Rudder Angle And Effective Size Of Rudder...

Discussion in 'Sailboats' started by saildog, Mar 5, 2006.

  1. saildog
    Joined: Dec 2005
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Grapevine, Texas

    saildog Junior Member

    Hoping someone can assist me with some sailboat design issues with a shoal keel (heavy) type sailboat. Thanks in advance.

    a. Is there a minimum and maximum effective rudder angle from centerline?Anotherwords, is there any reason for the rudder to swing more than 45 degrees, port/starboard?
    b. As the weight of the boat goes up, does rudder size also increase? If so, is there a formula for rudder size to boat size/weight?
    Thanks again...
     
    Last edited: Mar 5, 2006
  2. Skippy
    Joined: Nov 2004
    Posts: 568
    Likes: 1, Points: 0, Legacy Rep: 12
    Location: cornfields

    Skippy Senior Member

    Any foil will stall if its angle of attack is too high. I don't think the stall angle is ever much more than 16 degrees?

    From The Rules:
    "A rudder area of between 8 and 10 per cent of the total lateral plane or underwater profile is the desirable size for a sailboat." F S Kinney
     
  3. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    Since the lateral plane is smaller now then then, the rudder may be more than 10 % of the total.

    When a boat with a short keel turns, it rotates, spins, around itself, then you may need a rudder angle close to 90 degrees.
     
  4. Skippy
    Joined: Nov 2004
    Posts: 568
    Likes: 1, Points: 0, Legacy Rep: 12
    Location: cornfields

    Skippy Senior Member

    Also, if you're motoring slowly in a crowded area and need to take a very tight turn, 45 degrees or so may be necessary.
     
  5. DanishBagger
    Joined: Feb 2006
    Posts: 1,540
    Likes: 46, Points: 0, Legacy Rep: 523
    Location: Denmark

    DanishBagger Never Again

    Not to mention, a 90 degrees swing of the rudder is the closest you get to a brake.
     

  6. bhnautika
    Joined: Feb 2006
    Posts: 849
    Likes: 55, Points: 38, Legacy Rep: 571
    Location: australia

    bhnautika Senior Member

    Saildog the rudder angle doesn’t need to be over 35 degrees, as any more doesn’t add a lot to the turning moment. As stated in earlier posts, rudder area is usually calculated as a percentage of either lateral plane area or sail area. These percentages change with the type of boat (planing thru to displacement), for your boat as I imagine it, about 9 percent.
    For more “The nature of boats “ by Dave Gerr is a good read.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.