(46 CFR parts 42--47)
(46 USC chapter 51)
The principal Coast Guard office responsible for load line regulations and policy is the Naval Architecture Division (CG-ENG-2).
In general, most commercial U.S. vessels that are 79 feet (24 m) in length or longer (or more than 150 gross tons if built before 1 Jan 1986 on domestic voyages, or built before 21 Jul 1968 if on foreign voyages) must have a valid load line certificate when venturing outside the U.S. Boundary Line, whether on a domestic or international voyage. Domestic voyages are coastwise, offshore, or high seas voyages that return directly to a U.S. port (including "voyages to nowhere").
There are a few limited categories of vessels excluded from load line requirements. For example, small passenger vessels (i.e., less than 100 gross tons) that only operate on domestic voyages are excluded. Refer to 46 USC 5102 for vessel applicability specifics.
The purpose of load line assignment is to ensure the seaworthiness of the intact (undamaged) vessel. This is accomplished by:
International load line certificates are issued to vessels that meet the requirements of the IMO International Convention on Load Lines (ICLL); ICLL certificates are required on U.S. vessels that go on voyages to foreign ports or waters.
Domestic load line certificates are issued to vessels that meet the requirements of U.S. load line regulations (which are found in 46 CFR Subchapter E). With minor exceptions, the U.S. requirements for an unrestricted domestic load line (suitable for high seas voyages) are the same as the requirements for an international ICLL load line. For this reason, an ICLL certificate is acceptable in lieu of a domestic certificate.
Load line certificates (domestic or ICLL) are issued on behalf of the United States by the American Bureau of Shipping or one of several other USCG-approved classification societies. The choice of assigning authority is made by the vessel owner/operator. The Coast Guard itself does not issue load lines other than a "single voyage exemption certificate."
In order to be issued a load line (whether domestic or international ICLL), the vessel must be constructed to meet the load line requirements. This entails pre-construction review and approval of the vessel's design by the assigning authority. Surveyors then periodically visit the shipyard to verify that it is being constructed according to the approved design.
Upon completion of construction, the vessel is inclined so that its stability documents can be approved and issued. The freeboard assignment is calculated, and the load line marks are inscribed on the hull. Upon final verification that all of these steps have been properly accomplished, the vessel is issued a load line certificate.
A load line certificate is normally issued for a 5-year term, subject to annual "topside" surveys to verify that hatch covers, doors, vent covers, and other critical closures are in good working condition, and that there have not been any damage or unauthorized modifications that would compromise the vessel's seaworthiness. At the end of the 5-year term, the vessel must be drydocked to inspect the underwater hull, seachests and valves, etc, before a new certificate can be issued.
U.S. vessel owners and operators are subject to fines and penalties if a vessel is overloaded such that the load line marks are submerged, or the vessel is operated in violation of any restrictions on its certificate. Penalties are set forth in 46 USC 5116.
Foreign vessels in U.S. waters are required to have a valid international (ICLL) load line certificate. A foreign vessel may be detained in port if the Coast Guard determines that it is overloaded, or unseaworthy due to poor condition. The vessel won't be released to depart until the deficiencies have been corrected: excess cargo is offloaded, repairs have been made and a surveyor from the assigning authority has attended the vessel to confirm its compliance with ICLL regulations.
Historically, the concept of a load line evolved during the 1870s in Great Britain to guard against merchant ships being overloaded. Lloyd's Register established a minimum freeboard requirement for its classed ships, to ensure that a ship had good reserve buoyancy in heavy boarding seas. After considerable persuasive efforts by Samuel Plimsoll, Parliament extended the requirement to all British merchant ships; thus was born the "Plimsoll mark."
Similar load line requirements were adopted by other maritime nations, until they were internationally standardized in the Load Line Convention of 1930. The present International Convention on Load Lines (ICLL) was drawn up in 1966 and entered into force on July 21, 1968. It is periodically amended via the Load Line Protocol of 1988 (in force since February 3, 2000). The Convention and it's Protocol are administered by the International Maritime Organization (IMO), a specialized agency of the United Nations. Vessels of countries signatory to the Convention are required to have an ICLL certificate for international voyages. As of May 2012, 160 countries (representing 98.9% of world tonnage) are signatory the 1966 ICLL, and 96 countries (representing 95.51% of world tonnage) are signatory to the 1988 LL Protocol.
The United States is a signatory to both the original 1966 ICLL and the 1988 LL Protocol, and therefore U.S. vessels engaged on international voyages are subject to the Convention, as modified by the Protocol.
Load line regulations for U.S. vessels operating solely on domestic routes are developed by the Coast Guard, and reflect the less-severe operating environments of coastwise service. Special load line standards apply to vessels operating on certain coastwise routes and on the Great Lakes.
The statutory basis for the regulations comes from chapter 51 of Title 46 of the U.S. Code (46 USC chapter 51). However, some of the CFR regulations have been superceded by the recodification of 46 USC in 1988, which revamped certain load line requirements (particularly vessel applicability and penalties for overloading). Therefore, until the CFR regulations are revised, 46 USC chapter 51 must also be consulted.
For international (ICLL) load lines, the CFR regulations incorporate the original requirements of the 1966 ICLL. However, the regulations have not yet updated with respect to recent ICLL revisions. Therefore, the ICLL Protocol must be consulted for the most-current international requirements.
The following NVICs specifically pertain to load lines:
Guidance on the Passenger Vessel Safety Act of 1993
Initial & Subsequent Inspection of Uncertificated Offshore Supply Vessels, Including Liftboats
International Load Line Certificates for Small Passenger Vessels Operating Within 20 Miles of the Mouth of a Harbor of Safe Refuge
International Load Line Certificates for Small Passenger Vessels Operating Within 20 Miles of the Mouth of a Harbor of Safe Refuge (Change 1)
Equivalence to Minimum Bow Height Requirements for Load Line Assignment