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  1. #1
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    Glastron Surface drive

    I expect quite a few here have seen this photo of a one off CVX 20 Surface drive from back in the 70's.



    I know nothing about this boat but have always wanted one.
    A few years back a friend who is good at scrounging things up found this and had me in mind.





    Just what my wife wished I would never find, After it was burning my hands for awhile I hung it on the back of my Superboat, stared at it allot and chose to never cut the hull for the propshaft. We all agree to that.

    But late October, less than a month ago, what shows up on Farcebook, a 1976 CVX20 with an Oldsmobile milkshake maker in it. looks like someone was not aware you need to drain these engines up here off season. Works for me.



    Hull and wood is solid, clear coat is end of life, works for me.
    So out comes the big 455 milkshake maker



    And the cleanup and prep begins. The engine bay was white froth, dang that took days to clean out.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  3. #2
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    This is gonna be marty moose fantastic there Clark! Awesome!!!
    Hydrostream dreamin

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  5. #3
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    Once the initial mopping out and flushing the white froth I removed the Berkeley JE pump, that is set aside with hope someone wants it.



    Turns out the drive body is wider than the recess in the hull, so on with the suit, plug in the air supply and get to it



    Dang I am glad this is not back in the 70s when we would do this with just another shirt pulled over our head.
    So time to drill a few hole for brackets and hang the drive in place,





    Now I am getting somewhere. Turns out I chose to cut away some of the drive housing, mixed feelings on that.
    Climbed inside the hull and trimmed away the intake for the jet drive and set the transmission in the hull.





    At this point I was getting behind on time and weather was 'bout to change, which it did, temps dropped 40F and we are blanketed with snow now.
    I really want to make the transmission brackets. If it gets above freezing in the next few days I may get a chance, but till then it is wrapped in it's blanket for the season.



    I can not say this thing will scream but once it has it's L92 6.2 alloy block engine it might fly. It will end up more than 400# lighter than it was.
    Last edited by CharlieN; 11-22-2022 at 07:28 AM.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

  6. #4
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    That's a damn cool project!
    Let's go Brandon!

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  8. #5
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    Sun came out today and we are a few degrees above freezing, I had cleared the snow off the cover a few days ago so I could roll the cover back this morning. What this gave me was a chance to accurately measure the inner structure. Glad I did since my Cad drawing was a rework of my Sprint hull. They are further from each other than I thought.
    The transmission mount will be a different, simpler weldment than I thought. It will end up with a rubber sandwich set on the aft floor over the stringer.
    Looks like the engine mounts will also set above the stringer, I expect I will fabricate a weldment bolted to the block reaching out to cushions over the stringers. This will eliminate the cross structure that passes under the engine, curious how much that weighs.
    Maybe that gets removed while the hull is open.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  10. #6
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    Following.. Very cool

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  12. #7
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    A few pics from the day, went back out with the camera to snap a few.
    It is just a little snow but it does not want to leave


    The rough cutout in the hull, the white is FG dust, The aft portion where the sidewalls remain I will be leaving to brace the transom, not that there are any loads in that region.


    This is the engine mount structure under the Olds 455 and essentially the same for a 460 Ford.


    I expect for the L92 engine, I will build brackets from the block with cushions over the stringers. That is next year.

    And a closer shot of the transmission for this build. A ZF-45
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  14. #8
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    Very cool build. Is the prop shaft able to be trimmed or is it a fixed position?

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  16. #9
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    Thank you, and yes it trims, The drive housing mounts/ pivots on two lower pins with a single high mount ram.
    Propshaft mounts with a Ujoint onto the output of the ZF transmission.
    Of the shots I have with this just mocked up here are two shots with the housing/drive down and up.
    Not the best of comparison shots once I look at these.





    Last edited by CharlieN; 11-23-2022 at 05:00 PM.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  18. #10
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    This thing is gonna rock!
    Hydrostream dreamin

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  20. #11
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    Now that I finally have one of these hulls I am really liking it. I doubt it will scream, the pad is 12" wide with the inner strakes a few inches above them. I expect it will come out of the hole strong.

    My intention for the build will be powered by an l-92, alloy block 6.2. I intend to fabricate a nice set of jacketed headers and once tuned, power might be 440-450ish from what the Chevy guys here claim. So that is well more power than the Olds 455 as well as 350# lighter or so.
    I have no clue what this prop will be like, I need to live with it since I can not fund a custom shaft and a selection of Bravo props to search for the best.

    What open throttle will be, well time will tell. Maybe late next year.

    I am expecting it to be docile at speed, again time will tell.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  22. #12
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    Way cool.

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  24. #13
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    What a great project!

    Been a long time since Iíve seen one on here where someone is thinking outside the box.
    Love it!

    You make comments on the differences between the hulls but arenít they both CVX 20ís?
    If so, Iíd expect only differences being to accept/feed the jet pump?

    I had a CVX OB yrs ago and had a friend w/a jet.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

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  26. #14
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    Quote Originally Posted by Instigator View Post
    What a great project!

    Been a long time since I’ve seen one on here where someone is thinking outside the box.
    Love it!

    You make comments on the differences between the hulls but aren’t they both CVX 20’s?
    If so, I’d expect only differences being to accept/feed the jet pump?

    I had a CVX OB yrs ago and had a friend w/a jet.
    Thank you

    Growing up I never learned that I was not to just dig in and figure out how to do something.
    I grew up with very little money, heck still don't. But I always wanted what the other boys had, so I found I had to build what I could.
    Soon, as a freshman in HS all the kids with money were asking me to build what they could not buy since I had neat stuff.
    By 16yo I had boats, airplanes and cars which all had character.

    So as we see with this project, decades back I saw the one picture of the surface drive on the yellow hull. I have wanted on for decades, late next year I will have it.

    The CVX 20 hulls are quite different, The outboard has a rather deep Vee. I have been quite impressed how well it runs on top of 2-3' waves. Foot throttle only for me.

    The jet hull is a shallow pad-Vee. The pad is wide with the inner strakes only 1.5" or so above. I expect the hull design is to lift the rather heavy engine at moderate speed.

    I am looking forward to see how this drives with the lighter weight and far more efficient drive. Not to mention more power with stock vs stock engine.
    Last edited by CharlieN; 11-25-2022 at 08:00 AM.
    Regards,
    Charlie North
    If it ain't broke, modify it.
    80 21' Superboat with Yamaha 225 Excel power
    76 Glastron to be powered by a 6.2 L92 with surface drive
    87 Glastron CVX20 Hull

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  28. #15
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    Similar story here.

    The components in your equation look really good on the chalk board.



    Quote Originally Posted by CharlieN View Post
    Thank you

    Growing up I never learned that I was not to just dig in and figure out how to do something.
    I grew up with very little money, heck still don't. But I always wanted what the other boys had, so I found I had to build what I could.
    Soon, as a freshman in HS all the kids with money were asking me to build what they could not buy since I had neat stuff.
    By 16yo I had boats, airplanes and cars which all had character.

    So as we see with this project, decades back I saw the one picture of the surface drive on the yellow hull. I have wanted on for decades, late next year I will have it.

    The CVX 20 hulls are quite different, The outboard has a rather deep Vee. I have been quite impressed how well it runs on top of 2-3' waves. Foot throttle only for me.

    The jet hull is a shallow pad-Vee. The pad is wide with the inner strakes only 1.5" or so above. I expect the hull design is to lift the rather heavy engine at moderate speed.

    I am looking forward to see how this drives with the lighter weight and far more efficient drive. Not to mention more power with stock vs stock engine.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

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