Mudball

I would appreciate any ideas about improving the performance of my boat.

My info:
Boat: 1999 Donzi 22zx with a stepped hull. About 200 hours on the hull. In perfect shape, no wax, not blueprinted, not sanded.
Engine: Stock 1999 HP500 carb, top end freshed 25 hours ago.
Drive: Bravo 1, 1.5 gears.
Current prop: Stock 28p Bravo 1.
X dim: 6" from center of propshaft to center of aft V. Note that the step is large, though.
Top speed: Best of 78.2, with an average of 76-77. All GPS.
WOT RPM: Approximately 5,050 to 5,100 (hard to see the tach well at these speeds!). The tach appears accurate to a Snap-On shop tach up to 4k rpm, while on the hose.
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The midrange is very good. The hole shot is average. I don't believe I can afford to lose any hole shot bite in this process. I can blow the prop out easily now.
Also, at minimum plane, around 30mph, turning left blows the prop out, trimmed all the way in. Above 40, no prop blowout occurs.

Other notes that might help: A Mirage Plus prop (came on the boat!) chine walks like crazy on this boat at anything over 60, and blows out like no tomorrow at most speeds 50 and below when turning left (even trimmed all the way in!). It is VERY hard to get on plane with the Mirage Plus.

Now, I have little chine walk, except at top speeds. If I trim up too far, it happens. I just trim down a touch and it goes away.

I believe I need about another 150-200 rpm's to be in the optimal power band. Any way to achieve this with minimal changes to the tendencies to blow the prop out?

I don't mind losing a little cruising speed.

Bottom line: I would love to hit 80 just once without sacrificing too much midrange and getting out of the hole.

Thanks for any input.
Kent

bbladesprops

We like to prop that engine as close to the 5400rpm rev limiter as possible.

Your prop and rpm make that easy to do with a standard recipe Lab Finish. You will probably lose 1-2 at mid range but 80mph is very doable.