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Old 05-19-2016, 08:19 PM   #1
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Burn Rate Formula

OK TF. What is the mathematical formula for burn rate?

hours divided by fuel used

or

Fuel used divided by hours


Guess I am having too much fun.
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Old 05-19-2016, 08:22 PM   #2
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Are you asking if fuel use is normally recorded in gallons per hour or hours per gallon?
What boat? Is there a Prius of the sea???
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Old 05-19-2016, 08:35 PM   #3
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I usually look for miles/nautical miles divided by gallons.
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Old 05-19-2016, 08:49 PM   #4
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Gallons per hour is Gallons divided by hours. That's a long term average which includes idle time and sprints. Engine performance charts give fuel usage as an instantaneous flowrate IE at this RPM and this amount of load, the engine consumes that amount of fuel.
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Old 05-19-2016, 08:55 PM   #5
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Yes. but Gallons per hours only has meaning if you factor in kts/miles per hour.

If you are not trying to get your burn per mile, and therefore know what fuel it will take to get from point A to B, or simply how many miles per gallon your are getting, then why bother?
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Old 05-19-2016, 10:00 PM   #6
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Originally Posted by Alaskan Sea-Duction View Post
OK TF. What is the mathematical formula for burn rate?

hours divided by fuel used

or

Fuel used divided by hours


Guess I am having too much fun.
Burn rate would be gallons per hour.

However, usage rate would be gallons per nautical mile. Also, nautical miles per gallon is a ratio we use a lot.

However, your "hours divided by fuel used" which is hours per gallon is a ratio I can't recall seeing used.
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Old 05-19-2016, 10:11 PM   #7
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Burn rate would be gallons per hour.

However, usage rate would be gallons per nautical mile. Also, nautical miles per gallon is a ratio we use a lot.

However, your "hours divided by fuel used" which is hours per gallon is a ratio I can't recall seeing used.
Wish I would have said something like that!
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Old 05-19-2016, 10:13 PM   #8
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Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

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Old 05-19-2016, 10:16 PM   #9
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Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

Ted
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Old 05-20-2016, 06:18 AM   #10
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Lots of "Burn Rates"

THE USCG looks at hull "burn rates" for inspected vessels.

A wooden boat is 100.

The usual uninspected GRP boat is 500

An inspected pax carrying boat must use Fire Retarding resin to get back down to 100.

At perhaps a few cents a resin pound extra it makes one wonder why hulls of boats coating hundreds of thousands are still bought with 500 burn rate resin.

Maybe 1/2% difference in total boat cost,
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Old 05-20-2016, 06:33 AM   #11
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Lots of "Burn Rates"

THE USCG looks at hull "burn rates" for inspected vessels.

A wooden boat is 100.

The usual uninspected GRP boat is 500

An inspected pax carrying boat must use Fire Retarding resin to get back down to 100.

At perhaps a few cents a resin pound extra it makes one wonder why hulls of boats coating hundreds of thousands are still bought with 500 burn rate resin.

Maybe 1/2% difference in total boat cost,
Interesting - do gas boats have a higher burn rate than diesel generally?
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Old 05-20-2016, 09:57 AM   #12
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Burn Rate Formula

Quote:
Originally Posted by BandB View Post
However, usage rate would be gallons per nautical mile. Also, nautical miles per gallon is a ratio we use a lot.
"Rates" have a time component don't they?

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Old 05-20-2016, 10:06 AM   #13
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"Rates" have a time component don't they?

Jim
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Not necessarily. They have two components. One of those may or may not be time.

a measure, quantity, or frequency, typically one measured against some other quantity or measure.

Dollars per dozen is a rate just as much as dollars per hour is.
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Old 05-20-2016, 10:12 AM   #14
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Not necessarily. They have two components. One of those may or may not be time.



a measure, quantity, or frequency, typically one measured against some other quantity or measure.



Dollars per dozen is a rate just as much as dollars per hour is.

Of course. You're right. I was thinking of rate of change. My mistake.


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Old 05-20-2016, 10:41 AM   #15
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Of course. You're right. I was thinking of rate of change. My mistake.


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Old 05-20-2016, 11:01 AM   #16
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My cars tell me l/100km.
My boat tells me nothing, so I have to calculate it. At the fuel barge I look in my log for the hour meter reading at the last fill, do a quick head calculation: hours x "burn rate"= no of gals expected, fuel up, check to see if my "burn rate" has remained as it was, in GPH. Since I try to cruise at a steady rate of knots, my MPG should remain the same as it was.

FF: I know my FRP boat has a fast "burn rate". I don't care to know what it is, so long as I know how to get off if I need to.
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Old 05-20-2016, 12:38 PM   #17
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Your analysis is too rational for us simple folk. For instance, do you take into account generator use, fuel temperature, SG, calorific count, water analysis or sulfur content? If not, I don't either.
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Old 05-20-2016, 12:57 PM   #18
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Quote:
Originally Posted by O C Diver View Post
Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

Ted
Thank you Ted. This is what i wanted.
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Old 05-20-2016, 04:17 PM   #19
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Sun:

I take into account only:
location of my last note
hours since last fill
No of litres purchased
price
date
location of fill station
All of the other criteria you mentioned I leave for those much more anal than I.
Yes I have a generator, yes it gets used
I also use diesel for cabin heat and cooking
neither use a significant quantity.
I usually fill when the trim of the boat tells me to check the hour meter, then if I find there are more than 50 hours elapsed, I will start paying attention to when and where I might get a fill. If I still haven't moved to a favourable fill location by 100 hours I might make a trip just for that purpose, but so far, my random movements have worked out. So far I have gone 100 hours between fills only once.

More than you asked to know.

Keith
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Old 05-20-2016, 04:42 PM   #20
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Your analysis is too rational for us simple folk. For instance, do you take into account generator use, fuel temperature, SG, calorific count, water analysis or sulfur content? If not, I don't either.
Tom, I don't try to calculate my generator usage, I just figure that's part of the "cost of cruising" and calculate usage from fillup to fillup and divide the number of gallons by engine hours.

The vast majority of my cruising is done at or near hull speed (~9.5kts) so it's easy to calculate the gallons/hour.

If I wanted to, I could take the "miles traveled" off the GPS and use that to calculate miles/gallon or in my case, gallons/mile.
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