Ok Who is buying the GIN?
This is generally the point in the conversation that I say to the questioner; "Buy me a GIN and tonic and I will SHOW you." However since this in a virtual bar, I guess I will get to the point. Those little straws that come with the Gin and Tonic are what I really need.
All Spars, Masts, Booms, Bow Sprits, Whisker sprits, Boomkins, you get the idea only work in one direction... That is they are in compression only. The minitue you take them out of compression, even if they are the latest and greatest super strong unobtanium composite, then break. Spreaders wood, aluminum or what have you are the same deal. The spreaders are meant to hold the standing rigging off of the mast, in doing so they are in compression, since that is their deisgnated purpose most of them are only attached to the wires that they are holding off the mast by a little siezing wire, or some small guage aluminum plate. Some have neat little cast aluminum ends with cut outs for the wires, but again it only holds the wire OUT, not the spreader up.
The spreaders are held UP by the spreader brackets at the mast. Indeed it is a good idea to always step on the spreaders as close to the mast as you can get your feet, so that the spreader brackets hold up your weight, further out and you are betting that the friction of the spreader tip on the loaded shroud will be enough to keep the outboard end up even with your weight on it. Mostly it won't if you weigh more than say about 100 lbs.
The farther you are away from the spreader brackets the more force you place on the spreader section. The sections of the spreaders are manufactured like mast sections to be in compression. They are exactly wrong for standing on if they are the wing shaped spreaders. When you stand on them you put them in shear load, as the thinest and therefore weakest dimension of the section is the one that you are putting your force against...
Take the straw out of my Gin and tonic here, and Carefully grasp each end between the index finger and thumb in each hand. Keeping the ends in line with the straw push in toward the center of the straw, so that you are trying to push your fingers together. See it actually will take quite a bit of pushing on before it collapses. Now do the same thing with the other straw (Why do Gin and Tonics always seem to come with two straws?) while you are pushing I am going to reach over and push down slightly in the middle of the straw. What happend, it collapsed a lot easier didn't it?
Now if you only hold one end of the straw and push it against the glass you can see that it works as well, push down the end on the glass, it is really really easy isn't it? And the straw folds in half and collapses.... This last demo is a spreader in function, the straw pushes on the glass without being fixed to it. Your finger is the spreader bracket and the glass is the shroud. When you press down on the end of the straw which is touching the glass it is just like you were standing on the end of the spreader. OR that you were sheeting home the main with the lazy jacks tight, and no topping lift. Spreader in action.....
This doesn't address the discontinous rigs on the 39 and 46's but if you take the lower spreader boots off of these it should make sense still, and the lower spreaders on these are still in compression. The loads are to be applied along the long axis of the spreader, not on either of the short axis. They do have some other neat things going on here, which need to be considered when you are tuning the rig.
In short, a foot or so out from the mast is fine, more is running a risk if someone uses the lazy jacks as a topping lift....
Great day on the bay followed by a couple of glasses of red wine, so I will edit this tomorrow for spelling and understandability.
Guy
This is generally the point in the conversation that I say to the questioner; "Buy me a GIN and tonic and I will SHOW you." However since this in a virtual bar, I guess I will get to the point. Those little straws that come with the Gin and Tonic are what I really need.
All Spars, Masts, Booms, Bow Sprits, Whisker sprits, Boomkins, you get the idea only work in one direction... That is they are in compression only. The minitue you take them out of compression, even if they are the latest and greatest super strong unobtanium composite, then break. Spreaders wood, aluminum or what have you are the same deal. The spreaders are meant to hold the standing rigging off of the mast, in doing so they are in compression, since that is their deisgnated purpose most of them are only attached to the wires that they are holding off the mast by a little siezing wire, or some small guage aluminum plate. Some have neat little cast aluminum ends with cut outs for the wires, but again it only holds the wire OUT, not the spreader up.
The spreaders are held UP by the spreader brackets at the mast. Indeed it is a good idea to always step on the spreaders as close to the mast as you can get your feet, so that the spreader brackets hold up your weight, further out and you are betting that the friction of the spreader tip on the loaded shroud will be enough to keep the outboard end up even with your weight on it. Mostly it won't if you weigh more than say about 100 lbs.
The farther you are away from the spreader brackets the more force you place on the spreader section. The sections of the spreaders are manufactured like mast sections to be in compression. They are exactly wrong for standing on if they are the wing shaped spreaders. When you stand on them you put them in shear load, as the thinest and therefore weakest dimension of the section is the one that you are putting your force against...
Take the straw out of my Gin and tonic here, and Carefully grasp each end between the index finger and thumb in each hand. Keeping the ends in line with the straw push in toward the center of the straw, so that you are trying to push your fingers together. See it actually will take quite a bit of pushing on before it collapses. Now do the same thing with the other straw (Why do Gin and Tonics always seem to come with two straws?) while you are pushing I am going to reach over and push down slightly in the middle of the straw. What happend, it collapsed a lot easier didn't it?
Now if you only hold one end of the straw and push it against the glass you can see that it works as well, push down the end on the glass, it is really really easy isn't it? And the straw folds in half and collapses.... This last demo is a spreader in function, the straw pushes on the glass without being fixed to it. Your finger is the spreader bracket and the glass is the shroud. When you press down on the end of the straw which is touching the glass it is just like you were standing on the end of the spreader. OR that you were sheeting home the main with the lazy jacks tight, and no topping lift. Spreader in action.....
This doesn't address the discontinous rigs on the 39 and 46's but if you take the lower spreader boots off of these it should make sense still, and the lower spreaders on these are still in compression. The loads are to be applied along the long axis of the spreader, not on either of the short axis. They do have some other neat things going on here, which need to be considered when you are tuning the rig.
In short, a foot or so out from the mast is fine, more is running a risk if someone uses the lazy jacks as a topping lift....
Great day on the bay followed by a couple of glasses of red wine, so I will edit this tomorrow for spelling and understandability.
Guy
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