Examples of wave piercing hulls, please?

Discussion in 'Boat Design' started by solitaire, Sep 22, 2012.

  1. solitaire
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    solitaire Junior Member

    I know there are a few takes on the concept. I'm particularly interested in mono-hulls, trimarans or catamarans with quite substantial hulls/ amas. More so designs where the waves are parted to the sides, or where the hull dives into the wave and then parts it.
     
  2. groper
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    groper Senior Member

  3. upchurchmr
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    upchurchmr Senior Member

    Did you want a power boat, sailboat, dingy or passenger ferry?
     
  4. keysdisease
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    keysdisease Senior Member

    Attached Files:

  5. Ad Hoc
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    Ad Hoc Naval Architect

    That is a myth which seems to come up time and time again. If the hull was called wave slamming bow, would you react to the hull type in the same way??

    It is a name only. The hull does not part the wave, it is not a religious hull :p

    It is just a simple reserve buoyancy issue, no magic. You should read the comical debate here:
    http://www.boatdesign.net/forums/bo...rs-marketing-myth-design-ingenuity-30296.html
     
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  6. Red Dwarf
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    Red Dwarf Senior Member

    Ad Hoc - I read that thread, lots of interesting stuff in between all the pointless arguing.

    Can you comment on a design similar to what Groper posted above? I see many high speed cat ferries with a similar design. It seems to me that the wave piercers have very little reserve buoyancy to speak of and the center hull has a tremendous amount of reserve buoyancy. I guess the idea is waves up to a certain size are "pierced" by the small lower hulls and anything larger is ridden over with the central hull. Does this lead to a better ride? How about any increase in rough seaworthiness?
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    That’s correct. Thus the myth, the hull pierces the wave. Well, if you have a hull that is just 500mm wide, and say 5.0m long on a boat that is say 50m long, with the boat travelling at say 40knots or so, when the “bit that sticks out” encounters a wave, what happens…nothing!...there is insufficient buoyancy in the “bit that sticks out” compared to the whole hull. Thus it goes into the wave until the buoyancy of the main hull(s) pick up the wave profile.

    The centre hull as you point out, has a huge amount of reserve buoyancy. This came about when the first series of wave piecing hulls by Incat, one was called Tassy Devil”.??...can’t recall correctly i could be wrong, but around late 80s, suffered a major deck dive in the Sydney harbour; one person died. The design then was just 2 slender hulls alone with a raft structure some height above. The reserve buoyancy only occurred when the raft structure hit the wave as the vessel was increasing in trim and speed going into the on-coming wave. The slender hulls just kept going "into" the wave and at a certain point the hull was so far "into" the wave it dug-in, so to speak. Not lifting it clear of the wave, as it had no buoyancy. Thus the central bow was born.

    The only benefit of such hulls is shown below:

    WP adding bow length.jpg

    The waterline length is increased. Which, increases the L/D ratio thus lowering the resistance, and an increase in Lwl, reduces the vertical accelerations. That’s it, no magic.

    As to the ride quality. In the UK they have been termed the Vomit Comet. Make your own conclusion :p
     
  8. Red Dwarf
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    Red Dwarf Senior Member


    Thanks. Can you elaborate on the "vomit comet" result. What factors are leading to the poor ride?

    Is it the lack of reserve buoyancy in the bow extensions? If that is true then the bottom dashed line hull in your sketch should ride better and have all the benefits of a wave piercing design.

    I have noticed that the Gunboat 66 seems to ride very well with no hobby horsing and it is just a normal plumb bow catamaran.
     

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  9. keysdisease
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    keysdisease Senior Member

    I see wave piercing vessels as almost a transition between a standard catamaran and a SWATH vessel, but simpler. I have never ridden on one but the dynamics of the damping of wave action on wave piercers seems to be pretty straightforward.

    It also seems that they are pretty economical and fast. The specs for the Gold Coast 47 show 27 knots from 2 x 250 HP outboards, not bad for a 47ft boat:

    http://www.goldcoastyachts.com/Commercial-Power/CP-transport/GC47WP/GC47WP-index.htm

    SPECIFICATIONS

    LOA 47ft
    Light Displacement 14,500 lbs
    Heavy Displacement 21,500 lbs
    Passengers 30
    Engines 2 x 250 Yamaha
    Cruise Speed Loaded 23 knots plus
    Top Speed 27 knots plus

    This is an existing vessel, and they have made them all the way to over 100ft I believe, and in fact are building another big one now.

    http://www.goldcoastyachts.com/construction.htm


    Steve
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    It is a result of its size and the period/length of waves the vessel encounters.

    If you’re in a quartering following sea where the wave length exceeds the length of the boat, then the port bow can be in a crest of a wave and the stbd bow can be in a trough. The aft stbd hull is then in/on a crest and is picked up by the passing wave, as it has large buoyancy owing to the hull shape to get the w/j’s in, it thus trims the vessel, and pushes the bow down. But the aft port hull is in a trough. So you have a situation where the vessel finds itself with not enough buoyancy up fwd to having too much aft, and alternating between port and stbd as the vessel rolls and pitches in this sea state as the wave passes by. The resulting motion is a cork screw effect, and, has for many passengers been an uncomfortable motion. Subsequent vessels were fitted with ride control to dampen out this effect. They were also taken onto different routes where the prevailing wind/sea conditions did not promote this motion owing to their heading and encounter frequencies.

    There is more to it than just the shape of the bows, in terms of seakeeping and motions. Especially with multihulls. But having a hull shape, dashed in the image, would be no different, in the resistance/vert. accelerations, as one without, but with a “bit sticking out”; all other things being equal.
     
  11. rwatson
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    rwatson Senior Member

    Do you have a link to this info please ? I couldn't locate it with internet searches.
     
  12. groper
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    groper Senior Member

    I used to work aboard the vessel i posted earlier. Its motions were very nice and pleasant and by far the best among any other vessels that had a similar use in these waters. The partially sheltered waters of the great barrier reef is where we operated, so the worst sea states consisted of a short sharp chop and seas generally no more than 3m in a 30knot blow (so small wave height and high frequency). I frequently watched the bows submerge but the central pod almost never touched the sea surface, which i found quite surprising. Our crew quarters were located at the bottom of this central pod and it has a window facing aft. By going thru the smallish seas rather than over the wave tops, i beleive significant lowered the vessels pitch response in these conditions.

    The boat had a fully laden cruising speed of 33kts with 440 POB and the wave piercing design was an excellent choice for these kinds of operating conditions. I cannot ever remember needing to slow down even in the worst weather we get here. I would expect the design may not perform aswell in a different area with larger wave amplitudes and periods as slamming would most likely result.
     
  13. rwatson
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    rwatson Senior Member

    I have first hand experience with this phenomena.

    The ride is indeed very soft compared to smashing through on the monohulls in the same sea state.

    However, the fairly gentle up and down oscillation is accompanied by a lateral yaw, that is very effective in producing sea-sickness. This is exacerbated by the steering being controlled by the port and starboard thrusters. When one of the thrusters accelerates to correct the direction, it increases the yaw effect substantially. This would not be as pronounced of the used rudders.
     
  14. rwatson
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    rwatson Senior Member


  15. Ad Hoc
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    Ad Hoc Naval Architect

    Ive never found one on the web. I used to have a newspaper cutting from way back..but I can no longer find it.

    I'm certain this is the vessel is this below, Spirit of Victoria. You can see the lack of 3rd bow. The next vessel built a year later, was the one i recall, tassie devil, shown next to it, but with tihe 3rd bow to prevent the bow diving of the previous design.

    spirit of victoria.jpg evolution => tassie devil.jpg
     
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