Measurement is a fundamental part of any rating system. In order to have a boat's rating calculated, the boat’s characteristics need to be defined by taking the measurement of all parts that affect the boat's performance.

The International Measurement System (IMS) is a set of rules that defines what and how is measured on the boat. By using IMS, the complete boat can be measured, including the hull shape, appendages, propeller, stability, rig and sails. IMS uses WS Equipment Rules of Sailing (ERS) and its definitions are amended only for items specific to offshore boats. Same measurement procedures may be used in measurements of monohulls, multihulls or superyachts.

Measurements procedures explained in this section are for information and description only. Complete measurement rules can be found in the IMS Rule book.

Boats shall be measured by official measurers as appointed by the National Sailing Authorities. Use of ERS makes use of IMS easy for measurers of other international classes, while for parts specific to offshore boats and measurement principles in general, ORC regularly organizes measurement seminars.

How boat shall be prepared for the measurement?

Boats shall be measured dry in light ship condition without crew. Items on board include:

  • Internal ballast, if any
  • Batteries
  • Fixed and/or essentially permanent interior accommodation, hatch covers and floor boards
  • Fixed and/or essentially permanent machinery, electrical and plumbing systems.
  • Mast, boom, spinnaker pole and/or bowsprit with standing rigging and fittings
  • Any appendages including rudder, keel, centerboard, bilge board or any other foils
  • All fixed electronics, instruments, compasses, lights, antennas and masthead devices.
  • Pulpits, stanchions and lifelines.
  • Mattresses and permanently installed table, doors on their normal position.
  • Permanently installed stoves, heaters or other electrical devices.

Specifically excluded from the measurement trim are the following:

  • Water and any liquid contents of any tanks or voids in the keel or other appendages
  • Anchor and anchor lines
  • Deck and mooring lines
  • Any sails, including storm and emergency sails
  • Sheets, blocks, winch handles
  • All portable safety gear
  • Cushions, pillows and any other bedding
  • Cooking and eating utensils
  • Any food or stores
  • Miscellaneous portable and personal gear, books, navigational tools etc.

An easy explanation of lightship measurement trim would be that if the boat is rotated upside down, everything that falls out shall not be on board.

How the compliance with the certificate is defined?

All measured, declared or recorded values shall be as close as possible to those on the certificate. Differences are allowed only if the values on the certificate give a faster rating. The sail area shall be smaller or equal to that printed on the certificate.

The sails inventory of the monohulls shall include the largest of each when on board:

  • mainsail
  • mizzen
  • quadrilateral sail or sail set on the wishbone boom
  • headsail set on the forestay
  • symmetric spinnaker, asymmetric spinnaker
  • mizzen staysail
  • all headsails set flying
  • all asymmetric spinnakers having SHW/SFL < 0.85.

While sails inventory on the multihulls and superyachts shall include all sails on board.

Values declared by the owner such as crew weight or use of asymmetric spinnaker tacked only on the centerline shall not be considered as an issue of compliance with the certificate, and shall always follow appropriate rules.