Our experience and products are as diverse as the maritime sector itself; from the offshore platforms, mooring systems and support vessels of an oil field development to the tankers, tugs and passenger vehicles that serve your regional waterways; Alfa Seals understands your needs and delivers the technical support and efficient sealing solutions to meet the strict demands of the marine industries.
Requirements on seals and sealing systems
Replacement in service case
High operation reliability and long term lifetime
Resistant against hydraulic oil and seawater
Customized sealing solutions
Highest resistance against extrusion
Highest wear resistance
Low and constant friction,stick-slip free, good positioning in mounting space
Special influences in operation and from environment
Pivoting or permanent rotation
Hydraulic high and/ or low pressure
Resistance against grease, oil, seawater
Wide temperature range (for all climate zones worldwide)
Other influences from environment (sand, organism, ozon)
Sealing For Propulsion Systems
Conventional Propulsion Systems
The integrity of the entire propulsion chain from the motive unit (motor or engine) through to the propeller relies on effective sealing systems. Whether keeping oil in hard working line shaft bearings or preventing seawater ingress through the stern tube, correct seal profile and optimised material selection are vital to efficient equipment operation Alfa Sealing has been offering developed sealing products specifically for these arduous duties.
Propeller Shaft Seal
The sealing of the aft end of the propeller shaft as it exits the vessel beyond the stern tube is probably the most arduous to be encountered throughout the propulsion train. Not only does the sealing system have to exclude ingress of water but it must also prevent oil leakage whilst dealing with significant mechanical loads and vibration.
The recommended seal arrangement consists of four seals as shown above: two seals facing the seawater and a second pair to retain the bearing lubricant. The space between each seal pair must be lubricated to prevent dry running, overheating and premature wear, preferably with a constant supply of grease. Fabric impegranted rotary shaft seals are recommended for this position as there will usually be a certain amount of pressure from the head of seawater. A leak detection port is recommended between the central seals to collect any leakage and give early warning of the need to replace the seals.
Over the years, the use of azimuth thruster has changed the way operators do business. The increased maneuverability and efficiency gains allow tug operators to do more with the same installed power. Added maneuverability can also play a role in improving safety during certain operations.
Where propulsion and steering are combined in azimuth thruster or POD propulsion systems the demands on the sealing systems are at their most challenging. Rapid changes in direction of forces and shock loads require the seals to be robust in construction yet highly responsive. Maximum sealing integrity combined with ease of fitting and maintenance are primary features of the thruster seal arrangements described below.
The recommended seal arrangement consists of four seals as shown: two seals facing the seawater and a second pair to retain the bearing lubricant. The space between each seal pair must be lubricated to prevent dry running, overheating and premature wear, preferably with a constant supply of grease.
Propeller Shaft Seal
The recommended seal arrangement consists of four seals as shown: two seals facing the seawater and a second pair to retain the bearing lubricant. The space between each seal pair must be lubricated to prevent dry running, overheating and premature wear, preferably with a constant supply of Grease
Azimuth Swivel Seal
Fabric impegranted rotary shaft seals are ideally suited to the pressures and demanding mechanical conditions encountered in this application. The seal configuration is similar to that employed on the propeller shaft and the same lubrication regime is recommended. In larger units the bearing clearances and side loadings which may be encountered in operation can lead to quite high levels of eccentricity. If the expected eccentricity exceeds, please consult our Technical Support Team as we can normally reccomend seals to suit.
Input Shaft Seal
In view of its inaccessibility it is common to fit two seals in tandem as shown above, but care must be taken to ensure that the back-up seal is lubricated by either packing the interseal space with grease or providing an oil feed. An alternative method is to hold the back-up seal clear of the shaft by means of a thin-walled metal sleeve which can be removed when the primary seal wears allowing the second seal to operate.
Sealing For Steering & Stabiliser Systems
The function of a fin stabilizer, found at the bottom part of the ship’s hull, is to provide resistance to the excess rolling of ship in either direction. Many seafarers have not seen a real fin stabilizer until the ship goes to dry dock for hull inspection and surveys. This does not rule out the knowledge that every onboard engineer and officer must posses regarding the components and functioning of fin stabilizer system.
Stabilising the ship with fin forces
Sealing Arrangement for Fin Stabilisers
1,3 and 4 Fin & Crux seals
The seal arrangements recommended for both upper and lower crux positions and for the fin itself are similar, consisting of rotary shaft seals with each pair grease lubricated. Two alternative configurations are possible, with either both of the outer seals facing externally and the two inners facing internally, or the option of the inner two seals facing each other
The former arrangement affords maximum protection from seawater ingress and oil loss, whereas the latter can provide early warning of primary seal failure by collecting any leakage through the central leak detection port. It is usually only necessary to grease pack the seals on assembly for these applications.
Rudder, part of the steering apparatus of a ship that is fastened outside the hull, usually at the stern. The most common form consists of a nearly flat, smooth surface of metal hinged at its forward edge to the sternpost. It operates on the principle of unequal water pressures. When the rudder is turned so that one side is more exposed to the force of the water flowing past it than the other side, the stern will be thrust away from the side that the rudder is on and the boat will swerve from its original course. In small craft the rudder is operated manually by a handle termed a tiller or helm. In larger vessels, the rudder is turned by hydraulic, steam, or electrical machinery.
The effective sealing of rudders stocks and posts is particularly demanding as side loads can be extremely high and eccentricity of shaft movement is frequently encountered.
Our standart recommended arrangement for rudder stocks and posts is, as shown below, incorporating rotary shaft seals in a back-to-back configuration.
In casees where high shaft eccentricity is anticipated special designs are available.