Cape 31 One Design Class Rules


The intention of the Cape 31 One-Design Class rules is to ensure that boats are as close to identical as reasonably possible in construction, hull shape, weight, weight distribution, equipment, rigging and sail plan.

Therefore, coring, drilling out, rebuilding, replacement of material, grinding or relocating standard equipment, fairing interior or exterior parts of hull, hull appendages or rig that improves moments of inertia, or changes the standard shapes or contours shall be prohibited.

The Cape 31 One-Design hulls, hull appendages and rigs are measurement and manufacturing controlled.

The Cape 31 One-Design hulls and hull appendages shall only be manufactured by the licenced boat manufacturer appointed by the Cape 31 Licence Holder.

Cape 31 One-Design rigs shall only be manufactured by the licensed spar manufacturer appointed by the Cape 31 Licence Holder.

Cape 31 One-Design sails may be manufactured by any sailmaker.

All equipment is required to comply with the Cape 31 One-Design Building Specifications.

Cape 31 One-Design hulls, hull appendages and rigs may, after having left the manufacturer, only be altered to the extent permitted in Section C of the Class Rules.

Owners and crews should be aware that compliance with rules in Section C is NOT checked as part of the certification process. Rules regulating the use of equipment during a race are contained in Section C of these class rules, in Equipment Rules of Sailing Part I and in the Racing Rules of Sailing. This introduction only provides an informal background and the Cape 31 One-Design Class Rules proper begin on the next page.

The class permits in-house certification for hulls, hull appendages, masts and sails. However, they may also be checked through random independent inspection by official measurers.

When equipment and/or components are not allowed because they are not specifically permitted by the class rules, then this restriction pertains not only to the use but also the presence of this equipment/component on board.




Section A – General

The Cape 31 One-Design Class has been created as a strict one-design class where the true test when racing is between sailors and not boats. The fundamental objective of the class rules is to ensure that this concept is maintained, while preserving the Cape 31’s ease of handling, reasonable cost of ownership, safety and suitability as a true all-round racing boat.

    1. Class – SA Cape 31 One-Design Class
    2. Association – SA Cape 31 One-Design Class Association
    3. Rule – A rule in the Cape 31 One-Design Class Rules
    4. ERS – Equipment Rules of Sailing
    5. RRS – Racing Rules of Sailing
    6. OSR – Offshore Special Regulations
    7. LH – Cape 31 Licence Holder
    8. LBM – Licensed Boat Manufacturer, appointed by the License Holder
    9. LSM – Licensed Spar Manufacturer, appointed by the License Holder
    1. The LBM and LH have the authority to withdraw a boat’s Builder Certificate if the boat has been materially altered and therefore its right to compete in any Class event until the Builder Certificate has been reinstated.
    2. Blank
    3. The Class Measurer has the authority to withdraw certification of any sails that fail to meet the specifications in these Rules.
    4. Neither the Class Measurer, an official measurer, or an equipment inspector are under any legal responsibility in respect of these Rules or the accuracy of measurement. No claim arising from them shall be entertained.
    1. The Class is administered by the South African Cape 31 One-Design Class Association.
    1. Proposals to change a Rule shall conform to the requirements of the Association’s Constitution.
    1. Interpretation of ERS shall be made in accordance with World Sailing Regulations.
    2. Interpretation of the Rules shall be made by the Class Technical Committee in consultation with the LBM or LSM when appropriate.
    1. Blank
    1. The Builder Certificate shall record the following information:
      1. Blank
      2. Hull identification number
      3. Builder details
      4. Date of issue of initial Builder Certificate
      5. Blank
    2. The Builder Certificate becomes invalid if the hull, deck, foils or builder-supplied fixed fittings are altered in any way, including through damage, in breach of the Rules, except to the extent that it is permitted in these Class Rules.
    3. The Builder Certificate shall be reinstated once the Class Measurer confirms to the LBM that the boat has been restored to conformity with the Rules. Details of the relevant remedial work shall be recorded on the Certificate.
    1. Blank
    1. The Owner(s) shall retain the valid Builder Certificate, copies of which will be required on registration for all Class races or Class Regattas.
    2. A copy of each Cape 31’s current valid Builder Certificate shall be retained by the LBM and LSM respectively, and it will be each owner’s responsibility to ensure that copies of their boat’s documents are lodged with the Class Secretary.

