T400's

is it true that cleavers enable more stern lift...
I have a very narrow beam (6') 30' boat with twin 400s and 1.5 Bravos that should be going around 80mph but is stuck in the 60s. I'm wondering if there is so much weight in the back that its dragging. Bow lift is definately not a problem, nor is handling or hole shot. I have recently gone from a 23 mirage plus to a 21 mirage, went from 5k to 5500 and have more speed... am still testing. The boat came with the old cleaver style 23p mercury 3-blades and would turn up to 6k but I didn't measure the speed back then (it seemed over 70 and chine-walked without being scary) and since have bent one of the cleavers beyond repair. I'm wondering if a 25p cleaver would be the best choice for top speed. The engines dynoed at over 420HP at between 4-5k rpm. How important is it for the top speed to intersect the peak HP? It still pulls near 400 HP at 5400 according to the dyno sheet... does anyone just advance the cam a few degrees on these boats to increase the peak HP and RPM?

T400's

the x dimension is the factory recommended 14" and the cleavers were 14" versus the almost 15" mirages in diameter... were 25p cleavers even made by mercury for the 15 spine shaft?

T400's

I'm thinking a 25p cleaver would turn at least 5500, its not a step hull and these 400s make about 60 or more Hp than the engines I used to have
thanks

Griff

Prop diameter is not the x dimension.

The mirages are about the most bow lifting, least stern lifting prop you can have.

Try some Hydro QIV's, Rev 4's or even Bravo 1's.

Griff

BTW, you have a 7' beam.

T400's

I measured the beam, and its about 6.5, the X dimensions and the prop diameters both happen to be about the same. I still need to know if I can find a 25p 3 blade cleaver somewhere, I tried hydromotive 4-blade 23ps off my cigarette one year and it wouldn't pull past 5k either. The 21p mirage did hit 70 easily yesterday at 5500 with plenty of air under us, for some reason I couldn't get the GPS to give a readout. My point being that since there is a lot of weight on the tail and very little beam I need a stern lifting prop I think, I'm convinced its dragging its ass. Theres a nice 25p 3 blade hyromotive on ebay but I wonder where I'll find its mate. Thanks for your info on the mirage being the LEAST stern lifting prop around, I just found this out and I'm hoping for 80MPH plus when I get it right (the magic number!
It sure planes and comes out of the hole easy, it stays on plane at around 2100 RPM even with the 21s. I see a matched set of 25p cleavers on ebay but they don't look like they will match the hub perfectly, they look like the narrow hubbed choppers, even though it says for TRS etc

T400's

maybe I should go down in pitch and try some 4 blades, like a 21p hydromotive or Bravo 1? Or stick with a higher revving 3 blade?

Griff

More blade area = more stern lift. Go with a lower pitch 4 blade.

Where is peak torque on the dyno sheets????

T400's

if more blade area is more stern lift, then how is it that the cleaver lifts more than the mirage? I guess you mean a four blade with a more cleaver shape. The peak torque is slightly over 4k rpm and gradually falls off like most cams

Griff

Cleavers don't have any cupping for bow lift and the thick trailing edge lifts the stern. Mirages have a very high rake angle and are designed with bow lift in mind.

Propping the boat to run about 1000 rpms above the peak torque is a good rule of thumb. Maybe a little more or less depending on how fast the torque curve falls off.