Fuel Curve for 53MY

[Skip]

I took some readings last weekend - using my Floscans for MPG and tach reading, and GPS SOG for speed. My Floscan tach readings don't match my mechanical rpm guage in the pilot house so the data is off a bit (50-100 RPM lower than the mechanical tachs). Using SOG is also dependent upon prevailing conditions, but here is some of the data I got:

Tach Speed (kts) MPG
576 5.0 2.66
988 7.9 1.07
1512 10.3 0.47
1766 11.4 0.32
1950 12.4 0.27

The bay was choppy, and I didn't take the time to trim out the boat at each speed, but I thought the data might be of interest to some. I intend to average the data out over the season to develop reasonable fuel curves.

 

[Pascal]

i assume you have Naturals, judging my the 12.4kts at 1950...

try running at 1450... that should be about hull speed and should be much more economical than 1500+ and 10.3 kts. i'd guess you'll get about 0.9 NMPG.. there is a huge difference in flow as soon as you start pushing that big bow wake.

how clean is the bottom and especially the props? it doens't take much to drastically increase fuel burn once you start going faster.

it confirms that there is absolutely no point in even trying to push naturals beyond 9kts...

 

[MikeP]

mpg seems rather low - Here's a previously published Floscan chart for the 53MY that was posted here a couple of years ago. I can't recall now who posted it so I can't give the credit to whomever deserves it:

RPM Knots GPH Gal/NM
0640 6.3 1.8 0.3
1060 8.7 8.0 0.9
1100 9.1 9.0 1.0
1200 9.3 10.4 1.1
1400 10.0 16.2 1.6
1600 10.8 23.4 2.2
1700 10.9 27.0 2.5
1920 15.5 34.2 2.2
2200 18.3 44.4 2.4

 

[Skip]

Unfortunately, the engines are 8V71TI, but the hull and props have a lot of growth. If I had properly trimmed out the boat, the higher RPM performance would have probably been better.

Thanks for the older fuel curve.

 

[MikeP]

Last year our 53MY (TIs) topped out at around 10.8k at WOT due to barnacles on the shafts/props, no growth on the bottom. After scraping the barnacles off - took nearly two tanks of air! - WOT produced 17.8k. So I suspect your figures will improve dramatically once you clean 'er up!

 

[SKYCHENEY]

mpg seems rather low - Here's a previously published Floscan chart for the 53MY that was posted here a couple of years ago. I can't recall now who posted it so I can't give the credit to whomever deserves it:

RPM Knots GPH Gal/NM
0640 6.3 1.8 0.3
1060 8.7 8.0 0.9
1100 9.1 9.0 1.0
1200 9.3 10.4 1.1
1400 10.0 16.2 1.6
1600 10.8 23.4 2.2
1700 10.9 27.0 2.5
1920 15.5 34.2 2.2
2200 18.3 44.4 2.4

These numbers are almost identical to what I get with my 6V92's in a 53EDMY. Hull speed is 9.2kts for these boats, so that's where you get your 1nm/gal.

 

[Nonchalant1]

Unfortunately, the engines are 8V71TI, but the hull and props have a lot of growth. If I had properly trimmed out the boat, the higher RPM performance would have probably been better.

Thanks for the older fuel curve.

You're not getting her up on plane. Try adjusting the trim tabs to 3/4 down after you get the bottom and running gear clean. You should see the bow come down and the knots jump up to 16 to 18 if you run them at 2100 for minute or so, then back down to 1950 after the speed is up to 15 knots or so.

That fuel curve looks like the one I did a couple years ago on my 53MY with 8V71TIs with 1/2 full fuel and water. Your FloScan RPMs are extremely accurate, so your tachs are off a little, which is no problem if you know about it.

Doug Shuman

 

[Skip]

Thanks, Doug. I assumed the mechanical tachs were more accurate - glad to hear I can trust the floscan RPM.

 

[MikeP]

I wouldn't trust EITHER tach (engine or floscan) to be correct. Borrow or buy a photo tach and check the actual RPM at the harmonic balancer on the engine to determine the actual RPM vs indicated RPM of all the tachs on the boat.

A Photo tach is a superb diagnostic tool and, IMHO, should be part of every on-board tool kit.

 

[Pascal]

if these numbers are from a boat with turbos and you're only getting 12.5kts at 1950, I have a feeling your WOT RPM is way below 2300 and you're seriously overloading those engines!!!

or if you are getting 2300 at WOT then your props are not the right props for that boat.

something doens't feel right with those numbers.

 

[Nonchalant1]

I wouldn't trust EITHER tach (engine or floscan) to be correct. Borrow or buy a photo tach and check the actual RPM at the harmonic balancer on the engine to determine the actual RPM vs indicated RPM of all the tachs on the boat.

A Photo tach is a superb diagnostic tool and, IMHO, should be part of every on-board tool kit.

I believe that the FloScans are digital tachs, equivalent to photo tachs. I once compared one of them to a photo tach and they were identical, plus when I engage my synch, the FloScans show the engines within about 2 RPMs of each other all the time after they've settled down.

Doug