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    Information for Measurers


    This section of the RYA Technical web site is primarily intended to assist Measurers, and in particular, RYA Approved Class Measurers and RYA Sail Measurers. It, together with the Technical part of the World Sailing Website, gives details of the more common standard forms of measurement encountered, particularly sail measurement.


    The RYA approves Measurers for both International and National Classes, as well as training and approving RYA Sail Measurers. In the UK the RYA requires all National class boats and boats of many International classes to hold an RYA issued Measurement Certificate or one issued by a Class Association to which the RYA has delegated its Certification Authority.

    The authorities of RYA Measurers and RYA Sail Measurers are set out below.

    Unless otherwise stated Full (F) Measurers may carry out measurement of hulls, spars, foils, sails and equipment, weighing and buoyancy tests; Maintenance (M) Measurers may carry out measurement of sails and, when approved by their class association, spars, foils, equipment and annual buoyancy tests. RYA Sail Measurers are authorised to measure the sails of those classes that have adopted the World Sailing Sail Measurement Rules and, with the agreement of the RYA, have extended sail measurement authority to RYA Sail Measurers. 

    This part of the website provides Measurers with the basic definitions and principles of yacht measurement and serves as a guide for measurement procedures, some of which may not otherwise be described in class rules or measurement manuals.

    It has to be clearly understood that this is only a guide to Measurers and it is essential that they should refer to the appropriate current class rules and measurement manual, and to any relevant class drawings.

    Measurer's Responsibilities

    In addition to the responsibilities dealt with in the World Sailing Equipment Rules and Guide to Measurement, RYA Measurers also have the following responsibilities:

    a) A Measurer shall not measure a yacht, spars or sails in which he has any personal or financial involvement.

    b) A Measurers function is to examine the yacht, spars, sails and equipment as required by class rules and relevant racing rules, and to record his findings, either on the class measurement form - should he be measuring at the request of the owner - or in a report to the appropriate race committee.

    c) It is important that only RYA Approved Class Measurers and RYA Sail Measurers undertake the appropriate measurement and sign the measurement form or sails. Measurement by an unauthorised person will result in refusal of certification or the withdrawal of an existing certificate or endorsement.

    d) Should a Measurer be in any doubt as to the application of a rule or measurement instruction, he should refer the question to the authority responsible for the issue of the measurement certificate.

    e) Where a measurement is to be taken from A to B the straight line distance joining A to B shall be measured whether or not the line is parallel to an axis.

    Datum Lines and Points

    The accuracy of setting up datum lines and datum points is of fundamental importance, and it is essential that great care is taken in examining the individual requirements of classes. Measurement stations should be marked on the hull - at keel, sheerline and chines - working from a straight-edge placed against the transom. Any deviation due to the transom not being vertical and/or at right angles to the hull centreline shall be determined and allowed for before taking length measurements or marking measurement stations. Where the stations have been marked on the sheerline and keel, intermediate points may be marked by sighting across straight edges. If thread is used for the base line it is essential that it is stretched taut in order to reduce sag to a minimum.

    Measurement of Sections and Rocker

    With a chine hull, the chine beam measurement should be taken with some form of calliper. The distance of the chines and sheerlines from the datum are measured on both the port and starboard sides from a straight-edge across the keel. Ideally, the straight-edge should be supported at the datum line height. If it is placed directly on the keel, the distance of the keel from the datum may have to be added to the other measurements. Due allowance, where appropriate, shall be made for the thickness of the keel band. The heights on both sides shall be within the stipulated tolerances.


    Some one-design classes require the hull shape to be checked by means of templates. Sometimes Measurers are required to construct these from drawings but more often they are required to use official templates obtained from and authenticated by the measurement authority. Official templates are a faithful reproduction of the cross-section of the hull with allowances in respect of the permitted tolerances. It is important that the templates are accurately positioned and properly supported, since a small error in their position can seriously affect the clearance between the hull and the template. When the template has been positioned correctly, the clearance between the hull and template shall be measured. Although this may be done using a steel rule, frequently a more satisfactory method is to use a calibrated wedge or slip gauges. Some official templates may be hired from the RYA.


