Set back that Allison recommended...

[BigRWater]

I am trying a different, low HP motor. I still have the 225 Super Magnum that came with my Allison XB 2003. The 225 was on a 13 inch set back.
Things were not working out when we put the low HP motor on (115 Mercury). The hole shot was horrible and 56 mph was the highest speed we had attained with props we have.
My boat guy made recommendations & confirmed them with Allison.
The set back they recommended allows either a 6 inch or a 9 inch set back. We tried both 6 and 9, ended up at 9 inches on the Allison set back, and an additional 6 inches with the Hydraulic jackplate. I have now hit 64mph (with just me and my puppy) with a 25 pitch mercury prop.
My goal is 62 mph with a weekend warrior tournament load & people.

 

[BigRWater]

 

[Lotus 50]

Apparently I know nothing. I would have thought less HP needed more setback for top speed. Planing better with less setback makes sense. Interesting project.

 

[SLOmofo]

So your at 15" of setback? 9" jack plate, plus 6' Hyd. What year is your Xb2003. I think there is a distance difference from the end of the pad to the transom 1994 to 1995. Doesen't matter what YOU have, just remember there is a difference when other people suggest things. I have a 1994 XB2003 with a HEAVY engine, 3.3 JohnRude so I have a 4"-5" Rapid Jack manual jack plate. I can only get down to 5" because I mounted the trim ram horizontally inside the jack plate. Remember everything is a tradeoff...jack it to the moon, you won't take off soon, and a Bat Turn might be in your future.

Maybe... just maybe.... there will be a WAR2021 (Western Allison Rally) you really should join us. We are a great bunch of arrogant assholes. Some are bigger.... then theres the vertically challenged asshole. I'll let you figure out who that is.......Never a dull moment, especially if you are watching me fix my broken panda. The pleasure is all yours.

 

[BigRWater]

So your at 15" of setback? 9" jack plate, plus 6' Hyd. What year is your Xb2003. I think there is a distance difference from the end of the pad to the transom 1994 to 1995. Doesen't matter what YOU have, just remember there is a difference when other people suggest things. I have a 1994 XB2003 with a HEAVY engine, 3.3 JohnRude so I have a 4"-5" Rapid Jack manual jack plate. I can only get down to 5" because I mounted the trim ram horizontally inside the jack plate. Remember everything is a tradeoff...jack it to the moon, you won't take off soon, and a Bat Turn might be in your future.

Maybe... just maybe.... there will be a WAR2021 (Western Allison Rally) you really should join us. We are a great bunch of arrogant assholes. Some are bigger.... then theres the vertically challenged asshole. I'll let you figure out who that is.......Never a dull moment, especially if you are watching me fix my broken panda. The pleasure is all yours.

Yes. 15 inches of set back.
My XB 2003 is a 1998.
I would really like to come to War2021. I would learn a lot. The top people in every field have "Personality". I would like to meet them.

 

[BigRWater]

Apparently I know nothing. I would have thought less HP needed more setback for top speed. Planing better with less setback makes sense. Interesting project.

Apparently you do know. You are right. We attained top speed since changing to the 115hp with more set back.

We tried various other brackets and combinations, after being very disappointed with the performance when we changed motors. I won't bore you with everything we tried. This set up worked the best. We are sticking with this.

The person I bought the motor from has done 72mph in his XB 2003 he has a 16 inch set back and used a 27 pitch prop.
I don't have a 27 inch prop yet.

Planing is no longer an issue with any prop or load we have tried lately. We installed a 20 degree, 19 inch Allison Skid Planer. Its magic. At least for this 115hp motor.

Wirth the Mariner 225 Super Mag on this XB 2003 it never had any issues with anything performance related. But I bet that Super Mag would love this set up. The Allison 6/9inch bracket allows the change of shaft lengths also! 15 inch shaft (Super Mag) or 20 inch shaft (115 Pro XS).