Join Date: Dec 2012
Location: NE & Windwards
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Re: pointing, pinching, VMG
Some of this depends upon the program used to calculate vmg but the ideal is to have the best vmg with the sails perfectly trimmed and the tell tales horizontal.
Image you on a reach but need to be on a beat. While on the reach your boat speed is higher than on a beat (true for every sailing polar) and the telltales are perfect. You don’t touch the sheets and go to a beat. Now your boat speed falls but your vmg rises. This is an extreme example as in this scenario your sails will luff to to the point where drive will be lost. But there are multiple points before this occurs where your telltales will go squirrelly but vmg improve.
Suggest go on a day sail. Find a situation that reproduces your experience. Put the boat on AP course setting. Then fool with the trim watching vmg. Vmg will improve further when ideally trimmed.
The OP notes light air 7-10kts. Here you have two choices. Go for a very flat sail to prevent back eddies and maintain laminar flow across the sails. Or increase draft and cord to get the most drive from the sails. One will be faster. The sails will look very different although angle of attack is the same.
Examine your sailing polar. In general the point at which boat speed falls as you continue to head up is the point at which you are “pinching”. This is true cruising or racing. It’s built into the basics of your boat. You may not do as well as your polar as your sails age. I pinch to get around a headland or some such situation when cruising but try to avoid pinching while racing. While racing will try to stay right at the edge of pinching which requires a very alert helm. Someone reading the water (if light air) not just the wind indicators. Some one reading the natural oscillations of wind direction in moderate to light air. In heavier air although you need to consider that you also need to consider the seas trying to stall the boat so angle of attack may vary. This requires very alert trimmers keeping up with the changes the helmsman is making as necessary.