Need help regaining top end speed

[jefnmic]

I have a 1990 Force 150 and someone stole the original prop off of it. I replaced it with a Michigan 13x19 prop and have lost about 10 mph off my top end speed with the rpm's reaching 5K. Does anyone know what the original prop was on this motor or can advise me of what pitch would increase the top end speed.
Thanks,
Jeff

 

[erlindbl]

Re: Need help regaining top end speed

I don't think your going to find any specific prop tied to the motor. You didn't list what type of boat it's on. Each manufacturer selects the prop based on the boat (weight, size, hull type) and engine combination. I take it your Michigan Wheel is aluminum. Was the original a stainless or aluminum? Your going to lose a few MPHs going from a stainless to aluminum even if it's the same pitch because the aluminum are less efficient. You also need to know what the WOT RPMS on your boat are. I would think it would be above 5k for your engine but I am not sure. As a general rule your going to pick up RPMS as you go down in pitch in prop and your going to gain speed by going with a higher pitch. Most importantly you want to find a propeller that gets you to your engine's recommended WOT rpms with a regular load.

 

[jefnmic]

Re: Need help regaining top end speed

The boat is a 20 foot Quantum Fish n Ski. The original prop was aluminum as well as the replacement one. I get up to about 38 mph max that includes playing with tilt and trim. I use to get up to 48 mph. To me that is a significant loss of mph. I'm thinking that the WOT rpms are suppose to be 5500 rpms for this motor if I'm not mistaken. I'm just trying to figure out how to get the max mph with the right rpms for this boat without having to buy a bunch of different props. I just wish I knew what the original props pitch was cause it ran great with it. Thank you for your input erlindbl.

 

[steelespike]

Re: Need help regaining top end speed

Max rpm is 5,500.A 17" pitch should put you at about 5,400. 150 Developes its power at 5,250.Do you have any idea what your original max rpm was?

 

[jefnmic]

Re: Need help regaining top end speed

Thanks Steelespike,
So less pitch will give me more rpm's and increase my speed. I'm not real sure on original props rpms I'd have to say close to 5500.

 

[erlindbl]

Re: Need help regaining top end speed

A17P is not going to get you to 48 MPH... I have a 150 E-tec on an 18 foot runabout. I am currently running an aluminum 19P and I am right around 49-50 MPH at 5500-5600 Rpms. I would think the 19P would be the right prop for you if you are sure you were getting 48 (GPS?) before.

What RPMS are you seeing with the 19P you have on there now. I would guess it's not much over 5K if your only getting 38 mph. I think you are going to have to go down in pitch and see what happens. I would also ensure the engine is tuned and running correctly....