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Boat Forum / Building / February 2008rig tension gauge
I would like to buy a rig tension gauge for wires and rods up to 12mm (15/32"). Tho most common I found on the market are for diameters up to 5mm (3/16") with the exception of a professional device for bridges, elevators, etc. (Portable Cable Tension Meter for cables up to 7/8") which - of course - is great but would cost a little fortune. Any friendly suggestion? Daniel >I would like to buy a rig tension gauge for wires and rods up to 12mm >(15/32"). Tho most common I found on the market are for diameters up to [quoted text clipped - 4 lines] >Any friendly suggestion? >Daniel Loos makes the best known gauges for both wire and rod rigging. Available online, or at many chandeleries. >Loos makes the best known gauges for both wire and rod rigging. Available >online, or at many chandeleries. http://www.google.com/search?hl=en&q=loos+tension+gauge&btnG=Search >>Loos makes the best known gauges for both wire and rod rigging. Available >>online, or at many chandeleries. > >http://www.google.com/search?hl=en&q=loos+tension+gauge&btnG=Search I was going to post some links, but realized that the OP is not in the U.S. and would get more useful links by doing his own search where he is located. This link will at least let him see what it is he's looking for! Thanks for the addition. salty@dog.com ha scritto: >>> Loos makes the best known gauges for both wire and rod rigging. Available >>> online, or at many chandeleries. [quoted text clipped - 4 lines] > link will at least let him see what it is he's looking for! Thanks for the > addition. Thank you very much. I have also found few Loos retailers on this side of the Ocean. Unfortunately I will need both rod and wire gauges and for a couple of ranges which makes the total purchase rather expensive. The idea is quite simple so I wonder if it would be very difficult to construct a device myself; calibration would be an almost impossible issue but, at least, once the tension of the rig is nearly set at a correct value by an experienced rigger, a selfmade device could be helpful in equalling the tensions at both side of the mast and maintaining it in time. The mechanical device is for sure the easiest way but... any idea why a "twang hearing device" would not work? Maybe a piezo pick-up and an oscilloscope? In any string instrument the change of the pitch is strictly correlated to the tension (beside the mass/length, the stiffness coeff., etc etc of course), isn't it? Daniel >salty@dog.com ha scritto: >> [quoted text clipped - 24 lines] > >Daniel I think we are going to need a much more complete description of what you are trying to do. So far, we don't even know if this discussion is about sailboat rigging, although I'm assuming that it is. Once set using proper measuring devices, a "twang" setup might give you a way to make sure that corresponding stays or shrouds on opposite sides are at the same tension as each other, but wouldn't be trustworthy to tell you if they had changed from the original settings. There are other variables, such as ambient temperature and humidity. Those types of variables might affect both tension and the twang pitch produced. >salty@dog.com ha scritto: >> [quoted text clipped - 24 lines] > >Daniel Just a comment: Are you talking about a racing boat or a cruising boat? If a class racer then there should be some information about rig tension in some of the class groups. If a cruiser then generally speaking the rig is tuned by adjusting tension while under sail to make the mast stand straight, or have the required bend. Unfortunately, the latter description is only valid with older boats - my own for instance has two lower and one upper shroud (each side) and all can be adjusted at deck level. A more modern rig with upper shrouds terminated somewhere up the mast would obviously be much more difficult to tension properly at sea. One point to consider is that all rig tension is ultimately fed into the hull which is not a rigid structure, thus you actually want the lowest tension that will keep the mast straight with no slack wires on the leeward side. It is very possible to actually flex a hull by tightening the shrouds too much. You quite frequently see boats with a "hold down" strut tieing the deck to the keel to control this flexing. I would suggest that given that a boat is not a rigid structure and mast loading is a constantly changing number depending on sails carried, wind, waves, ballast, etc., it is more important to adjust the rig so that tensions on both sides are equal, rather then be adjusted to some specific tension. In my experience (cruising only) this can be done by simply "shaking" the shrouds to feel how