To your last point - sailboats move in response to the sum of the forces on them. Most sloops are designed to make it easy to balance the forces of the jib and the main, so that the center of effort is near the center of mass. If the sails are trimmed in this fashion you need very little rudder input - in fact it is easy to steer the sailboat with just the sails, if they are well trimmed.t If you let the jib a little out of trim, the force it imparts on the boat will decrease, and since the force on the main is constant, you’ll turn to windward. Likewise you can ease the main to turn to leeward if the sails are balanced and the rudder neutral. Handy trick if your rudder gets damaged.
An interesting note is that well-designed sailboats are designed to round up in the case where the headsail gets overpowered. As the sail gets overpowered, the boat will naturally try to turn away from the wind and also will heel further. The heeling of the boat will cause the headsail to lose lift and spill air before the main sail does, and the keel, which normally generates lift and drag to counter sideslip, combined with the now-more-powered mainsail, Generate a strong leeward yawing force aft of the center of mass which causes the boat to turn sharply into the wind. Rounding up only happens when you are losing control of the boat so turning into the wind ends up putting you in a safe mode where you can recover. There are a few boats out there where the keel is too far forward and/or the main spills air before the headsail; these boats round down in uncontrolled situations and can jibe unexpectedly – very dangerous.
An interesting note is that well-designed sailboats are designed to round up in the case where the headsail gets overpowered. As the sail gets overpowered, the boat will naturally try to turn away from the wind and also will heel further. The heeling of the boat will cause the headsail to lose lift and spill air before the main sail does, and the keel, which normally generates lift and drag to counter sideslip, combined with the now-more-powered mainsail, Generate a strong leeward yawing force aft of the center of mass which causes the boat to turn sharply into the wind. Rounding up only happens when you are losing control of the boat so turning into the wind ends up putting you in a safe mode where you can recover. There are a few boats out there where the keel is too far forward and/or the main spills air before the headsail; these boats round down in uncontrolled situations and can jibe unexpectedly – very dangerous.