Rig tuning Mirage 24

[shoblin]

Does anybody have information for tuning the running rigging on a Mirage 24. i.e. shroud tension and forestay and back stay tension.

thanks,

Skip

[aflanigan]

skip,

The lines you mention (shrouds, forestay, backstay) which hold up the mast are actually referred to as the "standing" rigging; the running rigging consists of sheets, halyards, etc. which control the sails.

Since you posted this under the "Racing" heading, are you looking for some tips on improving speed? Learning how to use mast bend and forestay/backstay tension control to optimize your performance can be very helpful whether you are a cruiser or a racer.

You should know that there is no particular reason (other than caution) why the standing rigging on a boat need be tightened substantially less than its maximum breaking strength; racing boats such as the America''s cup boats(according to comments that came with a borrowed LOOS tension gauge) work with very low safety factors (1.5, say), so they tighten their shrouds and stays fairly close to the breaking strength. But you probably won''t want to push the envelope that much, particularly if you have an older boat with stainless wire and swaged terminal fittings. You don''t always get a warning when these are about to fail.

Tension of 15% of breaking strength of your main shrouds and stays (and about 10% for the intermediate fore and aft shrouds which end halfway up the mast) is probably a good "rule of thumb" value to start with, anyway.

Remember to sight the mast to make sure it''s not bent, and also use a halyard to measure whether it is centered side to side (mark where the halyard touches the rail on port side of deck, then see if it touches the starboard rail at the same spot). You can also do "dynamic" tuning, i.e. check to see if there is excessive slack in the shrouds when sailing to windward in a good breeze.

If you are tuning after stepping the mast, hopefully you can replicate the length of the forestay as it used to be so that your rig is "balanced", i.e. mast rake is close to designed value. If it is not, you will probably notice greater or less weather helm (or lee helm) and can ajust the forestay and backstay accordingly to get things back in balance.


Allen Flanigan
Alexandria, VA

[shoblin]

Thanks for the response Allan. I was hoping to get LOOS guage type tension numbers for the inner and outer shrouds. This boat sails so beautifully I am a little stunned. Helm is balanced so well that I can take several laps around the deck and she holds her course. I detect no unusual slack in any of the shrouds. However I do note that she seems about a half know faster on port tack. Thought it was a fluke but seems to be fairly reliably duplicated. that is why I suspect the rig is not balance. I was going to borrow a LOOS guage but was hoping to have numbers available as are available for a J24.

Thanks,

skip

[sailingfool]

I wouldn''t worry about the rigging failing if you overtension the stays, as the failing point of the wire is probably greater than that the attachment points and the hull itself.

The first evidence that your rig is "over"-tensioned would be dimples in the hullsides where the chainplate knees/bulkheads oilcan the hull, or hatches and doors that stop operating when the backstay adjuster is ON. In most any racing fleet you see a few boats like this.

Since the purpose of the stays is only to hold the mast upright, you don''t need to tension then more than needed to accomplish that. If you have only a little slack, not flopping, when beating on a 15 knot day you should be all set. Any more tension than needed to remove slack, and you are stressing the boat for no purpose, and the boat will probably give before the rig does...