Speak of coincidences. After the long discussion of the best way to measure
fuel consumption (i.e., gallons per hour or miles per gallon) today's mail
brought the latest copy of SCIENCE, the publication of the Amer. Assn. for the
Advancement of Science. In it was an article entitled "The MPG Illusion."
(Larrick, R. P. and Soll, J. B. "The MPG Illusion", Science, Vol. 320, 20 June
2008, pp.1953-1954)
The authors, professors at Duke University, reported on a series of
experiments which demonstrated a systematic misunderstanding of MPG as a measure of
fuel efficiency. People, almost invariably, tend to undervalue the effect of
small improvements on inefficient vehicles. For example, if asked to estimate
which change saves the most gas, going from a car that gets 15 MPG to one that
gets 20 MPG, from a car that gets 20 MPG to one that gets 30 MPG, or from one
that gets 30 MPG to one that gets 44 MPG (a Prius). Most people chose the change
form 30 MPG to 44 MPG as saving the most gas when, in fact, it saved the
least. The big difference in MPG between the two cars gave a false illusion of gas
saving. However if the difference in fuel consumption is expressed as gallons
per 100 miles (GPM), the way most European do, a mistake in gas saving is
rarely made.
I haven't had time to put this into the context of boating yet but it seems
to me that the best metric for fuel efficiency is gallons per 100 NM rather
than gallons per hour or miles per gallon.
As an example of the various metrics, my Willard 30 uses .82 gallons per hour
at its cruising speed of 6 KT. That works out to 7.3 MPG or 13.7 gallons per
100 NM. If I want to calculate the amount of fuel I will use on a given trip,
it is far easier to use the gallons per 100 miles metric. For instance on a
200 NM trip I will use 27.4 gallons. Crossing the Atlantic, a 3000 mile trip,
would take 30 x 13.7 gallons or 411 gallons. Since my boat's fuel tank only
holds 120 gallons, I guess such a trip is out of the question.
Larry Z
Gas prices getting you down? Search AOL Autos for
fuel-efficient used cars.
(http://autos.aol.com/used?ncid=aolaut00050000000007)
Speak of coincidences. After the long discussion of the best way to measure
fuel consumption (i.e., gallons per hour or miles per gallon) today's mail
brought the latest copy of SCIENCE, the publication of the Amer. Assn. for the
Advancement of Science. In it was an article entitled "The MPG Illusion."
(Larrick, R. P. and Soll, J. B. "The MPG Illusion", Science, Vol. 320, 20 June
2008, pp.1953-1954)
The authors, professors at Duke University, reported on a series of
experiments which demonstrated a systematic misunderstanding of MPG as a measure of
fuel efficiency. People, almost invariably, tend to undervalue the effect of
small improvements on inefficient vehicles. For example, if asked to estimate
which change saves the most gas, going from a car that gets 15 MPG to one that
gets 20 MPG, from a car that gets 20 MPG to one that gets 30 MPG, or from one
that gets 30 MPG to one that gets 44 MPG (a Prius). Most people chose the change
form 30 MPG to 44 MPG as saving the most gas when, in fact, it saved the
least. The big difference in MPG between the two cars gave a false illusion of gas
saving. However if the difference in fuel consumption is expressed as gallons
per 100 miles (GPM), the way most European do, a mistake in gas saving is
rarely made.
I haven't had time to put this into the context of boating yet but it seems
to me that the best metric for fuel efficiency is gallons per 100 NM rather
than gallons per hour or miles per gallon.
As an example of the various metrics, my Willard 30 uses .82 gallons per hour
at its cruising speed of 6 KT. That works out to 7.3 MPG or 13.7 gallons per
100 NM. If I want to calculate the amount of fuel I will use on a given trip,
it is far easier to use the gallons per 100 miles metric. For instance on a
200 NM trip I will use 27.4 gallons. Crossing the Atlantic, a 3000 mile trip,
would take 30 x 13.7 gallons or 411 gallons. Since my boat's fuel tank only
holds 120 gallons, I guess such a trip is out of the question.
Larry Z
**************
Gas prices getting you down? Search AOL Autos for
fuel-efficient used cars.
(http://autos.aol.com/used?ncid=aolaut00050000000007)
