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A guide to static tuning of the standing rigging of the Tanzer T22, T7.5, T26 masthead sailing sloops

By Paul Coppin.

Prior to getting out the wrenches to begin setting up theTanzer rigs, an examination of the rig, particularly with regardto its weak points, is in order.

The Tanzer rig is a simple, single spreader bermudan mastheadconfiguration comprised of a fore and back stay (split in some variants), and a single upper and lower shroud eachside.  The rig has a moderate aspect ratio of just under3:1, supported on a relatively short and thick, non-bendablespar. The shrouds terminate in swaged eye fittings, to a singlechainplate, more or less in line athwartships with the mast. Themast is supported by an aluminum tabernacle, on a compressionpost attached to the principle bulkhead and stepped at thekeel.  On most models of this group the rigging wire is 1x195/32 stainless steel with a book breaking strength of 3300 lbs.

The features that are of particular interest to tuning are thesingle lower shrouds in line with the mast, the non-bendablespar, and the swaged eye fittings. Given the size and sail area ofthese boats there is adequate strength in the wire and mast,however, the rig layout is a compromise. For simplicity ofconstruction, the boats were equipped with a single lower so thatthere would not be a need to provide in the hull a loaddistribution network to accomodate a more desirable fore and aftlower shroud
configuration. Given the strength of the wire and components atthis size of boat, this was a "do-able" compromise.This move also reduced cost to the builder and the buyer. Whatthis decision means to the sailor though, is that there is noredundancy in the rig, and generally, the rig lacks adequate foreand aft support below the masthead; meaning, that no matter whatyou do, you will be unable to eliminate mast pumping. Keep thisin mind when tuning the fore and back stays and the uppershrouds.

The other principle weakness is the use of swaged eyes at thetermini of the stays. Properly swaged and healthy, the eyefittings will tolerate the strain parameters of the wire. Theproblem is that there is no way to determine the failure load ofa swaged fitting, without testing to destruction. It is equallydifficult to assess the health of a aged swaged fitting, sincecorrosion issues are typically deep in the swage, and may not bevisible at the interface. Swage failures are a frequent cause ofrig failures.  It is for this reason that you will findrecommendations for replacement of rig components on a plannedschedule based on so many years in service depending on the useand the environment.  Given the above, rig tensions shouldset conservatively, providing necessary support for the rig andits loads, and no more.

The textbook breaking strength of 5/32 1x19 wire is 3300pounds. The general case is that the maximum working load is 1/4 of the breaking strength, or 825 lbs.  This figure then isthe maximum to which a stay should be static loaded, based onnew, healthy wire, properly swaged (the truck and deck fittings mayvery well be another matter).  The factor of safety forshroud tension is 2.5-2.75 for main upper stays and 3.0 for mainlower stays. These factors define the wire size needed to supportthe rig, and are consistent with 5/32 wire. 1/8 at 2100 pounds istoo weak, and 3/16 at 4700 pounds is overkill, and only resultsin excess weight aloft.

Shroud tension should be more less equal between the upper andlower shrouds, and based on a standard of 10-12% of breakingstrength, around 400 pounds, or a scale reading of 41-42 on aStandard Loos Gauge. Sailing tests may show that this is a littlesoft, requiring one more turn of the screw which should bring youup to about 500 lb or 43-44 on the Loos. This is enough tensionfor these rigs, and more would not ordinarily be justifed.Tensioning the uppers significantly greater than the lowers doesnot make much sense in these rigs, given that there is no meansto prevent the spar from being forced into an "S"curve. I would not tension the uppers more that about 10% overthe lowers at the most, if I felt that the masthead was saggingoff too much. The mast, by its robustness, will only let youcompensate so much, before it begins to collapse downward. Have a problem with leaking chainplates? Like 700 lbs of tensionon the shrouds? Hmm.

Fore and back stay tension is typically set at 15% of breakingstrength of the wire, or 495 pounds, to start. Sailing tests can result in this increasing, but in no case should it ever exceed825 lbs. or 47 on the Loos, and for most boats a maximum of 600lbs. (45 Loos) would be reasonable. The stated load of 900 lbs inone of the T22 tuning guides is way out of line, and puts unduestrain on the rig, excess compression on the mast base and isguaranteed to put a fore and aft serpentine bend in thespar.  Equally,undue load on the shrouds will result in atransverse serpentine in the mast which can be clearly seen bysighting up the sail track. By pulling on each shroudindividually while sighting the track, the effect of tighteningthat particular shroud can easily be seen. Remember that once theshrouds are approaching proper tension, when you tighten up onone shroud, you may have to loosen its opposite by the sameamount.

Since there is only a single lower on the athwartships line,overtightening the rig only has the effect of pulling the mastdown and out of column, since the lower shrouds cannot offset that.Therefore, preserve your hull, rig and fittings by notovertightening the rig. Rig tension needs to  be set so thatdynamic loading of any one fitting does not exceed the breakingstrength of the wire. Setting it conservatively accomplishesthat.

Aft mast rake is accomplished by lengthening the forestay andshortening the backstay, NOT by reefing back on the backstay until you have it back where you want. Blocking up of the theleading edge of the mast foot may be required if significant aftrake is wanted. As described above, undue tension will pull themast back and also DOWN, bending the spar. Any bend in the sparweakens it, and the rig is not configured to support a bendyspar.

After the rig has been set, leave it for a few days and checkit again. Odds are, the settings will have changed as theflexible hull re-orients itself to the new loads. This isparticularly true if the boat has just been put in the water offthe cradle.  You may have to redo the tensions several timesuntil the rig and hull are stable together. On the T7.5, if youcan't close the door to the head, you may have the rig too tight!