fuel economy for 25 Cruiser

Sea Skipper · Posted: Wed Dec 12, 2007 12:50 am Post subject:

Sea Skipper is a heavily loaded CD25 with a Honda 150, that uses an OSP four blade 15-1/4 x 14 pitch prop. This prop has very little vibration at low speeds, excellent bite (low slip) and very little cavitation in rough conditions. Sea Skipper has averaged 2.39 nautical miles per gallen US over the past three seasons with this prop, covering a total distance of 4300 kn. Log is from the GPS (distance over ground) as the Raymarine log is hopeless. However, SOG (Speed over water) from the Raymarine is dialed in perfectly. Fuel usage is based on actual fill-ups (the Navman fuel flow meter is adjusted to read about 5% high). No adjustment has been made to allow for wind or current conditions which can be quite significant at times. Max recorded speed is 32 kn (SOG) at 5800 rpm. Normally in very flat water no wind conditions she will top out at 31kn at 5,750 RPM. To achieve this speed, the flaps (trim tabs) must be fully retracted and the motor trimmed out to the point where the boat just starts to pound. At 30 KN she tracks straight and true thanks to the Permatrim. Normally (99% of the time) I cruise her at 20 knots or less. Optimum fuel economy is 19~20 knots (about 4,650 RPM burning about 7.5 gallons per hour) with a secondary peak at about 16 knots. 20 knots is only usable in relatively smooth water. Best one day run was from Mistral Island (near Lagoon Cove in the Broughtons) to Winter Cove Saturna Island - a distance of 177 nautical miles in 9:45 hours. Johnstone Strait, Discovery Passage & the entire length of the Strait of Georgia were flat as a pancake that day. At first glance, the OPS 4 blade prop mentioned above might seem to have too low of a pitch, but I think it is the ideal prop for this boat & motor. A slightly higher pitch 3 blade might give slightly better fuel economy but worse performance in other respects.

JamesTXSD · Posted: Thu Dec 13, 2007 5:50 pm Post subject:

I came across the performance chart...

I find that we are running about 1 nmpg less than what this chart suggests, on average; and our speed at any given rpm is a bit less.

HTH

Al & Pat Parker · Posted: Thu Dec 13, 2007 7:40 pm Post subject:

In a quick look, that's the same Honda chart I posted on the previous page of this thread, without the dba sound readings. Yours doesn't have the info on what boat or what prop. .
My dealer, just today, "challenged" me to provide the same info for the CD-25 with the Yamaha 150, which I have installed. All I need is a fuel flow meter, maybe someday it'll get done. .
I did make up a chart with 2 different props,

or on my website with a little more data.

JamesTXSD · Posted: Thu Dec 13, 2007 9:09 pm Post subject:

The chart was from BoatTest.com for the CD-25, no info on prop. Compare the bold line to see the difference (likely a misprint on the NMPG on the chart you posted). I don't imagine I could get those fuel burn figures, even with a lightly loaded boat.

Sea Wolf · Posted: Thu Dec 13, 2007 9:17 pm Post subject:

journey on · Posted: Thu Dec 13, 2007 9:31 pm Post subject:

Well, I'll put my 2 bits in (again.) Journey On is loaded for cruising during our trips. I put an Michigan Wheel Apollo 4 blade 16" pitch prop on the Honda 150, mostly because it had a 16" pitch and was cheap.

During the summer the boats gas mileage was a little over 4 mpg. This includes both cruising at 7 knt. and a little 15 knt. get-us-home. We're cruisers, trying to get from place to place and see the world ( Journey On's Travels shows where we went, about 600 nmi.) At $4.00/gal in Canada, it was worth the extra time, and even better, we got to see the sights. When we had to move, the boat went through the chop at 15 knts, great ride but 2 mpg. Heavily loaded, speed costs.

By the way, the truck got 8 mpg. Towing that boat with two different trucks, the average is 8 mpg. We're staying closer to home next year.

Boris

Sea Wolf · Posted: Thu Dec 13, 2007 9:31 pm Post subject:

Dora~Jean · Posted: Fri Dec 28, 2007 10:41 pm Post subject:

I've always wanted to do a nmph vs rpm chart and finally got the opportunity this morning on the way home from Catalina. Smooth seas, very little wind. 3 persons on board, overnight gear for 3 days/2 nights, 90 gals gas (est), 5 gal water, stowed raft, motor and ice chest.

My boat has twin Yamaha 4-stroke 80's. I average 2.5 nmpg (2.2 - 3.0 nmpg depending on # people on board). I run 13 1/2"D x 15"P props, could stand 1 more inch in pitch or go to a 4 blade 15P.

The chart is interesting, it confirms what I have 'felt' -- that there is no significant transition from displacement hull speed to planing. I'm very happy with the performance in all sea conditions.

RPM . Nmph
1000 3.0
1500 4.1
2000 5.6
2500 7.0
3000 9.0
3500 11.8
4000 14.3
4500 18.0
5000 21.5