General Info on Jefa Bearings

The advantages of roller bearings compared with plain or gliding bearings.

The Jefa rudder bearing range is almost completely based on roller bearings (except for some heel bearings for skeg rudders). We strongly believe that roller bearings are the only bearings that should be used in rudder systems. The advantages of roller bearings compared with plain or gliding bearings are as follows:

• Extremely low friction: Even in the worst sailing conditions, roller bearings will guarantee a smooth rotation of the rudder shaft. Roller bearings provide an exceptionally low friction co-efficient, typically less than 1/10 of that of a plain bronze or plastic bush bearing.
   

• Nearly no backlash: There is virtually no backlash between the rudder stock and the Jefa roller bearing. In a conventional bearing, it's necessary to provide a running clearance to avoid excessive friction. This means that the inside diameter of the bush always has to be a couple of tenths of a millimetre bigger than the outside diameter of the shaft to guarantee rotation. On top of that there is a big difference in plastics suitable for gliding bearings and for roller bearings. The plastics suitable for gliding bearings mostly absorb much more water than those suitable for rollers. This growth has to be compensated by extra initial backlash in the gliding bearing. If the backlash is too small, the bearing will seize in time, allowing no rotation of the rudder stock any more. As it is unpredictable how much the bearing will grow (this depends on temperature, water type, the use of lubricants, etc.) , one tends to drills the hole in the bush to an oversize, creating even more backlash.
  The material used for the rollers in Jefa bearings is called Polyacetaal or Polyoxymethyleen (POM), mostly identified by it's trade name Delrin. Practical test and inspections on boats that have been continuously in the water for more than 5 years have shown a relative growth of the rollers of less than 0.05 %. Due to the construction and materials used in the Jefa bearings, the allowed backlash between the shaft and the bearing is between 0.03 and 0.05 mm. This extremely small backlash (in practice not noticeable) will stay constant over the lifetime of the sailing yacht as due to the roller arrangement no material on the shaft and bearing is lost in time.
   

• A longer lifetime of the rudder shaft: One off the big advantages of the extremely low friction co-efficient of the Jefa roller bearings is the fact that there is no surface rubbing present in the bearing. The rollers will always roll smoothly over the shaft surface, leaving it untouched, and guarantee the high tolerance between the shaft and bearing. Inside gliding bearings the contrary happens: Heavy constantly surface rubbing will take place between the shaft surface and bearing surface. This will not only mean that the bearing will loose material in time, but also the shaft will run in and loose material. With stainless steel shafts, this material loss in time will be a couple of hundreds of mm, with aluminium shafts the material loss is more dramatic. This is due to the difference in protection against corrosion of the the different metals. Stainless steel is non corrosive by its mixture of alloy elements. Aluminium is protected against corrosion by a thin layer of aluminium and silicone oxide on the shaft surface. Every time the shaft is rotated under load, a bit of this oxide layer is scrubbed off. The material will react instantaneously by forming a new layer of oxide, sacrificing some shaft material. In time this process could diminish the shaft diameter will a couple of tenth of a millimetre. Replacing the bush of the gliding bearing will not solve the backlash any more as the shaft is too heavily damaged. The only solution is to put a sleeve over the shaft with an oversized bearing. (For details see our conversion section).
   

• Easy to replace: The replacement of the bush in a gliding bearing should be done every couple of years to keep the system at a minimal amount of backlash. This is normally a heavy job as the bush is pressed into the tube, and after swelling it will be very difficult to get it out. Roller bearings normally don't have to be replaced. The only instance thinkable would be if the rollers can't rotate due to dirt falling into the bearing. Replacing the bearing is very easy and described in our maintenance section.

The construction of Jefa rudder bearings:

All Jefa bearings are produced on the high quality CNC (Computer Numerical Controlled) machines, guarantying a constant high quality.  Please take a look on the Jefa info section for further details. All aluminium parts are made of seawater resistant aluminium AlMgSi1 (see our materials section for further details on this material) and are black anodised after machining. The balls in the self aligning bearing, the rings underneath the bearing and the roller tracks are made of white Delrin. The rollers are made of high precision black delrin bar.

Why do Jefa bearings run directly on the shaft without an inner housing? 

