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Rudder Stocks

 

Design:

As every rudder stock is different, we always produce them to the specific customer requirements. In general the designer of the yacht specifies the material and dimensions. We can be of assistance if a calculation for a different material is required or if the design has to be modified for a more economic production. In a lot of cases designers draw a rudder shaft with a maximum diameter rounded off to a full figure (i.e.  Ø 70, Ø 80, Ø 90,etc mm). It could be that the calculated diameter is 2 mm less. This is a very costly round off that is completely unnecessary: To achieve a high tolerance surface of Ø 90 mm we would need to use a 100 mm solid bar profile. If the diameter of the rudder stock would be 88 mm, we could use a 90 mm solid bar profile. As the price of bar material goes up exponentially with the diameter, one can save a lot of money by acquiring the exact calculated diameter from the designer.
It is also important to avoid big steps in diameter of the shaft. A good rule to use is: To decrease the shaft diameter with for example 10 mm, one needs 30 mm of height.
One should also avoid having the same diameter of the shaft in the bottom bearing area and the area where the tiller arm or quadrant will be fitted. While mounting the shaft, a roller could get stuck in the keyway and drop in. Just above the bottom bearing, one should trim down the diameter with a couple of mm. This will also simplify the mounting of the rudderstock.
In situations where the two bearings are far apart, some calculation methods come up with a very small top diameter. This should be avoided, as these calculations are based on static loading. As a rudderstock is dynamically loaded (the worst is while motoring), the shaft may start to vibrate.
Attention should also be paid to electrically disconnect the rudder shaft from the rest of the ship. This is independent of the shaft material used. Connection to other materials will lead to a galvanic reaction and potential loss of material of the shaft.

Materials:

We can produce your rudder stock in the following four materials. Background information about these materials can be read on our materials page.

  • Aluminium AlMgSi1 (EN 6082)
  • Aluminium AlZnMgCu1,5 (EN 7075)
  • Stainless steel aisi316 ( 1.4401 )
  • Stainless steel aisi329 ( 1.4460 )

Spokes:

The spokes on a rudder shaft transmit the steering torque to the rudder blade. A stiff construction is therefore essential for a strong rudder blade.  Mostly the spokes are welded to the rudder shaft. Some people think the welding process is weakening the rudder shaft significantly. This is only true when too much heat is driven into the material. This heat could distort the original metal mixture. So it is essential to use MIG welding, a modern welding process that only heats the material very locally without disturbing the original shaft material. Various test done in the past and over 10.000 welded rudder stocks in use all over the world prove that the welding process, if done correctly, the weakening of the shaft can be neglected. It is also important to put the top spoke not too close to the critical point of the shaft. The critical point of a rudder shaft is just below the bottom bearing as the bending torque and side force is the highest on this point.
The spoke design depends on the material of the rudder blade and the way the rudder blade will be made.

Some examples:

Type 1

This spoke arrangement is the most popular. The construction is very simple,  cheap to produce, and also extremely stiff. The standard profile of the tang strips is 40 x 10 mm in aluminium and 50 x 5 mm in stainless steel.
This spoke design is ideal when the rudder blade is made in a form.  

Type 2

This spoke arrangement is preferable when the rudder blade is made out of solid wood and, after shaping, covered with glass fibre or epoxy as there will be no air pockets in the blade. The arrangement is also very stiff but more complex to produce and therefore more costly. The standard plate thickness used is 10 mm in aluminium and 5 mm in stainless steel.

Type 3

This spoke arrangement is ideal when the rudder blade is foam filled and made on one-off bases. The rudder profile is adapted in the spoke profile. Normally the thickness of the epoxy layers is subtracted from the rudder profile so all spokes together makes profiling the foam very easy. 
This spoke arrangement is also ideal for (hollow) aluminium rudder blades. On this way the shaping of the aluminium plate is much easier. The plate thickness should be subtracted from the rudder profile.
To produce these profiles we would need a 1:1 template, or a CAD drawing.
This arrangement is also stiff but complex to produce and therefore more costly. The standard plate thickness used is 10 mm in aluminium and 5 mm in stainless steel.

Type 4

This spoke arrangement is rarely used. Only when a specific classification bureau forbids welding on the shaft this type should be used. The round spokes are pressed into the shaft. Enough bars should be used to allow the rudder torque to be transmitted to the rudder blade. This arrangement is not very stiff as the bars will bend under load. 

 

Emergency tiller connection:

The top of the rudder shaft normally has a connection for the emergency tiller arm. This will be used when the normal steering system fails. We can produce any required connection, but we would prefer some proven solutions.


Some examples:

This emergency tiller connection is the most popular. The construction is very simple,  cheap to produce, and extremely strong. When the top bearing is mounted on the deck the big advantage of this solution over all other solutions is the fact that it doesn't stick out above deck level. As the inner part of the shaft is used for the emergency tiller arm, the outside surface is still usable for the top bearing. See more on the emergency tiller arm section.

This emergency tiller connection is used when the rudder shaft sticks out above the deck level or ends in a locker. The construction is very simple,  cheap to produce, and extremely strong. Sometimes it is used under deck. This is only possible when the top bearing is not located on deck level, but is situated on a lower level. One would still prefer the solution from type 1, but when the top diameter of the shaft is less than 50 mm type 2 is preferred.

The square top connection is the most conventional solution. A lot of designers will automatically draw this arrangement in the rudder drawing. However it's a very costly and time consuming process to produce as the rudder stock has to be milled to achieve this. Also the emergency tiller arm will be expensive as an inside square shape will have to be made. When used on deck level, the square will penetrate through the deck and a separate cover will have to be made. If the shaft ends in the cockpit floor it's also a blocking object and a "tow breaker". It is preferable to use type 1 or 2.