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Prop For cracker box

Posted: Tue Feb 21, 2012 7:30 pm
by Time
I'm trying to work out what prop to use for my crackerbox.

I'm running a 2.2L supercharged 255hp 290lbft 5000rpm engine.
with a 1.256 reduction box.

my options are a 12x17.5 3 blade
or a 13x16 4 blade

it will run a12 degree shaft angle.

I know that a 4 blade should be a both smoother running than a 3 blade.

Bearing in mind that with 10% slip:
12X17.5 = 59mph (66 theroetical)
13x16 = 54mph (60 theoretical)

cruise RPM will be about 2400-2600.
so the 17.5 would give 30mph
the 16 will give 27mph

The boat will be used for long crusing runs.

What are your thoughts?
What would you run and why?
what do you have on your boat now?