Max MPG in an R-23?

C

cruz-in

Well-known member
Joined
Jun 19, 2016
Messages
168
Fluid Motion Model
C-24 C
Non-Fluid Motion Model
18 foot cubby cabing Catboat
Vessel Name
Auuumn Wind
Hi All,


Read folks getting 3 MPG in an R-23 at speed. As an example, a recent post quoted running an R-23 at 4300 PRM, 30 MPH and getting 3.3 MPG.

Is this the Max MPG or would operating at a lesser speed increase the MPG?

If so, could, at reduced speed, the R-23 approach the R-21 for MPG?

Thanks
Dan
 
cruz-in":1g3c9q4n said:
Hi All,


Read folks getting 3 MPG in an R-23 at speed. As an example, a recent post quoted running an R-23 at 4300 PRM, 30 MPH and getting 3.3 MPG.

Is this the Max MPG or would operating at a lesser speed increase the MPG?

If so, could, at reduced speed, the R-23 approach the R-21 for MPG?

Thanks
Dan
Click to expand...

I'll have to pay more attention to it but at 4200 rpm, 24 mph we were somewhere in the 2.3 mpg range. We are on the Hudson River and do have currents to deal with. Have not seen anywhere near 3 mpg?
 
c2f7cffe957ad2a21e04cc61561181c8.jpg



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I'm getting 3.1 average. 60 gallons fuel. Full water. 2 persons aboard.


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Nopressure13":36iw3izg said:
I'm getting 3.1 average. 60 gallons fuel. Full water. 2 persons aboard.


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Click to expand...

Not doubting you. I'm at 4200 rpm, 24 mph, 2.+ mpg, 9+ flow. Same trim settings as you. Do I need to calibrate something?
 
Hello Champ. The speeds are matching up with the gps. I'm trimmed up 4 bars on the Yamaha gauge and no trim tabs.


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I think that a R21 with a 30 hp engine has a top speed is around 8 mph. I could be wrong. Traveling with a 200 hp outboard at displacement speeds 6 mph or less you might get up to about 5 mpg or better. But I doubt that would be happening too much. It sounds like you need to figure out what is important to you. A boat you like with a 200 hp outboard or a boat that gets exceptional fuel economy. Good luck finding both in the same boat.
 
Scuffy":33j85kaa said:
I think that a R21 with a 30 hp engine has a top speed is around 8 mph. I could be wrong. Traveling with a 200 hp outboard at displacement speeds 6 mph or less you might get up to about 5 mpg or better. But I doubt that would be happening too much. It sounds like you need to figure out what is important to you. A boat you like with a 200 hp outboard or a boat that gets exceptional fuel economy. Good luck finding both in the same boat.
Click to expand...

The motivation to my question was, one of the often quoted advantages of the R21 is fuel economy. As the R23 is the first Ranger Tug with an outboard, I thought understanding what best speed was for Max fuel economy would be interesting to myself and others.

As you mention the R21. It would be interesting to know the fuel economy of the R23 when run at R21 speeds.

It would not surprise me if, at R21 speeds, the R23 got similar mileage.

Now whether running an R23 (with a 200 HP Yamaha) for an extended period at R21 speeds makes sense is another question. IMHO, I think not, hence the pict of the R23 with a kicker outboard bracket on the Ranger Tug website. But I digress from the intent of the question.
 
I suspect that to a point, the slower you go the better the MPG.
The reason is that parasitic drag of a hull goes up by the third power of the increase in speed expressed as a ratio (very roughly and influenced by hull shape and how you hold your mouth as you make the calculations - and a bunch of other mathematical fun. )
My R25 ( a very large prop compared to an OB) gets progressively greater MPG as you slow down due to rapidly decreasing hull drag. It will reach ~8mpg down around 3 knots. Below that the MPG drop is likely due to increasing prop slippage - also start having a problem steering what with wind and waves.
For an OB, which is a small prop, I suspect that prop slippage will increase faster as you slow down. a wild guess is that your maximum efficiency will be around 5 or 6 knots.
But I have very limited experience with OB's, so reader beware. :mrgreen:
 
Nopressure13":r9skxfgq said:
d7107e9f8522e7ae4a8d8c583da3cb6f.jpg


1500 RPM, 8 MPH, and 6.4 MPG....am I reading that correct?

How quiet was the Yamaha at 1500 RPM? I suspect it just purred...

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Click to expand...
 
That is correct. Calm seas. Just me aboard. Slight tailwind but yes! She's so quiet. With the door closed, you can hardly tell it's running.


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My R21EC is averaging about 0.75 GPH at an average of 6 to 7 knots (best guesstimate). 8 to 9 MPG? My two previous R21EC's had similar performance.

I operated a Rosborough RF-246 with twin Yamaha 115 HP O/B's for a couple of years. Averaged about 2.25 MPG with an average speed of 10-12 knots (best guesstimate). On plane, from 18 knots up, it burned about a gallon of gas per knot of speed. About 1 MPG. It got the best mileage on plane; I'd get it up and throttle back until it just managed to stay on plane. That was around 12 knots and burned around 2-2.5 MPG. The RF-246 didn't care for R21EC speeds. At 6-7 knots it was pushing a lot of water, burning more fuel than at min. plane speed. At IDLE, it sipped fuel, but didn't like to run at such low rpm.
 
Speaking of 1500 rpm with the Yamaha, is there any info available on whether running it at that speed for an extended time is harmful?
 
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