Propeller Shaft Seals of Approval for Two Wärtsilä Systems

By George Backwell at March 08, 2014 04:10
Filed Under: Propulsion systems

Ships with Wärtsilä’s Airguard and Oceanguard propellor shaft seals have no need to change from mineral oil to a bio-degradable lubricant (formally ‘an Environmentally Acceptable Lubricant’) when they're in U.S. waters as these seals meet Vessel General Permit (VGP) requirements. How these particular propeller shaft seals comply, and more about these newish VGP amended regulations follows:


Seals,bearings and stern tube arrangement: Image courtesy of Wärtsilä

No oil-to-sea interface
Wärtsilä explain that Airguard is suited for merchant ship stern tube and thrusters, and Oceanguard for cruise, ferry and offshore stern tube, thruster and electric pod face type sealing. 

The Airguard and Oceanguard sealing systems have been designed with no oil-to-sea interface (the essential point): an air chamber or separation space within the seal captures any water or oil leakage, which is then transferred to inboard tanks for monitoring and further treatment. This stops oil drips or leakage into the sea. In the case of system failure, both systems also prevent any oil leakage. The manufacturers say that these seals are also designed to withstand abrasive waters and are compliant with all anti-pollution requirements.

Shaft seals and US Vessel General Permit (VGP)
The revised VGP came into force on 19 December 2013 and applies to non-recreational vessels that are 79 feet (24.08 meters) and greater in length in US waters. For these vessels, the VGP requires environmentally acceptable lubricants (EALs) to be used in all applications that have the potential for an "oil-to-sea" interface (which, as mentioned above, Airguard and Oceanguard seals do not have). The VGP states that oil-to-sea interfaces include any mechanical or other equipment where seals or surfaces may release small quantities of oil into the sea.

The most relevant components are the stern tube, rudder bearings, CP propellers, thrusters and fin stabilisers. However, any ship components that can potentially cause the leakage of lubricants into the sea are in principle to be considered according to the VGP.

Although environmentally preferable, EALs may have some major disadvantages. The most important one, according to classification society DNV GL, is that many conventional rubber (seal) materials are not compatible with the new EALs. Such lubricants will also absorb more water than mineral oils, so water control (i.e. sticking to the recommendation of the EAL supplier) becomes important to maintain lubrication capacity and keep the risk of corrosion and bacteria growth under control. Understandably, technical superintendents will rejoice if they have in place one of the Wärtsilä propeller shaft seals mentioned here.

For detailed information on the revised VGP visit:http://1.usa.gov/1diKHeL

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