The term "Yacht" covers all crafts over 24 meters of hull length (Lh).
Commercially are namely "Super-yachts", "Mega-yachts" and "Giga-Yachts" according to their size:
The Large Commercial Yacht Code (LY3) applies to a motor or sailing vessel:
of 24 metres in load line length and over or,
built before 21 July 1968, which is of 150 tons gross tonnage and over and which, at the time, is in commercial use for sport or pleasure and carries no cargo and no more than 12 passengers. Sail training vessels are included in this application.
Other Codes applicable to yachts are:
Marshall Islands Commercial Yacht Code.
The Cook Islands Large Yacht Code.
United Arab Emisses (UAE) Yacht Code.
The Passenger Yacht Code (PYC).
Chapter IX of SOLAS requires compliance with the ISM Code. This new chapter to SOLAS was added by the 1994 Amendments, and is mandatory for yachts :
over 500 Gross Tons,
which are engaged in trade (considered as cargo ships for the purpose of SOLAS).
Don't relax yet if you have a smaller yacht which is operating commercially! Resolution no. 3 of the Conference of Contracting Governments to SOLAS (adopted 1994) strongly urges Governments to implement as far as practicable the ISM Code for cargo ships (which includes yachts engaged in trade) of 150 GT and over, and requests Governments to inform IMO of the action they have taken to implement the ISM Code for those smaller ships.
The International Ship and Port Facility Security Code (ISPS) came into force in 2004 (SOLAS Convention Chapter XI). It is an amendment to the Safety of Life at Sea Convention (SOLAS) on the minimum security arrangements for ships, ports and government agencies. The ISPS Code and the Amendments to SOLAS apply to commercial yachts of 500 gross tonnages and upwards engaged on international voyages.
Other International Rules which could be applicable for your yacht are:
Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs).
International Conventions on Load Lines, 1966.
International Convention for the Prevention of Pollution from Ships 1973 as modified by the Protocol of 1978 (MARPOL 73/78) (Annexes I, IV, V and VI).
International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW).
24 m. > Lh <55 m
55 m. > Lh <100 m
Lh > 100 m