| > | But rotating booms might be tough with wishbone booms, why is it hard for the wishbone, or half wishbone to rotate around a fixed mast?
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| Because it is usually only attached with a single string, id the mast doesn't rotate, the attachment point on the mast needs to move as the sail does. This can be arranged using a strap, but adds complexity when the sail is raised, reefed and lowered.
I am not sure I understand, but, I am not sure I need to.
Is there more complexity/cost/reduced robustness/failure modes in rotating masts, or rotating booms? And/Or, what do I/We need to know about this to pick a solution for a boat?
Both are pretty robust. Masts are more expensive to set up and bearing alignment is critical.. Tracks, cars and bearings are expensive. The main thing you/we need to know is whether the tied on sail solution is better aerodynamically, and, if it isn't, whether the lower cost is worth the lower performance. All the evidence is that it is better, but there have been no full size tests apart from the ones on Bucket List which were promising, but with nothing to compare against, not much help. Most/all the potential problems with handling the tied on sail have been sorted, but again, not all have been tested full size.
If you think it interesting, I would love to know more about how this all works.
Easiest is if you ask questions, which I will answer. The fundamental point is that the turbulence behind a mast/sail is far worse on the lee side than the windward one. So a sail against the lee side of the mast works better. Attaching it is the problem.
A track on the lee side of the mast works, until you are caught aback, when it gets ripped off. Strings work, if they are tight. Hoops are easier, but not tight, particularly on a tapered mast. A string on them will pull them tight, but needs to be accurately tied, and changed when you reef. An endless line tieing the sails to the masts gets messy when the sail is lowered and the sail tends to blow away when lowered. So individual ties are required, with some means of tightening them, which is not difficult.
The next issue is attaching the halyard, downhaul and boom so the sail can be raised and lowered. Ideally with a simple, fail safe halyard lock so the luff tension does not change when the mast bends. We have solutions for these, but I suspect there are others.
Topic change;
Please find attached a Ex40F pic.
This is 8' folded, correct?
8'6" from memory. I don't have the file any more, it morphed into the Ex40, which will be on the web page 'soon'.
What is the approximate width of the Ex40F hulls?
The Ex40 hulls are 670mm ww and 450mm lw