three blade Vs. Two blade

[twinprop]

Hey everyone...I think this is kinda a simple question for all of you. I have a little 12' boat with a little 6h.p. johnson sea horse on the back. It has the orignal prop on it(1974) and it is a little two blade prop. I top out GPS at around 6.5mph. I am wondering if throwing a three blade prop will help me out at all getting a mph difference or too. I can get three blade prop for around $60 new. Would it really help me out at all, or am I just asking to much out of this little motor. Thanks for all the help

[twinprop]

come on people...please help me out

[REW]

It really depends.
i.e. it depends on how much load is on the motor, how much area in each of the props blade, and what the pitch of each prop is.

If you really want to do it - work with a dealer and try several props. It would be nice to have a tach, so that you could verify the engine rpm.

Because it isn't likely that you will have an electric tach - you could use a - push on tach - and simply put the tip of the tach in the spinning flywheel - with the cowel removed.

It is nice to get the engine turning at the maximum for the engine without overrevving. You might be able to borrow an engine tuning tach - that simply is placed into the divit on the top of the flywheel, so that ou can verify engine rpm.

Just because you go from a 2 blade to a three blade prop - is only part of the story. You need to get total prop area and pitch of a size to perfectly match your boat and motor.

You don't have a lot of power to work with - so it is hard to predict results.

Have a hand held gps - so that you can verify speed.
Use a hand held tach - on the motor so that you can verify engine rpm.
Check with the engine builder to determine the optimum rpm of the engine.

Finally - pick up 6 different props of sizes and pitches, and test them all.

On the water testing will determine the story.

Take care
REW

[twinprop]

thanks REW, I actually do have a little tach for the engine. It is one that wraps around the spark plug wire, probably not the most accurate, but it works. the nice thing is I live in a small town and the dealer would let me try the different props out. Thanks for the advice

[Miss Adventure II]

Did the same you are asking about years ago with I believe the same motor and a sears 12 foot boat. There was really no difference to speak of that we could see.( before gps) I am not able to recall what the prop pitch's were. All I remember is the 2 blade was plastic and the 3 blade was alum.

Hope it helps some
Miss Adventure II