New to boating prop problem

[ID18]

1) went from having WOT 5500 rpm 30 mph with 6 people to 17mph with 4 people
2) Current prop is aluminum manufact unknown
3) Current prop diameter and pitch 13.5 by 17P
5) Engine/drive make Force , model II, year 1992, and 90HP
6) 1992 Bayliner Capri 1800 BR. 18’ weight unknown

replacing the prop but would like to get more top speed. We just tube and boat. What should I do for a prop size?

 

[jimmbo]

I would be wondering why the engine lost power. What is the RPM with the 4 people?
It is a 3 cylinder? I think one cylinder is dead. Check for spark, compression, and that all carbs are getting gas

 

[ahicks]

<<<"went from having WOT 5500 rpm 30 mph with 6 people to 17mph with 4 people">>>

Pretty obvious SOMETHING has changed? Right now, focus needs to be on what that change is. Are you still turning 5500 at WOT? If not, my focus would be on the engine. If you are still turning 5500, you may have spun the hub in the prop.