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Surface Drive Prop Rule

879 Views 7 Replies 4 Participants Last post by  Car Biz
Is there a rule to go by as far as 200 RPM less per pitch on a suraface drive boat?


As most of you know i just got my 311 back together and have been tweeking some little problems here and there........ Anyway i am spinning my 16 1/2 x 24 4 blades @5700 this is at neutral trim or 0......... The motors stop making power at 4900........ I just picked up a pair of 17x30 3 blades to try. Just curious if i am in the right ball park.
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What kinda speeds were you seeing with all those r's?
RSCHAP1 said:
What kinda speeds were you seeing with all those r's?
62.8 GPS 3/4 fuel, gear,two people. I did the prop slip calculator it equals like 25% slip :eek:
What are typical slip #'s for a surface drive? I would think that they would be higher than the norm.
64LS1Nova said:
What are typical slip #'s for a surface drive? I would think that they would be higher than the norm.
That is what i was hoping someone would tell me :D That way i would know if this big of wheel is good for me.
I don't know what kind of power Cuda had in his 302 but I remember reading he was close to 80MPH - that sure would be sweet:D :D

How big's the rooster tail at 62? lets see some pics!
kjo43 said:
I don't know what kind of power Cuda had in his 302 but I remember reading he was close to 80MPH - that sure would be sweet:D :D

How big's the rooster tail at 62? lets see some pics!
yup........ Cuda had 161/2 x 26's i believe. I think the best was 78.6 with his. I think he made more power than me though. The other thing is the 302 is 1000 pounds lighter than my 311.


The roost is cool :D The only problem is i have to run the thing so dayum hard (4200) at cruise that the roost costs fuel :(
tried the 30's ran 63 @5200 at 0 trim (parallel to hull). I loved how the boat planed off easier but i did a prop slip calculation and i am at like 54% :eek:
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