TURBO BEARINGS PRIVATE LIMITED - turbo bearing

2025-01-02 14:22:39

Sphericalplainbearingcatalogue pdf

Figure 2. Disposition of the oil tanks feeding the chambers between the stern tube seals. Source: Wärtsilä. Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Thrust bearings consist of three main parts. Like most other ball bearings they assist in the support of an axial load and allow for rotation between two parts. There are many different variations of thrust bearings available, such as: tapered roller thrust bearings, cylindrical bearings, and spherical bearings. These bearings are often used in automotive and aerospace applications.

Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Cylindrical rollerbearing

Unlike ball bearings, roller bearings are designed with heavy loads in mind. These bearings are primarily based around a cylinder, meaning this bearing is able to distribute a load over a large area, carrying heavy weights. Also unlike ball bearings, roller bearings are not made to handle thrust loads.

Ball bearings were the response to reduce this friction and they do this job extremely well. However, the small contact surface of the balls, which reduces the friction so much, is also their biggest weakness i.e. the point loading of the balls can lead to compression, at high loads and the block jamming. Ball bearings are high performance blocks suited to running at high speeds, but their size and weight increase significantly as loads rise. So, the R+D for block bearings wasn’t finished at this stage.

It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Regular, plain old bearings that contain no rolling elements are widely used in the automotive industry. This is mainly because they have the ability to bear heavy loads and large carrying capacities. Not to mention they are usually the least expensive. Plain bearings also have a long life-span in comparison to other rolling bearings.

Radialsphericalplainbearing

A roller bearing is a cylindrical unit that is used to provide low-friction movement for a bushing or bearing block. A ball bearing is a spherical unit that accomplishes the same objective as a roller bearing. The real difference has to do with the contact surface between the bearing and the rail. For ball bearings (assuming a perfectly spherical bearing and no deformation), the contact surface is just a single point. Even once deformation is accounted for, the amount of surface where the ball is contacting the rail is limited. This creates an inherent strength limit for the balls. Roller bearings on the other hand, have an entire line of contact. This greatly increases the rigidity, stability, and maximum load capacity of the system.

As a general overview, ball bearings are rolling bearings that allow for a decrease in friction rotating between two surfaces; likely a vehicle and the pavement. This bearing will allow for changes in speed, by supporting radial and axial loads. They are essential in automotives and are one of the most common bearings used in the automotive industry.

Most ships are driven by the engine-shaft-propeller arrangement shown in Figure 1. The stern tube is a metal tube welded to the hull of the ship connecting the engine chamber and the outside of the ship. The shaft driving the propeller and later transmitting its thrust to the hull goes through the stern tube. A couple of journal bearings are placed within the stern tube, carrying the weight of the shaft and the propeller while allowing rotation of the shaft. To decrease the frictional torque on the bearings the stern tube is flooded with lubricant so the bearings operate while fully immersed in oil. Finally, to ensure the lubricant stays within the stern tube, two sets of rotary lip seals are installed at each end of the tube, namely stern tube seals. The stern tube seal is one of the largest rotary lip seals, along with the seal used in hydropower turbines and wind turbines. Figure 1. Disposition of the stern tube oil tanks in a ship. The function of the stern tube seals is to prevent water entering the stern tube as well as to minimize the lubricant spillage to the marine environment and engine chamber. To increase the reliability of the system, a few sealing rings are mounted in line at both ends of the stern tube conforming the aft and forward stern tube seals packages shown in Figure 1. This special type of sealing rings constitutes the only barrier between the stern tube lubricant and the environment. The propeller of a ship is located below the sea water level, hydrostatically pressurizing the outermost sealing ring. Note that the draught of the ship varies between the loaded and unloaded situations impacting the operating conditions of the seal. Furthermore, the hydrostatic pressure at seal #1 oscillates with the sea waves [1]. To counteract the head of sea water on the outermost seal, the spaces between the stern tube seals are independently pressurized by a set of oil tanks, as shown in Figure 2. By filling each tank to a particular oil height the hydrostatic pressure at each space between seals can be set. The pressure difference over each seal differs from seal to seal according to its position (#1, #2, #3, #4 and #5 in Figure 1). The disposition of the oil tanks, together with the working pressures within the stern tube, is of relevance for the performance of the stern tube system. Figure 2. Disposition of the oil tanks feeding the chambers between the stern tube seals. Source: Wärtsilä. Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

The earliest (and original!) blocks used plain bearings, but they have slowly given way to higher-performing bearings. Plain bearings have the least number of moving parts. A long lifespan and low maintenance with heavy load applications are the main benefits of plain bearings.

Spherical ballvolume

Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

RBCsphericalbearings

In small amounts of weight, this extremely common bearing is able to handle both thrust and radial load, making it a popular bearing with engineers. When ball bearings are in motion their main job is to transfer the load from the outer raceway to the inner raceway. This allows for a smooth spin. Ball bearings are commonly used in small wheels and hard drives, as well as other everyday applications, but are prone to deformation when under too much pressure.

