Correct Prop for 25hp Four stroke

[nate_4_01]

I'm just wondering if I can get a little more top end speed out of my boat. 2011 Mercury 25hp Four Stroke EFI on a 2011 14ft Smokercraft Big Fish. Motor is 162 lbs. Boat is 395. Current prop is 9.25diax12.5pitch Quicksilver. I am GPSing my speed at about 26mph now. Is there anything I can do to make the top speed closer to 30mph? Thanks.

 

[Mi duckdown]

Re: Correct Prop for 25hp Four stroke

without rpm reading who knows. 26 mph is pretty good.
that speed is good.
don't mess with it.
WHY WOULD YOU SPEND ANY MONEY. for 2 t0 4 MPH

 

[John_S]

Re: Correct Prop for 25hp Four stroke

And don't forget to figure all the gear, batteries, trolling motor, you and passengers. That usually makes up much more than the boat weight. As stated above, that doesn't sound like a low speed at all. On small outboards, pitch changes do not produce much in change in wot speed, but do change the wot rpms. You will degrade hole shot with increases in pitch.

Have you optomized your trim position?

Is the cav plate ontop of the water at planning speeds?

 

[steelespike]

Re: Correct Prop for 25hp Four stroke

My calculations if correct indicate your at about 4700 rpm. if slip is 10%.
But rpm should be checked with a tach perhaps borrow a shop tach or get an induction tach or an optical tach.

 

[nate_4_01]

Re: Correct Prop for 25hp Four stroke

Cav plate is on top at plane. I tried a few diff trim positions and this one seems to be best. 3 holes from the transom. at 4 it porposes quite a bit. i dont have much gear in the boat, one battery and me(185lbs) and my wife(110lbs). i would definately spend a little money if it gave me 4mph. im not sure of the rpms but if steelespike is correct that it is only 4700, would changing pitch and going to a stainless prop increase the rpms and give me more speed?

 

[DonHof]

Re: Correct Prop for 25hp Four stroke

I have a Lund (585#) with a 30 hp merc. It has a 9.25x11.00 prop.
I get 25 mph with me 180#, wife 150#, dog 6# full thank of gas 6.6 gals, and battery.

 

[steelespike]

Before making any prop change we need to confirm my rpm figures ,get a tach or perhaps borrow a shop tach.A tinytach or an optical tach can be reused on other motors.