S/P prop on a diagonal shaft

Discussion in 'Surface Drives' started by Sassriverrat, Sep 23, 2017.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Just a rough illustration of the set-up you envisage, would be helpful.
     
  2. Sassriverrat
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    Location: Chesapeake Bay

    Sassriverrat Junior Member

    It'll be a few days of learning cad to have any decent picture- so- google russian hydrofoil- take a long and narrow boat with surface piercing foils and traditional, downward-inboard shafts- now cut the shafts shorter so that instead of having submerged wheels, the are surface piercing. It's just a Russian hydrofoil with shorter shafts and surface piercing props. Does that give a picture?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    How do you maintain the same level of propeller immersion, if you intend them to be surfacing ? That is the most obvious question.
     
    Last edited: Sep 24, 2017
  4. Sassriverrat
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    Sassriverrat Junior Member

    Ok to somewhat tangent from this (I apologize for the delay- I've been at sea-I'm stationed on a ship), why can't a power boat have two foils- a forward one at a fixed attack angle and an after one with similar property except an adjustable trailing foil like an airplane? Than this could work with the surface prop. Ideas?
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    The problem I see is that under varying conditions, the prop immersion will vary considerably, and with that the engines revs, and the boat speed. Your props really need to be in the water all the time.
     
  6. Sassriverrat
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    Sassriverrat Junior Member

    Well the current thought being that if the prop is on the after side of a foil that is at or nearly perfectly straight, then altitude is adjusted via a hand-crank trailing flap like on a J3 Piper Cub and the propeller can be fine-tuned with throttle.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    You might chance on something that works, but more likely not, I'd say. Why SC props ?
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Hydrofoils are a science, a specialist thing that demands a lot of knowledge, many people can design a passable boat, very few a practical hydrofoil, I suspect.
     
  9. Sassriverrat
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    Sassriverrat Junior Member

    Between fascination with surface piercing and the want for efficiency while doing 45 knots (I know these two shouldn't go hand in hand), but I'd also like a boat that does that kind of speed in a one good chesapeake chop without drawing more than 5' of water tops in a displacement mode.
     
  10. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    I've ridden in one of these Russian hydrofoils.
    It only had foils forward. The narrow, V-hull aft planed with most of the hull out of the water while on foil.
    It was great up to a ~2 foot sea, then the a wave would strike the hull, create huge drag, slowing the boat before regaining flight.
    Once it dropped and the wave came over the bow and right through my front seat window.
    Sure was glad to be wearing my cruiser suit.
     
  11. Sassriverrat
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    Sassriverrat Junior Member

    Well that doesn't sound so fun! The Russian concept makes total send to drag the stern- I originally thought about that idea- but now flip it sound. Lift the majority of the boat while keeping a deep bow in the water
     
  12. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    It's easier to keep the traditional prop set up with foils forward but creates a generous "angle of plane" when on foil.
     
  13. Sassriverrat
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    Sassriverrat Junior Member

    Well I agree because your method simply adds foils to the bottom (assuming the boat has the mounting points). However, I think by have a very sharp bow with lifting strakes and foils aft would allow the bow to ensure height or altitude regulation while the foils managed the majority of the hull weight.
     
  14. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    You're going to go faster with less drag if the entire hull is airborne.
    What is it you're trying to achieve?
     

  15. Sassriverrat
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    Sassriverrat Junior Member

    Trying to make a 90 year old boat relive her glory days!
    Haha but in all seriousness:

    I'd like to achieve a top speed in the neighborhood of 50s and cruise at 45 knots. The boat has an EXTREMELY fine entry and had a L/B ratio of 6.5/1. The easiest thing to do would be simply add horsepower but being a round bottom, exceeding her current max speed would probably look at facing a negative GM issue and I don't need to roll her. (Currently does 27 knots WOT with 260 combined hp)
     
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