Article I – Requirement
1. To be able to carry the name of Interlake, a yacht, its spars, sails, and rigging must conform throughout with respect to the design, dimensions, and materials of the official plans and specifications of the Interlake Sailing Class Association.
2. In the event of a revision to the official plans that would affect equipment of a yacht, the affected equipment is eligible until replacement is necessary and then it must be in accordance with the revisions.
3. The yacht number must be permanently cut or burned into the keel of wooden hulls or drilled into the centerboard well of the glass-plastic hulls. These numbers shall be at least three inches high for identification at the time a certificate is issued.
4. Weight: A yacht, its spars, rigging, rudder and tiller shall weigh at least six hundred and fifty pounds. Yachts, as described, weighing less than the class minimum weight shall be corrected by adding sufficient weight. This weight may be any metal, but must be of block or ingot shape, fastened by screws or bolts. If steel or iron is used, it must be painted to prevent rust or corrosion. If the amount of weight added is fifteen pounds or less, it may be attached to the centerboard trunk. If the amount is greater than fifteen pounds, half of the excess must be attached aft of station 16 and the other half of the excess forward of station 2. All corrector weights must be labeled as to their weight and have their weight and location listed on the yacht’s measurement form.
5. Options: Nothing is optional in these specifications unless the word “optional” appears in the article or on the plans and then only within the limitations described.
6. Use of substitutes is always at the user’s risk.
7. After the boat leaves a licensed builder, continuous conformance of all specifications is the responsibility of the owner.
8. The purpose of the restrictions under which Interlake boats and sails are approved is to insure that, to as great a degree as possible, all boats and sails have identical racing capability. It is impossible to list every single variation that might turn up in the future, and it is impossible to make any set of restrictions in which, at some future date, someone cannot find what appears to be legal means of obtaining some racing advantage. Any boat or sail having features which are not consistent with this purpose will not be approved and cannot race even though there is no specific restriction preventing the item in question. Improvements and changes will be made only when these changes do not obsolete older boats from the standpoint of racing capability or when they can be accomplished by anyone at reasonable expense.
Article II – Hull Dimensions
1. Length Overall: 18′ 0″
2. Beam at Deck: 6′ 1½”
3. Beam at Chine: 5′ 2½”
4. For halfbreadth measurements, see Table 1 and the Official Plans.
5. All hulls must come from a mold approved by the Chief Measurer or must be measured by the Chief Measurer or a measurer approved by both the Executive Committee and the Chief Measurer. Upon acceptance, a measurement certificate may be issued by the Association. If at any time the boat or mold is found to be outside either the word or spirit of the rules, the acceptance and measurement certificate may be withdrawn or suspended for a suitable period of time. Final authority on all such matters will rest with the Executive Committee.
Article III – Hulls and Decks
Any construction technique or material not in the Official Plans, or hardware whose purpose is to concentrate weight in the center of the boat or avoid corrector weights in excess of fifteen pounds is illegal. Hulls and decks must be constructed of uniform thickness and density. To keep the class growing and current with good boat construction methods, the following are acceptable methods of constructing hulls and decks:
1. Wooden hulls and decks: To insure class lines and weight, the plans are a guide for sound boat construction with respect to strength and boat life.
2. Reinforced Plastic Hulls: The Interlake may be molded of reinforced plastic with or without “sandwich fillers” laminated between plies for stiffness. If molded without filler for “sandwich” construction, the thickness of hull and deck sections must be of sufficient cross-section to produce the same general rigidity of structure as a wooden boat. In addition, if not of “sandwich” construction suitable ribs, stringers, webs, etc. must be employed to prevent excessive oil canning of hull surfaces.
3. All points of stress must be additionally reinforced by extra materials to produce a hull of comparable strength and durability to the wooden model. Because of the constantly expanding variety of reinforcing materials, resins, sandwich fillers and production techniques, prospective builders or existing builders are required to present in detail their proposed construction methods and material and to secure approval of the Executive Committee, through the Measurement Committee, prior to any production of Interlake Class yachts.
4. It is the intention of the Interlake Sailing Class Association to maintain the extraordinary standard of quality of the boat and any deviation from the spirit of this by any builder may result in revocation of the issuance of measurement certificates and boat numbers.
5. The same principle applies to fastenings, fittings, hardware, and rigging.
6. Prior Review and Inspection: Before replacing or modifying a hull, deck, centerboard trunk, rudder, or floorboards, an owner is strongly encouraged to contact the Chief Measurer for review of the proposed modifications. The Chief Measurer shall review the proposed modification and the Chief Measurer or someone they designate shall inspect the completed job.
