Prop/engine height help

[jrocksho]

Hi, I have a '85 Performance Thruster 15' bass boat w/ '85 merc 115hp in-line 6 on a 8" or so jack plate. What would be recommended prop size and engine height?

Prop shaft is about 3-4 inches below keel. Cav plate is about 2-3 inches above keel. Ran 51 mph w/ 131/4x24p @4700 rpm WOT. Ran 46 mph w/
131/4x21p laser II @ 5000 rpm. HELP???

 

[Dhadley]

Re: Prop/engine height help

The correct motor height (X dimension) for any prop or motor on any given boat is a marriage between the hull technology and prop design coupled with set up parameters (set back, load, balance etc).

We'll assume for the moment you're trying to get to 5600. What model is the 24? 3 blade or 4? Brand etc? Have you tried raising the motor to gain efficiency?

 

[jrocksho]

Re: Prop/engine height help

You are correct, looking for higher rpm's. I don't know model of 24p, but it has the name Hopkins with a # 3U14. It also has original owners name engraved on it. Small round vent holes maybe size of pencil or little bigger.
3 blade.
I've raised and lowered engine several times. I just don't want to be too high for my water pick-ups. If I knew the highest safe measurement, I would like to go there and work my way down if needed.
My water pressure gauge reads low, but it always did. Water pump has been changed about 11/2 years and will get changed again soon. Gauge never reads more than 10 psi. Installed another gauge with same results. Was told that my gauge is tapped in wrong spot on water jacket. Is this true?
Mine is tapped between #3 & #4 plugs, was told it should be at top!!!
engine never ran hot, but i don't like the situation. thanks