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"Well since you are not moving, you would be getting zero mpg."
That misconception pretty much explains why you dont understand whats happening. you KNOW that if the engine is running and the prop is turning, you are NOT getting zero mpg. You are travelling in the water at the speed of the current. But you will believe a sensor that tells you the impossible is happening. I cant help you. Do it your way. I just hope your other seamanship skills are better than your grasp of navigation. Reminds me of stories of people who drive into trees or through intersections following their GPS.
Let's say you are offshore in the Gulfstream and the stream is moving 5 MPH. You are idling, in neutral, at 5 GPH. The stream moves you 5 miles in 1 hour. In 1 hour you have burned the 5 gallons of fuel.
Yes, you burn 5 GPH to idle in neutral, for 5 miles BUT, do you get 1 MPG at idle in neutral?
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2006 Pursuit 3480 Drummond Island Sportfish
F250 Yamaha's
You dont get it with a GPS if you cant factor in what the water is doing.
you are talking about navigation.
I am talking about figuring efficiency.
If you cant see that, I give up. Someday the lightbulb will go on, I think.
I think I'm getting it now:
5. If you are fixed in relation to the surface of the earth, you are actually still moving, and your GPS is giving you faulty data.
4. You can get non-zero MPG while traveling zero distance over the earth.
3. If you are drifting in a current, you are really not moving, and your GPS is giving you faulty data.
2. You can't tell if the water is moving with a GPS, but you can with a pitot/paddlewheel.
And best of all:
1. You can get more accurate fuel burn and MPG numbers with a pitot/paddlewheel than you can with a GPS.
Lets say the current is 5 MPH. You drive your boat against the current at 6 MPH (pitot reading)you are actually traveling 1 MPH but the motor is working extra to offset the current. More fuel. So if you look at your FMG its going to calculate your actual speed(1 MPH) to the fuel burn(lets say 10 GPH). So if you continued that for 1 hour you would have burned 10 gal of gas and only traveled 1 mile. But your pitot is saying your actually traveling at 6 MPH(but remember actual is only 1) after 1 hour which would be more accurate?
If you wanted to just neuturalize the current, the pitot thinks you are traveling 5 MPH. But your not. You are still in one spot. Now if it calculates your fuel burn to keep you still and then adds what it "Thinks" your doing that will be wrong too.
If your against the same current traveling 25 MPH according to the GPS but 30 MPH according to the pitot, after 1 hour how far did you travel? Its Miles per Gallon. If your burning 25 Gal/hr accouding to the GPS you will get 1 mile/gal. According to the pitot you will get more, maybe 1.3ish. because the pitot thinks you are traveling at 30 MPH but your not..your traveling 25MPH.
If you drive at 6 mph (flow measured) for 1 hour, you have driven that boat through six miles of water. If y0u burned one gallon of fuel, you are getting 6 miles/gallon fuel usage.
GPS tells you you have travelled one mile. in one hour. You have burned one gallon of fuel. You are getting one mile/gallon if all you think of is the GPS. But thats not correct. You traversed through six miles of water to get that one mile.
Drop a chunk of wood in the water when you start your run. After one hour, you will be six miles from that piece of wood. You and that wood are in the same medium which is no way fixed to the earths surface. The wood has remained stationary in the medium, while you have moved from that position.
Now, if you had a gps on the wood as well as on the boat, and could send the wood's position back to the boats computer,with proper programming, it could tell you that you had moved six miles from your reference point. This would be accurate. And this would be taking the water conditions into consideration. and your mileage would agree with the pitot tube. But you cant get this information from a single GPS receiver alone.
I think the confusion is that some are thinking of fuel flow and not ACTUAL fuel economy.
Fuel flows into the motor (after it's started ) whether you are moving or not.
How much fuel flows into the motor over a certain distance is the "average" economy.
In a "perfect world" of flat, no wind, no current or waves to contend with, a GPS SOG tied in with a flow scan or fuel meter will give accurate mpg/fuel economy figures.
You guys are forgetting alot of other "variables" when travelling over water..............it is not "as the crow flies".
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2006 Pursuit 3480 Drummond Island Sportfish
F250 Yamaha's
"Well since you are not moving, you would be getting zero mpg."
That misconception pretty much explains why you dont understand whats happening. you KNOW that if the engine is running and the prop is turning, you are NOT getting zero mpg. You are travelling in the water at the speed of the current. But you will believe a sensor that tells you the impossible is happening. I cant help you. Do it your way. I just hope your other seamanship skills are better than your grasp of navigation. Reminds me of stories of people who drive into trees or through intersections following their GPS.
If i'm not moving forward, by definition, even though I'm using gas (which could accruately be shown with GPH) I'm NOT getting any miles per gallon. I'm not moving..where do the miles come from? The water beneath my boat? I think my fm showing me a negative miles per gallon is a bit misleading, but If that's what you would want to see, than well, whatever.
If you drive at 6 mph (flow measured) for 1 hour, you have driven that boat through six miles of water. If y0u burned one gallon of fuel, you are getting 6 miles/gallon fuel usage.
GPS tells you you have travelled one mile. in one hour. You have burned one gallon of fuel. You are getting one mile/gallon if all you think of is the GPS. But thats not correct. You traversed through six miles of water to get that one mile.
I think I understand what your saying, but why is it important to know how much water you traversed through when you are trying to figure out your actual miles/gal? My only interest is traveled distance from lets say Point A to Point B.
GPS is great for navigation between fixed points. Its not great as the best sensor under all conditions to use to determine the best combination of factors for fuel efficiency. And the mpg you got today wont necessarily be the same mpg you will get tomorrow or next week over the same course if you just use GPS.
Dont get me wrong, I love GPS. Its a fantastic navigational tool. Three GPS receivers on a fixed structure will give you platform attitude, even.
another characteristic of GPS that doesnt matter much, but that it doesnt hurt you to know, is that its never an instantaneous value. Its using modified Kalman filtering techniques, which means your speed and course over ground are alway running averages. In fact, the first few fixes the system gets after an abrupt change are thrown out until the trend is recognized and catches up with reality. It wont react instantaneously to course or speed changes. thats not important to most people for most applications, of course. It was,to me, in a former life.
Ok ok...I will shut up about it after this. I really never meant to get so...so...pedantic about it. I guess I figured some people would think that it doesnt hurt to know what your instruments are really telling you, I think. And I saw some misconceptions. Thats all.
Ok, but what you are describing is not something I could usefully take into consideration. What is important to me is my actual miles per hr. Actual miles traveled. When the FMG calculates my fuel burn to speed then I can get an accurate MPG. Actual miles traveled.True, you are traveling through more water but when Im trying to get my best MPG thats not important to me. I also agree your MPG,GPH,Speed,fuel burn,etc will always be different depending on conditions, but most times you can make adjustments to reach your optimum fuel efficiency.
my pitot is crap anyway, its hardly ever close so why would i want to use it calculating my mpg. gph is a better gauge anyway which is the actual fuel burn and doesn't matter how much current or whatever else the pitot is reading.
my pitot is crap anyway, its hardly ever close so why would i want to use it calculating my mpg. gph is a better gauge anyway which is the actual fuel burn and doesn't matter how much current or whatever else the pitot is reading.
How dare you question the supremecy of the pitot for measuring boat speed and/or distance traveled?!
A couple of posters, in driving home the already universally-recognized fact that a pitot gauges speed throught the water, while a GPS gauges speed over ground, choose to ignore the fact that a pitot-based speedometer is grossly inaccurate over most of its range.
Re: Connecting Yamaha Gauges to GPS 
) whether you are moving or not.
