Clipper CENTURION 1869; rudder problems

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  • #11543
    Peter. H. King
    Participant

      Returning from her maiden voyage in February, 1870, CENTURION’s commander, Thomas Mitchell, wrote to Mr Greig, the the manager of Hood’s shipyard in Aberdeen where she had been built, as follows:
      “On the way up to London, the man at the wheel could hardly hold it for the rudder shaking. In London, I had a deep groove put in the back of it from the water line right down and it is quite steady now. You should not neglect this in your next wooden ship. It is very important as it would soon shake the screw all to pieces”.

      I am curious to understand the nature of this groove and its practical application. Was it a common feature? How did it improve rudder vibration?

      Any input would be appreciated.

      Peter King

      #11679
      Frank Scott
      Participant

        John Harland passed on the following information which should prove useful:

        This was sometimes called a ‘Chatter Groove’. There is a note about it in the Nautical Research Journal, Vol 19.2 (1972), and some contemporary models have rudders with this characteristic.

        Vortices that shed alternately to either side create periodic sideways forces on the rudder causing it to vibrate, particularly if the shedding is at the resonant frequency of the rudder. Similarly, it is forced vibration at a particular frequency that causes power and telephone lines to sing in the wind. The phenomenon of alternately shed vortices is an example of Von Kármán Wirbelstrasse (Vortex Street). An internet search will turn up quite a lot on this.

        The turbulence generated by the groove prevented rhythmic shedding of vortices from the trailing edge of the rudder (left-right-left-right) hence improving the steerage. Anyone who has sailed small sailboats should be familiar with the “hum” transmitted through a tiller at certain speeds.

        There are indications that the Vikings were aware of the problem, and that this is the explanation of the beading found on the trailing edge of some Viking rudders.

        #11859
        Peter. H. King
        Participant

          Many thanks, Frank.

          Very interesting. Was this in fact something which might routinely be implanted by the shipbuilder, or to suit the master’s experience as was the case with CENTURION?

          Kind regards,

          Peter King

          #11865
          Frank Scott
          Participant

            Clearly the concept was well enough known for the master of the Centurion to recognise that this was the best solution to the problem in his ship. How common it was I do not know.

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