What are the performance and behavior differences between a full keel and a fin keel on a sailboat, and when would I want to choose one over the other?
A full keel is very stable and gives you better tracking through seas - you don't need to adjust your helm much as you crest waves.
A fin keel loses some of this stability, but you gain manoeuvrability - the shorter keel lets you turn much more sharply.
Does a fun keel have a higher aspect and let you point higher into the wind?– EscoceDec 31, 2015 at 23:34
No, typically a full keel will actually allow you to point slightly higher if all else is identical as it runs the length of the hull, whereas a shorter keel is more at the mercy of waves and wind Dec 31, 2015 at 23:39
I disagree: a fin keel can generate more lift as the chord (ratio of thickness to length) allows the water to curve around it's surface. This stops the boat slipping sideways and allows the course made good to be closer to the wind. Note: that the boat may point at the same angle to the wind.– brendanJan 5, 2016 at 4:55
If you have a long fin keel, sure - but the advantage is really about the length Jan 7, 2016 at 19:01
Keels on boats are designed to offset the push of the wind on the sails by transferring the lateral force into a forward motion. The boat can't go sideways because of the keel, so it goes forward. In addition, the wind will push the boat hull over- rotating it to leeward, and the keel will balance that force to keep the boat upright. Full keel boats "track" better- they sideslip less- you'll be able to steer in a straighter line and your autopilot will work less, but give up speed and ability to "point" high due to drag. Fin keel boats were designed to reduce drag, and while they are faster & point higher, the keels are deeper in the water, and less able to operate (and anchor) in shallow water. Full keel boats tend to be slower, behave better in bad weather, are heavier. Fin keel boats tend to be faster, lighter, and more "active" in weather.
In choppy or rough seas a full keel actually lets you point higher. But I agree with the rest of your post Jan 3, 2016 at 11:59
That said, a high aspect ratio keel will help your upwind route - so a long fin keel could outperform a short full length keel. I need to post something on the aspect ratio question. Jan 3, 2016 at 13:04