Weather helm on starboard, port OK

Discussion in 'Multihulls' started by paxfish, Apr 13, 2015.

  1. paxfish
    Joined: Dec 2014
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    paxfish Junior Member

    Guys,

    We had a romping 50 mile sail on Saturday and found that there was a ton of weather helm on a starboard tack (we were on a very broad reach most of the day.)

    Port tack seemed acceptably balanced, with just a bit of weather helm. We tried messing with the daggerboards, and raising the windward dagger helped a bit (10%). I did not try both boards up, but should have I suppose. Both rudders were down.

    Hulls appear to be symmetrical and the mast appears to be straight. How should I be troubleshooting this issue?

    This is a Malcom Tennant cat built by the prior owner.

    we were under full and reefed main with a blade jib.

    [​IMG]
     
  2. mundt
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    mundt Junior Member

    rudder rake!
     
  3. paxfish
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    paxfish Junior Member

    So, the rudder rake appears to be the same on both sides also. I'll see if I can post a shot.

    I would consider running only one rudder, but raising and lowering them while in a seaway is a hairy proposition.
     
  4. mundt
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    mundt Junior Member

    rudder alignment!
     
  5. catsketcher
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    catsketcher Senior Member

    Gday Paxfish

    Tennants often have sloping sterns onto which the rudder is directly mounted. this outs the centre of pressure of the boards way aft of the pivot point. In fact to balance rudders beach cats pivot their rudders under the hulls to get some balance. Whilst they look nice, Tennant type sterns are not that good for rudders.

    Many Tennants make an aluminium housing for the top gudgeon to make the rudder vertical. I would even consider putting it slightly forward of the vertical for some balance as it seems like you have lifting dagger rudders and balance is hard to get with these.

    As to centre boards - I find that I get more weather helm when I have too little board down and am too close to the wind - near a beam reach. Was one gybe closer to the wind than the other? Also I get phases of weather helm when I run at 45 degrees to a major wave train - surfing or surging increases helm as each wave lifts the aft windward stern. Were the waves the same both tack? Also slight changes in heading can create big changes in apparent in these boats so it could be that you were slightly higher on gybe and had the rig running at full pressure and were lower on the other and the rig and jib was not working as well on the other.

    cheers

    Phil
     
  6. Gary Baigent
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    Gary Baigent Senior Member

    Later Tennants had vertical rudders, not raked aft like in his earlier days. Which was a fashionable mistake and produced heavy helm - and also lifted the transoms if helm movement was excessive. That lifted the sterns, pushed down leeward bow and resulted in the boat knife-ing up to windward - the fine bows taking over, so weather helm arrived while you tried to get back on course.
    Rudders need to be angled a few degrees forward of vertical to get helm balance correct. Also, as Phil writes, the main traveller being up too high on one board will also give you helm imbalance.
     
  7. nzclipper
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    nzclipper Junior Member

    jib sheeting the same on both tacks? My adjustments all float, so have to be careful to get setting right on both tacks.
     
  8. Tom.151
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    Tom.151 Senior Member

    Paxfish... very nice. I lusted after that boat. Good to see it went to someone that will appreciate it.

    I'm heading for the Chesapeake, where is that ramp/railway located?
    How wide a overall beam can be launched there?

    Thnx,
    TomH
     
  9. MikeDrummond
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    MikeDrummond Junior Member

    Check symmetry of the rudder sections. Look for differences near the trailing edge because aft camber shifts the CoE aft, which increases tiller load for the same rudder sideforce.

    A related possibility is a chamfered trailing edge. If the angle is not too great (say <45deg?) then it acts like a mini trim-tab and this tiny feature can dramatically affect your tiller load.

    Generally it's best to have chamfers mirrored for each rudder. Eg inside to outside on each rudder.

    Logic says the problem lies with the port rudder but I've found this may not be true, so check both.

    Easiest way to check is with packaging tape chordwise on the blade and bond a rough wood template with polyester filler. Once it has gelled (5mins) break it off the tape, clean up with knife, and invert to compare port to starboard shapes of the blade.

    Mike
     
  10. mundt
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    mundt Junior Member

    I had a similar problem on my reynolds 21, especially at high speed, off the wind. It was mostly due to the raked transom causing the rudder to be raked aft, which caused heinous helm issues. The shape of the blades might also be having some influence but I would bet that if you get the rudder rake correct it will alleviate most of your troubles.
     
  11. mundt
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    mundt Junior Member

    check mast rake too!
     
  12. rcnesneg
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    rcnesneg Senior Member

    Is the mast completely vertical? Put a large level across the boat and make sure the boat is level, then use another level taped to the mast and adjust the shrouds. If the mast is leaning to one side, it will cause weather helm on one side an lee helm on the other.
     
  13. paxfish
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    paxfish Junior Member

    Excellent! Thanks for all the items to check! I'll be busy Saturday...

    The rudders are raked forward a bit and the transoms are vertical. The gudgeons are the same but the rudder housing is longer on top.

    Gary B. I didn't experience any of the conditions you spoke of, thankfully!

    NZ Clipper - While jibing downwind, I believe the wind angle was the same on both tack and the jib was sheeted in similar fashion on both tacks.

    Tom - That railway is at Hartge Yacht Harbor and I think it is $280 a month. Big Bucks, but a very useful haul. I'd say my 20 foot beam was about the max.

    for the rest of you - I'll be checking and report back.

    Here is a vid that might provide some insight. The sails needs some attention, and don't trim all that great and that may in fact be part of the problem. I do think there is something in the config I am missing, or perhaps something is misaligned.

    Here's a couple of pics of rudder and transom:

    [​IMG]

    [​IMG]

    And here is a short vid showing the rudders and our trip.

    We did hit 17 knots in 15 to 20 knots of wind, so I was pretty happy overall. Considerable weather helm at those speeds though. I think the boat has more in her. Certainly with some fresh sails and reduced drag from the helm, she will boogie.

    Notice we have the windward dagger retracted to help a bit. We were well off the wind, and neglected to try raising both daggers.

    We had single reefed main at that time and the blade jib.

    Also -there is some rake in the mast - I may bring that forward a bit.

    https://www.youtube.com/watch?v=8XZLZZpoOYU&feature=youtu.be

    Your helpful comments are appreciated.
     
  14. Canracer
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    Canracer Senior Member

    You could always look at your jib fair-leads. They are spaced far apart and be time you get from one side of the deck to the other, it would be easy to forget the setting.

    If your really moving that fast then a subtle change in sail trim could make a very un-subtle change in the helm.


    Just thinking out loud.
     

  15. catsketcher
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    catsketcher Senior Member

    Ackerman

    Gday Pax

    From what I can see your tillers have no ackeman inset - the tillers look straight. What ackerman to use is up for debate but I would be intrigued about taking one tiller off the tiller bar when sailing and seeing what the other tiller does. Your foils look like they have a pretty sharp entry and this may make them more finicky than a rounder edge foil. I sailed the other week on a cat that had a problem with its lower gudgeon and it would go from having weather helm to lee helm as the wobbly gudgeon moved. A positive feedback mechanism.

    If you find that you could deal with some extra ackerman you can keep your tillers as they are and make a little plate on the inner end of each one the tiller bar attaches to. This is the same as bending the tillers in.

    Nice boat

    Phil
     
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