Calculate GPH

[Mischief Managed]

Re: Calculate GPH

Thanks for all the replies guys. A lot of good information here.

Is there a relatively inexpensive fuel flow meter solution? I'm seeing about $300 as the cheapest

Lowrance LMF-200 with to fuel flow sensors will be less than $300. I love mine.

 

[haulnazz15]

Re: Calculate GPH

I needed more RPM to stay at the same speed becouse of the force of the waves yet the increase in GPH wasn't caused by waves?

Here is one for you. I'm going from Cheaspeake Beach to Ocean City and back next week. It's 120 miles each way. I get 2.17 miles per gallon or 14 gallons per hour at cruise. How much fuel am I going to burn round trip?

THE INCREASE IN GPH IS CAUSED BY YOUR RIGHT HAND!!! You fuel usage increased because you increased the rpm's to combat the waves, NOT because the waves were present. If you left the engine running at the same rpms going with the waves versus going against the waves, your GPH WILL NOT CHANGE. Your MPG's obviously will, because you will have to run longer to go the same distance against the waves.

 

[Beefer]

Re: Calculate GPH

Umm... Here's my understanding (real world experiences) as to why I said GPH and MPG are directly related.

When cruising in dead flat calm (inshore) at 3500rpm, I'm moving at 24-25mph (GPS), an burning 8gph (FloScan), which is 3MPG (we'll leave decimals out for now). I use that as my baseline on my boat.

Last week, I went out in the GOM with a following sea. At 3500rpm, I was doing about 26-27mph, and burning a little less then 8gph (FloScan). Because of the following sea, I was surfing, and had less prop-slip, which equaled better efficiency (3+MPG). On the way back, with a head sea, at 3500rpm (which wasn't fun), I only got up to about 23mph, and GPH was more then 8 (almost 9), reducing my efficiency. There was increased prop-slip, and I would cover less ground in the same amount of time. This was because of climbing waves into the wind. Think of riding a sound wave at 20 mph, vs riding a straight line at 20 mph on a graph. You'll get to the end on the straight line faster then the waves, even though you are running the same speed, for the same distance between point A and B.

You will always get different GPH & MPG at constant RPM's, depending upon wind velocity (speed and direction), temps, wave size, wave direction, current, and tide. Each of those variables will have an effect on final figures.

From a math-standpoint, you can't have GPH or MPG as variables to figure the other one out. MPH / GPH = MPG or MPH / MPG = GPH. Change one, and they both change.

 

[haulnazz15]

Re: Calculate GPH

Umm... Here's my understanding (real world experiences) as to why I said GPH and MPG are directly related.

When cruising in dead flat calm (inshore) at 3500rpm, I'm moving at 24-25mph (GPS), an burning 8gph (FloScan), which is 3MPG (we'll leave decimals out for now). I use that as my baseline on my boat.

Last week, I went out in the GOM with a following sea. At 3500rpm, I was doing about 26-27mph, and burning a little less then 8gph (FloScan). Because of the following sea, I was surfing, and had less prop-slip, which equaled better efficiency (3+MPG). On the way back, with a head sea, at 3500rpm (which wasn't fun), I only got up to about 23mph, and GPH was more then 8 (almost 9), reducing my efficiency. There was increased prop-slip, and I would cover less ground in the same amount of time. This was because of climbing waves into the wind. Think of riding a sound wave at 20 mph, vs riding a straight line at 20 mph on a graph. You'll get to the end on the straight line faster then the waves, even though you are running the same speed, for the same distance between point A and B.

You will always get different GPH & MPG at constant RPM's, depending upon wind velocity (speed and direction), temps, wave size, wave direction, current, and tide. Each of those variables will have an effect on final figures.

From a math-standpoint, you can't have GPH or MPG as variables to figure the other one out. MPH / GPH = MPG or MPH / MPG = GPH. Change one, and they both change.

Absolutely agree. As you have shown, the difference in GPH is almost negligible 8GPH versus 8.8GPH (almost 9) when different sea conditions are present. When RPM's are held constant, and speed is left to be whatever it happens to be, your GPH should be pretty close to the same regardless of weather. Now fuel mileage will vary significantly with weather, as you have shown as well. Thank you for illustrating my point.

 

[Shamfarlango]

Re: Calculate GPH

Lowrance LMF-200 with to fuel flow sensors will be less than $300. I love mine.

Okay you have my attention. That model is $169 at west marine.
Would that be everything or do i need some type of connection or sensor on the fuel lines too?

 

[jigngrub]

Re: Calculate GPH

I'm curious as to why even worry about it? You use what you use, if you're going to own a boat you've got to pay to play... and if you have twin engines you should worry about it even less. You knew she was gonna be a gas hog when you bought her.

 

[Shamfarlango]

Re: Calculate GPH

Initially, it was just curiousity really. I absolutely agree that the price of gas or the GPH are not going to keep me off the water

Now i'm thinking that if it's relatively inexpensive, I could use it to find the sweet spot when cruising