new Merc 25 hp EFI 4-stroke on utility boat - pitch guess??

[BF]

Hiya,

I just picked up my brand new 25 hp Merc 4 stroke EFI short shaft tiller that will go onto a 16' aluminum fishing/utility boat. I bought a prop from the same outfit where I got the motor from. I guessed on the pitch, and the prop I got was a 9 1/4 x 11". Given that it's a fairly light boat, no floor or livewells.... I'm thinking I might be under propped (?). It was the most pitch this place had on hand (they mostly sell pontoons, and would send the motor out with an 8 or 9" pitch prop).

Anybody have experience with this particular motor on a similar boat?

Care to comment on how you think my guess for pitch will be? I didn't find any of the prop selector tools that I could find on line very helpful.

Here's a pict of the boat.

Thx

 

[steelespike]

Re: new Merc 25 hp EFI 4-stroke on utility boat - pitch guess??

Not an expert but::Try it out borrow a tach where you bought it.Very important to know rpm. as I understand it they like to prop 4 strokes for the high end of their rpm band.You'll need to find that out.GPS speed would be good to have as well.You also should fine tune the verticle height.If it has clamps start with the antivent plate even with the bottom.Raise it 1/4 inch at a time until just before venting becomes a problem.Use 1/4 inch sticks to support the motor and be sure the clamps have a good grip.
If no clemp it may have holes for verticle height.( not the trim adjust)
Once you get the rig fine tuned you can tell how your pitch selection is.
This could give you 2 or 3 mph and the best mileage.

 

[BF]

Re: new Merc 25 hp EFI 4-stroke on utility boat - pitch guess??

thanks for the reply... yes I will figure out WOT rpms etc. But, it's such a common type of boat, there must someone around here running one of these motors on one.... was curious about what they've found.

 

[longshanks]

Re: new Merc 25 hp EFI 4-stroke on utility boat - pitch guess??

Hi there

I'm running a 50 4-stroke on a 15' skiff. It does ok with an 11-pitch, but 12 is a bit better. You want to get that motor revving as close to max. rpms as possible. I believe there's an over-rev alarm on that motor (solid tone, combined with the engine stops accelerating). If you hit that with the 11 prop, you will want to try out a 12 or 13. As stated, best situation is to get a tach.

If they make it, you may want to consider a pirahna composite prop. Can switch blades/pitches free of charge at the dealer. Works great on my rig

good luck