Rudder shape and Size?

Discussion in 'Multihulls' started by soulofasailor, Dec 19, 2012.

  1. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

    I am wanting to re design my rudders [​IMG]

    when the boat is above 14 knots in speed, i have to use 2 hands to steer it, the boat will want to fall off, i really would like it to steer a little into the wind! Just wondering if this can be fixed?
     
  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    Are both your rudders at EXACTLY the same rake? Are they both EXACTLY in line with the hull centreline? Do they lift slightly at speed? (a pin through the stock and blade maybe better than relying on the downhaul line)

    Is it the same heavy load on both tacks, or just one?

    From the photo I'd say you need to angle the rudders forward a bit more

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. soulofasailor
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    soulofasailor Junior Member

    Rudders are all the way down in the picture, same load on either Tack and yes all is lined up! So this is why i might just make a set of these, so what type of material should i use for this?

    thanks
     
  4. Richard Woods
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    Richard Woods Woods Designs

    Anti cavitation (really anti aeration) plates make a big difference on transom hung rudders at speed, so they are worth trying as well

    You might have to trim the LE of the rudders in the stock area to make them more vertical

    Richard Woods
     
  5. soulofasailor
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    soulofasailor Junior Member

    Ok i am not sure what you said there, can you give me a link or something that i can look at? thanks
     
  6. Tim B
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    Tim B Senior Member

    Classic problem with transom-hung rudders. The rudder is not balancing as well as you'd like because there's too much area behind the "hinge". Sweep the rudder forward a bit (you won't need much), and it'll cure the two-hand steering problem.

    Having reduced the force on the helm, the whole boat will feel different. You can tweak rigging to help you point better upwind.

    Hope this helps,

    Tim B.
     
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  7. soulofasailor
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    soulofasailor Junior Member

    That seems like an easy fix but I would have to drill another hole and then I'm not sure how much room I have in the casing for rudders to swing up.. I will have to look again .so u don't think making another set out of wood would be better?
     
  8. Paul B

    Paul B Previous Member

    I used to sail R21s back when they first came out. I worked for the local dealer. Never had the problems you mention.

    I would guess you do not have enough rake in the rig, and you are probably dealing with the rudders kicking up a bit due to cleat slip and/or old stretchy line.

    Before building anything, or re-driling anything, you might want to chat with Randy.

    http://xscats.com/the-designer/
     
  9. Tim B
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    Tim B Senior Member

    Personally I'd try the easy fixes first. Then if you're still struggling, consider the more difficult fixes.

    Tim B.
     
  10. soulofasailor
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    soulofasailor Junior Member

    hey Paul I've tried to contact Randy , many times I don't know if you can help me get in contact with him to ask a question about raking??
     
  11. teamvmg
    Joined: May 2008
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    teamvmg Senior Member

    The boat is trying to bear off ie. you are having to push the tiller? this un-usual.

    This would mean that the rig is not ballanced on the daggerboards. If you let the jib sheets go - does the boat steer better?

    If so, Things to try.....

    Travel the jib out a bit [Open the slot]
    Are the boards right down?
    Make sure that the rudder blades are tracking parallel
    Have you got a nice tight leech on the main [Is it sheeted in nice and hard], even if you need to ease the traveller a bit to depower.
    Rake the mast back more
    Get those new sails that you are thinking about.
     
  12. soulofasailor
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    soulofasailor Junior Member

    @ Paul B

    I do not know if you got my last message i sent it from my phone! That is cool that you use to sail these boats , so how long did you own one have you flipped one? Tell me some stories i have not met anyone that has told me about the boat other then my sales guy! I would love to figure out these rudders!

    I came close once on the lake i sail on in flipping her! I only had this boat for a year now, and i think new sails will help her a lot on performance side. I have emailed Randy a few times on that site you sent me he does not return emails, i think he just does not want to be bothered with his older boats. Which in a way i can understand that, but on the other hand as a builder i would want my older stuff still being used!
     
  13. redreuben
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    redreuben redreuben

    Just thinking aloud, but perhaps an easy way of tilting the rudder forward some is to put a block between the transom and the rudder housing on the upper fixing point ?
     
  14. luckystrike
    Joined: Feb 2010
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    luckystrike Power Kraut

    Hi soulofasailor. If I understood the problem right you have a very strong lee helm in the boat.


    Just an Idea....

    In this case it could be that you have raked your rudder blade too much forward, meaning too much rudder area forward of the rudder's turning axis. So the rudder is overbalanced. The side pressure from the water let the big front area follow the pressure's direction and the whole rudder will flap for strong lee helm.
    Additional, your turning axis is crossing the blade diagonally, so nearly the whole tip is lying before the rudders turning axis. If the blade is a little flexible, this will prodruce some torsion into the blade and reinforce the effect.

    Have you ever tried to rake the rudder a little aft????

    What will happen if you let the rudder out of your hands? Will it flap to leeside out of control? Or will the boat go slowly to lee out of the wind? If the last, try more rake aft.

    Look at the picture. the yellow line marks the rudder's turning axis. The red line is the bottom of your boat, everything under the red line is the "active" rudder area in the water. For my taste it seems to be a lot of area before the turning axis, I would guess around 35 to 40 % and thats way too much.

    IMAG0304.jpg

    Best regards, Michel
     

  15. soulofasailor
    Joined: Nov 2011
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    soulofasailor Junior Member

    LuckyStrike WOW thanks for the repy, and time to write this. We the most puzzled thing is the guy i bought it from had this boat in the ocean and never had any issues with rudders, i called him and he said he cant help me because he never had this issue he said he use to sail with his fingers when the wind picked up!

    When i let go of the rudders the boat will just fall, it will go lee it will head down! The side the Sails are on.

    and when the boat increases speeds, i say above 10 knots it is bad i have to really hold on, with 2 hands! I am wondering getting new sails this year if that will help any i dont know?


    If i let the rudders go Aft it is very hard to steer they have to be all the way down. I wonder if i have them on the wrong sides , but that cant be because the middle rode that ties the 2 rudders together wouldn't be able to be PINed.

    I have not even started on anything yet it has been to cold here, and i have no room in garage. i have emailed this company they would do me a new set for 1k

    http://www.dotan.com/rudder_25/
     
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