At 06:05 8-1-2011, you wrote:
doug,
i understand about the sag when it fills with wind. it is due to the unstayed mast bending forward.
my idea is to compensate for the sag by pulling on the back end of the halyard with a constant tension, instead of just cleating it off as usual.
i've updated balestron.pdf in the files section to be more clear. please let me know if it is not.
simply put, the mast itself is used to put weight on the halyard via a total of 10:1 block and tackle (5x2).
i roughly worked out the numbers in my last post and it seems as if it could work. an update here: recommended forestay tension is 15-25% of the breaking strength ( http://68.171.211.157/how-to-use-90-91). a j/120 uses -12 rod ( http://www.jboats.com/pdf/j120specs.pdf), which breaks at 12.5k pounds ( http://www.sailingservices.com/standrigging/nitronic_rod.htm). so roughly 1100 kg of tension is desired, which is roughly 10x the weight of visionarry's mast, which has a similarly sized jib.
a few things to worry about:
1. the mast will move up and down as it sways front to back by roughly a meter. so extra bury is needed, which adds weight to both the mast and the hull. more so because the bottom bearing is not on the bottom of the hull, and so an extra horizontal bulkhead is needed.
2. a bearing which permits the mast to not only rotate side to side but also translate up and down is needed. more moving parts and complexity. something like what an oil rig uses might work. not sure those are all the same, but the one i saw in a science museum over the holidays had a four individual roller bearings facing a square tube.
3. what kind of G forces to big waves typically cause? large deviations either side of 1G wouldn't be so good with this rig.
rob, i was hoping to hear your opinion. is it too crazy?
ben
Ben, it is too crazy.
Don't forget the mast stops bending forward BECAUSE the tension goes down. When you find a way to keep forestay tension up the mast will bend further and further.
Perhaps you should research the CamberSpar by Bierig sailmakers when you worry about headsail sagging.
Regards,
Han.
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