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IMS – the International Measurement System – is
the world’s most sophisticated and thorough system of
measurement devised to provide the necessary data for
determining a boat’s theoretical performance potential. The
system includes a description of measurement principles and
procedures for determining the dimensions of a boat’s hull form,
appendages, propeller, stability, sails and spars, as well as
minimum standards of accommodation and equipment placement
consistent with accepted principles and practices of inshore and
offshore racing. In an attempt to better meet the needs of
regatta organizers, Racing division and Racer/cruiser division
yachts are also defined using the IMS.
Hulls
Any monohull, with the exception of “tunnel” hulls
can be measured in IMS using a procedure performed to create an
OFF file describing the body plan of the hull and its appendages
by using an ORC-approved hull measurement machine. Once a hull
is completely measured, an OFF file is generated using the ORC
supplied software by the Rating Authority with the help if
needed by the ORC Chief Measurer. Where a number of hulls of the
same model are built using the same moulds for hull, keel and
rudder, a standard OFF file for that model can be created and no
hull measurement will be needed for other boats built from the
same mould. ORC offsets file database include more than 9.000
different types of boats.
Appendages
Besides fin keels, other appendages can be measured
in IMS, including canting keels, bilge boards, centerboards, and
trim tabs.
Propeller
Propeller types – solid, folding, and feathering –
and their style of installation are defined and measured in IMS,
as is a minimum size so as to allow a boat to travel a minimum
speed under power related to its waterline length. The propeller
dimensions are converted in an equivalent surface, that is added
to the boat resistance.
Stability
Stability has a big influence on boat's performance.
The procedures for performing an in-water inclination test and
freeboard measurements are described, along with the allowable
equipment and its placement on board while in measurement trim.
The procedures for boats with canting keels or water-ballast
systems are also described.
Rig
The procedures and measurement points for the
mast(s), boom(s), spinnaker pole, and/or bowsprit are described,
along with limits on spar dimensions and materials used.
Location of measurement points in the rig plan is specified,
along with the procedure for determining spar weight and centre
of gravity. Other rig characteristics are also noted, such as
number of spreaders, fixed versus adjustable headstay, number of
running backstays, etc.
Sails
Different types of sails can be measured under IMS such as:
mainsail, jib/genoa, symmetric spinnakers, asymmetric spinnakers
including Code 0, mizzen, mizzen staysail or inner jib/staysail.
All the measurements are referenced to the relevant ISAF
Equipment Rules of Sailing (ERS) easily to understand for both
sailors and sail makers.
Heavy Items
The definition of default weights of ‘heavy items’ is
described and includes the following: anchor, chain, windlass,
bow thruster, electrical generator, genoa furler, mainsail
furler, heavy deck, deck headliner, air conditioner, water
heater, and desalinator. They have an effect on the VPP limited
to windward performances, through an adjustment of the pitch
gyradius.
Crew
The crew weight is taken into account in all VPP
calculations iterations, assuming it’s sitting on the sheer.
There is a default crew weight calculated with a formula based
on other boat parameters, but owners can declare a higher or
lower weight as they prefer, and they will be bound not to
exceed that weight when racing. This has obviously an effect on
performances.
Accommodation Regulations
Minimum interior accommodation regulations are defined in
detail so as to distinguish between eligible Racing Division and
Cruiser/Racer Division entries. The purpose of these regulations
is to control cost, promote safety and crew comfort, and to
standardize the accommodation and outfit of the yachts within
their respective divisions. Yachts are categorized in two
divisions: Racing Division or Cruiser/Racer Division depending
on their interior and accommodation features separating those
designed for cruising and longer stay on a boat from those
primarily designed for racing. |