Section B – Boat Eligibility & Equipment Inspection

For a boat to be eligible for Class racing, it shall comply with the rules in this section.

    1. The boat shall:
      1. Be in compliance with the class rules.
      2. Have a valid Builder Certificate.
      3. Blank
    1. In the case of a dispute at a Class event alleging non-compliance with the Rules where specific measurements are not stated, the Event Equipment Inspector shall adopt the following procedure:
      1. A sample measurement of the disputed item shall be obtained by taking the identical measurement from a randomly selected control group of five boats or items of equipment.
      2. The measurement of the disputed boat or items of its equipment, taken using the same technique as above, shall be compared to the sample.
    2. If any of the measurements obtained from the disputed boat or item of equipment lie outside the corresponding range of measurements found in the control group, the matter together with the details of the measurement methods and any other relevant information shall be referred to the race committee.
    1. If an event requires event limitation marks these marks shall not be removed during the event. If the event limitation mark becomes damaged or lost this shall be reported to the race committee as soon as possible.


The crew and the boat shall comply with the rules in Part II when racing in Class events. In case of conflict Section C shall prevail. The rules in Part II are closed class rules.

Section C – Conditions for Racing

  1. RULES
    1. The ERS Part I – Use of Equipment shall apply.
    1. Advertising shall only be displayed in accordance with the World Sailing Advertising Code. (See Regulation 20).
  3. CREW
      1. The crew shall consist of 4 or more persons.
      2. The weight of all crew members on board while racing, weighed in light street clothes, shall not be greater than 595 kilograms.
      3. Substitution of crew members, or a change in the number of crew members, will not be allowed during a regatta without prior written approval of the race committee.
      4. No boat shall have more than two World Sailing Group 3 sailors aboard while racing.
      5. Sailors without a current and valid World Sailing classification shall be considered Group 3 sailors.
      6. Class rules 15.1(d) and (e) shall not apply to an event designated by the Class Executive Committee as an “Invitational” event or regatta.
      1. The Driver shall be a current Class member in good standing, and meet the following criteria, except in the event of an emergency involving the safety of the boat or crew where the boat may be helmed by any crew member. Any such incident shall be reported to the protest committee/jury, which may penalise the boat. The penalty may be less than disqualification.
      2. Permitted Drivers in Class round-the-buoy races:
        1. Owners who legally own at least a one-third share of a Cape 31, have paid at least one-third of the initial cost and pay at least one  third of the yacht’s expenses and running costs, and members of their immediate family who hold a World Sailing Group 1 classification and are approved by the Class Executive Committee.
        2. Owner-nominated drivers who are approved by the Class Executive Committee, which, except in exceptional circumstances, shall havea Worlds Sailing classification of Group 1.
        3. Charterers approved by the Class Executive Committee.
      3. In Class round-the-buoy races a boat shall be helmed by a Permitted Driver (in terms of Rule 15.2 b) from the preparatory signal until the finish of the race, except that short breaks not exceeding 5 minutes are allowed for personal or shipboard needs, during which any Group 1 crew member may helm.
      4. In Class races designated in the Notice of Race as “coastal races”, a Permitted Driver (in terms of Rule 15.2 b)) shall start the boat, steer for the first hour, steer for approximately the last hour of the race, and finish the boat. Other than those periods, any Group 1 crew member may steer.
      5. The Class Executive Committee shall be the sole interpreter of who qualifies as an Owner.
