prop help

[powerplant454]

Ok so I have a 1976 15ft manatee tri hull with a 1988 80 hp merc on the back, does any one know the wheel size by chance and possibly any recommendations of what pitch I should use? Its going to be used for fishing/ cruising all help is greatly appreciated, also I tried to find the numbers on the original prop because all the ones I've ever delt with have the numbers stamped on them and they are no where to be found even after removing the paint from it

 

[alldodge]

See link below as to how to measure and determine
http://www.propellerhub.com/measuring-pitch.html

 

[powerplant454]

Thank you alldodge ill give it a whirl

 

[steelespike]

If we're guessing I would go with a 15".It may be too light but you can still use it by watching the rpm.
Diameter will be correct if it is intended for your motor. Diameter basically follows the pitch.