Accuracy of Yamaha FMS?

[Renovator]

How accurate do you guys find the Yamaha fuel management system to be with respect to fuel burn rate(mpg/gph) and total fuel burn as shown on the gauge? The reason for my question is that on my boat if the total fuel burned is correct, the actual mpg is considerably less based on the trip miles as shown on my GPS. Do these units ever need re-calibrating? Thanks for the input, I've got about 45 hrs on her now since the purchase in late September and so I am still steady on the learning curve. Boat is '05 Sailfish.

 

[fishingFINattic]

I have found the GPH and total gallons used very accurate - less than 2% error

The large error comes into the speed - it uses water pressure from the boat moving and converts this pressure to speed -

There is significant room for error with this method - moving with or against the current - plugged tube - just general error -

So - the no so accurate speed is divided by the pretty accurate gallons per hour giving a not so great value -

There are two ways to improve on this - one is to use speed from the GPS and have that sent to the Yamaha gauge (I think via nema connections) - two - if the gallons per hour is not super accurate there is a fine tune adjustment that can be done -

I hope this helps...

Tim

 

[G8RDave]

Mine has been very accurate. And. much to my dismay, my mpg don't come even close to the specs shown on Grady's site.

 

[HMBJack]

I concur 100% with the above response. Fuel Mgmt. (specifically GPH and total Gallons consumed) is very accurate on my Seafarer with a F225.
I average about 2nm per gallon depending on sea conditions and weight on board. Sometimes 2.3 nmpg, sometimes 1.85nmpg. Good luck.

 

[Tashmoo]

I have found mine to be incredibly accurate in both total consumed and MPG. That said my speed comes from the GPS as the F350 does not have a pitot tube.

 

[Renovator]

Thanks for the info. I'm thinking that the FMS may be set for statue miles instead of nautical miles as my GPS is. That would explain some of the difference. Based on my GPS I was getting less than 1 nm per gallon on my last trip (4 guys, gear, 1/2 fuel tank) seas had a 2-3' chop and a little tight but doable. We ran an average of anywhere from 3600-4200 rpm. It seems that I will have to monitor the fuel closely on my 60-70 mile runs to the ledge, I haven't made that trip yet but it may be closer on the fuel than I thought. Thanks and tight lines everyone.
Ron

 

[fishingFINattic]

Thanks for the info. I'm thinking that the FMS may be set for statue miles instead of nautical miles as my GPS is. That would explain some of the difference. Based on my GPS I was getting less than 1 nm per gallon on my last trip (4 guys, gear, 1/2 fuel tank) seas had a 2-3' chop and a little tight but doable. We ran an average of anywhere from 3600-4200 rpm. It seems that I will have to monitor the fuel closely on my 60-70 mile runs to the ledge, I haven't made that trip yet but it may be closer on the fuel than I thought. Thanks and tight lines everyone.
Ron

You should be getting much better than that!

My wife wanted the sailfish - I opted for the 265 since it held a little more fuel - I run 100 miles one way and have plenty of fuel left - your performance should be similiar -

My 265 with 200hp HPDI's fully loaded, 5 guys, ice, 250 gallons of fuel - I am 1.5 mpg (statue miles) - with two people on board, light on fuel (100 gallons) I see 1.7 to 1.8 often.

Maybe leave it set on GPH and use you GPS speed - divide the speed by the flow rate -

Another worth while effort would be to fill your tanks and reset your flow meter to zero - burn 150 gallons and refill - this will confirm accuracy of actual fuel burn -

Tim

 

[megabytes]

I believe the default for the FMS is nautical miles.

 

[gradyfish22]

Check that your fuel management and your gps are both in the same units, one may be rading nautical miles vs miles, or knots vs mph, that variation can throw your calcs off a little. As for the accuracy, it should be pretty darn close, I run offshore with full fuel...I mean when I leave I can see it at the fill and often refill it the next trip to run back offshore so checking the accuracy is sometimes easy for me, on a trip where I burn about 180-200gal and then refill the fuel Yamaha FMS will be maybe 2-3gal off at most, it is usually about 1.5-2gal under what I really burned, but I always assume it is slightly worse, plus the last 10% in each tank will never get touched since the pick up is likely not long enough to reach it so if your advertised tank is one size, your usable is less, many boaters do not factor that in as well. As for bad fuel numbers, how was the boat trimmed out, did you play with the engine trim to get it right, did you fiddle with the trim tabs, this all effects your fuel economy and can make a huge difference in your overall numbers, especially on long runs. Also, which tank you run and when and how you load the boat will effect your efficiency, all something you will need to play with to see what works best for your model. My 265 likes engines trimmed high and bow down in flat calm seas or a chop, in a sweel it likes engines trimmed up and no tab, it also will vary a little depending on which tank I have filled or am running off.

 

[grady23]

I've been around boats for most of my life and have never found a speed indicator that was run off an outboard accurate below 5 mph and is usually off by 3-4 mph at speed. Use GPS numbers for all calculations. As far as the accuracy of fuel burn, my '97 is accurate to within 2% everytime. It actually shows more fuel burned then actual. That's fine with me. I rather it be off and have more fuel then I really think I do.