Should I re-prop my boat?

[jester108]

I need to know if i should re-prop my boat? I have a 2001 monterey montura 226, with a volvo penta duoprop and a 280hp 5.7 gsi. I am getting about 45 mph @4200 rpms. The owners manual says I should be getting 4600 to 5000 rpms. My elevation is around 5000' and I have f-7 props. Also I dinged the props last trip out, it did not hinder the performance of the boat but I do feel some vibration at low speeds, so my question is will it hurt my out drive to still use until I ether re-prop or repair my props?

Thanks first time douprop owner

 

[steelespike]

Re: Should I re-prop my boat?

If your using the boat everyday through the season you should probably get the props repaired.
As I recall you lose about 3% per 1000 feet,and thats if you have the carb rejeted for the elevation.
I don't know how the Volvo numbers compare but a reduction in pitch will help your rpm.
A 1" pitch change will usually net about 200 rpm change.

 

[jester108]

Re: Should I re-prop my boat?

Thanks, I talked to one of the local mechanics and he said he thought it was about 200 rpms as well. The ding is not bad at all and I'll use the boat maybe 4 more times this season.

If I do re-prop maybe one size down will that do much for my top speed?

 

[Maclin]

Re: Should I re-prop my boat?

If your engine can rev higher with the F6 than the 4200 you see now, and hit more like the recommended 4600 then speed will be about the same.

VP DuoProp number changes within a series are about 2 inches pitch, meaning F7 to F6 would be about a 2 inch drop.

 

[Leardriver]

Re: Should I re-prop my boat?

With the RPM defict you are running, I would change to F5.

I always want to be able to hit the upper end of the RPM range, even though I never run there, so I can have lots of low end pulling power for watersports.

If the recommended range is 4600-5000, I want to hit 5100 with two people on board lightly loaded, so under a more normal load with a few people on board, a full gas tank, and towing, I can come out of the hole strong.

 

[jester108]

Re: Should I re-prop my boat?

I do believe the f-5 would be the right prop for my area. So if you run on the higher side of the rpm range, does that help your fuel consumption? I would think running your engine at a recommended range would also help fuel consumption.