reason for keel rise in fishing vessel

Discussion in 'Boat Design' started by vineethn88, Feb 1, 2010.

  1. vineethn88
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    vineethn88 Junior Member

    hi.
    i'm designing a fishing vessel . i wanted to know the significance of the rise of keel for fishing vessels. i need to know , why fishing vessels have keel rise at the fore end.kindly excuse for the ignorance. i'm a student of naval architecture & i'm supposed to investigate on this character.
    thanks in advance.
     
  2. vineethn88
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    vineethn88 Junior Member

    some suggestion & replies please.
     
  3. baeckmo
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    baeckmo Hydrodynamics

    Course keeping; simply put: The center of the lateral plane has to be aft of the center of mass and center of buoyancy, even when pitching amplitudes are high.

    As a bonus you get protection for prop and rudder.
     
  4. Joe Petrich
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    Joe Petrich Designer

    To help you search a little better keel rise is also known as "keel drag".

    Some other benefits of keel drag besides directional stability and prop/rudder protection is that you can have more volume in the hold area without having an overly deep forefoot and sometimes you can swing a larger prop for better efficiency.
     
  5. luckystrike
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    luckystrike Power Kraut

    Hello,

    Historic fishing vessel, in those days operating with sails, were able to glide over drifting nets. Sometimes there own when they had problems with manouvering. When you look at the profiles of schooners and cutters you will see nearly straight lines from the bow to the deepest point of the hulls. This also helps when you go over a net and it reduces the possibility to get "hooked" on the net.

    The gap between the end of the keel and the rudder is normally covered with a guiding strap of metal.
     
  6. gonzo
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    gonzo Senior Member

    Keel drag is necessary for boats getting hauled out on rails. Now with cranes, drydocks and lifts it is possible to have a straight keel.
     
  7. Joe Petrich
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    Joe Petrich Designer

    That would make sense for boats built in one geographic location using one railway. Since marine railways all have different slopes depending on the topography of the land and the difference in tidal heights at their location, and since different boats have different drag angles I don't think it holds true for all boats.
     
  8. tom28571
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    tom28571 Senior Member

    Had not thought about keel rise as being limited to fishing boats but after a quick examination came up with a possible addition to some of the thoughts above. Fishing boats are usually sailed short handed compared to others and need to track well while the crew is busy doing work other than steering. Ever notice that the feathers on an arrow are on the stern. Same reason.
     
  9. baeckmo
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    baeckmo Hydrodynamics

    ......and that's the implication of note #3 above......
     
  10. SamSam
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    SamSam Senior Member

    I'm just guessing here, but I would think it would be to help with steering, allowing the bow to swing one way or the other easier (less resistance) and also to keep the boat from "snagging" on things it might run into. Just a guess.
     
  11. gonzo
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    gonzo Senior Member

    Sailing ships have drag too. It is a design feature that is not restricted to fishing vessels. It makes it easier to be hauled and launched in railways too. The exact angle is not crucial, but pretty similar. Railways and keel drag developed simultaneously. Eventually, captains discovered that loading ships with a slight drag by the stern gave them better speed.
     
  12. vineethn88
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    vineethn88 Junior Member

    thanks you very much sir .
     
  13. Boston

    Boston Previous Member

    wow
    you mean the kid from the cape just in to learn as much as he can before beginning that retirement build has actually got on the designers don't seem to know

    all right then

    One of the first things my old grand Dad Robbie taught me to do was crawl on under there and shake that keel shoe loose. That and basic planking. The drag in the keel of a fishing boat is apply named, its meant to be able to touch bottom and not hopelessly ground the boat. More drag means a better chance of swinging her around and off the bank or whatever. Im sure it helps with protecting the prop but there was no prop way back in the day. On a lobster boat it does the same thing except some folks tunk up deliberately just to get in to the best spots. Its old school and I've not been involved for quite some time but that drag is not just a way to balance centers of lateral resistance. It got a real purpose for a boat thats likely to be working some shallow waters. a good solid lead or whatever shoe is also a must. hope that helps.

    B
     
  14. gonzo
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    gonzo Senior Member

    Sacrificial shoes are rarely seen nowadays.
     

  15. Boston

    Boston Previous Member

    Ive changed so many of those things it hurts just thinking about it
    all when I was a kid though
    dam its been a long time
    I guess a lot of things have probably changed

    had to be quick sometimes knocking one of those things loose
    once you get all the bolts out of it they tended to stick
    you couldn't really take a pry bar to it cause you might screw up the wood it was stuck to
    so we'd bang on em for a while and if that didn't get it to drop off and nearly kill you then we would try peeling it off
    generally a pain in the ***
    that and the boat wouldn't be very well balanced what with nothing under the keel
    I always was just waiting to get squished by one or the other
    was my least favorite thing
    probably why I remembered it
     
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