Is V-Drive transmission useful?

Discussion in 'Powerboats' started by APP, May 16, 2011.

  1. APP
    Joined: Nov 2010
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    APP Junior Member

    Hi
    Is V-Drive transmission useful? It is said that it is used in space saving installations, especially in Catamarans saving room in the hulls. Of course provided the Center of Hull Gravity is well calculated.

    A question is that some times the installation of the engine is inclined. How much is permissible? What about vibration and noise?

    Then there is also an inclined propeller shaft. Is there any loss of power? How many degrees inclination from DWL is permissible?

    I take the opportunity to attach some pictures of V-Drives.

    Best Regards
    APP
    View attachment V-Drive Pictures.pdf
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Of course V-drives are useful.
    If the layout of a boat limits the length of the engine bay, the choice is between stern drives or V-drives. The latter has less service issues and will prove to be more reliable.

    There is a loss of power from an inclined shaft, but just a few %, not more than from a stern drive leg. And vibration originates from the engine, not from a correctly installed drive system.
     
  3. APP
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    APP Junior Member

    OK. Thanks a lot!
     
  4. Tim B
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    Tim B Senior Member

    V drives were very common before stern drives became popular. Whilst stern drives do have a lot going for them, there is nothing wrong with running submerged props and V drives. You can even see applications where one engine is direct drive and the other is V-drive, though this is usually a survivability decision.

    The power "loss" from inclination is simply the sine of the shaft angle. 10 degrees is 17%. This looks significant, but it may be less than you would lose through a stern-drive (I don't know, but don't take it in isolation). However, you do get a bow-down trimming moment which can be nice, as it allows the CG to "drift" aft just a little.

    Damage may be a consideration, in that if you strike a stern drive it may make a mess, but you could replace it easily (assuming no major damage to the transom), whereas with shafts you could do a lot of damage very quickly.

    Tim B.
     
  5. APP
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    APP Junior Member

    OK thanks. What about the engine imclination? what is advisable? In some pictures it seems the engine is inclined by at least 10 deg. Oil circulation?
    Regards
    APP
     
  6. Aliboy
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    Aliboy Junior Member

    Your engine specifications will show a static inclination limit. The choice of gearbox angle, shaft angle, propeller diameter, and prop tip to hull clearance will all impact the final static engine inclination and must be calculated together. I would start with working out the ideal prop diameter for the boat and desired engine/hp, then shaft diameter, then required minimum tip clearance, then the minimum allowable shaft angle, then desired engine and allowable static inclination, and last what down angle options are available in the gearbox options. If you are struggling to reach acceptable angles with the gearboxes available, recalculate your performance with reduced prop diameter and increased pitch. This gives different tip clearance placement and hence reduced shaft angle. The compromise is in the prop performance, but it may be quite minor.
     
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  7. CDK
    Joined: Aug 2007
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    CDK retired engineer

    One advantage of the V-transmission is that the engine can be mounted horizontally, so you don't need to be concerned about how much inclination a particular engine can handle.
    Most engines can accept the 8-12 degrees angle in a conventional straight shaft setup, some marinized car engines in planing craft need minor modifications like moving the oil suction tube to the lowest point in the oil pan.
     
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  8. Tim B
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    Tim B Senior Member

    "The power "loss" from inclination is simply the sine of the shaft angle."

    My apologies for my incorrect TRIG, the vertical thrust component is sin(angle), the horizontal is cos(angle). This makes the horizontal thrust reduction 1-cos(angle) which for 10 degrees is 1.5%.

    This is a significant simplification, as it does not consider the effect of non-axial flow on the propeller.

    Sorry,

    Tim B.
     
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