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Measurement Definitions

Yacht Measurement Definitions

The measurements of a yacht as reported on her rating certificate or rating application form are critical to the establishment of their boat's rating. The responsibility for supplying accurate measurements rests solely with the owner of the boat. Although builder-supplied information can and should be consulted, particularly with regard to hull measurements, considerable variances between yachts of the same class can be possible. Variances in the dimensions of the rig are quite possible, and common, which could result in the rating being declared invalid if the owner supplied incorrect information. Spinnaker poles are principal violators, as many builders do not hold precisely to the 'J' measurement. In the hope of establishing some consistency in the taking and reporting of measurements, some guidelines are provided here. Refer to the diagrams on the next pages.


LOA Length Over All of the hull. Note bowsprit and or boomkins separately.

LWL Loaded Water Line. If unmeasured, use brochure LWL.

BEAM Maximum beam of the vessel.

DRAFT Deepest draft of hull. If center or dagger board yacht include draft with board up and down.

DISPL Vessel displacement(lbs.) Brochure or standard measurements such as IMS, ORC or ORR.

BAL Ballast of vessel in pounds. Note any additions or deletions from standard and the location.

I Fore triangle height, from deck sheer line abeam the mast to highest point of sail attachment.

J Distance perpendicular from fore side of mast line to the point of intersection of the forestay with deck.

P Luff length of mainsail from boom to head board in its highest position.

E Foot length of mainsail from the mast to clew in its most outboard position. P2 Luff length of mizzen measured same as 'P'.

E2 Foot length of mizzen measured same as 'E'.

IS Shortest Spinnaker hoist from deck sheer line abeam the mast to the highest point of sail attachment

I2 Highest Spinnaker hoist from deck sheer line abeam the mast to the highest point of sail attachment


Distance perpendicular from the luff to the clew of the largest jib.


Mainsail girth from 7/8 leech to nearest point on mainsail luff.


Mainsail girth from 3/4 leech to nearest point on mainsail luff.


Mainsail girth from 1/2 leech to nearest point on mainsail luff.


Mainsail girth from 1/4 leech to nearest point on mainsail luff.


Mainsail headboard width.


Sail Area (including main and 100% fore triangle + mizzen).


Spinnaker or whisker Pole Length measured with the pole in its fitting and set in a horizontal position athwartship.


Distances from the forestay deck attachment to the point of intersection with the outmost point of sail attachment with the bow sprit.


Spinnaker maximum Girth luff to luff. Fold on centerline, measure width, and multiply by two. Same as (SMW).


Spinnaker Luff length along red/green luff tape from head to clew on the largest spinnaker.


Length of asymmetrical luff from head to tack.


Length of asymmetrical leech from head to clew.


Length of asymmetrical foot from clew to tack.


Asymmetrical spinnaker maximum girth luff to leech.


  1. Folding and feathering props are not eligible for any credits
  2. For a credit the below must be submitted:
  3. A diagram, or photo, of the propeller installation
  4. Type - exposed shaft, keel exit, in aperture or saildrive
  5. Propeller characteristics

i. Number of blades.

ii. Diameter of the propeller in inches.

iii. Pitch of the propeller in inches

iv. Distance from the centerline of propeller to the trailing edge of the keel

v. Length of the propeller shaft expose from hull/keel exit to centerline of propeller.

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