      6. Class rules 15.2 shall not apply to an event designated by the Class Executive Committee as an “Invitational” event or regatta.
    1. All equipment shall be functional for its intended use.
    2. Boat shall carry an anchor and chain with a combined weight of which shall not be less than 8 kgs.
    3. The anchor line shall not be less than 8mm in nominal diameter and 100m long.
    4. Lifelines shall conform to the World Sailing Ocean Sailing Regulations Category 4.
    5. The port and starboard lifelines shall be of wire, manufacturer optional, and shall not deflect more than 60mm from a straight line between two points of support when a mass of 5kgs is attached at the point of maximum deflection
    6. The rear gate lines across the transom shall be closed while racing and shall not deflect more than 75mm when a mass of 5kgs is attached at the point of maximum deflection.
    1. The following may be fitted or carried:
      1. Electronic or mechanical timing devices.
      2. Tactical and navigational instruments and charts.
      3. Below-decks spinnaker bags, rollers, guides and retrieval gear of optional design.
      4. A jib hobble system.
      5. Cleats for gennaker sheets.
      6. A batten not to exceed 150mm added to the end of the bowsprit as a preventer for the gennaker sheet.
      7. Sheet-tail bags and winch-handle holders fitted to the sides of the cockpit.
      8. Footrests supplied by the LBM and fixed to the cockpit floor. Location is optional.
      9. Non-slip material on deck or bowsprit to promote safe movement.
      10. Protective plates attached to the deck under the gennaker turning blocks.
      11. An anti-chafe protective sleeve over the boom vang system.
      12. Padding on the lower lifelines.
      13. Tubing on the upper lifelines forward of the shrouds to protect the spinnaker.
      14. Lashing, tape and other anti-chafe gear on the hull, rig or sails.
      15. Mooring lines, fenders, spare lines, spare equipment, tools, sail bags, storage bags and other personal items that provide no sailing performance advantage.
      16. Portable toilet.
    2. The following items may be replaced provided that the replacement part is of similar size, weight, location, power ratio and performs the same function: Blocks, cleats, mainsheet swivel base, shackles, pins, turnbuckles.
    3. The following modification is permitted: Holes may be made, and local reinforcement applied, in the hull for the fitting of electronic navigation systems.
    4. The following are prohibited:
      1. Moving deck hardware from the factory installed position, and
      2. Making holes, bushed or unbushed, in the deck for the purpose of leading controls or tails below deck.
    5. The following may be replaced:
      1. Forward spinnaker sheet blocks to Harken 75 Ratchet or Ratchamatic.
    1. Blank
      1. Shapes and profiles may not be altered. No fairing is permitted.
      2. The hull, foils, sail drive and bowsprit may be lightly abraded to allow for the application of paint. The abrasion shall be the minimum needed to ensure adhesion of the paint.
      3. If a rigid “sanding block” is used, it may not be longer or wider than 300mm.
      4. Old anti-fouling may be removed using a commercially available antifouling remover.
      5. The final finish may be of any commercially available paint.
      6. Scratches and minimally damaged areas of the hull and appendages may be repaired by the owner or at the owner’s direction.
      7. Any more serious damage shall be repaired by, or under the direction of, the LBM. Details of such repairs shall be recorded on the boat’s Builder Certificate.
      8. Keel and rudder templates, approved by the Association, may be used by the Class Measurer to check foil shape conformity.
      9. All boats shall have commercially available anti fouling paint below the water line.
      1. Any significant damage to the mast, spreaders or boom shall be repaired by, or under the direction of, the LSM. Details of repairs to the mast shall be recorded on the boat’s Mast Certificate.
      2. Standing rigging may be replaced by the owner provided that the replacement rigging is of the same specification as the original.

