rudder placement

Discussion in 'Boat Design' started by phum, Jul 3, 2012.

  1. phum
    Joined: Apr 2009
    Posts: 61
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Sunny QLD. in the great South Land

    phum Junior Member

    Hello all,
    What is the most efficent position for the rudder.? On the stern as in photo (not my boat but similar) or underneath foreward of the aft waterline?
    Peter
     

    Attached Files:

  2. Silver Raven
    Joined: Oct 2011
    Posts: 437
    Likes: 12, Points: 0, Legacy Rep: 67
    Location: Far North Queensland, Australia

    Silver Raven Senior Member

    Gooday Peter - Gawd - you in the 'great south land' - (we just a stone's throw north of you - inland from Cairns - ha ha).

    Gad - zooks - such a big 'agruement' so early in the morning & so early in the week ! !

    Wow - this will sure - put the 'cat in the middle'

    1000 different answers - some very fine yachts - cruising, racing - big, meduim & large - have used many different positions & designs. There's about 4 big books - in just this 1 little subject.

    Personal choice has a lot to do with anyone's decision - I M H O

    Very important is the selection of the size - profile - section - foil profile & whether you choose to move the max thickness aft as you go deeper. Many a 'Master yacht designer' has labored long & hard to get all this as close to correct - as they thought was posible.

    I've some personal beliefs & pref's but - the arguements that will follow are more than I wish to get into.

    Great fortune in arriving at a suitable answer - that you can be personally happy with - OH & that does the job well (or better than well) Ciao, james
     
  3. whitepointer23

    whitepointer23 Previous Member

    even though i have a skeg hung rudder i would rather a transom hung rudder for cruising. no through hull fitting to leak and can be removed for repair or replacement easily. like james says, everyone probably has a their own preference, this is mine.
     
  4. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 208, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Peter

    If by efficiency you mean lift to drag ratio then you should use the hull as a reflective plane which effectively doubles the aspect ratio. That means immersing it somewhere fwd of the operational waterline.

    But the most suitable design depends on several factors. Also if this is a retractable keel trailer sailor then you want a rudder to match.
     
  5. phum
    Joined: Apr 2009
    Posts: 61
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Sunny QLD. in the great South Land

    phum Junior Member

    NO, it is a Sonata Keelboat similar to the one in the photo.
    The keel is already modified with a bulb.
    I am interested in steering performance of one verses the other.
    The stern hung rudder is not at its best broad reaching or beating when there is a bit of a sea running.
    Peter
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Mike has it right from an efficiency point of view, but as he also eludes to, there are several considerations in regard to rudder types and placement. What are your goals with the new rudder?
     
  7. phum
    Joined: Apr 2009
    Posts: 61
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Sunny QLD. in the great South Land

    phum Junior Member

    Make the steering more predictable. Hopefully keep the rudder in the water and the boat under control
     
  8. whitepointer23

    whitepointer23 Previous Member

    can you make a retractable or swing rudder. that way you can run a deeper blade to compensate for the stern lift on waves. might be an easy way to fix the problem.
     
  9. phum
    Joined: Apr 2009
    Posts: 61
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: Sunny QLD. in the great South Land

    phum Junior Member

    Anythings possible, BUT, the gudgeons are 9" apart and the load on them is considerable. They wear out quickly and are a weak point.
    I wouldn't want a swing or retractable rudder, don't think I could make then strong enough. I have already broken 2 blades and know of another one.
    These boats were designed as a trailer sailer but at some stage some were given a keel. No one thought that some of these boats would end up in places where no ts. would venture.
     

  10. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It sounds like you have multiple issues to contend with. My first thought is a better rudder. Better placement, plan and section forms as well.

    It appears you have enough room to get her "tucked under" the stern, while still permitting the shaft to come up aft of the cockpit (tiller sweep). You could try an end plate, placed at the LWL of you current blade, which would make the rudder work better at modest angles of heel. Can you post a picture or two of the full rudder? Also make, model and year of your boat?
     
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.