2 miles per Gallon vs typically 1 mile a Gallon!

Anecdotal. Use MPG in a strong tidal region and your results would vary, much, much more. Ask your self why aviation never uses MPG but rather GPH or ideally mass/hour.

Charlie, I agree a vacuum gauge is a simple measurement of engine load. I'm driving a rental car right now that has an "Eco Meter" which is really just a vacuum gauge. My problem with them is their failure mode is unannounced. A small vacuum leak will provide a spurious indication. A flow meter that stops working will be readily apparent in that it either stops providing data, or the false data is readily apparent.
 
Not incredible. Happens in most forums. Often. This thread went off on a tangent long before I added my 2 cents.

GeeBee, of course it's anecdotal. I didn't present it as an all-encompassing fact. I demonstrated why MPG is a better predictor of fuel consumption vs. distance or time (for me) than GPH is. Your results may vary :-)

PS- I boat in tidal waters, and the trip included strong tidal waters, so not sure what you meant by that.
 
Let me ask JoLin, you make a 100 mile trip. Your water speed is 10 knots. You burn 10 gph and you have a 5 knot following current. You have a 100 gal tank. What is your "mpg". Now take the return trip using the same mpg and tell me you are going to make it back.
 
A Nice but why don't you give us an example of a location where y will have 5 kts current either way, last time I checked, or.... Hells gate (NY not GA) is probably one of the worst place current wise. But that's just over a couple miles..

We cross the gulf stream as many as 8 to 12 times a year on average and depending on the speed we run at, we may see as much as a 15 to 20 % ground speed variation because of current. Not 50% .... What is freaky is running at hull speed and encountering anther boat running at hull speed at night and a it looks like we re in a crossing situation because our combined drift amounts to a 30 to 40 degrees angle so you see the other guy red light but it s cpactually meaningless.ll

Bottom line.... GPH MPG GPM...it's doesn't matter... An apple is an apple, and an orange is an orange
 
I'm w/ Pascal.

What do you want to measure?

MPG is useful for "speed through water". GPH is more useful for "speed over ground". Two different things.

GPH is useful for knowing how much fuel you have consumed ( so far ). ie: You have run for one hour. you burn 15 gal per hour. YOu have consumed 15 gallons. How far you have gone is not considered. You might be stuck on asand bar, but you are still down 15 gallons!

MPG can be handy for planning purposes.

Use the units that measure what you need to measure.
 
quote:
Originally posted by GeeBee

Let me ask JoLin, you make a 100 mile trip. Your water speed is 10 knots. You burn 10 gph and you have a 5 knot following current. You have a 100 gal tank. What is your "mpg". Now take the return trip using the same mpg and tell me you are going to make it back.
Click to expand...


I don't know what you mean by 'water speed.' Is that different from SOG? I've already demonstrated that even for much shorter legs of a trip, my GPH and average SOG vary wildly (read my post) depending on factors of speed limits, and water/wind conditions. It's highly doubtful that I would maintain a consistent 10 GPH burn for 100 miles. I have a 110 gallon tank. No way would I plan a 'leg' that was more than about 75 miles long (give or take a couple) before refueling.

Finally, a year ago I made a 200 mile round trip from the south shore of Long Island to Martha's Vineyard and back. My MPG was similar... about 1.14 MPG overall. I surmised that the reason it was a bit higher was due primarily to the fact that my bridge enclosure canvas was down for that trip, and up for this year's. Again, my MPG is amazingly consistent, where every other measurement is all over the map.

I know you're bound and determined to prove me 'wrong' for using MPG for planning, but let it go. I don't need to defend it- it works for me, the boat I own and the type of boating I do. I know diddly squat about avionics or why pilots always use GPH. Far as I'm concerned they can use whatever works for 'em. I really don't care.
 
A quick answer to, "I don't know what you mean by 'water speed.' Is that different from SOG?"

IF the water is perfectly still, then "water speed" ( ie: what the paddle wheel speedometer on the transom measures ) will be equal to SOG ( aka: Speed Over Ground; a GPS measurement ).

If the water moves ( any current at all ) then the two numbers will be different, since they measure two different things.

Speed through water or "water speed" is, literally, the velocity of travel through the water.

SOG is the distance traveled from one point to another point, over a specified time.

