flipping lug (lug nuts)

[Timothy]

I have a cat ketch which I am going to convert to a cat yawl. I was inspired to attempt the conversion by the Nigel Irens' design of the standing lug yawl "Roxanne"and what has been described as its stunning performance both upwind and off, and in all likely hood I will end up using the identical rig. However, Gary Hoyt's new offset square rig got me thinking about ways to avoid the "bad tack " problem If indeed it is a problem. In another thread (junk lateen yawl ?) I attempted to explore ways that this might be achieved. I abandoned my pursuit of the lug rig and explored various sliding gunter ,wing mast and luff pocket options only to return once again to the lug rig. My new design which once again has big engineering problems that even with modern materials might be impossible to overcome, unike Hoyts' offset square rig which has fixed arms that keep the sail far enough away from the mast to allow it to be clear of the mast even on the bad tack, has articulated rather than fixed arms and both the yard and the boom rather than being fixed to the arms are allowed to swivel. the boom has two arms that swivel on the mast in tandem maintaing the booms angle of attack parallel with that of the elliptically shaped mast.The arms travel is limited by the mast and as the sheet is eased they force the mast to rotate. The idea is that as the boat tacks and the sail is back winded it flips behind and to the to the other side of the mast and moves forward as the sheet which terminates at the mast pulls on the boom. I was encouraged that this might work as I learned that junk rigs are equipped with luff parrels the purpose of which is to keep the sail aft as when beating the sail has a tendency to move forward. The luff parrel is eased to allow the sail to move forward as the sheet is eased. In Hoyts' version the mast has a fairing that is free to feather reducing the drag of the circular sectioned mast . In mine the elipitical mast rotates and maintains the same angle of attack as the sail. If indeed this concept is workable has anyone got any idea of what effect the mast would have on overall lift versus drag.The only relavent example of this foil formation that I can find is that of of the sesquiplane, a biplane just preceeding the development of the monoplane. Attached are two short animations one of which shows how I percieve the rig might behave as it moves from one tack to the other and then is eased to run downwind and the other is an overview of the rig as it adopts the correct angle of attack for beating.

[Tcubed]

It seems to me a promising concept.

The dipping lug is one of the most efficient rigs possible with low tech engineering. Of course the disadvantage is having to 'dip' the sail(s) every tack or gybe, although there many ways of doing this and my personal favorite is the Cornish style.

Will write more later.

[bahadiregi]

Timothy ,
Your design looks very interesting but lift created by eliptical mast interferes the lift of the sails.I think that's why Garry Hoyt did not use eliptical section for the mast.His sleeve around the mast is rotating 360 degrees not creating lift.

Regards,
Bahadir

[Timothy]

I tried to find out if it is better to have the mast at an angle of attack to the wind producing lift or to have it oriented in such a way that it always is presented directly into the apparent wind producing as little drag as possible and acting in much the same manner as Hoyt's feathering fairing, but from what little Information I was able to come up with I could not reach any conclusion. Any way it seems that it is a moot point as I learned from Eric Sponenberg on another thread it would not be practical if not impossible to build a telescoping mast so if I wished to pursue the idea It would be with a tapered circular sectioned mast and conventional reefing system. At any rate I redesigned the arm so that the mast's angle of attack can be adjusted. Attached is a short animation attempting to show how I think the rig might work. I am going sailing for four months (no internet) so I will probably have time to make a model of the rig and see if it will actually self tack. I certainly have my doubts. In the end I will probably go with Nigel Iren's lug yawl design.