Headsail funnels the wind
This animation shows how a head sail will funnel the wind on the back side of the mainsail and thus allowing the mainsail to be hauled in tighter with out the wind stalling behind the mainsail. This allows the boat to head further upwind. You can see that when we remove the headsail the mainsail must be let out further to keep it from stalling.
The graphic is slightly wider than the blog column but we kept it big for the iPad format when we publish into our Dinghy Sailing book in iBooks – coming soon.