Prop for 75hp force on 22 ft pontoon

[syork6197]

Trying to get more speed out of my toon. Currently running a mercury 816706a40p14. From what i can find it is 10 3/8 × 14 pitch. I get 4000 at wot and about 15 mph with 2 adults and 4 kids under 12. Wot rpm for the motor is 5250, have yet to get that at wot. All help is appreciated.

 

[ahicks]

That's a big jump from what you have, so grabbing the right size to land you right on 5250 would be pretty lucky. I'd shoot conservatively, for something closer to 5000. That would be something with about 10" of pitch.

 

[Sea Rider]

Plan going boating with that combo as currently loaded most times, sometimes ? Load kills wot rpm. Currently loaded engine is 1250 wot revs under where it should run. Will need to drop prop pitch min to a 12 pitch to pull wot revs towards middle to max wot rpm range. Only possible to know testing prop on water as most times theoretical answers does not match practice ones.

Happy Boating

 

[syork6197]

With just me on the toon it still only gets 4000 at wot, however it will speed upto about 18 mph. Idk what the deal is, could timing be an issue with it getting the right wot rpms for the engine.

 

[ahicks]

Anything is possible, but if the engine seems to be running OK, it has the wrong prop on it.

 

[Sea Rider]

Was OB tached previously posting while solo boating and achieved in both cases just 4K wot revs ? If so OB is way over propped, a prop maximization will cure it. Better dial a prop that makes OB to rev to its max wot rpm range with you alone, add more boaters till wot revs drops to middle wot rpm range. That way OB will rev happily inside its safe middle to max wot rpm range.

Happy Boating