Fuel Efficiency
- Thread starter Roy
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The owner of our marina has a 40' single diesel trawler and I believe he gets about 5 mpg at 7-8 knot. In my 38' Carver, if I throttle back to 7-8 knots, I get about 1 mpg.
So yes, there are more fuel efficient technologies out there including the oldest - sail.
So yes, there are more fuel efficient technologies out there including the oldest - sail.
Marine engines operate under a more constant load than automotive engines. Like driving a car uphill all of the time. A hybrid going uphill all of the time is going to be using it's combustion engine most of the time.
There is a scale to efficiency that has been well known for a long time. WW2 era submarines were diesel electrics, a true hybrid power plant. So are diesel electric locomotives.
Making hybrid tech work on small boats is more challenging. For instance, hybrid cars make use of kinetic energy recovery on braking and deceleration. There is no opportunity for that in boats unless something like retractable paddlewheels are used.
There is a scale to efficiency that has been well known for a long time. WW2 era submarines were diesel electrics, a true hybrid power plant. So are diesel electric locomotives.
Making hybrid tech work on small boats is more challenging. For instance, hybrid cars make use of kinetic energy recovery on braking and deceleration. There is no opportunity for that in boats unless something like retractable paddlewheels are used.
At 5kn I get 4.5 mpg and at 8kn we get 3.2 mpg on the 411 with twin 380 QSB's.
I saw an interesting system on a new trawler being fitted locally - besides the single diesel as main propulsion they had added a secondary electric motor in the drivetrain. This could push the trawler at slower speeds (I believe it was around 4-5kn) and was powered by a secondary smaller diesel generator which used very little fuel. I thought that was a neat "hybrid" idea and have been wondering how difficult that would be to retrofit somehow.
I'm not sure that was intended as a "hybrid" system or as an emergency "get home" motor. I've seen several single-engine trawlers with a drive off the genset. Some hydraulic, some electric, one chain drive. To be honest though I doubt the genset is going to get any better mileage than the main engine.
It is a lot easier to use a more efficient hull form and less speed to get better fuel efficiency in a boat than to try to develop more efficient marine power. Something akin to a downeast hull and being satisfied with a slower cruising speed is my answer to the problem. The newer electronic diesels are a good deal more efficient at slower speeds, not all that much better than an old style diesel when nearer rated power. My 1977 34' Mainship Mk I burns about 2 gph at 7 knots with the original single Perkins 160hp diesel--no need to get all high tech.
trumanlake
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Kept an accurate log so far this year, right around 2.5mpg at 17 - 22 knots. Close to 500 miles and haven't gone anywhere.
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If you want fuel economy in a boat, get a sailboat, and drop in a small engine, then go at 80% of hull speed ( likely well below 10 kts ). You should get excellent mileage.
The issue is hull design and mode of operation. A displacement ( only ) design is very efficient. It is also limited to hull speed ( a simple rough estimate of hull speed is the square root of waterline length ) ie: you would be around 5 to 7 kts.
A planing hull "cheats" and exits the displacement domain, and "skips" over the surface of the water. When cruising, a planing hull has very little in common with a displacement hull. Once a planing hull "gets over the hump" it offers a speed far in excess of hull speed, at a cost of ( commonly ) 2 to 3 times the fuel consumption rate of a displacement hull.
Most of the 25 ft to 65 ft recreational hull designs are some form of compromise between the two "pure" types. Literally, YMMV.
btw: As others have stated, there are powertrains that offer better economy. The "catch" is that, in general, they are specific to an application, tend not to be useful in "small sizes" and are often, not only expensive, but heavy. The best way ( currently ) to improve mileage in recreational boats is to get a better hull design, or operate you vessel withing "displacement" speeds ( around 5kts ).
The issue is hull design and mode of operation. A displacement ( only ) design is very efficient. It is also limited to hull speed ( a simple rough estimate of hull speed is the square root of waterline length ) ie: you would be around 5 to 7 kts.
A planing hull "cheats" and exits the displacement domain, and "skips" over the surface of the water. When cruising, a planing hull has very little in common with a displacement hull. Once a planing hull "gets over the hump" it offers a speed far in excess of hull speed, at a cost of ( commonly ) 2 to 3 times the fuel consumption rate of a displacement hull.
Most of the 25 ft to 65 ft recreational hull designs are some form of compromise between the two "pure" types. Literally, YMMV.
btw: As others have stated, there are powertrains that offer better economy. The "catch" is that, in general, they are specific to an application, tend not to be useful in "small sizes" and are often, not only expensive, but heavy. The best way ( currently ) to improve mileage in recreational boats is to get a better hull design, or operate you vessel withing "displacement" speeds ( around 5kts ).
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Here's a gas vs diesel comparison in the same boat.
33' 13' beam planing hull
twin 454's 330 HP .7nmpg at most efficient planing speed - 15-16 kts
twin Yanmar 315 hp (about 250 CID) 1.3- 1.4 at best cruise 19 - 20 kts
RWS
33' 13' beam planing hull
twin 454's 330 HP .7nmpg at most efficient planing speed - 15-16 kts
twin Yanmar 315 hp (about 250 CID) 1.3- 1.4 at best cruise 19 - 20 kts
RWS
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The technology has been around for centuries - its called "Wind".
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As previously noted, that is not a "hybrid" system but a "get me home" set up also known as a "wing" engine. The set up has been arounf for a while.
tugboat kevin
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i enjoy watching the old wooden boats glide thru the water they are truley graceful and barly leave a wake... most plastic bubble boats are about as efficiant off plane as a loaded barge and just push a hole in the water with a huge wake somewhere along the line we forgot how to make a vessel glide thru the water sorta like a helicopter vs sail plane the chopper just beats the air into submission with lots of power and fuel while the sail plane slips thru the air both achive flight
I agree with you Kevin... but in our quest for speed, "compromises" had to be made. A hull form that can do 40 mph simply isn't that efficient off-plane. With the higher fuel prices though, I expect things are going to change eventually.
With lower design speeds there are a lot of savings:
1 Smaller engines (cost savings)
2 less fuel burn (cost savings)
3 less fuel carried (weight savings)
4 Lighter hull (weight and cost savings)
5 Smoother ride
6 less noise
7 less wake
(1-4 won't matter for some folks)
With lower design speeds there are a lot of savings:
1 Smaller engines (cost savings)
2 less fuel burn (cost savings)
3 less fuel carried (weight savings)
4 Lighter hull (weight and cost savings)
5 Smoother ride
6 less noise
7 less wake
(1-4 won't matter for some folks)
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Lets also not forget supply and demand weighed against the consumer. When the economy was flying high and everybody had instant ATM machines in their homes equity - people wanted the bigger faster boat as opposed to the slower hull styles.
The Maqinship MK 34 Trawlers origins date back to the 1st Oil problems in the US. The economy was bad similar to the economy we are in. I wish I had one and not the model I have. They can have soft decks but many have survived or been repaired. There were 3 models the MK1-3. Great boat they can be had for a song right now. I have seen a few modernized with new Cummings. This is a very nice boat for it's time and the current times.
Bill
Bill
Doesn't it need a pre-heater of some kind? I'd hate to try it and have it NOT work, then have a tankful I can't use and can't get out of the tanks.
Any marinas even offering B-20 yet or am I going to be hauling it down in 5-gallon cans?