is known as electric shock drowning. Metal surfaces of a boat leaking power into the water can create zones of high-energy potential. Stray current entering salt water is less of a problem than the same situation in fresh water. Salt water is a good conductor and it carries current away to ground quickly. Fresh water is a poor conductor and when alternating current forms an electrical potential near a boat, the current can paralyze a swimmer. Stray electric current has caused many drownings, but post-mortem examinations will not link this problem to the death. The problem can be reduced by prohibiting swimming near boats connected to shore power and ensuring marinas comply with National Fire Protection Association Standard 303 for marinas. Carbon monoxide In the early 2000s, several high-profile deaths due to carbon monoxide poisoning (CO) led to increased scrutiny of boating habits (especially the practice of towing participants immediately behind a boat, known as "teak surfing" or "platform towing") and the implementation of various warning placards to educate boaters of the hazards arising from these activities. Other CO-related deaths were attributed to high concentrations of CO gas from houseboat generator exhaust, where swimmers were able to access an area near the stern of the boats that collected the exhaust. This has led to improved pollution controls on modern generator sets, and changes in the designs of houseboats so that they discharge exhaust gases in a way that they can dissipate. The increased use of CO detectors, especially in boats with enclosed accommodation spaces, and a proper assessment of boat manufacturers, would help reduce the risk of CO poisoning. Licensing Depending on the country, boating on coastal waters and inland waters may require a licence. Usually, commercially boating on coastal waters almost always requires a licence, while recreational boating on coastal waters only requires a licence when a certain boat size is exceeded (e.g. a length of 20 meters), or when passenger ships, ferries or tugboats are steered. Boating on international waters does not require any licence, due to the absence of any laws or restrictions in this area. Some of the member states of the United Nations Economic Commission for Europe issue the International Certificate of Competence. The International Sailing License and Credentials (SLC) is a recreational sailing license valid for all yacht charter companies worldwide including Europe and the Seychelles. See also Yachting Boats Boat building Messabout Pleasure