For many years, the backbone of most block ranges were heavy plastics with aluminium or stainless steel structural side plates, which were used to transfer loads. As computing power advanced, designers modelled crucial load paths accurately to ensure sufficient strength from modern, lightweight composite materials. Today, blocks are lighter and smaller than those used a decade ago, making them perfect for the thinner hi-tech lines / ropes.

Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Spherical Ball bearingsize chart

Ceramic- Ceramic ball bearings are incredibly strong and can be polished to incredibly smooth surfaces. This enables them to handle extraordinary heavy loads with very low friction but their cost generally limits them to grand prix level blocks.

Self-aligningball bearing

Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

The propeller of a ship is located below the sea water level, hydrostatically pressurizing the outermost sealing ring. Note that the draught of the ship varies between the loaded and unloaded situations impacting the operating conditions of the seal. Furthermore, the hydrostatic pressure at seal #1 oscillates with the sea waves [1]. To counteract the head of sea water on the outermost seal, the spaces between the stern tube seals are independently pressurized by a set of oil tanks, as shown in Figure 2. By filling each tank to a particular oil height the hydrostatic pressure at each space between seals can be set. The pressure difference over each seal differs from seal to seal according to its position (#1, #2, #3, #4 and #5 in Figure 1). The disposition of the oil tanks, together with the working pressures within the stern tube, is of relevance for the performance of the stern tube system. Figure 2. Disposition of the oil tanks feeding the chambers between the stern tube seals. Source: Wärtsilä. Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Torlon- Is the commercial name given to the high-performance thermoplastic composite material and offer a performance upgrade to Delrin balls.

While there are dozens of ball bearings available on the market, that doesn’t mean that the automotive industry doesn’t have their favorites. Mechanical bearings are used between two automotive parts that allow for rotation or liner movements. These bearings will enhance the vehicles performance, bear heavy loads, and reduce friction. Today we’re looking at the top 3 bearings used in the automotive industry and why they just won’t turn anywhere else

Also unlike ball bearings, roller bearings are not made to handle thrust loads. The main difference is the type of contact. For a ball bearing, the type of contact is a point whereas for a roller bearing is a line. ... Difference between roller bearing and ball bearing lies in the type of rolling element

Sphericalplainbearingsize chart pdf

Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

The function of the stern tube seals is to prevent water entering the stern tube as well as to minimize the lubricant spillage to the marine environment and engine chamber. To increase the reliability of the system, a few sealing rings are mounted in line at both ends of the stern tube conforming the aft and forward stern tube seals packages shown in Figure 1. This special type of sealing rings constitutes the only barrier between the stern tube lubricant and the environment. The propeller of a ship is located below the sea water level, hydrostatically pressurizing the outermost sealing ring. Note that the draught of the ship varies between the loaded and unloaded situations impacting the operating conditions of the seal. Furthermore, the hydrostatic pressure at seal #1 oscillates with the sea waves [1]. To counteract the head of sea water on the outermost seal, the spaces between the stern tube seals are independently pressurized by a set of oil tanks, as shown in Figure 2. By filling each tank to a particular oil height the hydrostatic pressure at each space between seals can be set. The pressure difference over each seal differs from seal to seal according to its position (#1, #2, #3, #4 and #5 in Figure 1). The disposition of the oil tanks, together with the working pressures within the stern tube, is of relevance for the performance of the stern tube system. Figure 2. Disposition of the oil tanks feeding the chambers between the stern tube seals. Source: Wärtsilä. Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Metal or plastic sheaves roll directly on metal pins or bushings. Plain bearings are often comprised of a plastic surface and a metal shell. Another common kind of plain bearing will use a soft bronze bushing and a polished steel shaft. Their static and high-load capability make plain bearings suitable for vangs, backstay, runner and halyard turning blocks. However, full contact between two surfaces results in more friction, reducing their potential running speed.

For larger boats, blocks use a blend of ball and roller bearings. Roller bearings take the main line loads, leaving the ball bearings mounted around either edge to keep the sheave running smoothly, even with off-axis loads. This can be seen in the ‘2 stage bearing system’of the Ronstan Core Blocks.

In general, bearings are all composed of the same basic mechanics: a ball set within an internal or external ring. This setup allows for force to be placed on the ball, referred to as loading. There are two different types of loading with bearings; thrust and radial. If your bearing is working with a radial load, this means the bearing will rotate, or roll when put under tension. Alternatively, a thrust load will be subject to force dependant on the angle. Bearings have been around for hundreds of years and have many different uses, some of which include aiding in rolling (a tire), pulling, applications in hard drives, skateboards, and more.

Found on sailing boats of 35’+, these blocks are optimal for mainsheets, guy leads, backstays, after guys and tack lines.