It is entirely possible to cover 10 miles in one hour ( SOG = 10 miles per hour ) and ALSO maintain and average speed of 15 miles per hour "water speed", because the water was moving and you actually pushed through 15 miles of water to travel 10 miles over the ground.

I hope that highlights the difference between the two. It can, in some instances be a very important difference.
 
By the way, just for other possible readers of the thread:

For a particular vessel, the gallons burned per hour can and does vary by load and speed.

Ignoring varying load ( ie: actual weight aboard, heavy vs smooth seas or wind ), your hourly burn rate can vary a great deal due to speed. ( see engine curves from mfgr ). A quick peek will show that a gasoline engine at WOT will burn at twice the burn rate of operating at "cruise". While is is not necessary to memorize your particular fuel consumption curve, you should know the GPH for idle, slow cruise, high cruise and WOT. Additional experience with your equipment will allow you to judge how heavy ( weight ) loads change the numbers from light ( weight ) loads; ditto heavy weather conditions.
 
Let me tell you JoLin, if the next time you board an airplane, and the pilot is using "mpg" you should be afraid, very afraid.
 
As long as I've been flying, I never heard an airline pilot announce whether he was using GPH or MPG for the flight. Guess I wasn't listening. Thanks for the heads up.

I got your point a long time ago. What you continually choose to ignore are 1. My experience with my boat and which measurement gives me the most consistent results, and 2. Most importantly, the safety factor I build into my planning, which at the bottom line (calculating range between fuel stops) is probably similar to your own. That's the point, isn't it? I plan to refuel with at least 1/3 tank still in reserve. And I do.

Enough already.
 
Its all measuring the same thing... Example...

Let say I need to go Nassau fro Miami, a trip we do quite a bit. 160nm

If we're in a rush, At a slow cruise of 20kts we burn about 70/72 GPH but for planning purposes I use 80gph to make up for the current in the stream, as well as on the bank depending on the tides and also for chop or swell. So its 8 hours which at 80 GPH result in 640 USG. If I use GPNM, 4 gallons per nm.... My planned fuel burn is also 640 USG... And if I do NMPG 160 no at 0.25 also comes to, oh surprise..., 640 USG. Imagine that... Three ways of planning and they all come down to the same nr!

So use what you want, results are the same.
 
quote:
Originally posted by JimPend

First of all real boaters talk GPH, figure you time with wind, sea conditions taken into account. Then always include a 20% reserve.

Click to expand...


No "real" boaters use metric tons
 
quote:
Originally posted by JoLin

As long as I've been flying, I never heard an airline pilot announce whether he was using GPH or MPG for the flight. Guess I wasn't listening. Thanks for the heads up.

I got your point a long time ago. What you continually choose to ignore are 1. My experience with my boat and which measurement gives me the most consistent results, and 2. Most importantly, the safety factor I build into my planning, which at the bottom line (calculating range between fuel stops) is probably similar to your own. That's the point, isn't it? I plan to refuel with at least 1/3 tank still in reserve. And I do.

Enough already.

Click to expand...


Airliners deal in lbs/hr to eliminate the temp effects because you are dealing with such large quantities. Believe it or not at normal surface temps, you can have a 3% variance between volume and mass which is why you see those stickers on the pumps at Costco and many other gas stations about selling by volume.
You can know your boat very well, what you cannot know is the external conditions well. Winds, currents, etc that may have gross effects beyond conservative reserves. I have just pointed out a reason that your 33% reserve can become 30%. Then I pointed out that it does not take much current change to effect SOG while running at displacement speeds. Your reserve can be ate up real fast.

I have a fuel flow meter on my boat, and I have GPS. And yes I have a nice Garmin GHP 10 that can display all the parameters, GPH, NM/gal, Trip galons, etc. Even on Lake Lanier, I can note as much as a 20% difference in NM/gal when running with and against the river current depending on wind running at planing speeds. I have seen 25% on the Tennessee river. So if you are using miles per gallon, I hope you are not using the same figure all the time.
 
quote:
Originally posted by GeeBee

Let me tell you JoLin, if the next time you board an airplane, and the pilot is using "mpg" you should be afraid, very afraid.

Click to expand...


Why not just agree to disagree. Obviously some are adamant that GPH is the only way to go. Others say MPG. MPG works for me (and others) and no matter what you or anyone else says, I'm sticking with MPG. You feel the same way about GPH. Use whatever works for each person.
 
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