Force 15 hp propeller question re: pitch performance

[pecheux]

Good day, This 15 hp Force seems to have a 9diam X 8 pitch prop. I get good hole shot and the 14 footer planes with 2 people onboard + fishing gear. I also have a Johnson 9.9 and I get the same top speed with either motor when I am alone in the boat, so I wonder if there would be an overhall advantage to install a 9 pitch prop on the Force hoping to increase top speed but also not loosing planning capacity. On Iboat the only prop that has a 9" diameter is a 7" pitch or 9 X 9, any larger diameter size wont fit. I would appriciate comments. Thank you.

 

[fishrdan]

Re: Force 15 hp propeller question re: pitch performance

Odd... I'm running a 8x8 (8.25x8 or 8x8.25?) composite prop on my 7.5 HP Gamefisher,,, AKA Force. I was thinking of getting a 9x6 so I could use the 7.5HP as a kicker. From what I remember, while checking props for these outboards, the 15HP used a higher pitch than I have, something like a 9 or 10 pitch.

What year is your 15HP, maybe the gear ratio is different?

I don't think you'll gain much by going to a 7 pitch. An 8-9 pitch I would expect an increase, but you could lower your WOT RPM too much, depends on gear ratio, load, hull design, prop material.

I'm running in the low-mid 20's with my 7.5HP on a 14' jon boat. The run up to Hoover Dam is 10+ miles and it takes me a bit over 1/2 hour to get up there,,, against the current.

My reply probably wasn't much help, lower HP OB, different prop material, different hull design...

Do you know what the WOT RPM is right now? You'll probably have to install a "Tiny Tach" to get any good answer for prop selection... It could be that the Force is propped correctly right now the Force and Johnson are equal in performance.

 

[steelespike]

Re: Force 15 hp propeller question re: pitch performance

For some reason nobody wants to give up the year if their outfit.??
The 6" prop is only 1/2" step up from the smallest pitch.(96-98 motors).
In small motors a 1" pitch change can be pretty effective. It does appear you could increase the pitch.But you need a tach to know how much and to tell if your new prop is at the right rpm.
It does seem your 15 should beat the pants off a 9.9 I know nothing about the Force
15 but A 7 1/2" or 8" pitch seems normal.You might see if a Merc dealer can tell you the standard pitch.Merc handled Force near the end.Usually as pitch goes up diameter goes down.As you increase pitch your hole shot will slow.If your 15 refuses to plane a 14 footer with a standard prop.you have more problems than prop selection

 

[pecheux]

Re: Force 15 hp propeller question re: pitch performance

For some reason nobody wants to give up the year if their outfit.??
The 6" prop is only 1/2" step up from the smallest pitch.(96-98 motors).
In small motors a 1" pitch change can be pretty effective. It does appear you could increase the pitch.But you need a tach to know how much and to tell if your new prop is at the right rpm.
It does seem your 15 should beat the pants off a 9.9 I know nothing about the Force
15 but A 7 1/2" or 8" pitch seems normal.You might see if a Merc dealer can tell you the standard pitch.Merc handled Force near the end.Usually as pitch goes up diameter goes down.As you increase pitch your hole shot will slow.If your 15 refuses to plane a 14 footer with a standard prop.you have more problems than prop selection

Sorry, It's a 1997 Force by Merc (I know it's ex Chrysler) and it does not beat the pants off the 1981 Johnson 9.9 with 10" pitch prop when by myself in the boat except for the hole shot. I know they are not geared the same. By ear the RPM sounds normal for that (5200-5500) size motor. Since I would like a spare prop I thought I would investigate if a different pitch would be more performant. Will check with dealer since I dont know what the standard prop pitch should be. Thank you.

It appears the actual prop would be a 9x8 therefore an upgrade would be 9x9