speed calculations
 

What kind of top end speed should be anticipated from a set of 30 inch bravo ones spinning 5300 in a formula 311 1988 no step. (1.5.1 out drives bravos )sHOULD i CHANGE GEAR RATIOS.? iS 1.5.1 HARD WITH A 30 INCH 4 BLADE ON AIR TIME / REENTRY ?

Re: speed calculations
 

RPM divided by gear ratio times pitch times 5 divided by 5280 minus slip[10%]

Re: speed calculations
 

You must have some serious HP in those motors. With no slip factor your at 100mph. 10% slip would put you at 90.
Throttle control is the biggest factor in weather or not your going to tear up drives or not. With the kind of HP you must be pushing to spin the 30's @ 5300 on that boat I think drives are going to be an issue.

Re: speed calculations
 

I always used RPM divided by gear ratio, times pitch, divided by 1056, I've seen as
much as 18 percent slippage, borrow a GPS, and be sure.

Re: speed calculations
 

5280/5=1056 same way to get there...

Re: speed calculations
 

does hull style vary this greatly?

stepped? pad? cat? i would think they would vary greatly.... i haven't done much w/ speed formulas so i was just wondering..

Re: speed calculations
 

Efficient stepped hulls say a fountain,skater are more likely to have less slip like 8 to 10%.The higher the x dimension the more slip.Usually guys will raise the propshaft height to get more speed.They will turn more RPM.The raise in RPM is due less drag which the boat will RPM because it is going faster.It will RPM more because the slip% is higher.

Re: speed calculations
 

I have 30" labbed turning on 1.5 Ratio drive at 5200 I run 81 mph. Straight V. 650 HP.

I have read that 30" is the most efficient pitch on a bravo outdrive.

Re: speed calculations
 

The 32 is supposively the most efficient according to Mercury.You need some stairs on that Cigarette. :D :D

Re: speed calculations
 

I ANTICIPATE BETWEEN 80 AND 85 SOMEWHERE . Waiting on another warm day for a test ride !!!