Roller bearings were the compromise between plain and ball bearings. Rollers facilitate low friction at high working loads. Heavily-loaded lines run faster, smoother and are more easily adjusted compared to a plain bearing block. They can also be smaller and lighter than a ball bearing block, for the same working load, due to the increased contact between the rollers and the hub.

Figure 1. Disposition of the stern tube oil tanks in a ship. The function of the stern tube seals is to prevent water entering the stern tube as well as to minimize the lubricant spillage to the marine environment and engine chamber. To increase the reliability of the system, a few sealing rings are mounted in line at both ends of the stern tube conforming the aft and forward stern tube seals packages shown in Figure 1. This special type of sealing rings constitutes the only barrier between the stern tube lubricant and the environment. The propeller of a ship is located below the sea water level, hydrostatically pressurizing the outermost sealing ring. Note that the draught of the ship varies between the loaded and unloaded situations impacting the operating conditions of the seal. Furthermore, the hydrostatic pressure at seal #1 oscillates with the sea waves [1]. To counteract the head of sea water on the outermost seal, the spaces between the stern tube seals are independently pressurized by a set of oil tanks, as shown in Figure 2. By filling each tank to a particular oil height the hydrostatic pressure at each space between seals can be set. The pressure difference over each seal differs from seal to seal according to its position (#1, #2, #3, #4 and #5 in Figure 1). The disposition of the oil tanks, together with the working pressures within the stern tube, is of relevance for the performance of the stern tube system. Figure 2. Disposition of the oil tanks feeding the chambers between the stern tube seals. Source: Wärtsilä. Although various seal dispositions exist, the arrangement shown in Figure 1 and Figure 2 is the most common one. Seal #1 faces the water side and works as a dirt excluder. This outermost seal is rapidly worn out, hence seal #2 also faces the water. Seals #3 and #4 face seal the oil in the header tank, i.e. the oil lubricating the stern tube bearings. Ultimately, seal #5 prevents the leakage of the lubricant into the engine chamber. Figure 3. Stern tube seal aft package. Typically, all the seals of a stern tube are of the same type, irrespective of their position. Additionally, some manufacturers use special compounds for the seals in contact with the sea water where lubrication is particularly difficult. The stern tube seals are mounted on the shaft liners, as shown in Figure 1 and Figure 2. This way, the shaft liner can be easily replaced when grooved or corroded, thus avoiding the disassembly of the shaft. Additionally, it is simpler to machine the shaft liners down to the required surface finish. Sometimes spacer parts are mounted between the housing rings and the hull, offsetting the position of the seal tip. This way, a fresh un-grooved surface is provided to the seal tip, allowing for an additional use of the shaft liner. To prevent disassembling the propeller when replacing the seals, stern tube seals are cut, mounted around the shaft and bonded. Using a specialized glue and a heating device the two cut surfaces are bonded together in such a way that the splitting line becomes almost unnoticeable. The life of stern tube seals usually spans two and five years depending on the operating conditions. However, to prevent costly unexpected failures while sailing the seals are replaced every time the ship is in dry dock. Figure 4. Stern tube seal profile. Stern tube seals are usually made of fluoroelastomer compounds, specifically FKM compounds (see Figure 4). This saturated elastomer, often referred to by its trademark Viton®, stands out for its temperature resistance and inertness. The high bonding energy between the carbon and the bulky fluorine atoms shields the polymer back bond from chemical attacks. The inherent polarity resulting from bonding carbon and fluorine molecules makes fluoroelastomers extremely resistant to mineral oils and fats, i.e. non-polar media. Stern tube seals are generally manufactured via compression moulding although they can also be extruded. These production methods allow the manufacturing of complex geometries, decreasing the amount of tooling required. It is worth mentioning that rotary lip seals are not suitable for separating two liquids from each other. Therefore, even when several lip seals are installed in line, some of the lubricant is continuously spilled to the ocean. Furthermore, the loss of stern tube lubricant is considered an inevitable part of the normal operation of a ship [2]. Hence the lubricant tanks are periodically refilled to compensate for the amount of oil spilled to the ocean. The leakage of stern tube lubricant to the environment depends on elements such as seal design, vessel type, draught, shaft diameter and ship condition. As an example, the stern tubes of barge carriers, tankers and navy ships “consume” (i.e. spill) between 10 and 20 litres per day [2]. To the best of the author’s knowledge, there is no standard method for predicting the flow rate resulting from a particular stern tube arrangement.

Delrin- Commonly found in deck blocks and known as ‘acetal’. This is a thermoplastic specially designed for high compression, but low tension, thus suitable for low loads.

Industrial Engineer with focus on Tribology and Sealing Technology. Team player with an open-minded mentality author of several scientific publications and an industrial patent. Interested in Lean Management, Innovation, Circular Economy, Additive Manufacturing and Connected Objects Technology.

[Roller bearings: ‘Rollers’ are small tubes arranged around the centre of the bearing. Rollers are a ‘compromise’ between the plain and balls. Rollers wear faster than ball bearings, but can carry higher loads as they have a higher contact area.]

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