Need Advice on Prop Pitch for 204 Overnighter

[Glasser]

Hello all,


I always get great help here, so I thought I'd ask about prop pitch. I have a 1987 204 Grady White Overnighter that I just finished restoring. I'm currently performing sea trials.


She’s powered by a 2005 Yamaha 150hp four-stroke with a 2005 Yamaha 15hp four-stroke kicker. I need to lower my prop pitch and I'm looking for some advice.


I've tried two props so far:

• Stainless 21P, four-blade
• Aluminum 19P, four-blade

Both actually perform very similarly:

• WOT (wide open throttle) RPM: ~4600
• Speed at WOT: ~35–37 mph
• Speed at 3300 RPM: ~24 mph

As I understand it, I’m supposed to be getting closer to 5500–6000 RPM at WOT with this engine. What pitch would you recommend trying next?


Any guidance would be much appreciated!

 

[DennisG01]

Boy, to gain 1,000+ of RPM, you'd have to drop 5" or maybe even 7". That just doesn't seem right.

There might another explanation.

Is the hull bottom super clean?

Are you 100% positive that the engine is healthy? A couple quick things...
-- Compression
-- All injectors firing
-- Good gas

Are you trimming up the engine properly?

And... that speed might be roughly correct... maybe your RPM is off. Is there a setting on the backside for cylinders?

 

[Glasser]

Thanks for the ideas.


I do have clean gas, and I recently replaced the injectors. I also trimmed the engine up some during the runs.


The hull is in good shape—clean and recently refinished.


I’m not sure about compression yet; I haven’t checked that.

 

[DennisG01]

Before you do anything else, trim up more - till just before it ventilates or speed no longer increases.

 

[Glasser]

Before you do anything else, trim up more - till just before it ventilates or speed no longer increases.

Thanks for the advice. I did what you said and hit 43 mph at 5000 RPM with the 4-blade 19P. Any thoughts?