Shaft System Gives Reliable Service in Extreme Caspian Sea Conditions

Due to climate change, the northern Caspian Sea has not recently experienced the formation of the large ice-fields it has historically been known for. In recent years the ice navigation conditions on the Caspian have been relatively mild, except for the winter of 2017-2018.

The southern part of Caspian never freezes, but the north part develops ice very quickly because its waters contain less salt. This is due to the inflow of fresh water coming from the Volga, Ural and Kura Rivers. In the northern Caspian, the water depth is very shallow, which also contributes to quicker freezing.

Ice formation up to 80 cm during the winter period with ice ridges up to 1.2 meters is not unusual in the Caspian area. In certain areas, the ice will accumulate to an almost solid ice-water mixture down to the sea bed. When operating vessels under these conditions, the ship's hull and the propulsion systems are often subjected to conditions at or beyond their design limits.

Most workboats and tugs operating in the northern Caspian Sea therefore require icebreaker assistance when exposed to these conditions.

Shipowner Ark Shipping Ltd has been operating vessels in the Caspian area for almost 25 years, and has a solid reputation for excellence and innovation. Their vessels need tailored design to suit the requirements of the major oil and gas companies situated in the Caspian Sea. Ark Shipping is always pushing the boundaries of orthodox technologies, striving to provide their clients with unique and high-quality vessels to satisfy their needs in an efficient and safe manner.

When they decided to build new vessels, they applied their lessons-learned book and noticed that other vessel they operated suffered from accelerated composite bearing and shaft liner wear. They operate their vessels at shallow draught ice navigational conditions in combination with open systems. On previously chartered river icebreakers operating with closed system, they did not have similar accelerated wear problems, and they concluded the long lifetime is mainly because of the vessel's closed systems with Maprom water lubricated seals and bearings.

In 2014, construction of the hull for their new vessel AHTS Antarctic was started in Turkey. The hull is made from a special grade (within ice region) of steel which enables the Antarctic to endure minimum temperatures of -25 to -30 C°. Hull construction is optimized to create a relatively low-weight hull for an ice-class 1A vessel.

The Antarctic has a total propulsion power of 4923 kW (6600 hp). It has six rudders with triple steering gear and double cylinders. Three Cummins QSK60 engines drive three high trust nozzle-fitted propellers. This configuration ensures a high bollard pull and excellent maneuverability, even in icy and shallow waters. A bollard pull of 65 tons can be achieved when three engines are running at approx. 100% MCR.

Because of its requirement to operate for extended periods at shallow draught river and seagoing ice conditions, the Antarctic is equipped with an environmental safe Maprom closed water lubricated sterntube system. The closed system is created by using both an axial operating Maprom forward and aft seal on each end of the stern tube. The clean lubrication water is stored in a main (ballast) tank and is constantly recirculated by a pump to lubricate and cool the shaft the bearings and the seals. In freezing conditions, a plate type heater will prevent freezing of the lubricating water.

Because it contains no abrasive particles, the Maprom systems have demonstrated very low system wear of the bearings seals and shafts. This results in a very long, trouble free operational lifetime for propeller shaft systems. Compared to open water lubricated systems, Maprom seals have showed unmatched lifetimes of 17 years (80,000 running hours) and over 32 years (240,000 running hours) for the shaft bearing and liner combinations on demanding installations like pusher tugs, icebreakers and river/seagoing freighters.