive and not usually necessary and certainly not always economical... etc etc etc.

Our boat, not at all designed or set up for "economical" actually does OK at trawler speeds. Not great, others could certainly use less fuel... but not bad. And then lots of boats with more "economical" engine won't make 30 kts on demand, either.

-Chris

slowgoesit said:

Not sure why you think that "the underlying assumption is that a Gardner (not Garner) is twice is (sic) efficient." I never made that statement.
Fact is that I am getting 7.5 nm through the water, using 2.4 gallons/hour.

Interesting Fact: A similar Beebe designed boat, same hull, similar loading, with a Cummins 6BTA, 215hp version, at 7.5kts, he is burning 6.6 gph. You can draw whatever concussion from that you want, but both boats, side by side, same hull design, similar loading, etc, one goes 3.125 miles on one gallon of diesel, the other, 30 year newer design engine, goes 1.36 miles on one gallon of diesel . . . . . call it whatever it is, more efficient, whatever, just curious.

Click to expand...

6.6 gph would indicate that he's using somewhere around 120 hp to push the boat through the water. Either that, or that boat has a ton of accessory drag pulling from that engine (like running with that hydraulic gen heavily loaded all the time, as 12 kw will add about 20hp of demand plus hydraulic losses).



It's quite possible that something is just very poorly optimized on that boat, as even a 2 stroke Detroit isn't inefficient enough to account for that much more fuel burn than your Gardner.

slowgoesit said:

For instance in our GB36, re-engined with a Cummins 6BTA, fuel consumption was about 4.5 gph at 7.5kts, using around 80 to 100 hp.

Click to expand...

For another data point, our NT37 has a 2001 Cummins 6BTA 5.9 M3, 330 hp. Over the past 4,000 engine hours, at our cruising speed of 7.25 knots, we average 3.7 nmpg, which translates to 1.96 gph. And this is not considering that some fuel is used by the heater and the generator. Does not seem like a problem with the fuel efficiency of the engine.

twistedtree said:

And comparing one boat with a Gardner to another boat with something else is a nearly impossible task since there are so many different variables. It's comparing apples to gorillas. Even accurately measuring fuel consumption is highly problematic..

Click to expand...

Amen. I do find it curious that reported fuel economy always seems over-stated vs understated. I've only felt confident of fuel burn once. I delivered an N57 from Dana Point to Ft Lauderdale over a 25-day period. Roughly 4500 nms, 3000 gals fuel, and 500 engine hours plus 70 generator hours.

I was a guest on a Willard 40 with JD4045T from Long Beach to La Paz, about 1000 nms. From the sight gauges, appeared damn close to 1.5gph and we averaged 7.2 kts, but I didn't do the fueling and keep full records so only an informed guess.

I'm sorry, but someone has to say it. Anyone who thinks an old NA Gardner (or Perkins or Lehman) is more fuel efficient than the new stuff they're putting out is wrong. California paid millions to yank old engines out of fishing boats because they were inefficient. If truckers could improve their fuel mileage by running a 50-year old engine they'd be first in line. There are good reasons to run an old engine. Fuel efficiency is not one of them.

Peter

I just looked up some data on the Gardner 8LXB. It's rated 175hp at 1500 RPM. At full power, it burns 8.4 gal/hr, giving an output of just over 20.8 hp-hr per gallon. That efficiency seems to scale very well across the whole RPM range for that engine.



FWIW, the most efficient modern small-ish diesels are in the 20 - 21 hp-hr / gallon range. Some may get as high as 22. Many of the smaller, naturally aspirated engines are down in the 18 - 19 hp-hr per gallon range. 2 stroke Detroits are typically around 16 - 18.



So the Gardner is still quite efficient by modern standards. Not meaningfully better than most modern engines, but it's just as efficient as the majority of them.

My first theory was that Gardner made stationary and marine engines, which is a different beast than a "generic" diesel that may have to climb hills, shift gears, etc. I thought that maybe the newer engines had to be a jack-of-all-trades in order to make commercial sense. The difference would be a tortoise and hare kind of issue. The Gardner just plods along and it's efficiency is due to the fact that it only need plod along.

