Moving 1 Rudder aft...possible?

Discussion in 'Multihulls' started by ashskett, Feb 13, 2012.

  1. ashskett
    Joined: Feb 2012
    Posts: 1
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    Location: Tahiti

    ashskett New Member

    Hi there, I'm brand new here and have a limited knowledge in boat design so please bear with me!

    I have a 47ft Lagoon catamaran, currently in Tahiti, that is just going into a yard-period.

    We would like to replace one of our old and corroded Yanmar 3jh3e engines with a new Yanmar 3jh5E engine and KMG65E generator attachment.

    The problem we have is space. There is currently almost no extra space in the engine bay to accommodate the generator attachment, which is 105mm in thickness and fits between the engine and sail-drive. So we need to find this 105mm.

    There are two options for extending the engine compartment. We could move the aft bulkhead forward, into the master cabin and re-site the saildrive. It would need a lot of fibreglass work to do this and we would loose room in the master cabin, plus there could be a lot of unforseen problems.

    I think the better option would be to find out if we could move the rudder aft.

    I need to know how much of an effect on the handling moving the starboard rudder 110mm aft would have on the boat. I would have said very little, but being a mono-hull sailor what would I know!


  2. daiquiri
    Joined: May 2004
    Posts: 5,372
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    From the hydrodynamical point of view, you will extend the rudder force lever arm by some 1-1.5% when sailing on port tack. That is an almost unnoticeable difference, if the blade submerged area remains the same.
  3. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

    Tiller bar??

    Height of transom steps?? maybe moving it means distance between top and bottom bearing is shorter, so more stock loads?

    Lots of cutting and reinforcing in a very small space, maybe need to cut off the transom step for access?

    Richard Woods of Woods Designs
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