Americas News
Analyst Classifies 6 Causes for Loss of Propulsion After Fuel Switching for ECAs
Captain Jeff Cowan says the causes for loss of propulsion (LOP) incidents as a result of fuel switching between fuel oil and distillate bunkers can be loosely placed into six categories.
The first category is when LOP is due to the inability of the main engine to overcome the forces on the propeller from the forward momentum of the ship when operating with MGO or MDO, resulting in the engine stalling.
The second category of LOP incidents are said to result from problems in temperature control of the MGO or MDO.
"Heavy fuels must be heated (for the right viscosity to burn) and lighter fuels may not need to be heated, there are problems associated during the fuel oil switch over in both heating and cooling the different fuel oil systems (since the fuel oil is supplied through the same auxiliary systems)," said Cowan.
"Heating an MGO/MDO may cause "flashing" of the lighter fuel oil to vapor," adds Cowan, noting that fuel injectors will not work during flashing, causing a loss of power in that cylinder and LOP if loss of power occurs in multiple cylinders.
The third category of LOP are said to occur when either the fuel pumps or fuel injectors lose of fuel oil pressure for reasons that include excessive leakage through 'O' rings and seals.
"The introduction of distillate fuel into the fuel system causes leaks, sometimes excessive leaks. With MGO/MDO there is a very real risk of external combustion or fire," said Cowan.
Interestingly, the leaks typically stop when switching back to fuel oil bunkers, he notes.
The fourth category is said to result from the loss of sufficient fuel flow in order to maintain engine operation, particularly as a result of waxy formations in the fuel clogging fuel supply.
This can be brought on asphaltenes on the inside of fuel lines left behind from burning a low grade heavy fuel oil. When the distillate is introduced, it acts as a solvent causing a de-coking effect, clogging up fuel filters.
The fifth category is said to result from problems in the starting air system or the control air systems, although these are unrelated to fuel.
The sixth category of LOP incidents are said to be associated with mechanical failures outside the the previous 5 categories.
"Three scenarios stand out as most prevalent for determining risk," says Cowan, and explains that about 70 percent of category 6 LOPs were experienced during inbound transit, and most occurred during slow speed maneuvering, or as a result of transit duration, and complexity of maneuvering.
In April, it was reported that the US Coast Guard (USCG) has had "several reported incidents involving substantial machinery space fuel leakages while vessels were switching fuel oil to ensure compliance."
