Are there any boats out there that use skis for hulls?

Discussion in 'Boat Design' started by fernandodlc, Jun 9, 2014.

  1. fernandodlc
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    fernandodlc Junior Member

    Believe it or not I'm in love with this concept: http://www.seaski.com.au/

    The wig effect kills the looks and requires planar struts for the twin skis. I really like the idea of a SWATH transitioning to a planing cat though. I was wondering if you could exploit the effect in a different way.

    Could you use foils to raise the hull out of the water and onto a set of skis? A set of foils that gradually lift the boat further and further out of the water as speed picks up would enable you to benefit from swath at low speed.

    Using foils would allow you to keep the buoyancy of the skis relatively low so they could have very low cross sections allowing efficient and fast speed cruising off the plane. Of course that would allow the central hull to float at rest for even more stability.

    I'm basically on that oh so common quest for the perfect efficient, low power 2 person dinghy/runabout. Using skis seems like an efficient kind of planing hull. A single one will get 300lbs on the plane at around 15 knots well enough without much surface area at any rate.

    Long time lurker, first time poster so be gentle.
     
  2. upchurchmr
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    upchurchmr Senior Member

    I saw this quite some time ago.
    First off that is some really smooth "seas".
    They have had plently of time to come up with a real set of waves to see what happens when you plow into the back or front of a wave at 55kts.

    You need to think of different speed regiems.
    What is easiest to push from 0 to 5kts? SWATH?
    up to 10kts? probably a typical catamaran hull.
    10-20? possibly a ski
    20 up? possibly a foil - I really don't know the breakovers in ranges.


    Whatever you figure out for flat water will need to change for bigger waves, depending upon the size of the boat.

    I imagine a 5' wave gets pretty disasterous at 20kts +

    Don't take any of these ranges for real numbers, I'm no expert.
     
  3. Petros
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    Petros Senior Member

    not a "boat" but the Douglas "Sea Dart" used skis for take off. It taxied in displacement mode and used retractable skis to take off. It was the only super sonic sea plane ever built. The concept could work the same for boat hull because the aircraft is acting like a boat when on the water.

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  4. fernandodlc
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    fernandodlc Junior Member

    Well that's where I see the advantage of the ski, in rough water. Surely the low cross sectional area and planar shape would allow the ski to pierce through the wave? There's some footage on the site that looks fairly rough.

    The Incat ferries pretty much have skis on their side, much bigger I know but I don't understand why a ski would not be inherently wave piercing.

    55knts is pretty quick, I wouldn't like to hit a wave at that in very many boats at all.

    Just a thought experiment really, been thinking about this and I can't see what (if anything) I'm misunderstanding. Reaching out to people who know more than I do.
     
  5. fernandodlc
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    fernandodlc Junior Member

    boat - New Page.png

    That's kind of what I was thinking. If you can imagine those sponsons having a flat underside. Make 'em pointy and wave piercing no?
     
  6. fernandodlc
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    fernandodlc Junior Member

    They look pretty skinny, bet they don't have much wetted area. I wonder what speed that thing needed to be going to get enough lift to use them?
     
  7. Petros
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    Petros Senior Member

    take off speed of the sea dart is 120 knots, it lands on water at 125. It is a 16,500 lb aircraft with a little over 6000 lbs of thrust from the engines.

    check out this YouTube clip, very impressive:

    https://www.youtube.com/watch?v=SOrj2cSDO-M
     
  8. Rurudyne
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    Rurudyne Senior Member

    Yep. And in the process they learned more about jet engines ingesting lots of salt bearing spray. Did help designing better engines for planes taking off and landing not quite that close to the water though. Like those transitioning VTOL pogo planes, whose test pilots possibly thought about busting a gut laughing every time they heard someone complain about parallel parking, these planes really put their pilots to the test too with their high landing speeds on an unpredictable surface.

    That doesn't meant something that stays on the water won't do better though.
     
  9. BMcF
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    BMcF Senior Member

    No, they have two large sidehulls that are heavily immersed and operate only in displacement mode.

    I shudder to think what happens when the ski-supported vessel in that video actually encounters a largish wave.
     
  10. BMcF
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    BMcF Senior Member

    That is essentially what a surface-piercing hydrofoil design is and does....minus that last bit, the skis. Properly designed, hydrofoils have the advantage of being able to handle broaching and re-entry of waves a lot better than a ski would.
     
  11. Rurudyne
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    Rurudyne Senior Member

    "Shaken, not stiiiirrrrrd?!?!?!?!(Oh pin feathers!)No, I do not want one of those soft drinks instead!(When did I become the comedy relief in these pictures?)"
     
  12. fernandodlc
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    fernandodlc Junior Member

    Hydrofoils are very cool but too restricted in their use. That's what attracted me to the idea of skis in the first place, you could make something beachable.

    But fundamentally wave piercing as a concept is just about being pointy and not having too much hydrodynamic lift isn't it?
     
  13. fernandodlc
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    fernandodlc Junior Member

    Here's a vid: https://www.youtube.com/watch?v=t5qrmqFxSws

    It's not exactly armageddon but to me it looks like it cuts through the smaller stuff quite well.
     
  14. BMcF
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    BMcF Senior Member

    I've been directly involved in many, many the wavepiercer cats....I know that what they actually can do, and what they do not do. Lets just say that they are far, far removed from the "ski boat" concept.

    As soon as that ski-supported boat sees a wave that is even close to its own length, exciting things are going to happen. Same hold true for the wavepiercing cats...
     

  15. BMcF
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    BMcF Senior Member

    ?? What are planning to do..beach it while on full plane??

    Perhaps you didn't see the contradiction your concept created: On the one hand, you recognize that at low speeds, the immersion of the ski bottoms is large and you proposed using a ladder or surface-piercing foil setup to lift the craft on to its skis..and on the other hand you expect to beach it.
     
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