fuel economy for 25 Cruiser

[journey on]

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]

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.

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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.

Hank- Very good observations, interpretations, and conclusions!

The four blade has all those characteristics you mention, of course. Because of the extra blade area (one extra blade plus a larger diameter, in this case), it slips less, so therefore taking an inch or so off the pitch makes sense.

Good work and thinking!

Joe. :thup

 

[Dora~Jean]

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