By law, the operator of a marine VHF must obey the FCC provisions aplicable to that device. Although possession of the Rules and Regulations is not required, they may be obtained from the Superintendent of Documents, U.S. Government Printing Office.
Marine radio is actually quite critical. Weather on the water changes rapidly, especially in certain seasons. The ability to seek shelter on the water is limited. Thus that communications link for the boating community is critical for the safety of all boaters. http://www.boatsafe.com/nauticalknowhow/radio.htm
Marine radio is not unregulated like Ham radio. The FCC operates monitoring stations that monitor marine VHF transmissions listening for incorrect operation of marine stations. Sophisticated equipment provides for tracking violators through "voice prints" of transmissions made on the radio.Willful or repeat violators may receive a "Notice of Violation" citations, and be fined up to $2,000! You can see a chart fo what frequencies are for what types of messages here.
Boaters should normally use channels listed as Non-Commercial. Channel 16 is used for calling other stations or for distress alerting. Channel 13 should be used to contact a ship when there is danger of collision. All ships of length 20m or greater are required to guard VHF channel 13, in addition to VHF channel 16, when operating within U.S. territorial waters. http://www.sacdelta.com/safety/radio.html
Technically recreational vessels less than 66 feet in length are not required to have VHF radios. but if you plan to travel more than a few miles off shore, you should get a VHF radio, an emergency position indicating radio beacon, or EPIRB, and a second VHF radio or cellular telephone as well.