Changed Drive Gears - X Dimesion too High ? Looking for Advise
 

Background - 38' Powerplay, 750hp, ITS, Bmax Drives.

Boat Originally came with XR's with -2 shorties w/1" spacer installed, 1.5 gears was running 34 Bravo Ones - Speed was around 95 mph

Drives were changed to BMax. Only gears available at the time were 1.32, -2 Shorties w/1/2" spacer 26 Bravo Ones - speed around 90 mph (so says previous owner) I had to 88 mph, RPM still climbing at 5700 so I didn't push it.

Had drives freshened, reinstalled 1.5 gears, left 1/2" spacer in. Boat will NOT plane with 34 or 32. borrowed some 31 - 5 blades to get boat on plane, huge rooster tail now slip thru the roof.

My thought is that with the design of the BMax -2 lower and the increased leverage of the 1.5 gears that I need to drop the drive down. Question is how much ? Do I drop down another 1.5 inches thus negating my shorties.

Looking for some input.

I think only testing will tell for sure.
A 1" bigger spacer made a huge difference on my Pantera. It threw a 6' high rooster at neutral trim and had 24% slip. The added inch of spacer got rid of the rooster except when trimed high and slip dropped to about 16%.

The one thing that strange is the numbers you got from the prior owner. Normally going from a 1.5 to a 1.32 would only be about 4" of pitch difference, not 8" of pitch.

All of my research showed the boat originally had XR's 2" shorties with a 1" spacer and 34 Bravo ones. I also feel that the boat was under propped with the 26's it would have easily turned 28's and maybe 30's. I was at 5700 rpm and still climbing when I ran 88. I would like to be @ 5400 - 5500 rpm. The gears were mariginal so I figured time to back to the 1.5's while they were apart. Me feeling is an additional 1" won't be enough, since it already has a 1/2" spacer installed and I probably need an additional 1 1/2". I don't have a measurement for the x dimension, but it appears to be very high.

I do think you would be better off being a 1/2" too deep, rather than having issues getting on plane. I can tell you I was very surprised at the difference lowering mine an additional 1 inch made.

I am surprised that the gear change made that much of a difference though.

I have 2 standard Bmax lowers I will trade you.

What props are you using that will not plane ? Allot can be done with the props prior to dropping the drive depth, the key is in the hub tube length and placement of the diffuser on the larger pitch propellers in order to get the boat to plane. Are you having driveability issues at your top end speeds ? or is it just getting on plane ?

I have two xr standard length lowers with DWP that only have 50hrs and only 1 hr over 3000 rpm. I will trade you even if your -2's are in equal shape.

I believe that a BMAX vetrical shaft is larger than a standard XR so keep that in mind if you are looking to trade. If memory serves me right, Waconda now owns BMAX and may be able to help you.

I talked to JMS today. He and waconda are going to swap lowers and do some testing.

Good talking to you today Griff. Yes, me and waconda are trading lowers. He wants to try -2's on his outside drives on his BT and his standard length drives might be just what I need.

The XR's are not a direct swap for the Bmax's since the Bmax shafts are much larger. My drives are fresh, about an hour and a half on them. Done by waconda (Owner of the Bravo Shop, home of the Bmax).

I'll report back after testing this coming weekend.