Rudder end-plate?

Discussion in 'Boat Design' started by JerryW, Jan 24, 2014.

  1. JerryW
    Joined: Nov 2013
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Warrenton, VA

    JerryW New Member

    I have a Montgomery M-23 Cutter. See:
    http://msog.org/models/m23new/m23_thumbs.cfm

    The transom-hung rudder on this boat extends perhaps 8-9" below the fixed keel when the centerboard is up. While my current sailing ground (Potomac & Chesapeake) are mostly soft mud AND I'm almost always sailing with the CB down, I wonder about the wisdom of shaving off that rudder to make it equal to (or slightly less than) the keel and affixing an end-plate to the rudder. Bolger swore by them, but I think he found them most useful in extremely shoal draft boats.

    Thoughts?

    Jerry W
    sailing out of Port Kinsale on the lower Potomac
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    You'd be much better off with a kickup style of rudder, which can attach to the gudgeons you currently have.
     
  3. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    that might work for a boat that does not heel, but on a sailboat you run the risk of lifting most of the rudder out of the water when heeled over.

    also, it will be operating in the turbulent flow off the keel and center trunk, the extra length on the rudder is likely there to get part of the rudder below the disturbed flow coming off the keel and hull.

    You might be able to get make it shoal draft with two shorter rudders, angled outward about 10-15 deg on each end of the transom. it would keep a rudder in the water better, and they would be in the less disturbed flow field far way from the center line. This would also give you some reduncacy if you damage one of rudders as well.

    A simple high aspect ratio rudder is more efficient (less drag) than a shorter end plated rudder anyway.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    This boat is a wholesome cruiser, so the twin rudder arrangement, though it addresses the issue, is (IMO) a bit more then necessary. Kickup rudders are well proven, with many production boats employing them as well as custom designs. Most of my design include a kickup rudder. End plates work, but not as well as a deeper appendage. A kickup lets you have your cake while you eat it too.
     
  5. SamSam
    Joined: Feb 2005
    Posts: 3,900
    Likes: 199, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    I would wait until you actually have a few episodes that indicate there might be a problem and then think about it.

    Then again, searching 'rudder problems' on your site brought up a guy who ran into some sand and ripped out some of the rudder supports and he wasn't happy. You could make it a kickup or possibly substitute some breakaway (plastic) type of bolts in the supports.
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Any shoal draft boat with a fixed rudder deeper then it's belly, is destined to tear out the gudgeons at the very least, if not destroy the blade too. I think it's way too easy to design a kickup, cassette or other style of rudder, that can protect itself in a strike and frankly foolish not to. The very nature of shoal craft means, the bottom is a clear and present danger, so not offering some level of security in this regard isn't particularly reasonable.
     
  7. JerryW
    Joined: Nov 2013
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Warrenton, VA

    JerryW New Member

    PAR's last post (#6) sums up the worst-case scenario. I've uploaded a photo to Flckr of my rudder. It's at:
    http://www.flickr.com/photos/75439007@N06/12133226376/

    Clearly visible is the aft cut-out in the rudder so it can swing clear, or nearly so, of the boomkin. Twin rudders are probably out of the question with this big appendage on the transom.

    Since the boat is out of the water for the winter...and the rudder is at my house, I'm gonna take all the lines/measurements off it and ponder the fabrication of a kick-up rudder. For now, the safe thing will be "when in shallow water - keep the CB down!".

    Appreciate the responses!
    Jerry
     
  8. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 111, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    For those in need of a harder working rudder , the end plates do work for low speed better control.

    I have seen them made out of angle SS (1 1/2) and bolted to the end of the rudder to create a T and faced so the open side of the angle iron is touching the rudder , creating a diamond when installed.

    No idea which installation creates more force when slow turning .
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Using your existing rudder blade, you can cut it off, through bolt some aluminum plates to each side and reinstall the cut off lower portion, with a pivot bolt. I usually rig an automatic down haul, by way of an "over center" bungee cord, typically rigged behind the pintle straps.

    Attached is a very simple kickup, but shows the basics. This is for a much smaller boat, but the concepts transpose. If you look closely, you'll see a lanyard hole on the upper forward corner of the blade, where a bungee is attached, lead up along the leading edge of the rudderhead, behind the pintle straps and cleated. On this design I've run the lanyard in a groove, but you don't have to and instead of a bungee, I've spec's a spectra line to an auto release cleat.
     

    Attached Files:

  10. JerryW
    Joined: Nov 2013
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Warrenton, VA

    JerryW New Member

    Thanks PAR

    Thanks for the drawing PAR. I think I shall leave the present rudder as is and simply build a new rudder based on the principles of the design you graciously provided. That way, if I ever decide to sell this boat, the next owner will get the original [unmodified] rudder plus a proper kick-up rudder. I built, and still sail, a little Bolger "Nymph", so a new kick-up rudder should be within my grasp!

    Thanks all!

    Jerry
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 491, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The drawing I've provided is quite old and originally hand drawn. I use a different set of shapes now for the top of the blade and of course the blade plan form, though most of it remains the same. I radius the top of the blade to match the arc it'll swing through as it raises and lowers. This allows a more uniform "contact patch" between the blade and the rudderhead or cheeks, bracketing the rudderhead. All in all there are lots of little differences between the latest ones I've done and this one, now that I look at it.
     

  12. BMcF
    Joined: Mar 2007
    Posts: 1,065
    Likes: 83, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    Welcome to the forum, Jerry! Small world sometimes...I'm straight across the river from you and Port Kinsale Marina is one of our regular river stops.

    Crewing a friend's Swedish Maxi, with its deep draft and fixed keel, out off Tall Timbers for many years, I have an appreciation for the constant "battle with the bottom" that you alluded to. ;-)
     
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.