13 to 15. What do I do????

I have a 14ft aluminum boat with a 1985 25hp Evinrude long shaft. Right now it has a 10X13 pitch prop on it. At WOT it's doing 29MPH(GPS)and reving like hell with myself and my 2 boys in it. I haven't tached it yet but feel pretty sure it's close to top RPM by the way the wake looks.(more like a jet blast rather than a nice clean wake) I figure I might be able to get some more speed out of her. Has anyone put a 15 pitch prop on one of these or is that to agressive of a pitch for an engine like this. Right now it's got tons of holeshot.

Re: 13 to 15. What do I do????

kovman said:

I have a 14ft aluminum boat with a 1985 25hp Evinrude long shaft. Right now it has a 10X13 pitch prop on it. At WOT it's doing 29MPH(GPS)and reving like hell with myself and my 2 boys in it. I haven't tached it yet but feel pretty sure it's close to top RPM by the way the wake looks.(more like a jet blast rather than a nice clean wake) I figure I might be able to get some more speed out of her. Has anyone put a 15 pitch prop on one of these or is that to agressive of a pitch for an engine like this. Right now it's got tons of holeshot.

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What is it you are trying to achieve; more speed? The answer is yes, you can put a 15p prop on that motor. It should reduce your WOT rpm by about 400.

If the motor is reving to the top of it's RPM range or higher with the 13p then you will notice an increase in top end speed with the 15p.

If you don't need more speed then reduce your throttle a bit and cruise...the engine will be more fuel efficient at lower RPM.

Re: 13 to 15. What do I do????

Well I would like to get alittle more spped out of her. I just don't want to end up going the same speed and having no whole shot.

Re: 13 to 15. What do I do????

kovman said:

Well I would like to get alittle more spped out of her. I just don't want to end up going the same speed and having no whole shot.

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Well in that case you should really get a tack and find out what RPM you are at WOT with the 13p prop. The boat should be propped so that you are right in the middle of the recommended RPM range for the motor at WOT.

Adding pitch will give you more top end speed but will take away some from the hole shot. Think of it somewhat like changing to a higher gear in your car. 2" of pitch won't make it like starting off in 2nd gear but you get the idea.

Re: 13 to 15. What do I do????

If your doing 29 with you and the 2 boys your doing well.Motor is rated at
4,500 to 5,500 rpm. If your boat is what I call a small 14, under 14ft with a relatively narrow beam then it wouldn't get up as well as a full 14 footer with a load.Regardless of the actual size your doing well.After taching it you'll be able to tell better where you are at.A tinytach is reasonable and easy to install and will work on any 2 cyl.2 stroke.My feeling is a 15 might be faster with one but lose with a load.Depending on your present rpm a 14" might be a better choice if changing at all.Again depending on your rpm you might check and see if there is a Turning point Rascal for your motor.They can be very effective.

Re: 13 to 15. What do I do????

I looked up that turning point Rascal and found that they don't make a 15 pitch in my size. But they do make a 13 pitch. You see I'm kinda of a perfectionist when it comes down to small two stroke motors. I am however new to the outboard motor world and when I see something that I can tune, well lets just say I won't be happy till it's tuned just right. That's why when I saw the prop wash and the speed on the GPS the old gears started turning on how to make this thing faster. The boat is like new as well the motor. Got it at an auction for near nothing. So, I'm just having a ball with this boat. I just learned that my neighbour use to teach these motors to cadets in the army and he might have a few carburators laying around. He thinks they were off a 35hp. Do they make a 16 or 17 pitch prop for these sizes of motors?

Re: 13 to 15. What do I do????

Many times the Rascal works well same pitch.And it will tend to load the motor more than your present 13"
But if you like to fiddle try raising the motor vertically.The antivent(cavitation) plate just above the prop;even with the bottom of the boat is considered a starting point.Just add 1/4" sticks to the top the transom.
Sticks are just to hold the motor while you tighten the clamps.Raise it to a point just before venting (cavitation) becomes a problem.Be sure it pumps water and has a good grip.Under ideal conditions could result in 1 or 2 mph.
The rascal prop will allow more height without venting.Get that tiny tach first so you will know just where your at.Rpm and speed is very helpful.