I have a 1972 Evinrude 9.5 short shaft that I use as a kicker on my 18 ft boat. In this respect, the motor works great. Occasionally, I use it on a 12 ft v hull aluminum. It a a dog! With 1 person and gear it MAYBE goes 8 or 9 miles per hour. I feel like the motor itself is strong, but I think that a prop would make a world of difference. Typically this boat has 2 guys and gear in it, so I think that the little motor should be able to get 15 mph or so, if not more. I am basically clueless as to how to size them. Any help would be appreciated.

FB

You probably are not going to have many options, doubt they come in more than three or four pitches.  With the load you're talking about, I would go with the smallest the dealer has, probably about a 9" pitch.

I'll need more info from you to recommend a prop.

I need an actual speed, not a guess. A reading from a GPS would be preffered.

The rpms at WOT would be nice, but I can calculate the rpms based on the MPH and acceptable prop slippage.

I need to know the diameter and pitch on your current prop.

Also, how does the boat come up on plane? Slow? Does it plane with two people?

Way2Slow is correct, there are only five props available for that engine so you are limited in your choices. Ultimately you may have to go with a newer engine that has more of a selection of props available.

I'll try and get that information for you in the next couple days. A newer/bigger motor isn't really an option, not only financially speaking, but because the boat isnt mine. I have an 18 footer, well actually 17'10 or something, and my buddy has the 12. His motor for it took a crap. So we use one of my kickers ( i have 4, 2 non-op) whenever we use his boat. We usually use my boat, and we don't even use the gas motor alot of the time that we use his. But when we do, I wish it had some decent speed. It doesn't even plane, but it feels "close" and the motor is nowhere near what I would estimate as max operating RPM when WOT. If it just had a little more, it seems like it could overcome all of the drag, and be able to accelerate further after coming on plane. I imagine that it has the slowest pitched prop available, because it was purchased originally as a trolling motor and has never done anything else. It starts first or second pull everytime and runs great, just doesn't seem like its revving to its potential. I'll work on numbers, but I will be on the water tomorrow. Thanks guys.

FB

my question is since the motor is a '72, how long has it been since the carbs have been cleaned? I'd check that first before looking into another prop.

the motor itself is fine

Pull the cotter pin out and take the nut off the prop and around the edge of the prop under the nut should be the size of your prop.  To make a shot in the dark guess, I would go down two sizes but with those small motors it's hard to tell, small changes make big differences.

Had a problem like yours with a 15 merc. Used it as a kicker for years. My father went to use it on a 12 starcraft and it wouldn't even get it on plane. The problem was that it was all "carbon" up. from using it for years as a kicker. when you use it as a kicker you run it at slow speed to troll (long time) or at WOT to push the bigger Boat. even at WOT it doesn't get the RPM up because its just not going that fast. So the motor get all full of carbon. there are 2 ways to get the carbon out.

1. take it apart and clean all the internal parts.

take time and cost to much $$$

2. decarbon it your self

How do you decarbon it your self?

this is what a merc rep. told me to try. It worked on the 15hp Merc and on a 6hp johnson that also used as  a kicker.

get an 3 gal gas can. empty it and make sure its clean.

fill the gas can with "Hight test" gas 93 or 94 octane

get OMC's 4+2 fuel conditioner/stabilizer

don't read the back of the bottle, just dump the whole bottle in the 3 gal. gas

hook the motor up to a hose, or put it in a tank(which I did)

start it up and let it Idle for a hour ( it this is going to work it will start in the first hour)

If you see a light brown substance (looks like melting Ice cream) coming out the exhaust or floating on the surface of the water in the tank. It is working

let the motor idle for a few hours checking to see if "ice cream" is coming out of it.

after that take it out and run it. till all the gas is gone. see if that made a difference

I tried this on my merc and it made a great big difference. the motor ran great and the boat ran great. Infact for the rest of that year I was cleaning that "ice cream" off the back of the motor. It just kept coming out of the exhaust. Now remeber to use OMC's 4+2 or it might be 2+4 its one of those. This was a Merc rep not an OMC rep and he said that OMC"s 4+2 was the best to use for this application

I hope you don't mind me tagging a question in on your thread. I have a Tracker 1648 with a 9.9, 4 stroke Mercury. Is the 9.9 enough engine that I should be able to get on plane with just me and gear in the boat? I never really even considered it until I started reading all these prop threads. By gear I mean two batteries, 3 gallons of gas, a small tackle box and 3 rod/reel combos.