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Reply to: How do I calculate shroud loading?

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[quote=Wolfman]Wow, that is NOT an easy question to answer.  There are so many variables that I'm not sure anyone would have ever made that calculation.   You would have to figure out a design wind case and the worst case scenario for sail shape, boat trim, crew weight and position.  And then the worst case loading would likely be dynamic in nature not a static load, so you need to start taking into account movement.  Only the boat designers using 3D modeling tools are likely to have a handle on this.

Probably the simplest way of doing it would be to figure out  the static righting force applied by the weight of the boat and two crew members on the wire with one hull just out of the water and doubling it.  This is the maximum amount of force that the sail can impart and that you can handle without capsizing.  To do this you figure out where the center of gravity of the top hull is, figure out the boat weight and mulitply that by the distance to the center of the bottom hull.  Then you estimate where the crew center of gravity would be on the wire and multiply their weight by the distance to the center of the bottom hull.  Add these three numbers up and divide by the distance form the upper shroud to the center of the bottom hull.   Double it and you should be relatively close to the max working load.  Note that there is probably another factor of safety applied to make up for fatigue/dynamic loading as well as losing some of the wires in a wire rope shourd.  This is probably another factor of 2 but I couldn't tell you for sure.

I strongly suspect that most boat design is just done by trial and error, and there are a limited number of sizes that shrouds can come in.  Hence some boats have more problems with rigging and component failures than others.  Probably the newer designs have been modeled extensively but the people who did those calculations are unlikely to tell you how they did it (proprietary designs and all).

Dave.[/quote]

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