Section D – Rig

    1. The spars and their fittings shall comply with the class rules in force at the time of manufacture except those rules in Section C where the current rules shall apply.
  2. MAST
      1. Top of boom to the bottom of band at the mast head (P) shall be 12500mm.
    2. USE
      1. The mast as supplied and assembled shall be stepped in accordance with the rigging instructions.
      2. The mast butt shall not be adjusted while racing.
      3. The mast partners shall be firmly secured.
      4. The spreader bars may not be modified in any way.
      5. Use of tape, paint and padding on the spreaders, for chafe protection or marking is allowed.
  3. BOOM
      1. The back of the mast to front of boom band (E) shall be 4500mm.
    2. USE
      1. The intersection of the aft edge of the mast spar and the top of the
        boom spar, each extended as necessary, shall not be below the upper
        edge of the mast lower limit mark when the boom spar is at 90° to the
        mast spar.
    1. USE
      1. The shrouds may not be adjusted while racing.
      2. The shrouds and forestay must remain attached at all times while afloat on race days.
      3. Standing rigging shall not have any tension gauges.
    1. A boat shall not use purchases other than the following purchases:
      1. Main Halyard 2:1
      2. Jib Halyard 2:1
      3. Running Backstays not to exceed 3:1
      4. Mainsheet coarse tune purchase of 2:1
      5. Mainsheet fine tune not to exceed 16:1.
      6. Traveller purchase not to exceed 4:1.
      7. Boom vang purchase not to exceed 16:1.
      8. Headsail sheet purchase of either 1:1 or 2:1.
      9. Headsail traveller inhaul purchase not to exceed 8:1
      10. Headsail lead purchase not to exceed 8:1
      11. Outhaul purchase not to exceed 4:1 inside the boom, but the tail may be led through the mainsail clew and dead-ended to the end of the boom to achieve 8:1.
      12. The gennaker sheets shall be led through the standard block locations.
      13. Main Cunningham purchase not to exceed 8:1.
      14. Spinnaker retriever reverse purchase not to exceed 1:3.
      1. The core diameters of running rigging shall not be less than what was supplied by the builder. The material of running rigging shall be unrestricted. Yachts shall not change the diameter of any running rigging during a regatta of six or less consecutive days.
    3. Running rigging shall not have tension gauges.

Section E – Sails

    1. PARTS
      1. MANDATORY: The following sails must be carried on the boat whilst racing unless the permission of the Class Executive Committee or race committee is obtained:
        1. 1 X Mainsail
        2. 1 X Standard Jib.
        3. 1 X Heavy Weather Jib.
        4. 2 X Gennakers.
    2. GENERAL
      1. RULES
        1. Sails shall comply with the class rules in force at time of certification and be measured under “ERS“ Rules of sailing except where varied herein.
        1. Blank
      3. SAILMAKER
        1. No license is required.
        1. Blank
        1. If any sail is damaged and requires substantial repair, the sail will require re-certification which may require fundamental measurement.
        1. The class insignia shall be 600mm high and fit within 1.6m and 3.1m down from the head. Logo artwork is available from NCA.
        1. The construction shall be: Soft sail, single ply sail.
        2. The body of the sail shall be made from one or more of the following materials: polyester, mylar, aramids
        3. Sail reinforcement shall be made from one or more of the following materials: polyester, aramids, mylar.
        4. The sail shall have 6 batten pockets in the leech. The upper three shall be full length and extend from leech to luff. Among these six there shall be one gaff batten, extending from the top aft corner of the leech to the luff, and the angle of this batten is unrestricted. The spacing of the remaining battens is optional. The batten material is optional.
        5. A window is permitted.
        6. One reef position shall be fitted. The reef shall be fully functional and positioned to allow the leech and head to pass under the backstays under tension. Minimum Luff length reduction of 1300 mm.
        7. Moulded sails are not permitted.
        8. The following are permitted: Cunningham, 1 reef, camber stripes,
      3. DIMENSIONS (given in millimetres and max size)
        1. Mainsail may not extend past bands P and E on the rig.
      Mainsail  Maximum
      HB 1115 Headboard Width
      MGT 1520 Main Girth Top
      MGU 2120 Main Girth Upper
      MGM 3040 Main Girth Middle
      MGL 3790 Main Girth Lower
      1. The construction shall be: Soft sail single ply sail.
      2. The body of the sail shall be made from one or more of the following materials: polyester, mylar, aramids.
      3. Moulded sails are not permitted.
      4. The jib luff shall have hanks of any material.
      5. A window is permitted below half height.
      6. The following are permitted:
        1. Camber stripes
        2. Any headsail may be fitted with a maximum of four battens not longer than 960 mm
        3. The battens shall have one end placed on the leech.
        4. The battens shall be removable.
        5. The top batten may be full length.
        6. The batten leech angle is optional
    1. DIMENSIONS: (given in millimetres)
      1. Jib – Standard
        Maximum Minimum
        Luff 12450 12350
        LPG 3660 3600
        Leach 11760 11660
        JH 110 N/A
        JGT 560 510
        JGU 1030 980
        JGM 1900 1850
        JGI 27702720
      2. Jib – Heavy Weather
        Maximum Minimum
        Luff 10780 10680
        LPG 3520 3470
        Leach 9980 9880
        JH 110 N/A
        JGT 490 440
        JGU 900 850
        JGM 1740 1690
        JGI 2620 2570
    1. An A2 and A3 are allowed.
    2. USE
      1. A gennaker retrieval line may be attached to the sail.
      2. A single line may be attached to the clew for attaching sheets
      3. Sheets may not be spliced to sail
      1. The construction shall be: Soft sail, single ply sail.
      2. The body of the sail shall consist only of woven ply nylon material.
      3. Primary reinforcement may include other materials.
      4. Windows are not permitted.
      5. Minimum cloth weights are:
        1.  A2: 36 gm per m²
        2. A3: 46 gm per m²
    4. DIMENSIONS: to be measured as a gennaker (given in millimetres):
      1. A2 Gennaker
        Maximum Minimum
        SLU 15730 15630
        SLE 13740 13640
        AMG 9530 9430
        ASF 9790 9690
      2. A3 Gennaker
        Maximum Minimum
        SLU 15290 15190
        SLE 13650 13550
        AMG 7750 7650
        ASF 9190 9090


