Some mpg, mph data

R

Ray

New member
Got my Lowrance EP-60R hooked up to the Raymarine A98 this weekend. Took some data going out and back ~20mi each way. Just some data for anyone reading and interested.

2007 C-Dory 25, 2007 Honda 15., Full fuel, half water, no waste. 2 passengers (~290lbs combined).

Going out was 5-10mph wind from the aft quarter with 1/2-1ft waves
Coming back was <5mph wind from aft, glass to light chop - early measurements (low RPM) affected a bit by current

graph_data.jpg

nmpg_graph.jpg

nmph_graph.jpg

Ray
 
Not sure if I'm reading your chart correctly, but are you stating that you get 40% better fuel economy at 5500 RPM than you do at 4000 RPM?
Seems contrary to anything I have ever seen in my own experience.
 
Yep. Them's the numbers - more like 35%.

I don't believe *MY* (loaded) boat was fully onto it's most efficient level of plane at 4000rpm with speed somewhere around 11-12kn there.

Going faster (the slope of the speed graph gets steeper) allows for more rapid increase in mph for a representative gal/hr.
 
Here's a couple of graphs I made from the posts of Daydream and Anna Leigh in 2005. I believe they're in statute miles as opposed to nautical miles. There's not much difference. I believe that Journey On gets about 4 nm/gal at ~2300 RPM and ~6.5 to 7knts, loaded for cruising.

So everything's consistent, given that we're not looking for great accuracy. The rise in the MPG after ~3500 is that the boat has risen on plane and is offering less resistance to sliding through the water (if you've remembered to use the trim tabs.

C_25_MPG_0.jpg C_25_RPM_0.jpg

Boris
 

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Despite our beliefs that the C Dory planes at a low and efficient speed, I believe that both Ray and Borris's data show that you are really on a more efficient plane--for those boats on those conditions--at the higher speeds. It is interesting, and to me not too surprising.
 
I borrowed your table to post on another forum where there was a question of efficiency of 25 foot boats. I note that you put "STW"--which to me means "Speed thru the water". I suspect that you actually measured GPS speed, which is speed over the bottom. Speed thru the water would be measured by a paddlewheel, and takes into account current, speed over the ground (GPS) ignores current.
 
Correct, Bob. Apologies - Should be SOG.
Also pointed out to me, my boat has a Honda 150hp, not a 15.hp - fat fingers......
 
My data at least was in nautical miles, I have never use statute miles. Also note that the Daydream and Anna Leigh data was collected when both those boats were considerably lighter than they are now. The Daydream data was before being gooped up with a kicker, a generator, a freezer, massive cooler, solar panels and other assorted stuff. I have not seen 3 NM per gallon since then except at 6 knots!
 
Pat, thanks for the update. I certainly couldn't remember.

And, yes, C-Dorys are VERY sensitive to weight. And, yes, Judy has found ways to pack more stuff on board as we go cruising. I on the other hand, have tried to lighten the boat, just can't remember how.

Boris
 
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