7. Deck and Cockpit Options: Cockpit coaming, and splashboards are optional.
8. Cockpit Flooring: Permanent cockpit floorboards may be constructed of ½” plywood maximum. Permanent floorboard frames may be ¾” wide if of hardwood or 1½ inches maximum if softwood. Spacing is optional, but must be uniform throughout. 16″ OC (On Center) is recommended. Permanent floorboards must cover the entire width of the cockpit to within 1.5″ of the sides, and have a minimum length of 95″. Removable floorboards and their supports may be of any construction, but must be removed prior to weighing the boat.
9. Deck Requirements: A deck must either be a fiberglass deck from an approved mold or meet the following requirements. Modified fiberglass decks must meet the following requirements except for 9 a. Material and 9 c. Crown.
9a. Material: Wood with a minimum density of 22 lb./ft3 and a minimum thickness of 3/8″ or plywood with a minimum thickness of 5/16″. Fiberglass decks must be ½” minimum end grain balsa, balsa plank, or klegecell. Verticel and similar honeycomb materials are prohibited. Carbon fiber, Kevlar, E-Glass, and similar ‘exotic’ materials are prohibited except in very limited areas requiring special reinforcement. Further recommendations include all joints to be secured with epoxy, all exposed wood to be sealed with epoxy, and ultraviolet inhibitor applied to all areas exposed to sunlight. The upper part of the deck exposed to sunlight must be covered with fiberglass cloth and epoxy to prevent weather damage.
9b. Deck Frames, Beams and Stringers:
1. Athwartships deck frames ¾” thick and 2″ wide if curved to follow deck curvature or 1 ½” wide at the shear if trimmed to follow the deck crown as shown in the diagram. A ½” x 1 ½” shear clamp strip is also recommended as shown in the diagram.
2. Longitudinal stringers approximately equally spaced with minimum dimensions of ¾” x ¾” and recommended dimensions of ¾” x 1 ½”. Four stringers are required if the frames are on 24″ centers but only two stringers if the frames are on 12″ centers.
3. Center deck beams from the stem to the centerboard trunk and from the aft edge of the cockpit to the transom ¾” x 3″ or an alternate box section as shown in the diagram.
4. Side deck supports of 3/8″ plywood minimum from the inboard edge of the deck to the chine and thence to the shear. These supports are to be solid wood or plywood.
9c. Crown: The crown of the deck must be 4.00 in a chord of 7′ or a radius of 18′ 6½” as shown in the diagram. The deck crown measurement is made at the forward edge of the mast and the optional splashboards must be removed for the measurement. The maximum error is 0.500″.
9d. Cockpit: The cockpit must be between Stations 7 and 16. The side deck, including seats, must be 12.5″ – 16.5″ measured as follows:
1. Lay the deck crown template athwartships at any location.
2. Measure inboard six inches from the edge of the deck. Over this region, the maximum deviation below the template is 0.500″.
3. Measure inboard 12.5″ from the edge of the deck. A vertical line down from this point 12″ must contact the deck as shown in the diagram.
4. Measure inboard 16.5″ from the edge of the deck. A vertical line down from this point 12″ must not contact the deck as shown in the diagram.
9e. Other Openings: Halyards, control lines, and spinnaker sheets may pass through the deck providing that the openings for that purpose only. Openings should be sealed or protected to prevent water intrusion into the deck material.
9f. Mast Step: The area under the mast step must be reinforced or suitably constructed to withstand the rig loads. The loads must be supported by the top of the centerboard trunk or its forward extension.
9g. Rubrail: A wooden deck must be equipped with a wood, plastic, or aluminum rubrail with a cross-sectional diameter of 3/4″ minimum.
10. Mast Step: No mechanical device shall be allowed to change the foot of the mast; otherwise, optional to type and material. May be mounted on deck.
11. Centerboards: Any material may be used. The thickness shall be between 0.187 and 0.250 inches. The size and shape must conform to the official plans. The centerboard pivot bolt must be located 2.5″ ± 2.0″ forward of station 8 on the official plans. Any existing boat as of July 1, 1990, not conforming to the centerboard pivot bolt location is eligible under ISCA Constitution, Article IX paragraph 3. Any reconstruction of the hull by removing and replacing the centerboard trunk must then conform to the centerboard pivot bolt location that is stipulated above.
