jdnca1

I have no problems getting on plane with twin 28 Daytona and 2" short drives with Bravo props...the Imco cavitation plates make a huge difference as do extension boxes.

IMO the "load" on the drive changes quite a bit when going to 5 blade wheels, I know people who had no isseus breaking drives to having lots of issues just from going from a 4 to a 5 blade prop...prop shafts in particular on the small shaft stuff. I always look at "slip" as kinda being a clutch, it doesn't bite as hard and hence doesn't load as hard. With "stock" power it's probably not that big of a deal, bigger power though it makes a difference.

CheckedOut

I am also starting to believe that the Imco lowers also help get on a plane. Seems like the boats that have problems all have the Merc std lowers. Perhaps that is due to the cavitation plates always being installed in conjunction with the imco lowers?

One thing is for sure. I absolutely needed a tunnel tab on my boat. Also planing strategy is everything. If i dont roll into it right forget it, I might as well start over. Here's an example of how to do it right on my boat.

http://www.youtube.com/watch?v=jd6QhpTmTNY

jdnca1

I have no tab either, and it comes right up..full of fuel and people...no big deal. IMO the Imco cavitation plates are the difference...someone should try just that to see. Boxes also help a bunch...before I had boxes it was a little tough to get on plane with a load of people and fuel...and that was with Std length lowers..(Leading edge)

grads2112

I disagree about 5 blades causing drive failures. I have had five blades on my boat for 4 seasons (200 hours) and have not even seen a tiny flake of metal when changing my drive oil. I think part of the reason for this is that with 5 blades I can throttle it up with no blowout and the boat pops on plane at about 2500-3000 r.p.m.'s. With four blades I have a ton of blowout and must run it up to 4000+ r.p.m.'s then it finally bites and gets up on plane. You want to talk about stress on a drive? The motor is putting out some serious torque at those kind of r.p.m.'s and for the prop to hook up at that point causes a huge amount of stress on the drive. Kind of like running your car up to the red line and popping the clutch.

jdnca1

Grads- while I agree with the planing argument you make, I'm talking more about running...when the drive loads and unloads a five hooks way harder than a four blade and stresses the drive more. This is where the failures went up in a big way with 5's vs 4's. With planing the only real issues I've seen people have are with prop shafts..."small" ones in particular. With 525's it's probably not that much of an issue on drive load with the 5 bladers anyway, and is a factor in why your drives are doing so well.

Now the applications I'm referencing are for bravo's seeing 800-1000 ft/#...things change in a big way with these input Tq levels. Big shafts, "X" series gears, and Billet caps to stabilize the case are HUGE in making drives last at these levels. About the only issues we have been seeing with the abouve changes are that the pinion gears finally fatigue and either break on loose teeth. Have been having great luck just changing out the upper gear sets (pinion / drive) every 50-75hrs to "cure" the fatigue issues.

grads2112

I agree with what your saying jdnca. I also think another reason why my drives are doing so well is I never hammer the throttles down once I am up on plane. I mean don't get me wrong, once I'm doing 100 m.p.h. I'm pushing the sticks as hard as I can, I just don't slam them down at 40 m.p.h.

CheckedOut

This brings up a good point, well more of a question really. Is there a certain point (power wise) where 4 blades are impractical? It seems like all of the big power cats and most everything running with sixes have five blades. Do four blades just slip too much to be useable once you pass 700 or so hp?

grads2112

Just my .02 cents but I think boats are running a much higher x-dimension these days and require a 5 blade to bite.

stormbauer

Well that is very interesting information. My situation is that my 33 will run 125 at 5,800-5,900 RPM with current 30P Bravo's (non labbed). The motors are 920 HP at 5,700 RPM and put out 890 Ft#'s ! So far draive has been on - Teague's. I do not want drive problems but would like to get up around 130 ish. Like I stated boat gets up on plane easily.

Adrenaline Junkie

Best thing to do would be to borrow someone's labbed 5 blade 32's for your boat (my guess)..or maybe even labbed 5 blade 34's. Take the speculation out of the equation.

I'd let you use my labbed 34's - but I threw a blade on those and have been using my 4 blades since (and lost about 8 mph).