Some other producers of rudder bearings use an extra housing between the rollers and the rudder shaft. Twenty years ago, Jefa Marine took the decision not to use that system as we can only see downsides with this system. The big problem with that extra inner housing is the control of the backlash between that housing and the rudder shaft. Any backlash in a rudder bearing is multiplied by the long distances between the bearing and the connecting steering lever. The mechanical reduction of the steering system itself also heavily multiplies the backlash. A small backlash of for example 0.1 mm in the rudder bearing could result in a backlash of a couple of centimetres on the steering rim. Independently of the solution chosen, the rudder shaft tolerance has to be very precise. Lets take an example of a 90 mm rudder bearing arrangement. The bearing inside diameter will have to be made to 90.00 millimetres. The rudder shaft will have to be 89.95 to 89.97 millimetres. Only by producing both items on this extremely high tolerance one would get a satisfactory solution. Now we get to the difference in bearings with an inner housing and the Jefa bearings: The mounting on the shaft. A bearing with an (aluminium) inner housing with the above tolerances will in practice be nearly impossible to push over the shaft. The dimensions as given in the above example are theoretical as every dimension has a tolerance. Sometimes both tolerances will be at the wrong side. (In our example the bearing would have an inside diameter of 89.98 and the shaft would have an outside diameter of 89.97). A bearing with a solid aluminium inner housing would not be mountable any more. The Jefa bearing however would be a bit stiff to mount, but it will be reasonably easy to do. This is due to the fact that we advise in our installation instructions to rotate the bearing on the shaft while pushing it to the correct place. Due to this rotation, the rollers will twist a bit in vertical direction and allow the bearing to be "screwed" on. Due to this phenomena, Jefa can produce the bearings with a much tighter tolerance compared to inner housing bearings. Often the producers of inner housing bearings put multiple O-rings inside this inner housing to camouflage the backlash present, but as soon as any loading will be put on the bearing, the backlash will be present with all associated irritations.

The difference between self aligning and non self aligning bearings:

Under load, every rudder stock will bend in proportion to the forces applied. The amount of deflection will vary according to the size and the material of the rudder stock and the position of the bearings. When this deflection is high, it causes very high point loading on a non self aligning bearing, which results in excessive friction, and in the case of plain bearings, self locking. The friction is not always correctly identified, but put down to either hydrodynamic forces on the rudder blade or inefficient steering. Where the plain bearings are replaced with self aligning roller bearings, the steering characteristics are transformed, and what may have been considered as heavy steering suddenly becomes so light that the steering can actually be made more direct by reducing the wheel turns. This doesn't necessarily mean that that self aligning roller bearings are the only good solution. On cruising yachts, with relatively big rudder stocks and the bearings not too far apart, normal roller bearings could also provide a satisfactory solution. The ease of installation is also an important factor in the choice between normal roller bearings and self aligning roller bearings. The self aligning type may be more expensive to purchase, but one saves precious and expensive installation time as the self aligning type can be installed in the hull at a very early stage without the rudder stock present for alignment. The standard roller bearings can only be installed at a stage where it is possible to put the rudder in the hull as the bearings will have to be carefully aligned to the shaft. For details see our installation in GRP or wood epoxy hulls section.

Different types of Jefa rudder bearings:

This section will explain the best employment for every type of Jefa rudder bearing. Dimensions can be found in the bearing section, combining sealing systems can be found in the sealing system section, and the appropriate installation instructions can be found in the installation section.

Type 41000 standard bottom roller bearing (Click on the images for a larger view)

The 41000 series Jefa rudder bearings are the first type of roller bearings that were produced by Jefa marine. In the past 20 years more than 10.000 of these bearings have been produced. This bearing is typically suitable for GRP or wood core cruising yachts where a light revolving and backlash free rudder system is required that will not be stretched to the limits as on racing yachts. The bearing is also perfect as hull bearing for skeg rudders as the skeg will prevent the shaft from bending. The disadvantage of this bearing is the fact that due to the high tolerances between the shaft and bearing it has to be glassed in combination with the shaft present in the yacht. For one-off projects this is mostly not a problem. For production environments Jefa marine can supply a dummy shaft (a rudder shaft without the part that normally sticks out beneath the hull). This bearing should not be used in aluminium and steel hulls. It's better to use the 43000 series self aligning bearings for these types hulls.
The bearing can be sealed by a rudder tube or double lip seal inside the top register.

The 4S000 series bearings are suitable for GRP and wood core cruising and racing yachts. This bearing type combines a very simple installation with a very smooth operation under all circumstances as the bearing will always be aligned to the rudder shaft.  The bearing consists of an aluminium outer housing with an inside sphere turned out. A one piece delrin ball is located in the sphere and is sealed to the outer housing by an O-ring. The inner housing is pushed inside the delrin ball and also sealed with an O-ring. This construction creates a watertight situation between the rotating inner housing and the fixed outer housing. The inner housing will always have one set of rollers. It's therefore important to check that when the bearing diameter is above 90 mm, the maximum working load isn't exceeded. If the calculated working load is above the maximum working load, one should choose bearing type 43000.
The bearing can be sealed by a rudder tube or double lip seal inside the top register of the inner housing, or for maximum security a rudder tube in the top register in the outer housing.

