High tech sailing yachts

odessaFor the really high tech sailing yachts, constructing the keel from one material throughout is not strictly necessary. The fin is considered to be the wing producing side force and holding the ballast weight down.

So in these very high performance and/or racing boats the fins and the ballast are separated and the keel fins are entirely made of carbon fibre. The bulb is then still made of lead and is connected to the lower end of the fin to maximize its effect on the stability of the yacht, while having also the maximum weight available in the bulb, because no weight is "wasted" in the fin. Some (racing) rules however do not allow this application anymore. In some special applications, such as for instance IACC yachts, also forced steel fins of very high quality steel alloys are being used.

But also "cheaper" solutions such as the use of bronze for the fin construction materials are known. Lead still being the favoured material for the bulbs. When dagger boards are being used in combination with canting keels almost all of them are manufactured from carbon fibre reinforced resins. The rudders are originally made of wood just like the hulls. The rudder stock was from steel or bronze. With steel and aluminium alloy hulls the rudder blades and the rudder stocks are constructed from these metals also. In the situation of GRP hulls the rudder blades were constructed from GRP also and depending on the emphasis on performance in the design under consideration the rudder stock was from stainless steel of aluminium alloy.

Originally the two sides of the blades were made separately and the rudder stock glassed to one side before the two sides were joined together. Later high density foam cores were used to shape the blades and the rudder stock laminated in before hand. Sometimes wood cores were used also. For high performance applications nowadays complete carbon fibre rudder blades with integrated full carbon rudder stock are made in one piece. The main considerations for the material choice for the rudder are:

  • weight,
  • strength and
  • stiffness.

In the case of a rudder in particular the weight is considered important, because the reduction of the longitudinal radius of gyration of the yacht is considered to be of great importance for reducing the added resistance of the yacht sailing in waves. Strength and stiffness are obvious requirements. Stiffness is essential because with free hung rudders deflection of the rudder stock leads to the rudder getting stuck in the bearings.

 

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