Looking for right prop size

[99xjjoe]

1975 crestliner muskie 15' fiberglass trihull with a 1976 merc 500(50 hp thunderbolt) long shaft.Merc serial #4359415(if anyone can break down this number for me). I need the prop size and pich of this motor with this boat. Everyone i spoke to just ball parks a size and i want the best performace prop size for 2-4 people. Thanks Joe

 

[Silvertip]

Re: Looking for right prop size

You didn't read the "sticky" right at the top of this forum that says READ THIS FIRST?? You have given us absolutely nothing to work with. The proper prop is one that allows the engine to rev at or very near the upper end of the manufacturers wide open throttle rpm band with what you consider an average load. Speed will be whatever that prop provides and that's as good as it gets. That is not a serial number. It is a Merc PART NUMBER. As such it merely identifies that prop -- just like calling you 99xjjoe. Means nothing except for a way to identify the part on the shelf. The best prop size for 2 - 4 people means the load will change by up to 400 pounds so right off the bat you are aksing for the impossible. If your boat doesn't have a tach, you have no idea whether or not the prop you have is best.

 

[99xjjoe]

Re: Looking for right prop size

yes im missing alot of info just like the motor is missing a prop(so i have no baseline).....so what i have found online is WOT range should be 4800 RPM-5300 RPM. Alot of websites have props for my motor but 9'' to 16'' pitch size. 4359415 is the serial #, thats all there is on the plate.

 

[steelespike]

Re: Looking for right prop size

I would start with an 11" pitch.Just an educated guess. Hopefully it is undersized. You could still use it but be aware of your rpm.If it ends up over sized you shouldn't use it for an extended period
Like a season as it could lead to premature repair problems.
Especially if your running with 4 aboard.You will need a tach (tinytach will do) and a gps.
You need to know how well the prop is doing.Also will help you to know if your setup is working.