Conference unifix::sailing

    Ah yes, a question forgotten in .0.  
    There is no way to take up slack in the steering cables, other
    than a pair of tensioners mounted directly on the quadrant.
    How does one apply sufficient tension while mounting the thimbals
    at the quadrant end?
    Don

    My boat is very similar to yours underwater (38' LOA, 26' water
    line, 6' draft, half moon rudder at 30 degree angle from vertical).
    This boat is equipped with tiller steering.   I can only move my
    tiller through ninety degree swing.   
    
    I don't know if this helps but at least it is one example of a 90
    degree swing.   I've had some heart thumping moments where I have 
    wanted  more but suspect that it wouldn't have done much more
    anyway.

90 degrees is plenty. Most rudders stall somewhere between 30 and 45 degrees,
depending on a whole lot of factors - rudder form, whether there is a skeg or
not (I assume your rudder is mounted on the keel deadwood, which probably raises
the stall angle). Very few rudders are having much effect when cranked past
45 degrees. You should have no problems at all with this reduction.

Ross Faneuf

    Ross,
    
    Thanks for the information.
    
    Yes, my rudder is at a steep angle mounted off the deadwood. Looks
    like half a very narrow valentine heart. With an axis at perhaps
    30 degrees off the verticle. 
    
    When you speak of stall, I had never really thought about that. I
    assume it is like an aircraft wing. Your rudder is controlling as
    long as you can keep the water flowing fairly well around it. Too
    steep an angle and it cavitates on the back side. Yet seems like
    the steering would just come from the pressure of the water against
    the forward side of the rudder, swinging the hull around its axis.
    Could you elaborate?
    Don

    Ross,
    When you mentioned stalling at 30 to 45 degrees, did you mean
    15 to 23 degrees off either side of center?
    Don

    An answere to my own earlier question regarding tension in steering
    cables.
    First of all, I went to Jamestown Dis. for my cable. 1/4 the cost than
    from Edson.
    2ndly, the fellow gave me the wrong cable. 1 X 19 rather than 7 X 19.
    3rdly, I tried to hook it up.
    4thly, somehow managed but the 1 X 19 cable so stiff, turn the wheel
           and the hull almost moved first.
    5thly, realized my mistake, bought 7 X 19 cable.
    6thly, bought 4 extra cable clamps. Made up loops at the tiller end of
           runs. using nylon line, I applied tension on the cables in the
    	   same plane as the quadrant. Took the two other cable clamps and
           clamped the cables where they exited the sleeves. Took a piece
    	   of stiff wire and made a model of the cable from the exit of the
    	   cable, around the quadrant and to the pin. Used this to mark
    	   the real cable for placement of the loop. I made the loops.
    	   Low and behold, a nice fit! and I even have some threads left
    	   on the tension screws!!!,

    Those angles are off the centerline, and are very generous. The reason is
    that individual situations vary so much that any attempt to give valid
    numbers is asking for trouble.
    
    It's true that after your rudder stalls, that you still get turning effect
    due to its drag (which is about all a stalled foil produces). But you
    get a much better effect if the rudder is still producing lift. In that
    case, the lift is in the form of a sideways force (draw it if you like
    to see how the forces resolve) which in effect pulls your stern to the
    side you want it to go. These forces can (and should) be quite large,
    and ordinarily provide most of your steering power. The same applies
    to the auxiliary rudders or paddles which provide power for wind vane
    self-steering systems.
    
    A few generalizations which are usually true:
    
    	- Rudders hung on a skeg stall at higher angles of attack than
    	  spade rudders with no skeg. The advantage of skeg rudders is that
    	  wetted surface is reduced, not that steering performace improves.
    
    	- Cranking in a turn gradually rather than abruptly tends to lower
    	  the degree of separation of flow on the rudder, and may in effect
    	  increase the stall angle. This is probably true, but but is an
    	  effect which has been reasoned out rather than carefully measured.
    
    	- Rudder performance improves when it is carefully faired, and its
    	  roughness is reduced to a minimum. Barnacles and other marine
      	  growth may dramatically reduce the efficiency of your rudder by
    	  destroying its foil properties.
    
    
    Ross Faneuf
    

    Thanks Ross,
    
    My rudder is simply a flat glued up mahogany surface. Should
    I consider giving it some foil shape. I know there are a lot
    of other things I need do to improve performance in rig and
    smoothing out the bottom, but adding some foil shape is an
    easy one. Or is the gain not worth the effort considering
    Hope is not a racer.
    Don

   Re: .8
    
     Don,
    
     What is the thickness of the trailing edge of the rudder?
    
     Hydrodynamically, planing it down to a taper in cross section will
    reduce drag as lots of drag is always created by "bluff" bodies
    - that is, objects that come to an abrupt (squared off) end rather
    than a smooth taper. But th amount of drag created by this effect
    on your rudder may be small compared to other effects.
    
     However, reducing the cross section of the rudder could, if the
    rudder and attendant forces were large enough, reduce the strength
    of the rudder, and may cause warping.
    
     You could always build another one and experiment :^) :^) :^).
    
    	Gregg

     

    I would have given the same advice. The only noticeable gain you're likely
    to see is tapering the trailing edge of the rudder close to a knife edge,
    and making sure the leading edge of the rudder or skeg is well rounded.
    This will reduce drag, but will not increase lift very much. Turning the
    rudder into a genuine foil shape might significantly increase lift and
    reduce the drag a bit more, but probably isn't worth fussing with. 
    
    Ross Faneuf
    

    Hello Jeoff Burr,
    
    You are probably off sailing now and not reading notes. Just
    wanted you to know your steering pedestal is afloat again on
    "Hope".
    
    And how sweet it is!!! What a pleasure after 4 years of dogging
    that worm drive unit I had. 
    
    And I'm having to do a better job managing sails now. With much
    less rudder angle, I'm learning to trim now. Really expect to see a
    much improved boat, and beat a few of my own ETA's.
    
    Thanks folk for your input and advice. See you in Newport for two
    weeks begining Aug 5th.
    
    Don