tight they are and by looking up the mast. (Turned into quite a long comment :-) Bruce-in-Bangkok (Note:remove underscores from address for reply) >>salty@dog.com ha scritto: >>> [quoted text clipped - 55 lines] > >(Turned into quite a long comment :-) While it's important to have the rig tuned tight enough, it's also important to note that the biggest danger of stress and wear/fatigue to the rig is for it to be too loose. If I was going to pretend that I could eyeball a rig without using the proper tools and get it set pretty close to where it should be, I would rather err on the side of slightly too much tension rather than too little. Once a rig is tuned, if you then want it looser, you must loosen the rig below your intended settings and then tune UP to it. Simply loosening a stay or shroud is not a reliable way to adjust it accurately. It's not 100% science to tune a rig, but if you ignore the science part, you can get yourself into a world of hurt. >Thank you very much. I have also found few Loos retailers on this side >of the Ocean. Unfortunately I will need both rod and wire gauges and for [quoted text clipped - 13 lines] > >Daniel Isn't the tension at both sides of the mast always equal with the mast leaning to one sise or the other if the stays are tightened unevenly? Drew Dalgleish ha scritto: >> Thank you very much. I have also found few Loos retailers on this side >> of the Ocean. Unfortunately I will need both rod and wire gauges and for [quoted text clipped - 16 lines] > Isn't the tension at both sides of the mast always equal with the mast > leaning to one sise or the other if the stays are tightened unevenly? This is a good question that made me think. Yes, probably yes! The mast itself is not able to give any resistance and for an obvious physical law, in static condittions both shrouds will have equal tension. Responding to some of you: I am referring to a classic cruiser-racer sail boat designed by S&S in the 80' with a quite tall rig, LOA 41'. Two orders of spreaders and only one rod vertical shroud running from the deck to the outer part of the first spreader. Assuming that the rigger did the right thing, from the deck I can only operate on two opposite vertical shrouds and two opposite diagonal. I have read several things on how to adjust the mast and have a pretty good idea; my original post was based on the belief that a tension gauge may improve the adjustment but you make me think that maybe this is not true. I enjoy very much your comments and advices and thank you all. Daniel >Drew Dalgleish ha scritto: >> [quoted text clipped - 34 lines] > >Daniel The problem would be to establish what is the proper tension. The designer would have used the hull's resistance to being heeled to calculate the load on the rig, and thus the strength of the stays and shrouds, but how tight? As another poster has said, you don't want the rig too loose as the mast flopping back and forth puts undue stress on things. On the other hand excessive tension may deform the hull to the extent that you get stress cracks in the gel coat (actually saw this on two catamarans rigged in Thailand. Most authorities on tuning rigs say that (1) the mast should be vertical; (2) the mast should be straight; and (3) the lee shrouds should not be unduly loose. (note: I am avoiding mast fore and aft bend). Googling +sailboat +"rig tuning" gets some 4,000 sites on this subject. http://bbs.trailersailor.com/forums/articles/index.cgi/noframes/read/92 for example. I would offer one caveat though. Not all posts on the Internet are actually authoritative. Many are made by individuals who are really just describing "how they did it" and "how they did it" may actually be incorrect. My suggestion is unless the procedure is described by a known authority (Brian Toss, for example) take it with a grain of salt and do more research to determine whether the poster actually knows what he is talking about. Bruce-in-Bangkok (Note:remove underscores from address for reply) >Isn't the tension at both sides of the mast always equal with the mast >leaning to one sise or the other if the stays are tightened unevenly? No. The wind is often from one side of the boat, for one thing. If tension is the same in no wind, it will not be once the wind hits the sails and creats a side force. I have sailed more than one boat that usually had at least one slack wire. Always slack on the downwind side, upwind was always tight. Casady >>Isn't the tension at both sides of the mast always equal with the mast >>leaning to one sise or the other if the stays are tightened unevenly? [quoted text clipped - 6 lines] > >Casady I was reffering to the tension before any external forces are added. |
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