oily water separator
At the time of Fir's diesel conversion (circa 1951), having oil in the bilge was not considered a big problem. The oilers for the main shaft are set to drip oil. And when the bilge was pumped either for cleaning or in an emergency, a small amount of oil was simply pumped overboard. During Fir's last refit in 1988, an oily water separator as added. Unfortunately, the manufacturer no longer supports the controls to the unit. The controls are critical because it is our only assurance that oil has been removed from the water we want to pump overboard.
Section 311 of the Clean Water Act, as amended by the Oil Pollution Act of 1990 applies to ships and prohibits discharge of oil or hazardous substances in harmful quantities into or upon U.S. navigable waters or into or upon the waters of the contiguous zone, or which may affect natural resources in the U.S. EEZ (extending 200 miles (320 km) offshore). Coast Guard regulations prohibit discharge of oil within 12 miles (19 km) from shore, unless passed through a 15-ppm oil water separator (5ppm in the case of Alaska) and unless the discharge does not cause a visible sheen. Beyond 12 miles, oil or oily mixtures can be discharged while a vessel is proceeding en route and if the oil content without dilution is less than 100 ppm. Vessels are required to maintain an Oil Record Book to record disposal of oily residues and discharges overboard or disposal of bilge water.
In addition to Section 311 requirements, APPS implements MARPOL Annex I concerning oil pollution. APPS applies to all U.S. flagged ships anywhere in the world and to all foreign flagged vessels operating in the navigable waters of the United States, or while at a port under U.S. jurisdiction. To implement APPS, the Coast Guard has promulgated regulations prohibiting the discharge of oil or oily mixtures into the sea within 12 nautical miles of the nearest land, except under limited conditions. However, because many ships are foreign registered and because APPS only applies to foreign ships within U.S. navigable waters, the APPS regulations have limited applicability to ship operations.
We want to operate in several areas (like Alaska) that have no tolerance for oil spills. So, getting an oily water separator on board and dialed in is critical.
Oily water separators primarily work on the principle that oil is lighter than water. In a slurry of oil and water, the oil will float. There are two types of systems. The first is a centrifugal filter that spins the slurry and separates oil and water by weight. These are the most efficient systems and there is no media to replace. The second type of system makes a first (and maybe second) cut based on the differences in weight i.e. fill a tall tube of slurry and the material at the top is all oil. But, the final pass is by a filter that absorbs oil. So, this second type of system requires filters that have to be replaced.
The centrifugal systems are top of the line but they are expensive. Once we clean up our bilge, we ought not be producing much oil. So, a filter based system like the one pictured above is probably the best bang for the buck for our situation