12. Rudder: Outboard rudder of the size and shape as shown on plans. May be pivoted, but must be all the way down during races. Minimum weight for the complete rudder assembly, not including the tiller, is 8 lbs. Rudder profile above the waterline is optional. As of June 1, 1979, optional rudders (spade) will not be allowed. Existing boats with optional rudders (spade) will be allowed, but must be registered with the Class Secretary by June 1, 1979.
13. Chain Plates: The center of the chain plate hole shall be 8′ 4″ ± 1″ aft of the bow excluding rubrail.
14. Hardware: Optional except: (Amended 5/20/2013)
a. In addition to devices permitted in the ISAF rules, hand lines which do not extend beyond the gunwale are allowed.
b. Mast steps which permit the mast to pivot are not allowed.
c. A communication device may be carried on the boat with the power off, for use only in case of emergency to give help to a person or vessel in danger as allowed under Fundamental Rule 1 of the ISAF Rules.
d. No electronic device capable of a racing benefit is allowed on the boat while racing, except that a device may be used if its only capability is
1. display the heading direction of the boat, either the heading itself or a number that is calculated using a fixed or adjustable tacking angle;
2. display the time of day, elapsed time, or countdown time;
3. record video, speed, position, and time data, with no display capability and only for later access ashore.
e. The Organizing Authority may allow, but not require, VHF radios or other specified communication devices to be used while racing for the sole purpose of communicating between the Race Committee and competitors. If VHF radios or other specified communication devices are to be allowed at an event to communicate between the Race Committee and competitors, the Notice of Race must so state.
15. Centerboard Trunk: The centerboard trunk forms a guide to keep the centerboard vertical relative to the hull, holds the centerboard in place while it is fully or partially retracted, and may serve as a mounting location for various hardware. The centerboard trunk must meet the following requirements:
15a. Materials: The trunk must be rigidly attached or molded to the hull in a fixed vertical position. The sides of the trunk must be constructed of marine plywood 0.500 inches thick or material to provide equal or greater stiffness.
15b. Enclosure: The trunk must either completely enclose the centerboard or the top edge of the trunk may be shortened to expose the centerboard if the trunk meets the requirements of Section 15c below.
15c. Reduced Centerboard Trunks: The top edges of the centerboard trunk must extend past the upper corner of the board in all positions. The top edges of the trunk must also be 14.5 inches minimum above the top of the keel. The portion of the trunk enclosing the upper front corner must lie at least 21.25 inches from the centerboard pivot bolt. Forward of the pivot bolt, the height must be at least 21.25 inches as shown in the diagram. The trunk must be completely enclosed or a reinforcing flange extending at least 1.00 inches laterally and 0.25 inches minimum radii must be attached to the flat portion of the trunk as in the diagram.
16. Flotation: Minimum 13 cubic feet of any combination of: 1) solid unicellular foam, such as Styrofoam or equivalent, having a density of 4 pound per cubic foot maximum, and/or, 2) marine purpose airbags; all of which must be securely fastened into the hull. Balsa wood enclosed in fiberglass-impregnated cloth is considered equivalent. Supposedly airtight compartments are not considered equivalent. All existing boats shall meet this specification by April 1, 1998.
Article IV – Spars and Rigging
1. Mast: Exact size and shape as shown on plans. Pear-shaped metal extrusion only. Any change of the mast at the partners or step shall be prohibited during races. Metal mast must be sealed or foamed ensuring flotation. As of January 1, 1980, existing wood masts will be allowed until replacement is necessary. Front of mast shall be 6′ 8″ aft of the stem.
2. Boom: Exact size and shape as shown on plans. Pear-shaped metal extrusion only. The boom section shall not bend more than 1 ½” horizontally and 1 ¼” vertically when supported 6″ from each end and loaded in the exact center with a weight of 75 lb. The spars shall be maintained straight and any rigging made purposely to bend them shall not be allowed.
3. Standing Rigging: At least 1/8″ in diameter. There shall be a forestay and two shrouds and any change in the set of them during a race shall be prohibited, except in the case of emergency. The forestay shall be 8″ aft of the stem at the deck and lead to a point on the mast that is 18′ 0″ above the deck. The shrouds shall lead to points that are 18′ 0″ above the deck.
4. Jib and Main Halyards: There shall be a jib halyard and a main halyard, which shall lead down the outside of the mast and shall not be used as stays.
