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  1. #1
    Member River Rocket's Avatar
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    Have you ever wondered?

    What the prop and lower unit look like on your XB21 at speed?

    Here is a video experimenting with side views.





    Here is a video from the front. After the first video I added the yellow pin to show the center line of the gear case. I need to run both video's again in clear water with the new pin.
    Allison XB21 2+2
    Mercury 300R




  2. Blazer Boats Moderator Rebel1's Avatar
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    #2
    Very cool!

  3. Member
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    #3
    I have described this to people and told them each blade comes out of the water on each revolution and they look at me as though I am crazy.

    Now they can see the proof.

  4. Member mittenbass's Avatar
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    #4
    Really cool video. Thanks for posting.
    Brad Luchsinger

    2003 Allison XB-21 BasSport 2+2
    2004 Mercury Racing 250XS


    1998 Xpress X70
    1998 Yamaha Vmax 150 TRP

    2002 Triton 200XP

  5. Member mgeod's Avatar
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    #5
    That motor pulls like a freight train !!

  6. Member
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    #6
    What size jack plate and how high is the motor prop to pad?

  7. Member
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    #7
    Looks like your water intakes would be out of the water above 70 mph? Intakes setup different than typical?

  8. Member
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    #8
    How were you getting any water to the outboard with the case up that high near the end of the video?? Have you installed a remote racing water intake?
    2013 Allison XB-21 BasSport Pro
    2023 Mercury Racing 300R
    Bravo FS 30P
    ProMax 30P

  9. Member River Rocket's Avatar
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    #9
    In the second video, I'm 4.5" above at the end. Very little water to the motor. I just wanted to see what high looks like for shallow water takeoff.

    The R has much lower water intakes. It can run at least 1/2 higher. I lose water pressure at around 2" over. I lose speed anything over 1-5/8". So between 1-5/8" and 2" I'm just running higher to run higher.

    11.5" of setback
    Allison XB21 2+2
    Mercury 300R




  10. Member River Rocket's Avatar
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    #10
    Here is the same style video I took of the 300XS with 11.5" of setback (I think) running at 1" over. Boat is running 99 when strung out. Its a short lake so the top end isn't very long.

    Allison XB21 2+2
    Mercury 300R




  11. Member
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    #11
    Excellent as always Geoff!
    2024 Xpress X21 / Yamaha 250 SHO
    2022 Allison XB-21 BasSport Pro Elite / 2022 Mercury 300R (Sold)

  12. Member
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    #12
    excellent video. Ya know, it sure looks to me like the water is definitely flowing off the skid planer. And you stated your engine height is over 1" above the pad? It's easy to see the point of the sporty above the water line. I've always been told "there was no way the water coming off the lip of the pad could be hitting the underside of the skid planer before it gets to the nose cone of the gearcase". I'm glad you posted this video Geoff..thanks!!
    2013 Allison XB-21 BasSport Pro
    2023 Mercury Racing 300R
    Bravo FS 30P
    ProMax 30P

  13. Member River Rocket's Avatar
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    #13
    Agree Craig. No way the water isn’t hitting the skid planner. It’s in the water in the 100’s as well, so I don’t see a scenario where the boat isn’t riding on it.

    I put the concave cut in mine to give me more pressure at higher motor heights. It gave me another 3-5psi at WOT.

    I did another video yesterday in clear water. You can see the pvs holes venting and the pickups on the lower taking water. I have 45 minutes of video to edit. I have rpm and water pressure overlay as well so it should be cool to see how everything interacts.
    Allison XB21 2+2
    Mercury 300R




  14. Member basscatlildave's Avatar
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    #14

    98 Bullet 20XD
    225 Pro Max

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    #15
    Geoff, I'm glad you are making these videos. There are some guys from the old school who would never believe in a million years that the dynamics you are capturing are really happening. Dispels some pretty old notions on the cone, blades, etc. I appreciate all the effort you have put in.

  16. Member
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    #16
    Geoff, great videos of your allie. Only wish it was a Stroker. Keep them coming as no mater what boat brand this is very interesting to watch.

  17. Member tritontr21's Avatar
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    #17
    Hey Geoff great video! Hope you are ready to video the back of my 2+2 again this winter lol
    Jay McDaniel
    2003 Allison XB21 BasSport Elite 2+2
    2019 Mercury Racing 300R

  18. Member River Rocket's Avatar
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    #18
    Quote Originally Posted by tritontr21 View Post
    Hey Geoff great video! Hope you are ready to video the back of my 2+2 again this winter lol
    It's on!!!!! Is your motor out of break in yet?


    FYI, I'm leaving the poles in Minnesota this year. I'm not spotting you anything........
    Allison XB21 2+2
    Mercury 300R




  19. Member fishnfireman's Avatar
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    #19

  20. Member River Rocket's Avatar
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    #20
    Thanks guys. Its fun playing around. At some point I need to start fishing.....

    I wanted to get another launch on camera. This time I tried a little lower. Unfortunately we are in algae bloom here. My go to clear lake isn't that clear. It will be soon and I will try again.

    This video starts with a 4.5" over hole shot. I fish a shallow river and I wanted to see if I could get out at 4.5" over and what it looks like. The boat had no issues launching the 32 Promax out. I need to shift the camera over so we can see the venting better, but this is a good shot of what happens as the prop spins up. I slowed the video down to see it better. Pretty cool.

    After I get out the motor comes down quick to even with the pad. I run for a little while to cool things down. Then I run another test at 70. You can see at even with the pad the water is getting pushed forward off the nose cone. It is also very turbulent and pushing the sides of the case. In general it looks like a mess flowing around the case. Thus the reason the boats always feel so bad running fast with the case low. Towards the end you see me come up to 1.5" over and everything cleans up.

    Enjoy.

    Allison XB21 2+2
    Mercury 300R




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