When searching for your dream liveaboard sailboat, the variety of keels may raise some questions as to which one is the best?
The truth is, they are all good and bad at the same time. You have to find one that fits your needs and demands, and has drawbacks that you are willing to accept or don't bother you.
In general, keels are either fin or full. Within these two broad categories are a multitude of variations, but in general, they fall into these two camps.
Fin keels are characterized by their long, high aspect ratio projections from the bottom of the hull. They provide greater performance and less drag, but they are not as strong as a full keel. The hulls have a shallower bilge which results in less wetted surface area, all leading to greater performance.
Full keels are characterized by their low aspect ratio projections, running the length of the hull. They provide less performance, more drag, and add lots of weight to the yacht. This may sound like a horrible keel choice, but it does have two strong characteristics. It is strong and it creates a nice slick to windward when hove to.
Full keels offer a greater area of attachment to the hull and spread the forces from the keel over more of the hull. This very strong attachment to the hull resists breaking under normal and extraordinary conditions.
Normal loads on the hull-keel joint are experienced when the yacht heels over and the keel acts as a lever arm with the ballast at the end. This load is torquing on the hull, trying to turn the hull back to a vertical orientation. A full keel will spread this force out over a greater area and lead to less stress cracking in the hull at this junction.
Extraordinary loads occur when a yacht is grounded. When the keel smashes into the seabed, all that force is transmitted to the hull via the hull-keel junction. Spreading this massive force over a larger surface area decreases the pressure at this junction and reduces the risk of damaging the yachts hull. This means that a full keel boat will survive coming in contact with the bottom with less risk of damage or holing.
A full keel provides more drag through the water when hove to and sliding sideways. This added drag will lead to a slower rate of drift and provide a very disturbed slick to windward which will calm the approaching seas from breaking waves into rolling waves.
The negative attributes of a full keel is the increase in wetted surface area adds lots of resistance which leads to slower sailing speeds. A low aspect ratio of the keel is simply less effective at producing lift when compared to a keel of the same surface area that is high aspect ratio. This is why racing yachts all have very deep fin keels.
If performance is your top priority, a fin keel will be your desired keel platform. If you want a bit more forgiveness with exploring new waters and will be satisfied with a slower boat, a full keel will be a great platform to look into.