Slender non-planing foil assist catamaran?

Discussion in 'Hydrodynamics and Aerodynamics' started by S V, Dec 28, 2020.

  1. DogCavalry
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    DogCavalry I aim to misbehave.

    Lol! I chose that specifically to tease our good friend Mr Efficiency, who was convinced I was chasing a dangerous pipe dream. I still get a chuckle out of it, and I'm still grateful to him for doing his best to give good advice. On my own head if I don't follow it! :D
     
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  2. S V
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    S V Junior Member

    I am more into EU/East Europe market. If you look at biggest rivers in there, they are not much better than Asia - dirty, poluted and full of rubbish. They are more like highways with some ships being faster and some much much bigger. The erosion is the least of concern there.
     
  3. S V
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    S V Junior Member

    DC, I read all your thread. Impressive build! Even more impressive is the determination and orientation to result. It looks a huge boat to build in a garage.
    Since this thread is more suitable for the performance question - what topspeed at which weight of the boat and what engines do you expect/predict?
     
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  4. Ad Hoc
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    Ad Hoc Naval Architect

    That's because:

    These are all 'guesses'.
    It does not = a working mature design.

    Changing numbers, like musical chairs - heck, anyone can do that.
    Thus until there is a mature working design, it shall remain in the realm of pure numbers and abstract, rather than reality.
     
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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    SV, if BMcF is not enthusiastic about foil assisted displacement cats, I would scratch it from the list, he appears to be very knowledgeable on such matters. Apart from anything else, and it seems there is a lot "else", a boat that is largely supported on a fully submerged foil, would seem a nightmare to trim.
     
  6. DogCavalry
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    DogCavalry I aim to misbehave.

    I'll be looking for decent ysed outboards in a few more months. George Crouch, based on a huge amount of empirical testing, figured sea sleds were the fastest things on water for any given power to weight ratio. So my boat should be roughly 4000# without cargo, maybe 12000# stuffed. I could go as low as a pair of 60's but that would feel sluggish. I'd love a pair of 120s. With those 45 knots light, 25 knots loaded.
     
  7. DogCavalry
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    DogCavalry I aim to misbehave.

    In my head, while making ibeams on the tablesaw. I reckon a 10m by 25m sea sled, 7m high, 1800 hp, for 250 passengers in seats. 30 knots top speed. That packs them in like passengers on a bus or aircraft though.
     
  8. DogCavalry
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    DogCavalry I aim to misbehave.

    Foils are a terrible idea. A very expensive way to guarantee a disaster.
     
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  9. BlueBell
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    BlueBell "Whatever..."

    So, S V, what's a good target capacity: 200?
    Max 250 but how many on average on board?
    Each way, or just one way?
    200 people at 100 kilos each, with luggage and stuff
    That's a ~20 tonne payload.
    30 knots cruising speed is that right?
    Fuel load?
    Depending on your circumstance, a Sea Sled may serve you well.
    But it's going to be big.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Actually, it wouldn't hurt to do a study on such a boat for the application under discussion, it certainly won't have to contend with lumpy seas, which has to be considered the sled's Achilles heel, but he would have to think in terms of surface chopping prop(s) drives.
     
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  11. S V
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    S V Junior Member

    Its a 20 tonnes total boat. 14t for ship, 50 passengers. River boat, 5m width is more or less a limiting factor. 33-35kts service speed
     
  12. S V
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    S V Junior Member

    :) Its the same words when people first saw airplane.
     
  13. S V
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    S V Junior Member

    Sorry to dissappoint, but you need about 4000-5000Hp for that...
     
  14. S V
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    S V Junior Member

    All the hulls have only one side on the water, so only pressure side. The only real benefit is to get the area of contact smaller. Sleds make the contact area smaler by mixing water with air, as a bonus - a little ram effect. Winged structures (aerofoils, hydrofoils, propellers, screws, helicopter blades, wide body of racing catamaran, Adastra yacht etc.) in layman terms have two sides: pressure and suction. And suction side has more lift than pressure side, so wings always win because they work on both sides. The idea of hydrofoil assist is to make inefficient lifting device - that is hull, to contribute less. This is the exact reason paddle wheels are extinct.

    That is impressive numbers right there. So, you are aiming 50lbs/hp @25 knots, my aim is at least 50lbs/hp @30-32knots, 40lbs/hp @35-36kts
     
    Last edited: Jan 2, 2021

  15. BlueBell
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    BlueBell "Whatever..."

    Could you post your Statement Of Requirements?
     
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