[C36IA] prop pitch and engine problem

[Darin Duphorne]

I'm post-survey, but still pre-purchase of a 2000 C36MKII with a Max- 
Prop 3-blade feathering prop.  I've read enough of the forum posts to  
get an idea what rpm and hull speed I should be getting but it's  
really weird, and I can't tell what might be causing the issue other  
than prop pitch.

In the sea trial, I was only getting about 4.5kts under full power in  
flat lake conditions.  Free rpm was around 2850 and loaded rpm was  
about 2800 (50rpm droop -- not enough).

We asked seller to repitch to confirm, and he's been having a diver do  
it with no success.  Here are the things they've tried...

15x18	4.5kts	2800rpm
15x20	6.7kts	1800rpm
15x18	6.8kts	1900rpm
15x16	7.0kts	16-1700rpm (yikes!)

It's weird!  I can't imagine an engine related issue, or it wouldn't  
get to 2800rpm, I wouldn't think.  Compression problems when loaded?

Any ideas?