Around the world wind vane woes

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  • 21 Jul 2018 02:13
    Reply # 6391048 on 6389679
    Anonymous wrote:

     

    Rudders, course stability...

    OK, Paul,

    maybe not a milestone, but that rudder surely should be an eye-opener.

    It has grown into a dogma that long keels with integral rudders are best for cruising, while short keels are not. Try to suggest modifying the rudders of a Rustler 36 or an OE 32, and I bet one will meet a storm of protests. Surely, long keels mostly make sailboats directionally stable, and also adds yaw damping, which is very good for cruising. However, the downside is that their rudders are both unbalanced and they sit in the dead water right at the end of the keel. The result is that the tiller response is nothing like that of a freestanding rudder with an efficient foil section, fitted way aft.

    I see now that many fin-keeled yachts in the cruiser-racer league are not directionally stable. They may still be easy enough to handle, as long as the rudder is OK, but this instability puts big loads on the rudder in a seaway. In case it quits, the boat becomes almost impossible to get back under control.

    My Johanna was close to perfect when it came to course-stability and easy helming. There was a ‘propeller shaft skeg’ plus a half-size skeg at the rudder. The rudder was thus supported by it, but also had a generous balanced section below it. The result was that the hull was (just) directionally stable, while tiller forces were very light, and the rudder response was good. However, her finkeel was on the small side and with a rather in-efficient section, so upwind performance was not quite as good as one should expect.

    For serious cruising, I think the best underwater profile is a longish keel of some area (or with a cb. added), and with an independent spade-rudder way aft. To safe the rudder from destruction, it should either be supported at the lower end, as on LC, or it should be designed to kick up in case it hits something hard.

    Arne


    In complete agreement with you. I like balanced rudders but only if properly supported at the bottom. The cantilevered ones have no place on a cruising boat as they are much to fragile. Also important  is choosing the correct NACA profile. I used the 15% profile (NACA0015) as that seemed appropriate for the speed range that LC operated in. For faster boats, a 10% profile might be better, however, if control is your aim, the fatter section will always be the safer one if there is any doubt.
  • 20 Jul 2018 07:09
    Reply # 6389679 on 6383218
    Anonymous member (Administrator)

     

    Rudders, course stability...

    OK, Paul,

    maybe not a milestone, but that rudder surely should be an eye-opener.

    It has grown into a dogma that long keels with integral rudders are best for cruising, while short keels are not. Try to suggest modifying the rudders of a Rustler 36 or an OE 32, and I bet one will meet a storm of protests. Surely, long keels mostly make sailboats directionally stable, and also adds yaw damping, which is very good for cruising. However, the downside is that their rudders are both unbalanced and they sit in the dead water right at the end of the keel. The result is that the tiller response is nothing like that of a freestanding rudder with an efficient foil section, fitted way aft.

    I see now that many fin-keeled yachts in the cruiser-racer league are not directionally stable. They may still be easy enough to handle, as long as the rudder is OK, but this instability puts big loads on the rudder in a seaway. In case it quits, the boat becomes almost impossible to get back under control.

    My Johanna was close to perfect when it came to course-stability and easy helming. There was a ‘propeller shaft skeg’ plus a half-size skeg at the rudder. The rudder was thus supported by it, but also had a generous balanced section below it. The result was that the hull was (just) directionally stable, while tiller forces were very light, and the rudder response was good. However, her finkeel was on the small side and with a rather in-efficient section, so upwind performance was not quite as good as one should expect.

    For serious cruising, I think the best underwater profile is a longish keel of some area (or with a cb. added), and with an independent spade-rudder way aft. To protect the rudder from destruction, it should either be supported at the lower end, as on LC, or it should be designed to kick up in case it hits something hard.

    Arne


    Last modified: 21 Jul 2018 09:42 | Anonymous member (Administrator)
  • 20 Jul 2018 02:20
    Reply # 6389545 on 6388503
    Anonymous wrote:

    Paul,

    I am glad to hear that the new rudder of the mighty La Chica passed that ultimate test by controlling the boat with only the mainsail up.

    I think LC’s rudder should be regarded as a milestone in yacht design.

    Not only does it handle any sail forces, but I bet it improves handling in a nasty quartering sea as well.

    Hi Arne,

    The rudder design is not all that revolutionary as I have used it in a motor sailer that I designed while working for Angelo Lavranos in Cape Town back in 1979. However putting a rudder like that on a traditional heavy displacement double ender is somewhat unusual. I've since noticed that Bob Perry is doing a similar arrangement on some of his modern full keel designs.

    Behaviour in quartering seas is what set me looking for another rudder option. LC with her old rudder was difficult to steer under those conditions but once again the new rudder sorted that out. Proof would be that LC was sail from Auckland to Christchurch, a distance of about 800 miles. She did it with a novice crew and a mostly running and reaching. Elapsed time was 6 days including the last day when she had to motor. However as she only does 3 to 4 kts under motor, that did not help the daily run average...


  • 19 Jul 2018 09:43
    Reply # 6388503 on 6388351
    Anonymous member (Administrator)
    Anonymous wrote:
    Anonymous wrote:It would not surprise me if Paul could control LC even with the fore-sail dropped.

    Arne

    LC could sail under main alone on all points of sail, without any issues once I made my rudder modifications.

    NB. LCB is going to get similar mods to her rudder.



