This information may help you identify your rudder's performance and in some cases, your sailing performance. We are going to talk about small boat rudders that are controlled with a tiller. They are attached to the transom behind the boat in most cases. One rudder that I like the best is a following rudder. The blade that's in the water is behind the rudder's pivot point. If the boat is going in a given direction, the rudder will follow the boat. The other type of rudder is an over center rudder where some the blade is in front of the pivot point. This type of rudder is designed to have built-in power steering. As the blade is moved to make a turn, the part that's over center will move in the opposite direction and reduce the effort required to make a turn. This type of rudder is really designed for big boats with big rudders and wheel steering, but sometimes they find their way into little boat. Over center rudders with tillers move all the time on their own. You have to steer all the time to maintain a course. They require too much work on little boats.
Other types of Com-Pac rudders are the flat metal type and rudders with a shaped blade. Most users say they like the shaped rudders because they feel better. Maybe the extra drag turns them into a following rudder? What you feel is what you feel.
Rudder lift is defined as more pressure on one side of the blade than the other. This pressure is generated by sliding sideways when you are on a windward tack. The keel gets its lift that way and the rudder does the same thing. When you correct your course, the rudder can change your direction up to 3 degrees and still maintain lift. More than 3 degrees and rudders stall. If you are going fast enough, the rudder creates a roster tail and lots of drag. The smooth shape of a shaped rudder's leading edge helps reduce drag, but its large cross-section will increase the overall drag of most rudders with a shaped blade.
Rudder performance is a function of sail plan balance. You can put your hand on the tiller and feel the pressure required to maintain a course. A well-balanced boat should require very little pressure on the tiller. If the sail camber is aft in both sails, you need to increase halyard tension on both sails. Maximum camber should be at the 50% point in the main and 33% in the jib on most boats. This should balance the boat and ease the pressure on the tiller. Moving the load in the boat will also help. Feel the pressure on the tiller and then move your body and your crew forward a few inches or feet keeping your hand on the tiller. The pressure should be less as you move forward. The top of the mast is tilting forward over the boat's center of lateral resistance. This will reduce weather helm and rudder performance will increase. Trying to feel weather helm in a tiller while an over center rudder is doing its own thing is difficult.
A good rudder is a rudder that doesn't break or bend in severe situations. The last major failure around here was on a medium size boat sailing across Pamilco Sound. The aftermarket rudder bent 90 degrees and the boat had to be pulled into Silver Lake on Ocracoke Island. I think severe conditions could be as little as 25 knots of wind and 2 foot seas. Little boats that weigh more than other little boats need a strong well make rudder. They do more work on heavy little boats.