Prop selection for my 1968 Mercury 650

I am a new boater so take it easy on me. I just took my new to me boat out for the first time on Sunday and she ran great. My boat is a 15ft 1968 fiberglass runabout. I can't say there is a performance issue, but I just want to know more about the current prop on my boat and what it brings to the table. Most of my boating will be cruising with some tubing with the kids. I have the prop which is currently on and two others I have been told are good. All props are Aluminum as far as I can tell. Let me know if you have any comments or suggestions. Thanks in advance....Joe


1. Current prop- 48-37900A3-15P 3 blade
2. Spare #1 48-31072-17 2 blade
3. Spare #2 48-31076-15 2 blade.

Re: Prop selection for my 1968 Mercury 650

Ayuh,...Your picture is Too Big,... Resize it to 640x480,+ repost it...

The Prop is all about the motors RPMs at WOT...
If your "In Spec", the prop is fine...

Re: Prop selection for my 1968 Mercury 650

Hi Joe,

Nice looking Classic Boat.
The 2 blade 17" P prop is for a light load like one or two people. It will give you your highest speed.
The 2 blade 15 P will give you more power on the take off and a little higher rpm at full throttle. Some times if you have a heavy load they do not get enough bite in the water and will plane a little slower. This depends more on the boat load and hull design. The 2 blade will allow the engine to wind up into the engines power band quicker which is usually a good thing with your 65HP.
The 3 blade 15P prop will give you more bite in the water so the engine will start pulling at a lower rpm which can work good for skiing or tubes. It just depends on how good the skiers are. You will have to try each prop to determine how they work in different situations and which one you like the best for what you are doing that day.

Re: Prop selection for my 1968 Mercury 650

Corm, thanks a ton for the advice. Looks like I will have some fun messing around with the props. Weather permitting, I will have her out again this weekend...

Re: Prop selection for my 1968 Mercury 650

A tach and a gps will help you get the most from your setup.
A tiny tach is reasonable and easy to hook up.