What is world's biggest planning hull boat and how fast?

Discussion in 'Boat Design' started by Squidly-Diddly, Sep 16, 2020.

  1. mudsailor
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    mudsailor Junior Member

    I don’t think she has a stepped hull!
     
  2. DogCavalry
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    DogCavalry I aim to misbehave.

    Looks like it in this image. Don't know for sure.
     

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  3. Olav
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    Olav naval architect

  4. DogCavalry
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    DogCavalry I aim to misbehave.

    Olav, any guesses why waterjets?
     
  5. KeithO
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    KeithO Senior Member

    Guessing:
    1) Elimination of the transmissions weight
    2) Elimination of the appendage drag at high speed which is a big factor at the top end
    3) At higher speed its possible that the impeller may be more efficient than a prop since impeller to housing clearance can be tightly controlled.
    Steering when coasting would be "interesting", given all the momentum...
     
  6. BlueBell
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    BlueBell "Whatever..."

    I've captained a 3000HP 47 passenger jet boat. Hamilton 42 jets.
    I see your point.
    Differential thrust for steering in the "momentum" phase?
     
  7. DogCavalry
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    DogCavalry I aim to misbehave.

    The only apples to apples comparison I've managed to find had identical hulls of the same power, one with i/o, the othrr with jets. The i/o was 15% faster, with proportionally better mileage.
     
  8. DCockey
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    DCockey Senior Member

    Waterjets are commonly used on large, high speed vessels. For example both the US Navy Freedom class and Independence class litoral combat craft have waterjet propulsion.

    From Performance by Design, Donald L. Blount (design manager for Destriero), p 153:

    Flush-inlet waterjets have made significant inroads at the preferred propulsors for craft requiring operational speeds of greater than 25 knots. Considering overall propulsive efficiency, they offer a distinct advantage at higher speeds.

    In addition, requirements for reduced vibration and navigational draft often support the decision to select waterjets in favor of other propulsors. The combination of gas turbines driving waterjets is particularly well matched for large vessels requiring high power levels. Both are free-turbine fluid machines with power characteristics proportional to rpm cubed. Thus overload/offload boat conditions are readily accomodated by this combination of propulsion machinery.
     
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  9. jehardiman
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    jehardiman Senior Member

    Be careful here what you call a "stepped hull" and a 'stepped hydroplane". The hull form is very different and, while both are to increase speed, they are done by different methods for different reasons. Multiple stepped hulls make their appearance in the early 1910's Gold Cup racers and are used to reduce drag by aerating the flow next to the hull (and realistically you could say sea sled functions in a similar way). 3 point stepped hydroplanes, which appear just pre-WWII as small outboard boats and bloom post-WWII with high power to weight aircraft engines, are fully supported on small patches of solid water. Multi-stepped hulls begin to disappear in the mid 1930s because of prop aeration issues and as the need for sustained speed in a seaway moves most small military patrol craft to polyconic and V-hulls, however there has be a slight resurgence in the concept married to a V-hull in recent years. Handling of both types in a seaway can be an issue.
    There is very little to chose from between the weight of trans-shaft-prop and the weight of a waterjet at those DHP levels. And a well designed impellers are always less efficient than a well designed propeller...except when the prop comes out of the water or cavitates by being to close to the surface for its diameter/power. Modern small all-weather combatants usually select jets because of reduced draft and better functioning in rough water/short steep seaways at speed.
    Edit: right before I posted this DCockey chimed in above.
     
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  10. gonzo
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    gonzo Senior Member

  11. jehardiman
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    jehardiman Senior Member

    I think it is funny that David thinks that an LCS is a "large, high speed vessel" while I think of it as a "small patrol craft".
     
  12. gonzo
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    gonzo Senior Member

    Actually, it is a fast ferry.
     
  13. jehardiman
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    jehardiman Senior Member

    Well, we know what happened to HSV-2...
    (Edit: Sorry HSV-X1 was returned HSV-2 burned like the BELKNAP)
     
  14. DCockey
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    DCockey Senior Member

    Do you mean HST-1? HST-2 has operated between Portland, Maine and Yarmouth, Nova Scotia frm Spring until Autumn from 2016 through 2019. It was scheduled to operate between Bar Harbor, Maine and Yarmouth, Nova Scotia during 2020 but the start of that service has been delayed until 2021 assuming the US-Canada border reopens.
     

  15. jehardiman
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    jehardiman Senior Member

    No, HSV-2 was hit by a missile of Yemen and while not significantly structurally damaged, burned out.
    HSV-2 Swift - Wikipedia https://en.wikipedia.org/wiki/HSV-2_Swift
     
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