Reply To: Magic Numbers
Lee asked the question,
Jim / Greg you agree? I’d have thought if you were using a softer mast as a second mast you’d also want a flatter sail as you’d be using it only when it’s in overpowered conditions[/quote]
Lee, I will try explain my theory for you. I am sure you understand the theory anyway but it may help others who might not.
I will extract a section of Greg’s reply and I think this supports my theory as correct.
So if Ken has gone from 229 to 265 in the side his new mast has quite a bit less stiffness and probably is a lot more dynamic. This is why he feels it easier to sail with in a breeze. And it probably is!
I really think the f/a bend makes less difference than the s/w. I am sure Jim would agree that a sail can be made for pretty much any f/a bend and the f/a tip affects rake and how hard it is to pull the mainsheet in. The sideways is what lets you either sail upwind in a breeze or makes you struggle.
So here is the theory.
The F/A numbers are not a problem as long as the sail matches the mast. If you can take up your sail shape by sheet tension and open the leech by using Cunningham as you become over powered then a flatter sail is not required. You are achieving the optimum sail for the conditions.( do not get me wrong you still need the best F/A numbers suited for you, but this article has only dealt with the side numbers changing to improve performance using the original sails from a stiffer rig.)
The force that allows you to drive the boat forward in a breeze comes from the side bend, too stiff the mast looses its dynamics and the boat needs much heavier righting forces to maintain forward motion. In simple terms the rig is too stiff and the leech of the sail will not open dumping unwanted power.(you become over powered) Only weight of the crew will correct the force required. Too soft and it has the opposite effect the leech opens/falls off too soon and it will never power up.
The secret is in the Title Magic Numbers. Getting the correct numbers for you.
It is all good stuff and I am pleased the topic is creating some interest. I welcome other comments.
I hope Jim, Greg, and maybe Charlie can reply it may help others to understand better and support the theory.
After all if we can make the boat easier to sail by supplying information to this effect then it can only be good for the class.
As a point of interest when the rig changed over from Metal to Carbon the 2 main reasons being the lack of world wide suppliers and the ability to tailor fit a rig to suit individuals.
