My 18' Nitro is having a hard time getting on plane, with 3 people and some gear, one had to sit on the bow, and it still did not want to get ontop of the water. Right now there I'm running a 22p SS on a 125 Merc Tracker. What Pitch should I change to for easier planing? I'm not to woried about top speed, I know there are trade offs.

Thanks to all...

What RPM's are you pulling? Generally a change in pitch by 1 degree adds or decreases RPM's by 300 or so. Each motor is unique, another 125 Merc might require a different pitch prop than yours. I found this out when I banged up the prop on my Yamaha 60HP 4 Stroke. I had to actually check my prop to find it's number and it was indeed different from other 60HP Yammies in the showroom. Trim down all the way when you want to blast off, then gently raise trim as you get on plane. I had 4 people in my boat last week and it really didn't take a great deal to plane.

The tach is somewhere around 5100 at 55mph. I do have the trim all the way down when tring to get on plane. There is a jack plate on the boat, and they are new to me, could there be a problem with the way it is adjusted?

That 22 is a little too much prop for that 115 to get that big a boat on plane.  Is this a bassboat or a fish and ski?

I'm guessing a 21p may work better, a 19 even better.

This is a Bass boat...

What is the redline for the engine? If it is 6000 RPM, you need to go with a 20pitch. I'm going to say it likely is not the J-Plate.

In general, if a 22 is turning 5,100, a 20 will turn 5,400 - 5,500 and a 18 will turn 5,800 - 6,000.

How many people do you normally.  Prop the boat for a normal load and then, so what if a person have to move forward on the rare occassion you overload it.  If you do this often, then invest in a smaller prop that will get that extra load up.

If the boat won't turn in the high 5's with your normal load, then it was overproped when you got it.

The two stroke motor should be proped to turn near it's max recommended rpm for the normal load.

As mentioned looks like you are underpowered running a 125 on an 18' boat.  That boat is probably rated for a 150 or 175.

Beofore you buy any prop you should try it or one like it with the load you plan to use it with.  Don't buy and 18" prop and then go try it with just you, a light load of gas and empty live well, it will most likely over rev the crap out of it.  One or two hundred rpm over max is not going to hurt, you can always back out slightly.  They cost too much just to buy them and find you bought the wrong one.