33ft Brown & Bassett Gentleman’s Racer

Discussion in 'Boat Design' started by WildHorses, Jul 18, 2022.

  1. WildHorses
    Joined: Jul 2022
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    Location: Oklahoma

    WildHorses Junior Member

    05F60FFD-AF0F-41FF-8AE8-FEED64022EBC.jpeg Thanks for the add guys. I had just acquired this Brown & Bassett 33ft Gentleman’s Racer that is running the WWII Era RollsRoyce Merlin/Meteor 27liter V12, and I look forward to scanning these pages to gather insight to some possible changes to make the boat better.

    As of now I would really like to get the final prop rpm higher rather than further pitching to the prop to gain more top end, because I am already at a 20in 28 pitch prop with 700hp and 1500lb torque @2400, so I would rather gain more prop speed than adding more launch torque pressure to the prop, but I am not finding any Velvet Drive options better than the 1:1 I am already running.

    Don’t get me wrong, the boat cruises a nice 50-55mph @ 2500rpm, but I am wanting to get the engine revs down, while also gaining top end potential the boat feels capable of.

    Here is a YouTube link of the boat on operation a couple weeks ago.

     

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  2. Scuff
    Joined: Nov 2016
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    Scuff Senior Member

    Nice! Any pics of the engine?
     
  3. WildHorses
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    WildHorses Junior Member

    Sure FF4B4C7B-87CB-42E0-A433-F84378ED664B.jpeg
     

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  4. philSweet
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    philSweet Senior Member

    Have the normal marine race mods been made to the Merlin? Crank weights, cooling system revision? What boost are you running - stock low boost gearing? What exactly have you got for a tranny in there now? Do you have an antiknock system and what does it consist of?
     
  5. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    I think that's the Meteor version (tank), not the Merlin (aero). Anyway, there are some overdrive transmissions on the market, but the question is if they fit without major changes. If they don't, one option would be to have a custom shop change the gearing ratio in the existing trans, wich basically means keep the housing casting and fabricate all new gears to fit. The next step is an all custom job, housing included.
     
  6. WildHorses
    Joined: Jul 2022
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    WildHorses Junior Member

    This one is the Meteor version that is much more friendly to being marinized and running on standard fuel, which is a huge benefit for sure.

    I am running a 1:1 Velvet Drive with a 20in 28 pitch prop to currently allow a 55mph cruising speed, and will be changing to a 30 pitch prop to get some additional top end while lowering the current 2k revs for that 55mph cruising speed, but I would really prefer to find an overdrive option to garner more prop speed than adding more pitch, I just can’t seem to locate a source for any Velvet Drive overdrive or compatible options.
     

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  7. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    So what is the real objective to lowering rpms? Are you trying to extend the maintenance interval on the bottom end rebuild?
     
  8. WildHorses
    Joined: Jul 2022
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    WildHorses Junior Member

    I have more than enough Hp and Torque that is being wasted with the lower rpm/speed, and I would like Lower Rev’s for obvious longevity reasons, so it is really a matter of just zeroing in on an optimal setup by getting the prop rpm to a proper range versus over torquing the prop shaft and transmission with pitch.
     
  9. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Some of the cited prop data don't end up the way I'd expect when crunching the numbers. You say it's a 20"*28" screw, fine, but what blade number, blade area, blade profile, shaft dia, distance between bearings etc?
     
  10. WildHorses
    Joined: Jul 2022
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    WildHorses Junior Member


    What do you mean? Working with GPS for speed, but the tach that may be a bit off being cable drive, so also going by what I know is the WOT of the motor.

    I don’t have the location measurements right off the top of my head, but it is a triple blade 1 3/8in 20in and 28 pitch Michigan brand bronze prop on a very sleek hull.

    All the pics below are just under 2k rpm.
     

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  11. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    Going off foggy memory but zf used to do a .8 and change to 1 for the 280-325 straight shaft jet applications. At your rpm the 325 would be in the zone especially spinning that size wheel. Guessing the merlin is an oddball bellhousing size. It might be easier to go with a custom adapted gear built with the exact ratio in mind vs trying to cut custom gears. Twin disc does a 5114 in a .93 but that's a whopper of a unit.
     
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