Japanese/Asian fishing boats - stablilty - design

Discussion in 'Powerboats' started by Standpipe, Dec 18, 2014.

  1. Standpipe
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    Standpipe Junior Member

    hi all,


    Japanese/Asian fishing boats have very large flaring bows,larger than the "Carolina flare". Can someone explain how this affects stablity and and how excessive roll is prevented from a bow like this.

    How is this a design advantage over a "normal" bow found on other vessals such as the downeaster.

    Thanks
     

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  2. NavalSArtichoke
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    NavalSArtichoke Senior Member

    I think the shape of the bow has more of an effect on keeping the boat dry in rough seas. I don't think the bow shape can limit excessive roll, not when there are other, more effective means to do so.
     
  3. TANSL
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    TANSL Senior Member

    Stability calculations take into account only the closed volumes. Therefore, if the boat has not a watertight forecastle deck, forms of the bow does not influence the stability. When there is a watertight forecastle deck, the curve of the GZ presents a relative maximum value before the absolute maximum of the curve, when the ship starts to get in the water the bulwark of the ForeCastle deck.
     
  4. Standpipe
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    Standpipe Junior Member

    Seems hard to believe that all that extra windage and weight from that huge bow will have little/no affect on stability..... but I have to defer to the experts.
     
  5. TANSL
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    TANSL Senior Member

    All that vindage can make the boat move more with the wind or navigate better in head seas, etc. but reserve buoyancy of the boat, which is what determines its resistance to immersion, does not change if more closed volume is not added.
     
  6. rasorinc
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    rasorinc Senior Member

    Maybe AD HOC will chime in to answer your question.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    NSA's got it :)
     
  8. Standpipe
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    Standpipe Junior Member

    Ad Hoc.....

    How do these boats, ride and handle the rough stuff?

    And who produces this hull form?
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    No more or less than any similar sized fished boat anywhere else in the world.

    The only difference being the period of encounter and wave length of the sea state these vessels experience on a daily basis. Which is the reason for the bow as it is. Long crested seas coming from ocean swells deep out in the Pacific along with the coastal regions short steep seas owing to the archipelagos that surround Japan, for example.

    Thus those flared bows are to keep the boat dry.
     
  10. Alik
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    Alik Senior Member

    Wetness is important factor of seakeeping. Unfortunately, today forgotten in favor of vertical accelerations. Look at axe bow shapes - they spray up at sea state 3 ;) wipers are the most critical on those boats as they are working permanently.
     
  11. Standpipe
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    Standpipe Junior Member

    Thanks Ad Hoc....



    The broad bow of the Japanese boat seems like it eases waves out of the way rather than slicing through.....like a axe.

    The Japanese know something about rough seas - I would think. I wonder why nobody in the West has bothered to investigate this hull forms strenghts. For some reason - to my novice eyes - it looks like a simple hull to build and suited to many arrangements.

    Maybe as Ad Hoc said -
     
  12. Mikeemc
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    Mikeemc Junior Member

    another thing is in some parts of the world the bottom conditions aren't so good and the waves are closer together. skiing down the back just to plow into another is bad enough but getting into back wash at the same time you need that big bow flair, you just slam into it. In the gulf stream when you get northeasters the waves get closer together , being driven by the wind. troughs can get 50 feet deep and you come up busting through a wave you couldn't see. big flair bows helps.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    You need to eb careful not to fall for the hype but also to understand what the difference is (and there is one) between such bow shapes.

    If a vessel is in predominately head seas, a fine entry bow with a deep forefoot, deeper than the main keel line (as on an axebow) helps to reduce vertical accelerations, owing to increased damping. But that's all it does and in head seas only. If the wave profile goes beyond the deck line, there is insufficient y buoyancy up fwd to correct any unwanted trim


    With a flared bow, this has an increase in buoyancy above the waterline. Thus in large seas, the vessel does not find itself being susceptible to large trims as in a fine entry bow. Since the wave profile is picked up by the additional buoyancy. But too much can lead to unwanted yaw in large following seas, which can initiate a broach. Thus, there is a fine line.

    That's all.

    Each has their own merits, but no one hull/bow shape is ideal for all conditions. Since it depends upon the prevailing wave encounter frequency period and amplitude.
     
  14. outdoorplay
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    outdoorplay Junior Member

    I may have this complexly wrong, but excessive roll is caused from the Haul design and swell conditions
     

  15. Standpipe
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    Standpipe Junior Member

    AD HOC....

    I have to read what you say several times....Great info.

    No magic bullet for all sea conditions.

    I've been looking at the "buy boat" type designs with the pilot house aft and a forward cabin. CMD Marine has a design

    http://www.cmdboats.com/pc36.htm?cart_id=4b46905a8acc39780926e0b55629d421

    Benford has one - strumpet
    http://www.benford.us/index.html?trawler/

    Hartley has another in steel
    http://www.hartley-boats.com/seah37.html

    I thought these Japanese fishing hulls may be an addtional option for such a design ....I guess not.
     

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