On 19 December 2013, the revised Vessel General Permit (VGP) issued by the US Environmental Protection Agency (EPA) came into force. The VGP covers 27 discharges from all merchant vessels of 79 feet or longer which are sailing in the US coastal and inland waters. Recreational vessels are excluded, but not if the yacht is in commercial use or carries paying passengers. The rule covers all vessels with a keel-laying date after 19 December 2013. In addition, the new VGP applies to existing vessels when they drydock after 19th December 2013. This note deals only with the impact of these regulations in respect of sterntube seals.
In general terms where there is a seawater / oil interface an Environmental Approved Lubricant (EAL) must be used unless the use of such a lubricant is “technically infeasible”. The US Environment Protection Agency (EPA) has defined the concept of “infeasibility” as follows:
2. If it is possible to change out conventional seals for seals of a material compatible with an EAL, this must be done
3. If the working life of the seal is reduced such that the sealing system will not last until the vessel’s next drydocking, then use of an EAL will be considered technical infeasible and a statement of technical infeasibility can be issued by the manufacturer. This statement must be kept on board the vessel.
1. Vessels fitted with Airspace Seals.
GL / DNV have confirmed that in the airspace seal there is no seawater / oil interface in normal operation. This means that the vessel does not have to comply with the regulations and can continue to trade with traditional seal materials and mineral oils. However the vessel should carry a copy of the GL / DNV confirmation. Alternatively the vessel can, at the option of the owners / operators, use an EAL, in which case they must fit Viton Pod sealing rings. Rings which have been used with mineral oil cannot subsequently be used with an EAL. A full five year docking period is possible under normal trading conditions using the EAL and Viton Pod.
2. Vessels fitted with a flushing system to the aft seal.
Vessels fitted with a flushing system to the aft seal can achieve a five year docking period provided that certain technical conditions are maintained, and consequently these vessels must use an EAL. With the introduction of the “mini” Airspace seal and the new SC3 seal with Viton Bio sealing rings (available from early 2015), there are now three options in order to comply:
1) As per our previous advice, the standard ring material can be changed for Viton Pod. The operating temperature in the aft seal should be kept at 55°C with an alarm at 60°C. The seal must be flushed in accordance with the operating instructions of the seal and the maximum water in the sterntube lubricant must not exceed 1%.
2) If the tailshaft is going to be withdrawn, it may be possible to install the additional pipework through the sterntube in order to fit the new “mini” Airspace seal. The “mini” Airspace seal is designed specifically to fit into the space of a normal 3 rings sealing system. Although there will be additional costs incurred during the initial installation, there are other savings and advantages for the owner, especially if it is intended to keep the vessel in the fleet for a reasonable period of time following installation. Because with an Airspace seal there is no seawater / oil interface, normal mineral oil can be used together with the cheaper Viton Blank seal material. Since EALs are often three to eight times more expensive than mineral oils, there will be considerable savings in oil costs. These savings will be repeated each time that the oil must be replaced. Furthermore the Airspace seal is inherently safer than a three sealing ring design in that it can continue to function as a seal even if the two outermost rings are destroyed by a fishing line.
3) If the tailshaft is not being withdrawn or if the owners are not planning to keep the vessel in their fleet for a long period, as from 2015 it will be possible to retrofit the vessel with the new SC3 seal and Viton Bio sealing rings. In this case the extra costs of the EAL will have to be incurred but the installation costs of the new seal will be considerable less than that of the “mini” Airspace. The advantage of this option over the first option of using Viton Pod sealing ring material is that the Viton Bio sealing rings, which are only available for the SC3 seal, are much more resistant to the effects of EAL when this is mixed with water. The result is that there are no special limitations on normal operating temperatures or normal water contents in the oil (5% in the sterntube) in order to achieve the full five year docking period. Whilst this option is a little more expensive that the first option, the increased operational robustness of the seal will make it much easier for the crew to maintain for the full drydocking period.
3. Vessels with a five year docking period and no flushing system to the aft seal.
Where there is no flushing system to the aft seal it is not technically possible to achieve a five year docking period.
Consequently, in accordance with the US EPA definition of technical infeasibility, these vessels can be provided with a ‘Statement of Technical Infeasibility’ and can continue to operate with traditional seal materials and mineral oil. We recommend that the vessel should carry on-board proof the of the last drydocking date and the date of the next planned drydocking is in accordance with class requirements in five years’ time in order to support the statement of infeasibility which will be provided by SFK Marine (formerly known as SKF Blohm + Voss Industries).
4. Vessels with a 2 ½ year (or less) docking period and no flushing system to the aft seal.
It is technically feasible to trade vessels with no flushing system for up to 2 ½ years using Viton Pod seal rings and an EAL for a period of two and an half years. Consequently either Viton Pod seals must be fitted and an EAL used, in which case the seal must be operated at a temperature of 55°C with an alarm at 60°C and no more than 1% of water in the sterntube, or the vessel should be retrofitted with the new SC3 seal and Viton Bio sealing rings, see above.
5. In all of the above scenarios Aluminium anodes should be installed instead of zinc anodes.
Vessels have to change from zinc to aluminium or magnesium anodes when feasible. The material selection depends on the main area of operation, for salt water the recommendation would be aluminium and for fresh water magnesium. If zinc is used after the first drydocking after 19 December 2013, then the ship must document proper reasons why aluminium was not selected. SKF Marine will issue an infeasibility statement should aluminium anodes not be possible to use for technical reasons.
For further information please contact: PGericke@simplexturbulo.com
It is important to understand that the reaction of bio-oils with seawater varies from bio-oil to bio-oil. In some cases, the resultant mixture can be very aggressive towards the sealing ring materials which have been standard up until now. SKF Marine has developed a special Bio Seal. This is the only seal currently on the market which can ensure five year docking periods without any restriction on normal operating parameters when using approved EALs. Please contact us, since the list of approved oils is constantly being updated.