The 43000 series bearings are suitable for all types of hull material. This bearing type combines a very simple installation with a very smooth operation under all circumstances as the bearing will always be aligned to the rudder shaft.  The bearing consists of an heavy duty aluminium outer housing with an inside sphere turned out. A two piece delrin ball is located in the sphere. The inner housing is pushed inside the delrin ball. Above 79 mm, two sets of rollers are mounted to achieve a very high working load. As the delrin ball is mounted in two parts, the bearing is not watertight between the outer housing and inner housing, so a tube has to be used in the top register of the outer housing to achieve a proper sealing.
This bearing is normally used in applications where the working load of the 4S000 type bearing isn't sufficient. For aluminium hulls this bearing can provide the perfect solution: The outer housing can be welded into the hull, providing a very strong and fast installation and also saving a very expensive big tube. For details please see the installation in aluminium hulls section.

The 42000 series bearings are suitable for all types of hull material. This type of top bearing can also be used on tiller steered boats. The rudder head will rest on the delrin ring, achieving on this way the vertical locking. In yachts with a steering system a locking ring on top of the bearing will take care of the vertical locking. A special type of the 42000 series bearing (42...STP) with integral stops in combination with our tiller heads is available in 35 and 40 mm. The disadvantage of this bearing is the fact that the top of the rudder stock and locking ring stand out above deck. If this is not acceptable, one should choose the bearing type 42000Z.

The 4SF000 series bearings are suitable for all types of hull material. This bearing type combines a very simple installation with a very smooth operation under all circumstances as the bearing will always be aligned to the rudder shaft.  The bearing consists of an aluminium outer housing with an inside sphere turned out. A one piece delrin ball is located in the sphere and is sealed to the outer housing by an O-ring. The inner housing is pushed inside the delrin ball and also sealed with an O-ring. This construction creates a watertight situation between the rotating inner housing and the fixed outer housing. The inner housing will always have one set of rollers. It's therefore important to check that when the bearing diameter is above 90 mm, the maximum working load isn't exceeded. If the calculated working load is above the maximum working load, one should choose bearing type 44000. The disadvantage of this bearing is the fact that top of the bearing, the rudder stock and locking ring stand out above deck. If this is not acceptable, one should choose the bearing type 4S000Z or use it under deck.

The 44000 series bearings are suitable for all types of hull material. This bearing type combines a very simple installation with a very smooth operation under all circumstances as the bearing will always be aligned to the rudder shaft.  The bearing consists of a heavy duty aluminium outer housing with an inside sphere turned out. A two piece delrin ball is located in the sphere. The inner housing is pushed inside the delrin ball. Above 79 mm, two sets of rollers are mounted to achieve a very high working load. As the delrin ball is mounted in two parts, the bearing is not watertight between the outer housing and inner housing, so the bearing should either be used under deck or a special cover will have to be made to achieve a proper sealing.
This bearing is normally used in applications where the working load of the 4SF000 type bearing isn't sufficient.

Type 42000Z top roller bearing with integral cover and locking ring (Click on the images for a larger view)

The 42000Z series bearings are suitable for all types of hull material. This bearing is the perfect solution as top bearing for cruising an cruising/racing yachts as it combines a horizontal roller bearing with a vertical roller bearing and a deck cover. Due to the vertical roller bearing arrangement, the rotation of the rudder shaft is extremely smooth. The bearing is ideal as a deck or cockpit floor bearing as it doesn't extend beyond the deck level, especially when the deck flange is let into the teak deck. In combination with emergency tiller arrangement type 1 a quick and save access to the emergency steering is achieved. The bearing is available in three sizes, so one should take notice of this when designing the rudder stock.

The 4S000Z series bearings are suitable for all types of hull material. This bearing is the self aligning version of the 42000 type and the perfect solution as top bearing for cruising/racing and racing yachts as it combines a horizontal self aligning roller bearing with a vertical roller bearing and a deck cover. Due to the two way vertical roller bearing arrangement, the rotation of the rudder shaft is extremely smooth, even on racing yachts where the rudder could be lighter than the water so generating an upwards lift. The bearing is ideal as a deck or cockpit floor bearing as it doesn't extend beyond the deck level, especially when the deck flange is let into the (teak) deck. In combination with emergency tiller arrangement type 1 a quick and save access to the emergency steering is achieved. The bearing is available in specific sizes, so one should take notice of this when designing the rudder stock.