Rudders and Weeds

Discussion in 'Boat Design' started by The Q, Jul 8, 2021.

  1. The Q
    Joined: Feb 2014
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    Location: Norfolk, UK

    The Q Senior Member

    Having spent hours designing an efficient high aspect ratio, new rudder for Blue Moon (16ft open keel boat). I now read local forums of the weed problems in our sailing area The Norfolk Broads..
    This article shows what we are up against, the problem has now spread from there to everywhere, huge amounts of weed which is encouraged by the fact they've cleaned up the water..

    Weed growth raises questions over safety of Hickling Broad users | Eastern Daily Press (edp24.co.uk)

    So I'm looking for solutions..
    A sharp blade fitted to the hull immediately in front of the rudder? DSC_2235-300x200.jpg


    Traditional craft's shallow spoon rudder? resize20180402-8802-pkbofh.jpg
    I'm not in favour of a skeg hung rudder because I actually sail mostly on rivers and we are tacking every 30 seconds or so and a skeg would be most inefficient.

    A the moment I'm leaning towards a shallower draft, 45 degree leading edge, a vertical trailing edge, and the rudder top hugging the underside of the hull.

    Has anyone got any better ideas?

    What ever it is it will be properly aerofoiled.
     
  2. fallguy
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    fallguy Senior Member

    The main thing will be access to clear it. I'd try to make a kickup rudder up n over the back, maybe using the same socket? Stuff in front of it won't likely help. Weeds have a tendency to tangle and are hard to cut.
     
  3. The Q
    Joined: Feb 2014
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    The Q Senior Member

    IMG_20210420_154758.jpg

    I should have added the stern is retrousee, so it's not practical to have a stern mounted rudder, the rudder post is about 18inches in from the most aft point. Also I sit 6ft forward of that, similar in sailing style to an international 2.4mR.
     
  4. Doug Halsey
    Joined: Feb 2007
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    Doug Halsey Senior Member

    You'll need to practice getting into & out of irons quickly, and sailing backwards. Sometimes that's the best you can do.
     
  5. The Q
    Joined: Feb 2014
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    The Q Senior Member

    Sailing backwards I know about.... On tidal rivers with strong currents either way , and not a lot of wind... that much hasn't changed over the years..
    Work - East Anglia Film Archive (eafa.org.uk) our 1908 regatta the only thing that has changes is the right hand bank as you view it is now all houses and trees, I can remember those boat sheds being pulled down to be replaced by more housing.
    as can be seen in our 2015 regatta. Some of the same boats competing.
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    9646180D-8913-401F-94CF-53908BEBBF74.png The shape of the rudder would also be more or less inclined to gather weeds. The spoon rudder you show looks like floating veg would really catch the top of the rudder easily. Weeds once up there really are trouble.

    And the bottom of the boat ahead of the rudder would also potentially reduce weeds. Think more skeg with a sharp leading edge. Although tons of veg could render it useless I suppose.

    Another possibility would be a swing rudder. The top of the rudder would be tight to the boat perhaps with a small weed director to keep the hinge clear. Then if you encounter weeds, you swing the rudder up (and down) to clear them. This is not unlike what happens with an outboard. An outboard in the veg uses the prop to cut them, but the boat generally has to be reversed to do so. In sailing, the loss of rudder, would be sort of the equivalent. If you didn't want to lose heading, then some sort of a pusher may work. It would be some type of spatula like thing that pushes the weeds down, in hopes they clear the rudder bottom.

    In all cases, rudder, pusher, etc. must be angled back to assist the flow off the equipment.

    I did a 5 second drawing of a rudder and a weed pusher that could be built in a box. When not in use, the weed pusher would be up and reside in a trunk like a centerboard.
     
  7. The Q
    Joined: Feb 2014
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    The Q Senior Member

    A weed pusher would be interesting.. I think I could incorporate one, but not this year. maybe after a years trials with what I've got. Your rudder shape is roughly what I'm thinking of now, I've done some initial sketches. I'm looking at a draft reduction of around 6 or 9 inches from the original high-ish aspect of 2ft 6 inches..
     
  8. The Q
    Joined: Feb 2014
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    The Q Senior Member

    whilst still researching weed and rudders I cam across this article.. Twin Rudders For Bluewater Cruising | Oyster Yachts
    the relevant passage is.
    "We tested a lot of other things as well, but the rudder testing was most interesting and was totally supportive of all that we had learnt to be true in the field. For a given side force and leeway angle the skeg rudder and the spade rudder were in a roughly similar ballpark, whereas the twin-rudder equivalent was in another world altogether. For example, with the twin rudders set to just two degrees to the flow, the spade rudder needed to be at over six for an equivalent moment, and the skeg-hung rudder at eight – all for the same yaw moment."

    So If a twin rudder set up produces more force, then therefore the rudders can be a reduced size, therefore reduced weed collection...

    Also Although most twin rudder set ups are on wide bodied boats as they may lever a single rudder out of the water. I wonder if there is a beneficial effect on control of the boat for a narrow bodied boat like mine. As it will spend more time heeled over and therefore a single rudder would spend a lot of time not steering entirely port starboard but levering the boat into or out of the water..
     

  9. The Q
    Joined: Feb 2014
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    Location: Norfolk, UK

    The Q Senior Member

    Further net wanderings came up with this.. RS Elite Rudder Weed Deflector https://www.rssailingstore.com/Catalogue/RS-Parts/RS-Elite/Foils/RS-Elite-Rudder-Weed-Deflector-ELI-UA-100
    Now this I can make, I have the materials, it could be screwed on with 3 or 4 screws. So if it's a failure it could be taken off easily. So for the first season after her launch she will carry this, if it works with the old rudder then the high aspect design rudder will be made, If not... eerr um.. Undecided..
    Though I think the version I will make will have a rounded front to the plate and a hollow at the back so it can sit closer to the rudder..
     
    Last edited: Jul 13, 2021
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