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shroud attachment

Postby dean francis on Sun Oct 22, 2006 8:31 pm

Hi All,
Having occasion to slightly reposition my forestay fitting on the mast has me reaching for the rule book.
Measurement rule 102 states "shroud position from base of mast, i.e. closest point of shroud bearing point to base of mast min 3511mm max 3524mm.

This then set me thinking (a dangerous thing in itself)!

Here in Adelaide the shroud bearing point measurement has been taken from where the pin connects the shroud to the hole in the tang on the mast, but as the tang itself connects via rivet to the mast some 40mm further up, is this now where the bearing point is on the mast? Is that part of the tang before it connects to the mast really an extension of the shroud?
Given the rule tolerance is only 14mm and I have seen tangs that vary considerably (up to 30mm) in where the hole and fixing point to the mast are I would be interested in any comments or ruling. Also to what effect differences in fixing points may have on mast characteristics.

Regards,
Dean
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Postby Mike Simpson on Sun Oct 22, 2006 10:54 pm

Dean

I have just observed measurement of my mast and another by John Dixon (Vic Measurer).

He measured to the low point in the hole in the tang as shown on the "callout" in diagram #25A on page 51 of the current building notes.

This matches the "old" system where the thimble in the eye of the stay or shroud is directly attached to the tang and the measurement is to where the bearing point of the thimble bears on the tang.

This seems to indicate that the tang is considered part of the mast for measurement purposes but a pin or shackle used to connect the stay is not.

This cuts your margin for error down to the diameter of the pin.

Does that help?

Any comment from measurers??

Mike Simpson
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Postby andrewb on Mon Oct 23, 2006 5:44 pm

You might want to look at the Equipment Rules of Sailing on the ISAF site (http://www.isaf.org/technical/ERS2005-2008.pdf). Page 15 shows the definition for shroud attachment point. If the hidden Sabre rules (i.e. building notes, that probably no 2nd hand boat has) are different it would be worth considering changing them to reflect the ERS.
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Postby Mike Simpson on Mon Oct 23, 2006 6:11 pm

Thanks Andrew - Worth consideration.

Measuring in accordance with the ERS would require a gauge to project the stay/shroud centreline onto the mast and the mast would need to be rigged on the boat to get the stay/shroud angles correct.

I'll raise the matter of complying with the ERS when clearing the revised rules to accommodate the recent changes with the measurers.

Certainly our present system does NOT accord with the ERS!

Mike Simpson
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Measurement of shroud measuring point

Postby Phillip Johnson on Tue Oct 24, 2006 12:49 pm

The shroud and forestay measuring points are taken at the lowest point of the hole in the tang ie the bearing point for the thimble or shackle pin depending on the arrangment. There is no measurement requirement for the distance between the hole in the tang and the attachment point on the mast. This is a hangover from when all boats were rigged using fittings from the guide that is now not part of the building notes. I have observed many masts with significantly different distances between the shroud attachment hole and the attachment point on the mast but I have not noticed any significant performance differences. Perhaps someone out there has. As for compliance with ISAF measuring rules I do not believe that we have any obligation to conform although it can be useful at times. We already measure our sails in the same manner I believe.

Phillip Johnson
National Measurer
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