Increasing use of slow steaming and super-slow steaming has prompted concerns from insurers about possible damage to main engines designed for high-speed, full-load operation if they are operating at low power for extended periods.
International Union of Marine Insurance president Deirdre Littlefield said that insurers were “concerned” about the impact on machinery from the growing trend of slow steaming, now being strongly advocated by a number of operators as the way forward to combat high fuel prices until seaborne trade picks up.
“Many large, high-speed diesel engines are designed to operate only at sustained high service speeds,” she said.
The concerns arise from the trend among ship operators, particularly container lines, to adopt slow steaming as a strategy to reduce fuel consumption and adjust capacity.
Many liner services have reduced service speeds down to below 20 knots, while some are looking at even slower speeds of less than 15 knots.
Maersk Line has indicated that trials on its ships show that they can operate at engine loads down to 40% without any adverse effects and that it is possible to operate at even lower loads down to 10%-15%.
When slow steaming first emerged, leading engine manufacturers voiced fears of possible long-term damage because they warned that engines were not designed to operate at low loads.
But as the practice has spread, engine suppliers, including MAN Diesel and Wärtsilä, have issued guidance to operators about how to limit potential damage and recommended operating procedures.
MAN Diesel superintendent engineer Lars Christiansen told Lloyd’s List that the issue was relevant for containerships as they tended to have large engines relative to the vessels’ size. He said that engines could be operated down to 40% load without doing anything, but he advised that engines should be fitted with slide type fuel injection valves to limit deposits.
Operating at less than 40% load could cause more serious risks, Mr Christiansen said. For example, it could cause a reduction in air intake with the result that auxiliary air blowers were running continuously.
Cutting the number of turbochargers in use risked increased load on the main engine bearing.
MAN Diesel recommends the installation of a turbocharger cut-out system.
Engines should be operated for an hour a day with at least 70%-80% power to clear out the system, he added.
“The biggest risk is not to the engine but the exhaust gas system,” Mr Christiansen said.
“The exhaust gas boilers are critical. If there is too much fouling of the boilers there is a risk of fire and damage.”