Then I looked at Wikipedia (the font of modern knowledge). It turns out that Gardner made a diesel for the Bentley in the 1930's. 80 mph and 30 mpg. So much for my hypothesis.

https://en.wikipedia.org/wiki/L._Gardner_and_Sons

mvweebles said:

California paid millions to yank old engines out of fishing boats because they were inefficient. If truckers could improve their fuel mileage by running a 50-year old engine they'd be first in line. There are good reasons to run an old engine. Fuel efficiency is not one of them.

Peter

Click to expand...

I agree with your conclusion, but for the record, the reasoning behind the engine swap subsidy was not efficiency (which would reduce GHG), but criteria pollutants (NOx and PM mostly).

As has been pointed out, there *is* actually a slight tradeoff between efficiency and criteria pollutants - you generally want higher combustion temps (via higher compression ratios for NA engines) for peak efficiency (Carnot's law shows max theoretical efficiency scales with combustion temp). But at high temps, the O2 in the air starts reacting with the Nitrogen, creating NOx.

That said, the efficiency hit for emissions reduction is relatively small - certainly not on the order of 20% or 50%.

Simi 60 said:

Wow, an 8lxb seems generous for a 50fter
Our sister from another father ship at 55ft has a 6lxb
They considered a 6lxb for ours @ 60ft during the rebuild but went nta855 Cummins instead
Friends with the 65 ft milkraft hull with a few feet extra beam have an 8lxb.
They report a similar fuel burn to ours @ 7.5 to 8kn

Click to expand...

Simi, I totally agree. I actually would have preferred a 6LXB. Plenty of power, and I would have had/saved about 20 more inches in my engine room! It may have been the case that the original owner was not able to source a 6LXB, but could get an 8LXB. I honestly don't know.

On fuel economy being overstated (can we even use the word "economy" for a boat?!?
Anyway, fuel burn at cruise was measured by disconnecting two fuel lines, one out of the Racor filter to the engine, and one FROM the engine, returning to the tank. Both were given longer hoses, and placed into a five gallon fuel tank (with level marked), so fuel draw and fuel return from the engine were to the same source, then run for exactly 60 minutes at 7.5k ts speed over ground (roughly slack tide, little current). 1300 rpm, EGT of 430 deg F, 3.5 on the CPP pitch lever. Then I reverted back to my normal fuel supply, shutting off the valves to the portable tank, and removing the fuel hoses from the tank. Back at the dock, I refilled the tank back to the original marked level. 2.39 gallons per the state inspected, verified, certified fuel pump. . . . . soooo, that's where I came up with 2.4 gallons/hour. Please let me know if my method was in error.
I chose to do do it this way rather than using a flow meter or such because I wished to eliminate any possibly calibration error. . . . of course the state certified fuel pump may have been grossly in error, registering only 2.39 gallons when in fact it pumped in 5 gallons, or it's possible that the portable 5 gallon tank looked like it was about half empty, when if fact it really only had 2 ounces of fuel remaining. After all, anything is possible, but I feel pretty confident about methods.

Your method is pretty accurate for a number under the conditions you had at the time. Load on your hydraulic generator as well as sea state will have some effect though. I'd expect your worst case burn in a heavier sea state and with more generator load to be 3+ gal/hr.

Wait a minute, my 34 year old mechanical diesel engines burn less fuel than those "modern" electronic controlled engines with all the spaghetti hanging off them? I feel all better now.

ancora said:

Wait a minute, my 34 year old mechanical diesel engines burn less fuel than those "modern" electronic controlled engines with all the spaghetti hanging off them? I feel all better now.

Click to expand...

To put it simply, no, they don't.

socalrider said:

I agree with your conclusion, but for the record, the reasoning behind the engine swap subsidy was not efficiency (which would reduce GHG), but criteria pollutants (NOx and PM mostly).
...

Click to expand...

That is what I remember. CA and the US EPA required engine changes to meet emission requirements and improved fuel efficiency was not part of the requirements.

socalrider said:

That said, the efficiency hit for emissions reduction is relatively small - certainly not on the order of 20% or 50%.

Click to expand...

