Feature 1 | GREEN SHIPPING
Zero oil means zero environmental impact
Seawater lubricated propeller shaſt bearings use no oil-based lubricants and can bring 0-EI (zero environmental impact) below the waterline, writes Craig Carter, director of marketing at Tordon Bearings, following the company’s presentation to the IMO’s DE56 meeting in February.
A
t February’s meeting of the IMO Sub-Committee on Ship Design and Equipment (DE56), a presentation
was made relating to the development of a mandatory code for ships operating in polar waters. The presentation entitled, “Eliminating a source of oil pollution on ships operating in polar waters” specifically addressed oil-based propeller shaſt lubricants below the waterline during the normal operation of a ship. Aſter the presentation, a member of the
German delegation asked why seawater lubricated bearings were only being considered mandatory for ships operating in polar regions, when it appeared logical to broaden the scope of this proposed regulation to all regions? Indeed, a valid question.
Using oil-based lubricants Currently, the majority of commercial sea-going vessels use an oil lubricated white metal propeller shaſt bearing system. Te
lubricant used is typically a mineral oil (SAE30) and typical stern tubes contain 1500 litres (396 US Gallons) of oil. Sealed systems have been used since the 1950s. Te oil is contained using shaſt seals at the forward and aſt end of the stern tube below the waterline. Te purpose of the seals is to keep oil from leaking out into the seas and into the ship, as well as prohibit the ingress of seawater which may contaminate the oil. However, seals leak oil and some ship owners have paid heavy fines for violating oil pollution laws.
Two types of oil leakage There are two sources of oil discharges from propeller shaft seals: operational – where oil leaks in order for the seals to work and accidental – where there is damage to the sealing elements, allowing oil to escape into the sea (or allowing seawater to contaminate the oil). Historically,
‘operational discharges’ of lubricating oil have been considered A 142,000dwt tanker equipped with seawater lubricated propeller shaft bearings.
Modern seawater bearings have been used for over 10 years without any serious issues arising says Thordon’s Craig Carter.
normal, and as the discharges have been below the waterline in smaller quantities, in large part ship owners have not been concerned. Tis has changed over the past decade with better oil detection methods (such as satellite) and increasingly larger oil pollution fines. Operational discharges from stern tube
leakage have only recently been quantified. Te first authoritative study on stern tube oil operational discharges was from Dr. Dagmar Etkin in 2010. Her research was done on port oil discharges from ships, but the author estimates that if the same rates of discharge occur at sea as they do in port, the estimated worldwide annual inputs of lubricants into marine waters both in ports and at sea might amount to four times the port estimate. She estimated that total worldwide use of oil-based lubricants from operational leaks and discharges would then be about 130 million to 244 million litres (34 million to 64 million US gallons.) annually. Tis would be equivalent to 137 individual oil spills of equal size to the Exxon Valdez disaster in 1989.
32 The Naval Architect May 2012
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80