What Size Prop?

[Ric Flair]

Hello Folks,
I hope everyone is safe in this somewhat troubled world we live in currently. I need to ask a question, and I hope someone can guide me. I know what my experience is telling me, but I hope someone can offer a suggestion on my little motor.

Boat: Early 70's Boston Whaler 14' Skiff. (I am sure it has some wet stringers)
Engine: 2002 Mercury 30HP (2 Cyl- 2 Stroke) Rated at 5500 RPM
Prop Now: 10.5 x 13 Aluminum.
Compression: 125 Lbs Each Cylinder
Engine Turning: 4050 RPM (Just me in the boat with 6 Gallons gas in the nose)

My little motor is lugging I need to get my RPMs up at least 1000. Tach is brand new and verified correct. My experience tells me that dropping two sizes in pitch will pick up maybe 550 -600 RPMs. What about the width of the prop? I am a little lost on what to do from here. Can someone suggest a prop size which will get me where I need to be?

Thanks
George

 

[QBhoy]

Hi George

just to get a little more of an idea...are you planing at 4000 rpm you mention ? If so what kind of speed are you seeing ?

 

[Ric Flair]

Thanks for the response.

YES, I am fully planed at 4000....wide open throttle, planed and maxed out. I would just like to get a few RPM's out of her so it does not lug.

Thanks

George

 

[QBhoy]

The natural response would be to go down to a 11” pitch....but only if you’re sure that your engine is set up right for the boat. An example of this causing your issue would be if you required a short shaft for you hull...and your engine was a long shaft...or you may have a foil fin installed on the lower unit that’s causing a little drag by not being set up right. (My opinion is not high of such things).
Other things may be carb issues etc etc.

I know a fella who has a 40hp Yamaha on a 14ft light hull speedboat. He has a 13” pitch and it runs much higher rpm. Perhaps you do just need to go down a couple of inches with your 30hp...if all else is well.

 

[Ric Flair]

ThankYou . Carbs are 100% (Freshly boiled and rebuilt) The engine is a short shaft. But you know what? It does have a Doel Fin on it, and I never actually thought about it CREATING drag. I am going to pull that thing off and take it for a spin. I will let you know. Thanks for the suggestion.

 

[jimmbo]

Don't forget to verify that the Tach is accurate too.