So you over filled the fuel tank or some part of the fuel system was replaced and that cup of waste fuel blew off the dock and into the water.
Everyone has done it, nobody meant to do it, just be more careful next time.
The instructions are the same for both diesel and gasoline. Lubricating oil is a different story and since you need to be very careless to get crankcase oil in the water you deserve the extra work. Okay, lines crack and fittings fail on transfer pumps but unattended transfers and the gallons of oil that result are unacceptable. Poor fuel handling hurts everyone in the long term.
What to do:
If engines are running shut them down.
If the vessel is diesel turn off all electrical power including the main switch.
If the engines are gasoline fueled do not operate any switches or equipment. Gas pumps say not to use your mobile phone at the pump while fueling. This is your call but putting the phone in a dry bag or other watertight container is a good idea.
Identify the leaking fluid.
Identify the source of the fluid.
If no leak is visible check the bottom of the bilge at its lowest point. Leaking fuel and oil can collect here and be discharged along with rainwater by the bilge pump.
If the vessel and crew are not in danger power to equipment can be restored.
Repair or shut down leaking equipment, close all related valves and monitor the situation.
At the same time other crew members need to contain the fuel in the water. This is best done by deploying oil booms downwind of the spill.
Much of the fuel will be absorbed by the material in the booms. Both gasoline and diesel will evaporate from the water, the booms just keep the remnants from floating away. Lubricating oil will not evaporate in a useful time frame so all heavy oils must be fully absorbed.
Old timers remember the days of a little soapy water in a spray bottle at the fuel dock. This soap emulsified the fuel so it was no longer visible on the surface. The fuel sank to the bottom where it was incorporated into the sediment. We didn't know, don't do it any more it's a bad idea.
Clean up what you can and dispose of everything properly. In most places that means hazardous waste disposal. That can be very expensive so small amounts of oil boom and rags can be taken to municipal dump sites where residential users can get rid of used motor oil, paint, etc. This is not entirely legitimate so plan to pay for large amounts of waste. It's better than throwing everything in the regular trash.
Oil soaked materials need to be in tightly sealed metal drums or dried in the open air before disposal to avoid fire from spontaneous combustion. This is not a myth and many fires start this way so be careful.
What Goes in My Fuel Spill Kit?
There are the items that are required by regulators like oil booms and other absorbents. These items depend on the size and use of your vessel. The coast guard usually sets most regulations for safety equipment so that is your first stop for information.
Closely related is the list from your insurer or classification society. This might require additional oil booms or fire extinguishers. Oil and fuel spills are potentially high liability events so preparations and procedures are carefully documented. Documents will gladly be provided by your agent.
The personal touches are what makes a fuel spill kit special. It reflects the years of experience of a master or engineer. Some of the standout items include; JB Weld two part epoxy for temporary repairs to get back home, a ten pound bundle of rags, a laminated card of spill response with emergency numbers for the area, and oil drying compound for floors and decks.
Possibly the best and most interesting item in a fuel spill kit is a bag of wooden golf tees to plug lines and fittings in an emergency or when you don't want to spill during maintenance or repair.