5. Racing Bands: Two ½” bands of contrasting color must be placed on the mast a distance of 21′ 0″ apart with the lower band 22″ ± ½” above the deck at the upper edge of the lower band. A ½” band of contrasting color must be placed on the boom a distance of 12′ 3″ from the after side of the mast to the inner edge of the band. All parts of the mainsail, including the headboard, must be confined inside these bands during races.
6. Spinnaker Pole: The spinnaker pole must be 7′ – 8′ 1″ in length.
7. Whisker Pole: Used to hold out the jib before the wind. It must be 8′ ± 1″ in length. One end of the pole must be securely affixed to the front of the mast while being raced.
Article V – Sails
1. Dimensions: Maximum dimensions
Luff 21′ 0″ 16′ 0″
Foot 12′ 3″ 7′ 0″
Leech 23′ 3″ 14′ 4″
Mid-Girth 7′ 10″ 4′ 2½”
Headboard horizontal and vertical 6″ N/A
Foot Roach N/A 9″
For Spinnaker, see the drawings
Foot roach shall be measured by establishing a line from the tack to the clew. No part of the foot of the jib may be more than 9″ beyond this line.
Official insignia to be located on the mainsail between the upper and intermediate batten.
Official number to be located on the mainsail between the intermediate and lower battens.
Official number (not insignia) to be placed on spinnaker also. Number on spinnaker to be 10″ high centered in the bottom two-thirds on both sides.
2. Sails: Main and Jib material to be not lighter than 3.8 oz. per square yard. Each new boat may have not more than two suits of sails and each boat is limited to one additional suit each year thereafter and shall be of the type as shown on the plans. Main battens: the upper and lower battens shall not be more than 30″ in length while the intermediate batten shall not be more than 36″ in length. The jib battens shall consist of three, not more than 12″ in length. The mainsail must carry the official numbers and emblem. Each new sail must be measured and may be marked for identification. The sail must hoist on conventional track and slides on wooden spars and booms. The metal spar and boom may use either slides or the sail bolt rope in the throated extrusion. Reef points must be parallel to the foot of the sail. Leech cords are permitted. Sails must be of a woven fabric. Silk or Mylar sails are not allowed. Windows are allowed in sizes up to five square feet total in the mainsail and four square feet total in the jib.
3. Sails are measured with the cloth pulled out to its normal size as set on the spars. Except at the main headboard, the points of measurement at the corners of the sail shall be taken at the intersection of the extended lines of the extreme edges of the sail, including bolt ropes or tapes, but not including hoisting pennants, external cringles, etc. All leeches to be measured with two pound pull.
4. Zippers: Zippers are not allowed in mainsail or jib.
5. Spinnaker: Maximum spinnaker dimensions are shown in the attached drawing. Only one spinnaker is permitted on board on any one race.
6. Spinnaker Hoist: The spinnaker may not hoist to more than 18′ 6″ above the deck.
7. Spinnaker Material: The spinnaker shall be of woven material.
8. Correct Number: The correct number, a minimum of 10″ high, must be displayed on both sides of the mainsail and spinnaker.
9. Royalty: Sail royalties shall be paid for all sails, and the royalty patch shall be permanently affixed to all Interlake sails.
10. Limitations of Acquisition of Sails: The acquisition of new or used sails by the owner of an Interlake, for use on that boat, shall be limited to one suit per calendar year. The use of a sail(s) in any race in a sanctioned event, a local regatta, or a fleet race, shall constitute acquisition, subject to the exemptions listed below. The date of the acquisition of a new sail is the date of shipping out of the loft.
The sailmaker shall mark the sail with the date of the shipment on the sail immediately below the royalty label.
The purchaser of a newly manufactured Interlake may acquire two suits of sails in the calendar year in which he acquires that Interlake. Any sails retained by the new owner from the ownership of a previous boat, or acquired with the purchase of the boat, shall count as sails acquired, and shall subtract from the allowance for the purchase of new sails, if such sails are to be put to competitive use on that boat. This rule does not apply to any sail which at the time of acquisition is more than five years old.
If an owner acquires a sail, or a suit of sails, which he does not feel competitive, he may retire such sail(s) within fifteen (15) days of the date of first use, and may acquire a replacement sail. The Chief Measurer shall be notified of this action in writing prior to the acquisition of replacement sails. The intent of this paragraph is to allow newly acquired sails which are non-competitive to be retired from competitive sailing without prejudice, and is not to allow the acquisition of additional suits of competitive sails. The owner shall certify in writing in his notification to the Chief Measurer that he has retired the sail(s) only because they are non-competitive in his opinion. This exemption procedure may not be used again within five years of the date of notification of the Chief Measurer.
