2004 honda bfp20 prop change on pontoon

[woodyjoe]

I thought I would post results from my recent prop change for those interested. Motor is a 2004 honda bfp20. Boat is 18' pontoon. My issues were I couldn't get rpms into proper specs which was 5000-6000 at wot. I also felt like I should be getting more than 8 mph. The prop I removed was a 4 blade 9.25x10 which was the standard prop for a honda bf20. My motor is a bfp20 which is the optional power thrust motor. My new prop is a 4 blade 10x7 power thrust prop. This is the standard prop for the bfp20.

Results....

Rpms at wot throttle increased from 4100 to 5200 at wot, which is with the recommended range. I also increased top speed 1/2 to 1 mph. I was hoping for a little more increase in top speed. Although I did get the rpm results I was aiming for, there is also a negative result I was hoping I wouldn't get. Before prop change, at a comfortable cruising speed of 5 mph rpms were around 3000. Now at the same speed, rpms are at 4000. The effect of that is I will be using more fuel and there is an increased noise level at the speed I commonly run it at.

I think I may try at least one more prop change to get better results. What I would like is a prop that will still keep my rpms in the 5000-6000 range or at least close to 5000 but also run at a few less rpms at my 5 mph cruising speed. I'm not sure I can get both because of the reciprocal effects. The fuel mileage is not a big issue. The pontoon is on a relatively small, private restricted hp lake and is only used 2-3 times a week.

Any suggestions on my next prop change would be appreciated.

There are few other prop choices I have. I could go up an inch in pitch to an 8 and go back to a 9.25 diameter. I could change from 4 blade to a 3 blade. There are a few other combinations for a honda 20 hp but choices aren't infinite.

[boocat]

I'm thinking 3 blade.

[teecro]

You would be better off in the range of 9.25 inch diameter with a 6 or 7 inch pitch 3 or 4 blade, the 3 blade will return a tiny bit more top end speed...

Keep in mind increase RPM does not always mean increased fuel consumption. If the load is reduced despite an increase in rpm the consumption may go down.