A full keel sailboat is not known for high speed or performance, they are known for being sturdy. The full keel provides a lot of wetted surface area which leads to more drag through the water and slower speed. The low aspect ratio appendage extends out below the hull and provides little lift for its size which translates into less ability to point into the wind.
This may sound like a horrible keel design, but it does have some very promising attributes. A full keel offers a lot of strength to the bottom of the boat. The keel attaches to the full length of the bilge and the forces exerted on the keel are transferred to the hull over a very large area.
This extensive contact between the keel and hull means that the keel will be better able to withstand the normal and the extraordinary forces that can be applied to it. If you are sailing along in a storm, the forces on the keel are going to be tremendous and well distributed to the rest of the hull. If you aground, your biggest concern will be getting off the shoal and not getting a haul out to check for damages.
When a fin keel runs aground, the forces can lead to cracks in the keel and hull from the amplification of these forces. When a full keel runs aground, it sits on the bottom awaiting the captain to kedge off. The yacht will rest on the bottom on the long edge of the keel. Forces will be well distributed and subsequent damages will be minimal.
While full keel vessels tend to be slow and unable to outrun a storm like a high performance fin keel yacht could, they are very capable of comfortably riding out the storm. The large keel will produce a significant slick to windward as the yacht drifts laterally while hove to. This slick is comprised of disturbed water that will act to calm breaking waves into simple rollers. Heaving to with a full keel will produce a powerful slick that will magically calm large breaking waves well before they reach your yacht, keeping you safe and dry as you wait for the storm to blow past.
The last issue with full keels is they love to go straight. They will track in a straight direction all day long without little input from the helm, no matter the winds or sea state. If the seas are rough and pounding into the bow or stern quarter, a full keel yacht will hold a straight course. This does make it very easy to balance the sails and lock the helm, as the keel will keep you on a straight track for quite some time with no input from the captain. The problem with a full keel shows up when you want to turn and the keel wants to continue straight. You will find that you need to move the rudder much more to get a reaction on a yacht with a full keel as opposed to a yacht with a fin keel.
A fin keel yacht will turn with the slightest twitch of the helm, a full keel yacht will require you to turn the helm quite a bit and then wait for the yacht to respond to the new rudder position. Tacking really exemplifies these issues, as full turns through the wind are desired and expected. A fin keel will turn through the wind and continue moving quickly in the new direction without losing speed. A full keel yacht will slowly turn through the wind and then come to a complete stop.
The full keel is now laying perpendicular to the direction that the yacht wants to travel and the yacht will come to a stop. The large keel will act as a large wall in the water that will stop all forward progress of the yacht. The rudder is useless as there is no speed and no water moving over it to provide steerage. The yacht will then lose forward momentum and the wind blowing on the headsails will cause the yacht to be pulled downwind. The wind will push your yacht to leeward as it begins to gain speed. Once you have enough speed, the rudder will become effective again and you will be sailing on your new tack. This slow tacking makes short tacking very difficult and each tack will cause you to lose some ground that you have fought for while working to windward. Combining these facts with less ability to point to windward and you can quickly see why it is so important to plan your tacks ahead of time to minimize your losses and get you to your windward destination.
While full keels are by far the least efficient design, they do offer incredible strength and versatility on a sailing yacht. If you want to explore new waters where you may run aground and wish to travel across large open waters, a full keel will keep you safe and on course.