    A Measurer should report any obvious use of tolerances to change the design lines or shape from that intended by the class rules. Where an item is quoted as having a dimension within a range, this is not a tolerance.


    Only accurate weighing machines shall be used. The machines should be tested annually by a Weights and Measures Department or by a weighing machine specialist. Some weighing gantries, scales and load cells may be hired from the RYA.

    Weighing should only be carried out in still air, and hulls, together with any required equipment, should be dry.

    RYA Prescriptions

    The following are RYA prescriptions to the World Sailing ERS.

    a) Guide to Sail Measurement - Responsibilities and Authorities
    Within the UK the RYA is the ultimate authority for National and most International Classes. In cases of doubt regarding the measurement of these classes Measurers should refer to the RYA. Under no circumstances should an RYA Measurer contact the World Sailing direct.

    RYA Sail Measurers and RYA Approved Class Measurers are Official Measurers with authority to carry out initial measurement of new or replacement sails for the classes detailed in the table above.

    b) Guide to Sail Measurement - Event Measurement Checks
    The appointment of the Senior Measurer at World Sailing Class World Championships held within the UK requires the ratification of the RYA. In addition it would be helpful if the Senior Measurer at other major National or International Class events held within the UK contacted the RYA prior to the event.

    c) Part B - Fundamental Measurement
    B1 - Tools and Equipment
    RYA Sail Measurers, when first appointed, are supplied, direct from the RYA, with a standard measuring batten and sail endorsing stickers.

    d) Part B - Fundamental Measurement
    B3 - Measurement Points
    When using the RYA standard batten to extend the curved edge of a sail it should be held at its ends only with one end at the measurement point and the greatest length of the batten against the sail edge. This will give a uniform and repeatable extension of the curve.

    e) Leech points are easily marked by a pencil placed in the fold.

    f) Part B - Fundamental Measurement
    B9 - Advertising
    Limit of Sailmakers Mark from tack:

    Appointment of RYA Sail Measurers

    The RYA will arrange Sail Measurement training courses and publish details of upcoming courses on the website. Applicants will be advised what to expect and what to bring. Courses will not normally be run for fewer than four applicants.

    Near the end of each course applicants will be required to take a short two-part assessment covering the theory and practical elements of the course. On completion of the course, the assessment papers will be marked and a recommendation as to appointment or otherwise made to the RYA Technical Officials Group who are responsible for approving RYA Sail Measurer applications.

    Appointments will remain valid, subject to that detailed below. Once appointed, RYA Sail Measurers are required to attend a revalidation course every four years. For further details on how to become an RYA Sail Measurer, please contact

    Termination of Sail Measurer's Appointment

    An RYA Sail Measurer's appointment will be terminated if:

    • They cease to be an RYA Personal Member. Or
    • They do not attend a revalidation course within a year of being requested to do so by the RYA. Or
    • They fail to attain the necessary standard. Or
    • They are dismissed by the RYA Technical Officials Group.

    An individual whose appointment as a Measurer has been terminated may re-apply, but will be required to attend a training and assessment course and be assessed satisfactorily before re-appointment.

    Appointment of RYA Class Measurers

    The appointment of RYA Approved Class Measurers is carried out by the RYA Technical Committee on the recommendations of Class Associations.

    In the first instance applicants should contact Class Associations.

    There is no term of appointment, although all Approved Class Measurers are required to be Full Personal Members of the RYA, and maintain their RYA Sail Measurer qualification.

    Termination of RYA Class Measurer's Appointment

    An RYA Approved Class Measurer's appointment will be terminated if:

    • They cease to be an RYA Personal Member. Or
    • They fail to re-register with the RYA within three months of being requested to do so by the RYA. Or
    • They are dismissed by the RYA Technical Committee.

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