Prop Recommendation for 1968 Merc 500 Short Shaft

[marksa1458]

Required Info:

1) Problem Description - Venitlation/Prop Spin
2) Brand/Type - Mercury Prop, aluminum
3) Current Size - 10 3/4 diameter and a 12 pitch 2 blade
4) Wide open throttle 4600 rpm and 35 with an average load on the old gauges installed
5) Engine - Mecury, Outboard, Short Shaft 500, 1968 50 HP
6) Best I can tell 1964 Duo Runabout, 14 feet long 600 lbs

Since installing this motor to the boat, in a stop to wide open throttle or turn the engine will rev up and forward motion will slow. I have tried two different props and even a re-hubbed prop with the same issues. Looking to try a 3 blade and wondering what is the best pitch to use?

 

[steelespike]

Re: Prop Recommendation for 1968 Merc 500 Short Shaft

A nice old boat.
The antivent plate(just above the prop)should be about even with the bottom of the transom.
I think your speedo is not accurate.Perhaps you can borrow a gps to get an accurate speed.
If it does turn out to be accurate then the tach is suspect.Boat can't do 35 at 4600 rpm.
A Tinytach is reasonable and will work as a hand held or installed.Just be sure to mention it is a multi cylinder motor.
Let us know the height.