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View Poll Results: Are you cruising any slower to save diesel?
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Old 13-01-2008, 01:12   #31
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Originally Posted by MidLandOne View Post
I hauled some figures out for just one of those in order to give an idea - the very best fuel consumption in miles per gallon measured accurately on acceptance trials while off the plane were nearly 25% more than those when the boat was on the plane so in terms of mpg was much more inefficient off the plane.
The grammar in my above could be confusing, would have been better written as -

" - the very best fuel consumption in miles per gallon measured accurately on acceptance trials while off the plane were nearly 25% worse than those when the boat was on the plane so in terms of mpg fuel consumption was much more inefficient off the plane."
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Old 13-01-2008, 07:08   #32
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2 qts per hour, don't think I can burn much less...;-)
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Old 16-01-2008, 22:27   #33
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I don't know Wheels. I am not sure if MidlandOne was referring to miles per gallon or gallons per hour when measuring efficiency. The former is a true measure of efficiency but the latter is not. Gallons per hour is easily measured from modern engines fuel burn rate meters but determining gallons per mile requires an accurate speed meter plus an accurate fuel consumption meter.

Perhaps some boats are capable of getting better miles per gallon barely on a plane than they are at hull speed?...this would make sense...but eventually as speed increases, the MPG would have to drop below that of full displacement speeds.

It would be interesting to hear back from Midland with more details.
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Old 17-01-2008, 03:40   #34
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It would be interesting to hear back from Midland with more details.
Hi David - I haven't got the exact figures with me as I am on my boat until tommorrow evening but I had referred to them from the sea trials documentation of one of the vessels prior to making my earlier posts. The vessel was a commercial one so while a very powerful vessel it was not an especially light one (it was actually required to carry quite high deadweight compared to a pleasure vessel and constructed to Lloyds so scantlings were not light) and a catamaran (but I know monohulls that perform the similarly).

The following comments are based on miles per gallon, as were my earlier posts, (actually the sea trials figures were gallons per mile as it was a thirsty boat ) which as you say gives the true measure of efficiency.

From the time the boat I used to get some example figures was properly on the plane right through to maximum speed the fuel use in miles per gallon was essentially constant ie going faster increased fuel consumprion per hour as one would expect but the miles per gallon did not increase, they were essentially constant.

In the period from slow speed up until the boat was fully on the plane the best fuel consumption in miles per gallon was nearly 25% worse than the consumption on the plane. That is it was most economical to operate the vessel, as far as fuel consumption was concerned, on the plane. And once on the plane then from a miles per gallon point of view it did not matter how fast the boat went fuel consumption in miles per gallon was essentially constant (within experimental error).

In this case the fuel flow was measured by the engines' ECS's supplemented by equipment on board with the engine manufacturer's representative and speed measured by GPS on reversed runs. This vessel had an exact sister vessel which I was also on for sea trials some weeks apart from the other one and the overall results were essentially identical and the fuel flows for each of the engines on both boats matched that of all the other engines within minor variances, so validating the results.

I have not been in the position to be part of such measurements for heavy deep vee hull forms but I would wonder if they would be able to produce figures more efficient at planing speeds than at displacement speeds as the above vessels, for example, do.

I would also wonder if low powered ones, whether monohulls or cats) would be able to too. For example, I am quite familiar with some cats which do reach "planing" speed but really they just make it whereas the boats above, for example, can nearly double their speed as between getting on the plane to maximum speed and pretty much sit on the water while doing so rather than in it.

But perhaps such deep vee'd or low powered vessels would be better classed as semi displacement and when in full displacement mode probably approximate a displacement hull and show similar fuel efficiencies as those. Of course, a semi displacement vessel becomes less efficient in terms of miles per gallon the faster it is driven.
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Old 21-01-2008, 11:10   #35
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Does running a diesel engine in a sailboat at a lower rpm really save fuel? I thought that it is best to run them at the recommended rpm for the best economy. In my case that would be about 2500 rpm for my engine that is rated for 3600rpm.
Hermann Klein, an executive at Germanischer Lloyd classification society, said: "The number of shipping lines reducing speed to cut fuel costs has been growing steadily." His organisation runs safety surveys on more than 6000 ships worldwide.
"Slowing down by 10 per cent can lead to a 25 per cent reduction in fuel use. Just last week a big Japanese container line gave notice of its intention to slow down."
Shipping was excluded from the United Nations's Kyoto Protocol to slow climate change, but many nations want the industry to be made accountable for its impact on the climate in the successor to Kyoto.
In Hamburg, the Hapag-Lloyd shipping company is not waiting for 2012. The company in the second half of last year cut the standard speed of its ships to 20 knots from 23 1/2 knots, and said it saved a "substantial amount" of fuel.
The calculation used in shipping is complex: longer voyages mean extra operating costs, charter costs, interest costs and other monetary losses. But Hapag-Lloyd said slowing down still paid off handsomely.
"We've saved so much fuel that we added a ship to the route and still saved costs," said Klaus Heims, press spokesman at the world's fifth-largest container shipping line.
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