Bob from Va asked about forestay tension and mentioned that some sailors keep the forstay tight going upwind and slack off while going downwind. The following is an explanation of why the above is done. As an aside, when I work with racing crews who are trying to improve I first start out by having them just sail the boat as they normally would. That helps me pick a starting point. When the skipper calls for his first sail trim adjustment I ask him what he was trying to accomplish and sometimes I get correct answers and other times incorrect ones - sometimes my first question also stops further question, which is the opposite of what I want to do. With my "on the water seminars" the crew has to explain every sail trim adjustmentbefore they make it. Since most have spent 3 hours in my classroom that is very easy for them. Anyway, the point of this is that when you see a dock neighbor making sail trim adjustments ask him why and what he is doing. Hopefully, you'll get the correct answer. Unfortuantely for me I never did and that is why I decided to figure it out for myself. Headstay tension affects both jib draft depth and draft position and to some degree twist. You are also messing with the mainsail when you make these adjustments and that is why I say to beginners to intermediates to not mess with it until your very sure of what you are doing. With most production boats you can't bend the mast anyway. You can only rake it back. On a masthead rig you control headstay sag with the backstay. On fractional rigs like America Cup boats it is controlled with running backstays. In Bob's question what we are actually looking at is the forestay is tightened when you crank on the backstay and it becomes loose when when the mast is straightened. Going downwind the mast should be straight. Actually, it would perform better if it was leaned way forward. If you could actually bend the mast (like a J boat) what would happen is that the jib Draft Position would move forward. When you straightened the mast the Draft Position would move aft. As you do this you are also changing the Draft Depth (belly) in the top and middle of the sail. As you can see you have to have a knowledge of draft depth, draft position and twist to understand what I'm talking about. Sagging the headstay provides a fuller sail and is usefull in light conditions and chop. Eliminating the sag flattens the sail, which is good in stiff winds. The bottom line is that the more you sag the headstay the less forgiving your performance band is. You are narrowing your margin of error and in other words, you should know what your doing and what results you are after when you attempt this.