Years/Decades ago, as the new emission diesels where replacing the older, more fuel efficient engines, there was a run on the semi models using the older engines, since they were much cheaper to operate compared to the newer, required engines. The caused a bump up in sales for semi and medium duty trucks using the older engines, followed by a crash in sales for the new trucks.

From memory, the older semi engines were getting 7ish MPG and the new engines were going to be 5ish MPG. That is a pretty significant decrease in MPG, and thus, an increase in fuel costs.

Years ago, we were looking at a boat build that used JD engines. Looking at the engines across the different emission tiers, you could see an increase of fuel usage, I think 5% to 10% depending on HP burned. We showed this to the builder, who sent a note to the JD representative, who never responded.

The irony of all of this emission requirements, is that the US EPA contracted with several universities in the US to stuffy the health issues of of diesel emissions. Their test was to use a medium duty truck, with a 7.3L diesel, that had it's exhaust piped to a box that contained a person who would then breath said exhaust. The test subjects where people, who had bad health to being with, and they thought it was a good idea to make these people breath engine exhaust. Eventually, this "study" was stopped.

https://www.forbes.com/sites/larryb...eds-of-unsuspecting-subjects/?sh=3dccfad32d75

A judge dropped a lawsuit because of jurisdictional issues.

Later,
Dan

slowgoesit said:

Not sure why you think that "the underlying assumption is that a Gardner (not Garner) is twice is (sic) efficient." I never made that statement.

Click to expand...

I'm confused too. Here's what you said in your initial post:


"I find it difficult to understand why some new, modern, state of the art engines burn twice as much (or more) fuel than my Gardner 8LXB, designed, I believe, in the 1950's, and built in 1978 burns."


Is that not the same thing? This whole conversation is very "Alice in Wonderland".

Those gardeners with an adjustable pitch prop is about the best set up you can get! >3 NM per gallon is exceptional. The best part of your set up is that you don't have all that Electronic BULLSH*T that constantly breaks. Mechanical diesels are the only way to go in MHO. Fuel and Air.....that's all they need and they just keep going and going and going. Important when cruising don't you think??

I have and have had a bunch of diesels in my life, light trucks, heavy trucks, small cars boats, generators, tractors, excavators. The most efficient was a highly modded VW golf TDI that could get over 50 mpg on the flats if kept under 70. It had all pollution control devices removed and had been dyno'd at 170+ hp. I'm sure it polluted like crazy as when you held your foot to the floor she smoked like crazy. I'm currently running a 2020 Chey Silverado 3.0 diesel that no matter what you do it never smells or smokes like a diesel. It replaced a 2016 Colorado diesel that was pretty much the same. Ironically the much bigger and more powerful Silverado gets about 4 mpg better, I think the little 4 banger diesel in the Colorado was under too much load and just worked too hard ( my lead foot no doubt played a critical role in this) . The new breed of electronic diesels are cleaner, but at the cost of a lot of maintenance and significant additional operational costs. The verdict on the new truck is still out as the first 30k miles have been trouble free, unlike the Colorado which was a shop queen and by the time I dumped it at 90k miles had cost GM almost $10k in repairs. My previous 7.3 Duramax's were pretty much trouble free diesels.. go figure.

When we had Vouunteer ( 47' Seiner hull design 60k pounds and a N/A 120hp John Deere ) it consistently achieved 2.2- 2.3 GHP INCLUDING running a cruise generator and daily generator use on our summer trips up into B.C.

The use was figured using a 100 gallon day tank calibrated in 2 g. increments. It was refilled around the 40 hr of running time mark, tide currents and weather were never considered in the equation. I think some boats achieve high NMPG because of a bunch of factors that if all things align perfectly they hit that sweet spot. The high NMPG numbers that KK42, Diesel Ducks, Dashews boats and other LWL boats get seems to point to this. Personally I admire the clean burn of the new diesels, but if I were looking at a Passagemaker with a newly rebuilt Gardner or a brand new high tech clean electronic diesel the Gardner would win hands down.

When the high tech boat craps out in Paradise the tech will be probably delivered by a boat with a old diesel clattering away.
New isn't always better.
HOLLYWOOD

OP, with all due respect, you are throwing things against the wall and hoping they stick. Kudos to SoCalRider and TT for sticking with the facts and referencing the relevant Thermodynamics involved.