2014 R31 Sedan graphs: Speed VS RPM and Speed VS Fuel Rate

[Dale777]

Since I've had a number of people ask me about the Speed versus fuel burn and Speed versus RPM on Tangent (2014 R31 Sedan), I decided to capture multiple data points by taking lots of pictures of the chart plotter on 2/8/2015 while cruising on very, very calm seas from Cape Haze to Fort Myers Beach, FL.

Next I took those data points from my camera and graphed them in Excel. Once graphed, I then create a 4th order polynomial curve fit on the graphs. The results are now in my gallery.

I would be very curious to see how these results stack up against what other Ranger Tugs experience. Please comment if you have comparative data for your Tug.

Click on the thumbnails below to get the full size images of the graphs:

 

[coreychamness]

Dale,
I won't be able to validate right now since my R-31 is winterized but that looks about right. I can't pull 19.8 kts though and can't usually get 3400 rpm. I can check in a couple more months. Hope you are enjoying the winter down there.

Corey

 

[knotflying]

Nice job Dale. A bit different than the R-27, but it doesn't break the bank. Especially with lower fuel prices.

 

[ttlmac]

Dale, thank you for plotting this. I must say, it is amazing the level of information that is shared on tugnuts. I work in the aerospace industry and the smart guys in my company are always fitting data to polynomials. Didn't expect to see this for my boat.
My 2014 R31 sedan is in storage now, but my performance is similar but a couple knots slower, and probably a couple tenths nmpg less. My peak RPM I think is around 3100. I added a hardtop and some additional junk to the boat, which may explain the difference. Your curve implies that the sweet spot for good fuel economy at a decent speed is about 15 knots. I think my boat is similar.
Thanks for the data.
Tom
Indian Summer II

 

[Longbranch Louie]

Your chart looks very close to what we experienced in our 31. Most 31 owners we talk with had a pretty common feeling that "if your going to 9, you might as well be doing 15", as the burn will be similar and you arrive sooner. And many times she rode smoother on top of a chop at 15. Several times we have left South sound late and still made it in time for cocktails in La Conner. I found that waiting to fill the water tank when you get there helps a little too.
Your right about the fuel prices being down. Last July prices we paid 4 bucks a gallon and we just got fuel at Des Moines for 2.15.

 

[Dale777]

Tom,

Thanks for the comments.

It occurred to me that many people look at fuel usage in "Gal/Hour" instead of the "NM/Gal" that I showed in my original post. So, I have now included a graph for "Speed" VS "Gal/Hour", also. Click on this thumbnail for such a graph:



For any Tugnuts, for any model Ranger Tug, what are your typical burn rates versus speed or RPM versus speed numbers? I'm really curious.

One clear takeaway for my boat is that once I reach 10 Knots, if I'm comfortable doing so, I might as well run up to 15 Knots as far as fuel economy is concerned. And, at 10-15 Knots, I don't exceed 2900 RPM which is about 83% of the max RPM.

 

[knotflying]

Gallons per hour is fine, but in my opinion distance per gallon is a far more informative calculation. If I told you I was burning 50 GPH it would sound horrendous, but if I was going 200 MPH that tells a much better story of 4 MPG, which I would take any day.

 

[lashobe]

I really appreciate you posting this analysis. We have the R 31 bridge model and usually run full fuel to a half tank. You work backs up my own qualitative observations. I always monitor the Garmin knts/gl and observed that flat response curve from about 10kts to 15 or so. I was skeptical of this but your multiple data points convince me that is the reality. So when the seas are right, no more 12 knts/hr! Thanks for sharing your analysis.

 

[dialtone]

And then I told my wife "you see that grand banks over there" yea we will be home before dark. He'll be home around midnight.

 

[coreychamness]

Dale, your gal/hr looks a little different than I recall for my CB. For me usually the gal/hr is more important than the nm/hr since I am not really going anywhere other than out and back which is time based. I think I used more fuel on a run down the Potomac to meet someone at a destination at full speed than we did the entire rest of the summer just putting around at 7-8 kts. We have some lengthy no-wake zones too that limit us to 5 or so which is where your data looks a bit high as compared to mine.

Corey

 

[Dale777]

MORE data points:

In my original post, I did not have very many data points at lower speeds, so I've gathered a lot more data points at various speeds - this time with 4 people aboard. However, the sea conditions varied a lot, with wind and tidal flow, as I gathered the additional data points. So, I think that explains a lot of the variability that you see at lower speeds in the charts below, but the overall trend is still clear. Click on the thumbnails to get a larger image.

Speed VS Fuel Rate (NMPG):



Speed VS RPM:


Anyone else now have data to share?

 

[Kaptajnen]

Our R 31-S (Hull #1 /2019) is equipped with an enclosed Camperback and running with 2 onboard, full watertank and 50% fuel, the sweet spot is around 3000 RPM.
That gives us a speed of 15 - 18 NM per hour, depending on wind and waves, and approx. 1.75 NM per gallon.
We usually have the trim tabs fully down for better visibility in busy Puget Sound. We also keep both Radar and our Vesper AIS going for the same purpose.