Article VI – Table of Tolerances
Hull Under Over
1 Length Overall 1/2″ 1/2″
2 Half breadths at deck and chine stations 8 & 12 3/8″ 3/8″
3 Half breadths at deck and chine stations 4 & 18 1/4″ 1/4″
4 Frames, position from correct center 3/8″ 3/8″
5 Contour lengthwise and athwartship at each station 3/8″ 3/8″
6 Freeboard 1/4″ 1/4″
7. Warning: Contour tolerances allow for sag in a true hull and boat should be built in sizes on plans.
8. Rudder: Measured with a full size pattern, must not vary more than 1″.
9. Other Hull Dimensions: Other dimensions not covered above or shown as optional in the specifications, shall conform to the specifications shown below:
If over 10′ 1 % 1 %
If 5′ to 10′ 1½ % 1½ %
If under 5′ 2 % 2 %
Sails and Equipment Under Over
10 Linear tolerances on sail dimensions 100% none
11 Batten lengths 100% none
12 Linear tolerances mast and boom 5% none
13 Mast at deck 4″ 4″
14 Jibstay may be shifted fore or aft 2″ 2″
15 Sidestay (vertical measurement) 1/2″ 1/2″
16 Chain plates 1″ 1″
17 Centerboard length and width 1″ none
18. Position of Other Rigging: Optional.
19. Items Not Covered: Anything not covered herein shall be decided by the Association Measurement Committee, but be subject to appeal to the Executive Committee.
Article VII – Honor Awards
1. Chevrons may be displayed by the first three place skippers of the National Championship Series, the Regional Championship Series, and the local fleet champion.
a. First place will be awarded three chevrons.
b. Second places will be awarded two chevrons.
c. Third places shall be awarded one chevron.
2. Chevron colors shall be as follows:
a. National Championship Series — Gold.
b. One black chevron may be awarded to local fleet champion.
c. Indiana Region — Red.
d. Michigan Region — Green.
e. Northern Ohio Region — Blue.
f. Southern Ohio Region — Orange.
3. The size and shape of the chevrons and numerals, if displayed on the sails, shall be as indicated on the diagram.
4. The chevrons and numerals, if displayed on the sails, shall be affixed to both sides of the mainsail as follows:
a. The apex of the chevrons is to be 6″ from the leech, point up, and oriented to point along an imaginary line parallel to the leech.
b. The apex of the lowest chevron shall be 7′ from the clew of the mainsail.
5. The last two digits of the year in which the award is made must be displayed beneath the chevrons as indicated in the diagram.
6. Additional receipts of the same award in subsequent years may be indicated by placing the two year digits 1″ below those of the last award.
7. Numerals are to be the same color as the chevrons.
8. Honor awards are made to the skipper, not the yacht.
Article VIII – Notice to Builders
1. The Interlake Sailing Class Association owns all rights to the title, and interest in the original plans and reserves the right to refuse to issue a number or grant a measurement certificate to any yacht.
2. A manufacturer of Interlake sailboats must receive approval from the Interlake Sailing Class Association.
3. An individual building an Interlake must obtain a set of official plans and specifications from the Interlake Sailing Class Association.
4. Official class numbers are assigned to a completed boat when the measurement certificate is awarded. Certification fee is set by the Interlake Sailing Class Association. The Secretary-Treasurer will issue a five boat block of consecutive numbers to the builder. Each block must be paid within 30 days. A new block will not be issued while two blocks are unpaid.
Article IX – Advertising
There will be no displays or signs on the mainsail and jib other than the identifications recited in the Specifications and shown in the Plans, a class royalty label, a sailmaker’s identification of customary size and placement, and a stamp signifying Chief Measurer approval. In addition to the displays or signs permitted on the mainsail and jib, spinnakers may carry additional display(s) or sign(s) provided the additional display(s) or sign(s) do not obstruct clear observation of the sail number and are first approved in writing by the Chief Measurer. An application to the Chief Measurer for permission to use an additional display or sign shall include a sketch of the proposed additional display or sign. The Chief Measurer shall deny permission for any additional display or sign that could be construed as advertising for a for-profit entity, or is by its nature political, racist, sexual, vulgar or obscene. Any signs or displays that existed before May 1, 2014 and which were compliant with the then existing rules shall be allowed until replaced. There will be no advertising on hulls or spars other than a manufacturer’s mark. The Board of Directors may grant temporary exemptions to this rule in writing for boats provided to an event or for club-owned boats while used in club programs.