    Rudders, rudders, rudders...

    Paul,

    I am glad to hear that the new rudder of the mighty La Chica passed that ultimate test by controlling the boat with only the mainsail up.

    I think LC’s rudder should be regarded as a milestone in yacht design.

    Not only does it handle any sail forces, but I bet it improves handling in a nasty quartering sea as well.

    Another boat, which was much improved with a new, balanced rudder, was Karlis KalninsOtterbelly (Magazine 74, p.26).

    My own 6.5m centre-boarder, Frøken Sørensen, came with something that could only be described as an oversize rudder. With its streamlined blade set in its lowest, forward position, it was well balanced and easy to turn. Even though FS’s hull had very unbalanced lines, with a thin, sharp bow and a wide stern, the boat behaved perfectly well, and never broached on me  -  mostly thanks to that rudder.

    Last, but not least, we should not forget Bob Groves’ (Badger copy) Easy Go. Bob fitted her with a big, well-balanced rudder (no skeg), and his home-made Belcher OGT Mk I windvane was able to steer that vessel directly, with no trimtab or servo (See Mag. 51, p.16).

    Soooo,  I guess I’ll keep on nagging about rudders.

    Arne


    Last modified: 19 Jul 2018 19:29 | Anonymous member (Administrator)
  • 19 Jul 2018 08:40
    Reply # 6388481 on 6383218

    Badger would run happily at 7 knots under self steering gear (including the trim tab), under just mainsail, but not for long: the increasing size of the seas would mean that she would get thrown around a lot and it would get harder for the steering gear to bring her back on course.  Her happiest speed was to make 17 miles in 3 hours.  At one time we had a balanced rudder, but the balance was removed when we fitted the skeg.  This made no noticeable difference in her steering, which was a bit surprising.

  • 19 Jul 2018 05:06
    Reply # 6388351 on 6386870
    Anonymous wrote:It would not surprise me if Paul could control LC even with the fore-sail dropped.

    Arne

    LC could sail under main alone on all points of sail, without any issues once I made my rudder modifications.

    NB. LCB is going to get similar mods to her rudder.


    1 file
    Last modified: 19 Jul 2018 05:10 | Anonymous member
  • 18 Jul 2018 21:49
    Reply # 6387938 on 6383218
    Anonymous member (Administrator)
    David,
    I read your answer, and I apologise. I should have asked you for more details backstage, before going on the forum.

    My (weak) defence is that I admitted that I my hunch was in the armchair category.

    Sorry mate!

    Arne

    PS, 19th July:
    Er..., but why did you change to ketch, then?

    Last modified: 19 Jul 2018 19:54 | Anonymous member (Administrator)
  • 18 Jul 2018 12:56
    Reply # 6386976 on 6383218

    Arne wrote:

    My armchair guess is that the big Tystie, with her shallow, broad-chord, unbalanced (?) rudder, would be a challenge to any steering system, manual or automatic, in particular with the sloop rig.

    Not so, Arne! I have to indulge in some Norwegian-style plain speaking, and say that your armchair doesn't sail as well as Tystie does. How do you imagine I could surf at 10 knots on a regular basis, if I didn't have enough control? 

    The rudder  has 100mm balance, which is the maximum possible with the prop just ahead of it - it overbalances if the helm is put over hard, due to the prop wash. With the low AR sloop rig, I moved across the mast on a run, so that the helm loads were in no way excessive. 

    I designed the servos with 30 degree inclination of the power axis, so that they trail, and resist fast yawing. And I also designed them strong, with plenty of servo blade area. This helps a lot downwind, because the biggest problem when travelling fast is that the apparent wind is varying hugely. This is the major reason that raceboats not constrained by the rule for this race, to use only technology available in the '60s, use electric autopilots. Even the Minitransat 6.5. This is the major reason that I kept the speed under 7 knots, to keep the apparent wind stronger and more constant. The problem with many vane gears is not a lack of power, it's a lack of sophisticated control of that power.

    Last modified: 18 Jul 2018 21:39 | Anonymous member
  • 18 Jul 2018 10:33
    Reply # 6386870 on 6386797
    Anonymous member (Administrator)
    David Doran wrote:

    Or, Arne, you could install a Split-Junk or Aero-Rig for a balanced single sail plan reducing your rudder loads downwind  :)


    I see that. It will let one drive the boat harder, downwind. One can even rig an ordinary junkrig so that the sail is shifted closer to the centreline when running before (photo below). However, I think we only solve half of the problems this way. Even I, with very little offshore experience, can tell that the waves coming in on the quarter do their best to broach any boat, and this factor is stronger than the forces from the sail. These golden globe contenders have all Bermuda rigs (poor sods), and their steering gears are still struggling.

    When we focus on junks, I think we have put too much weight on the rigs, and too little on their 'underwater wings'. To solve the downwind problem, I therefore think it is better to make big, efficient, balanced   -  and madly strong  -  rudders, just like Paul did to La Chica  -  and the Chinese have done all the time. It would not surprise me if Paul could control LC even with the fore-sail dropped.

    Arne


    Last modified: 19 Jul 2018 08:14 | Anonymous member (Administrator)
  • 18 Jul 2018 08:37
    Reply # 6386797 on 6383218

    Or, Arne, you could install a Split-Junk or Aero-Rig for a balanced single sail plan reducing your rudder loads downwind  :)

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