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there are way too ,any variables to answer your question. It depends on the boat, the boat size, weight, kind of prop and pitch etc.
The maximum speed of the 125 mercury is dependent on the boat it is on. It can only push some boats 2mph, while other boats that are light and have a small wetted surface can run 60. To find the theoretical maximum, you should find the maximum pitch prop offered for that engine. The maximum pitch prop I can find for that engine is a 24p. The gear ratio for the lower unit is 2.07:1 . If you can turn the 24p prop at the maximum recommended rpm 5250, the fastest the boat could possibly run is 57.1 mph. The propeller is not 100% efficient, so you should factor in the slip of the propeller. With the inefficiency (slip) factored in, the boat would be more likely to run 55mph. If you can find a higher pitch prop for that engine, you can get it to run faster speeds. A 27p prop would run about 60mph.
Usually pitch is set according to horsepower AND boat size. You could try a taller prop, say a 10 pitch, but you are going to lose RPMs because to engine is cutting through more water. It's a give and take situation. If you can get the boat to a good prop shop near the water, most will let you try different props until you find the one you like.
A bent blade on your prop will make your boat pull one way or the other.
There are to many variables that go into that question . Boat weight , motor size , prop pitch and diameter , form of the boats hull ( flat or a v hull ).
I have a 15hp Nissan 4-stroke on a 14x32 Jon Boat and have a 13" pitch Powertech Prop and I get a max speed of 34.5mph.
The propeller size is determined by the engines wide open throttle RPM Let take an example of an18' boat with a 125 hp engine with a rpm range of 4500-5500. In most cases you purchase a boat with some sort of propeller on it. Let's say this motor has a 21 pitch prop on it and at wide open throttle under a normal boat load, the engine turns 4900 rpms. Well it's in the range so it's the correct prop, right? Well yes and no. For the health and longevity of the engine it's okay, but for overall performance, you want to run a propeller near the top of the range. An 1" of pitch in a prop can change the RPM 200-400. If you need more RPM decrease the pitch and vice versa for less. Remember this is a trial and error and not an exact science. Factors like loading the boat, fuel and water all have to be considered.
I have a 12x22 on my 50 hp merc-2010 model , pushing a 20 ft. Toon. Does great.
Yes...with correct mounting, prop pitch, and a well operating engine, you can drag waterskiiers around behind a 17' boat with 90 hp.
prop wash
i don't know :D
it will not fit but they do sell counter rotator props so if your in forward gear and the motor goes reverse, you have the counter rotating prop