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.

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???
Bruce

I usually look for miles/nautical miles divided by gallons.

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.

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?

Alaskan Sea-Duction said:

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.

Click to expand...

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.

BandB said:

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.

Click to expand...

Wish I would have said something like that!

Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

Ted

O C Diver said:

Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

Ted

Click to expand...

Thank you Captain Obvious!

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,

FF said:

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,

Click to expand...

Interesting - do gas boats have a higher burn rate than diesel generally?

BandB said:

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

Click to expand...

"Rates" have a time component don't they?

Jim
Sent from my iPad using Trawler Forum

JDCAVE said:

"Rates" have a time component don't they?

Jim
Sent from my iPad using Trawler Forum

Click to expand...

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.

BandB said:

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.

Click to expand...

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


Jim
Sent from my iPad using Trawler Forum

JDCAVE said:

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


Jim
Sent from my iPad using Trawler Forum

Click to expand...

Wifey B: Well, I rate your answer a C or a 4 on a scale of one to ten. Omg now I've really confused things by using rate as a verb.

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.

KO

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.

O C Diver said:

Miles per Gallon (MPG) = miles traveled / gallons consumed
Burn Rate (Gallons Per Hour [GPH]) = Gallons consumed / Hours running

Ted

Click to expand...

Thank you Ted. This is what i wanted.

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

sunchaser said:

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.

Click to expand...

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.