houston we have a problem!!!!!

ok so i just finished building this 20inch hydro, 25 including strut and hardware, and anyway... i think its cavitating![:@]
my hardware is inline and its running a sv27 brushless motor on 12 cells, with just a 2 blade prop that a guy down the hobbie store reckomended, it had no tag or information, but honestly i think its a nitro hammer prop!!!

the prop sits about 2 inchs under the water from center shaft to water line when just sitting there, but as soon as i take off even slowly, it starts to catch air or cavitates or something like that, its more like its sucking the air in from above it. and its not a flex shaft so i cant just angle it more.

the prop is 31mm in diameter, plastic, and like i said its a 2 blade.
i dont no how to fix this problem, i think its cavitaion because its not peircing the surface but i know theres more to cavitation than that.
i was thinking maybe a 3 blade prop or a bigger 2blade or something??

ill pop a pic up alittle bit later if you need 2 hav alook at the hardware and where its positioned.

if anyone has any input at all, any questions about the boat that they need to know to help me out, just fire away!
any feed back at all would be muchly appreciated!

Cheers,

Corey