Quinte Fishing

Hey guys,

I know some of you have flo tech meters on your boats, so I have a question for you. Do outboards always produce the same GPH at a given rpm, or does that increase and decrease based on load and trim? I know that MPH is effected by load and trim, but I figured that the GPH would stay constant at differing RPM's.

Just curious as I am trying to figure out where my boat gets it's best Fuel efficiency. MPH is calculated by MPH/GPH so if I can figure out my GPH I'll get to know how to save some money. Less gas burned = more lures for me.

Thanks guys.

With out the right gauge you will be guessing. That said I know from watching the guage and operating my own boat that it gets the best efficency at about 3500-4500rpm (load dependent). Its at that point that you're on plane and trimming it up and the engine just seems become a little quieter and you can tell thats its not working too hard.

_________________
Dan Elliot - A bad day on Quinte is better than a good day at work !!!
http://www.quintefishing.com

Hey guys I did some research and this is what I found, not sure if it is accurate but it seems like a good place to start:

"Here is a little metric I picked up recently (from where I cannot remember):
Compute your engine's fuel consumption at wide-open-throttle (WOT) as approximately equal to HORSEPOWER/10 = GallonsPerHour (gph).

Then, approximate the fuel consumption at a particular throttle setting as a linear percentage of the wide-open-throttle consumption.

Let's try this out with my boat:

Engine Rated Power = 70 hp
Est. Fuel Consumption WOT = 7 gph

At WOT the engine is turning about 5500 RPM.
At cruise of 4400 RPM, the fuel consumption should be about:

7 gph * (4400/5500) = 5.6 gph

At 4400 RPM we are doing about 28 MPH and burning about 5.6 * 2 = 11.2 gph, giving us a Mileage of about 2.5 Miles per Gallon (mpg).
(I had to double it because we have twin engines.)

So we are getting 2.5 mpg from our fairly low-powered set up of twin 70 HP engines.

Taking this same approach, I approximate LHG's fuel consumption, running a larger boat with bigger engines. He comes in like this:

200 HP --> 20 gallons per hour at WOT (6000).

Now for him to cruise at 28 MPH he is only running his engines about 2200 rpm, so he is burning about:

20 gph * (2200/6000) = 7.3 gph

Thus his fuel consumption is about 14.6 gph while making 28 mph, for a mileage of about 1.9 miles per gallon.

This was quite surprising to me! I thought I would would be much farther ahead with a smaller boat and smaller engines, but it turns out my fuel economy is only 0.5 mpg better, and that is only an approximation!

After cruising together for a week, it almost seemed like we were using about the same amount of fuel, implying that the fuel mileage was closer than shown above.

I also think that the approximation for fuel consumption versus engine speed is a little off. The fuel consumption is probably not linear with crankshaft speed, and it is likely lower at lower speeds than would be suggested by a linear approximation. This would again work in favor of the boat with larger engines running at lower speeds.

Comments and other observations welcomed,

--jimh"

quit worrying about your gas lol... i fish with a guy in fl with a boat very sinilar to this grady white (35') ONLY HE RUNS 3-300'S ON THE STERN LOL... wide open he burns aprox 88 gals an hr he told me... the figures below show for a twin engine at over 70 gph.. all i know is he never charges me for gas thank the lord lol...

Grady-White Express 330 Test Result Highlights
•Top speed for the Grady-White Express 330 is 50.8 mph (81.8 kph), burning 71.5 gallons per hour (gph) or 270.63 liters per hour (lph).


•Best cruise for the Grady-White Express 330 is 31.3 mph (50.4 kph), and the boat gets 1.22 miles per gallon (mpg) or 0.52 kilometers per liter (kpl), giving the boat a cruising range of 384 miles (617.99 kilometers).


•Tested power is 2 x 350-hp Yamaha Four-Strokes.

Your best GPH would be at your hull speed, the fastest the boat goes before going on plane. you can look up the formula for finding your hull speed or estimate it as the speed where the wake comes of the boat at the stern quarter or about the top speed of your kicker unless you have a big kicker that can plane the boat, for a 23 ft boat its around 7 mph. anything faster and your $ goes into making a wake.

I know this isn't really what you are looking for but its good to know if your low on fuel and want to avoid a tow.

Thanks a lot guys. It's nice to know how to get to the hole without spending a fortune. I don't fish tournaments so there is no need wasting money on an estimated 15 - 20 kph.