Mainsheet Swivel Strengthening Modifications Allowed

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Mainsheet Swivel Strengthening Modifications Allowed

Post by Vento Solare » Thu Dec 06, 2018 11:33 am

Interpretation by Class Measurer as Approved by the Technical Committee

Use of the Harken HSB135 (originally specified by J/Boats), Harken 144 Standard Cam Base Swivel (direct replacement for HSB135), or Harken 1574 Offshore Cam Base Swivel is authorized. Additionally, piece parts used on the mainsheet assembly such as clevis pins, washers, backing plates, U adapters, etc. may be sized to increase the strength and durability of the mainsheet swivel and block assembly. No modification that alters the purchase, location or mainsheet endpoint termination points is authorized.

Background

The mainsheet swivel assembly and associated parts have exhibited many failures that include deformation of the U attachment between the swivel and lower block, bending and breaking of clevis pins that attach the lower block, failure of the pin that holds the lower block and failure of the swivel assembly plastic upper bearing race. Discussions with Harken indicate that the newer materials used in sails and lines that stretch less contribute to increased loads on the swivel assembly. High loads can be mitigated through procedures to reduce transient shock such as jibes, but this is not always possible.

The J/109 Technical Committee consulted with J/Boats and Harken to determine what might be done to improve the durability of the mainsheet swivel. It was determined that the existing system could be strengthened in a number of ways. Harken can provide mainsheet swivel HSB456, Description: #14CAM BASE-LG SWV J109 UPGRADE. This has been upgraded with a larger diameter pin mounted in the swivel and stronger Harken model H-29180A, U-Adapter with 1/4in pins made for the J/109. This assembly is bolt in compatible with the existing system.
Harken and the Class Measurer contacted the Oyster Bay Boat Shop to discuss designing and supplying a metal plate that would bolt over the top plastic bearing race. This would transfer the load from the plastic race through the metal plate to the four #10 mounting screws, thus preventing deformation of the plastic race. The plate is currently being designed and when available, the part number and ordering information will be posted.

Harken researched existing products to determine if there was a stronger assembly that could be used. The research showed that no products existed that used the same mounting hole location as the Harken 144 swivel. It was found that the Harken 1574 Offshore Cam Base swivel had increased load capacity in a similar configuration, but the mounting bolt pattern was larger and would require the four mounting base holes be drilled.

The table below provides a comparison of associated parameters for the two Harken swivel assemblies.

ParameterHarken 144Harken 1570
Height 5 3/4” 5 15/16”
Weight 13 oz 23 oz
Minimum Line Diameter 1/8” 1/4"
Maximum Line Diameter 1/2" 5/8”
Fastener Spacing 3/4" 1 1/16”
Fastener TypeFour #10 screws Four 1/4-20 screws
Cam Cleat Harken 150 Harken 280

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