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MAST STEP SPECIFICATION PDF – Mast Step Measurement Form & Diagram Acrobat Reader Required LINK – Shields Class Association : Mast Step Placement Rule : Section IV: 5.11 (June, 2004)
On June 12, 2004, the Shields Class Governing Board met to consider the Technical Committee’s unanimous recommendation that the Class adopt a new Specification to govern mast step placement. The Governing Board unanimously adopted the proposed Specification. Unless any Fleet objects, the new Specification will automatically become effective as of the first day of the 2004 National Championship Regatta for boats competing in that regatta, and it will become effective for the Class at large on January 1, 2005. If any Fleet objects within 60 days, under Article IX of the Class Constitution, the proposed amendment to the Specifications will be placed on the agenda for a member vote at the Annual Meeting, which will take place at the 2004 National Championship Regatta. The Specification is the result of six months of intensive effort by the Technical Committee. It is somewhat complex, but its complex nature is dictated by the nature and character of the variations in existing boats which is described below. BACKGROUND Early in the process of developing information, the Technical Committee and the Governing Board recognized four conflicting facts: The boats have been built over many years by several different builders. In spite of the generally-understood prohibition against moving mast steps, the Technical Committee recognized (as a result of informal analysis over the years) that in fact there is some variation in the horizontal (fore-and-aft) step placement on existing boats. It seems clear that some of this variation is not accidental but has been the result of efforts to improve performance. We know that step location in combination with partners location can in fact affect performance, and the Governing Board therefore believes that step location (like partners location) should be fixed or constrained by class rule in order that the boat be truly one-design. Accordingly, it was decided to measure a large number of boats to see how much variance there was in the actual step locations in the boats that are actively racing, and to work towards the writing of a new rule (or a clarification of the existing rules) based on those findings. The theory was to find a definition for step location that would satisfy the desire for certainty without requiring wholesale changes in numerous boats, particularly if there was no evidence of “rule-beating” intent. The Technical Committee, with the assistance of Fleet measurers, measured the step and partners locations of more than 35 boats in four different fleets (Newport, Larchmont, Marion and Seawanhaka). This effort quickly revealed two things that made the measurement problem more difficult: first, the vertical location of the steps in the boats, i.e., the mast “bury” (distance of mast step below deck) varied by more than three inches, because the liner molds and step construction techniques have not been the same in all boats over time. Second, the measuring point (the forward edge of the bow chock) which the class rules have used for years to locate the partners may not be completely consistent for all boats, although the variation is probably not great. The same hull and deck molds have been used for every boat built. Because the deck mold registers perfectly inside the hull mold when the deck is installed, the Technical Committee and the Governing Board concluded that the molded deck flange, where the fiberglass turns down at the aft end of the cockpit on centerline, is a trusted point common to all boats and can be considered a consistent measuring point for locating the step. From this point one can measure in a straight line to both the partners and the step. There is a teak coaming of varying heights and angles fastened to this fiberglass deck flange that could interfere with taking accurate measurements. A special 3-inch hook was fabricated to reach over the coaming and to hold the end of a tape measure to facilitate the measurement. The hook is designed to fit against the after edge of the cockpit coaming so that consistent measurements can be taken forward of that point to the after edge of the partners and the after edge of the step without having to correct for the height of the coaming. Any method that insures accuracy of measurement may be used. The measurements the Technical Committee took are shown in the attached Table 1, “Mast Step Measurements.” We decided that this table should be distributed generally to the class for all to see. Without extensive quantitative analysis, it seemed clear to us that the better-performing boats generally shared three characteristics: 1. Partners were located at or near the maximum aft location permitted by the rules. (Indeed, we found that some of the better-performing boats had partners that were aft of that position, and the owners were asked to correct that problem.) Specification 2.2 says that the aft edge of the partners shall be 135 3/8 inches aft of the vertical projection of the mooring line groove in the bow chock, with a tolerance of plus or minus 3/8 inch. That means that the permissible maximum aft location is 135 3⁄4 inches aft of the bow chock measuring point. 2. Steps were relatively far forward as compared to the overall mean position of the steps in all the boats measured. 3. (As a result of the above) a rake of at least 1.25 degrees aft, and sometimes up to 2.83 degrees or more. THE NEW MAST STEP SPECIFICATION The new Specification limits how far forward the mast step can be located. For any given boat, Table “X” (which is a part of the Specification) shows the maximum forward limit of the after edge of the mast where it rests on the step. This measurement is taken from the aft cockpit coaming, a point called “AC”, and will produce a rake of exactly 2 degrees if the partners (measured from the bow chock) are located as far aft as the long-standing class specification permits. The maximum forward step measurement, (“X” in the table) is derived from a trigonometric formula that depends on two variables: first the distance from the surface of the deck to the top of the bearing surface of the step, called “Bury” and second the distance from AC to the maximum permissible aft location of the after edge of the partners, called “Pmax.” See the “Shields Mast Step Measurement Form” for a graphic representation. The text of the new Specification follows: 5.11 Mast Step The mast step shall be located on the centerline of the boat and shall consist of an aluminum casting (as supplied by Cape Cod Ship Building) that is fastened to a fixed horizontal foundation. After the effective date of this Specification, the mast step shall not be moved except under the supervision of a fleet measurer, who shall record the boat’s “Bury,” “Y” and “X” dimensions after the step has been moved so as to be in a position to certify that the step location appears to be in conformity with this Specification. The maximum permissible forward position of the mast step shall be determined as follows: 1. Measure the maximum permissible aft position of the after edge of the mast partners (135 3⁄4 inches aft of the mooring line groove in the bow chock, see Specification 2.2). Mark this position (“PMax”) on the deck at centerline. 2. Measure the distance (“Y”) from the aft edge of the cockpit (on centerline at the surface of the deck behind the coaming, Point “AC”) to “PMax.” 3. Measure “Bury,” the distance from the upper surface of the deck at the aft edge of the partners to the surface of the mast step flange upon which the mast sits. 4. Using dimensions of Bury and Y, find the dimension “X” in Table X. “X” is measured from Point AC to the intersection of the aft edge of the mast where it rests on the step. (b) If the actual distance from Point AC to the intersection of the aft edge of the mast where it rests on the step is greater than “X,” the mast step shall be moved aft sufficiently to comply with this Specification.
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