propellers and altitude

L

Lew 25

New member
Finally after a long winter I got my boat to Yellowstone Lake yesterday. Went 40 miles on very smooth and very rough water. WOT was 4700 rpm at 7750 ft. At 4200 ft WOT was 5100. Sea level WOT is 5600 rpm. CAT CLAW has twin 35 hp Hondas and 11 1/4 X 12 three blade props. wOT for these twins is 4600 to 5600 rpms. I think I want to get to about 5300 to 5400 rpm At Yellowstone. Probably add 300 to 400 lbs to present weight for normal use at YL. Would like MANY opinions on props to educate me. Many thanks. Lew
 
For the larger engines, we drop the pitch 2" for every 3500 feet:
Sea Level is 15" Powell is 13" and Yellowstone is 11". I have all 3--and have used all at Powell. Even though you can run the boat with the 15, it is really lugging the engine. Because I was not getting my full WOT on Powell (which is about 5800 at sea level, light boat). I tried my 11" pitch, because I was running a heavily loaded boat. I did reach 5800, but my usual displacement speed, was at an higher RPM, that went back to the 13" pitch.

The 25 I drove back from Oak Harbor last fall, had the sea level prop--and it did OK--fairly light--we took the water and food out--fuel was just enough to get down the lake--and ran at 17 knots with no problem--Marie followed me with our boat and the 13" prop--ran well.

For your boat, I probably would drop to 10" pitch (but that is a rare props pitch for the Honda 35) That should bring you up to 5100 at WOT. Honda lists a 12 1/4 x 9, and that would be ideal for Yellowstone.
Probably get the RPM up to 5300.
 
Thanks DR. Bob. I finally decided on a 12x9 in SS. Results-----WOT 5400 and 5300 on different 35 s at18.6 mph. Cruise is 13 mph at about 4200 rpm. Would like 1 or 2 mph more but this still on plane and OK. Trolling speed is great. Lew
 
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