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I just posted to an identical thread on Cruising Sailors BB.
With mastheaded boats especially and with woven dacron sails (not laminates) its Easy to reshape a sail to readjust the position of maximum of draft to move closer to the boats conceptual 'CLR'. When sailing on 'just the main' simply over tension (bar-tight) the halyard (and cunningham if you have one) to move/reshape the (dynamic) CE or position of maximum draft forward. The closer the point of max. draft comes to the CLR the better the boat will behave, the rudder will not drag almost 'sideways' through the water, etc. and you on most boats will be able to adequately sail with ONE sail; not as good as with two but still adequate and not 'cross controlled'. Yeah sure some poorly designed unbalanced boats wont do this but thats an exception rather than a rule. Additionally you can: 1. trip the leech to make it flatter aft by totally releasing the vang and 2. dont apply any hard or moderate force to the mainsheet which will tend make the leech hook to weather and thus increase overall camber.
The same methods can be used to very adequately sail (even point moderately) with just a genoa with just a small modicum of overlap for the very same reasons. Ya' just gotta know how to reshape a (dacron) sail. Especially on cutters with the mast at approx. 50% of boat length the single-up big genoa is going to match the CE over the CLR almost 'naturally' ... because most true cutters have the total sail plan CE located in FRONT of the mast by design; most sloops will usually have the CE behind the mast.
Sailing sans mainsail up ......
There is almost NO mechanical nor stsructural reason that having one sail up will adversely affect the loading on the mast and rigging ('cept one ... later/below) that will adversely affect the integrity, etc. With respect to forces transmitted to the mast, etc. it stands to reason that less than two sails will generate less than two 'sails worth' of force and if the rig can stand adequately with 2 sails it sure in hell can stand the applied forces of one sail.
The only exception is when then the reduction of sail area/mass changes the 'excitation frequency' of the mast and the mast begins to oscilate or pump at this new harmonic/induced frequency caused by the change of mass or wind loading -- and that will quickly fatigue the rigging terminals, etc. But that same pumping condition can be found occasionally when sailing with Two or more sails .... and all you have to do is change the 'natural frequency' of the mast by changing the rig tuning, pre-bending the mast, changing the sail pressure by sheet tension, or applying running backstays, etc.
In thinking to answer LaBatts comment/question of why the BIG sail has less controls ..... roller furling/reefing cant stand the loads that one can apply in proper sail shaping/setting and thus hardly noone remembers how to do it or even that it can be done. Secondly the laminate sails simply cant be shaped by 'edge tension' so the shape that you buy is the shape youre going to have - period. Then think about those ALSO with in-mast/in-boom furling who simply cant adjust/re-shape ANYTHING.
Last edited by RichH; 09-04-2007 at 04:21 PM.