BS 1 Interior dimensions

Description mm mm
Forward bulkhead to Aft Mast collar opening 25 2
Companion way bulkhead (aft) to Forward edge of front engine mount 95 2
Fuel tank size (Length) 480 2
Fuel tank size (Width) 220 2
Center Structural rib (Aft edge) to Centerline of Mast foot bolts (Aft) 440 2
Center Structural rib (Aft edge) to Centerline of Mast foot bolts (Forward) 620 2

BS 2 Exterior dimensions

Description mm mm
Forehatch opening (diameter) 660 10
Forehatch track 1360 10
Forehatch slider (length) 735 10
Forehatch slider (width) 650 10
Mast collar/Deck opening (length) 300 10
Stansion to stansion (3rd from stern) 3070 10
Companion way (Length) 600 10
Companion way (Width) 670 10
Pulpit gap (bottom) 195 5
Pulpit gap (middle) 265 5
Pulpit gap (top) 460 10
Toe rail front to Pulpit base 265 10
Forestay pin to front edge of forward pulpit base line 90 5
Total tiller arm reach 1230 10
Helm/Trimmer footstep (Length) 1250 10
Traveller track length (End cap – End cap outer edge) 1510 10
Jib track length (End cap – End cap outer edge) 490 10
Jib track to Hull edge 375 5
Transom to Aft edge of rudder box 1210 10
Chainplates position (Front edge going forward to forestay pin) 4275 30
Chainplates position (Aft edge going aft to corner of transom) 5020 30

BS 3 Appendage dimensions

Description mm mm
Bottom of sprit to Center Bobstay hole 650 5
Saildrive blades folded (Length) 300 5
Saildrive total (length) 520 5
Hull to bottom of sail drive 350 5
Aft keel well to Front edge Sail drive 900 10
Front length on Keelfin (Stock) 65 2
Aft length on Keelfin (Stock) 180 10
Bottom of hull to deepest point of bulb (Perpendicular) 2240 10
Bottom of hull to tip of rudder blade (Perpendicular) 1695 5
Bowsprit forward of bow (Length) 2025 10

BS 4 Keel Weight

The weight of the keel, including the carbon keel fin, keel bulb, fin-to-bulb attachment pins, bulb fairing, primer and paint, and two M20 keel locking bolts shall be between 715 and 720 kgs.

BS 5 Engine, drive leg and propeller

The engine, drive leg and Gori propeller shall be the standard Yanmar engine (raw water-cooled model) coupled to a saildrive; or equivalent equipment as supplied by the LBM. Approved engine is model number Yanmar 2YM15.


Cape31 Sail Plan




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