With the choice of fin, you can significantly influence the properties of the board. The choice of fin is partly about the basic properties that you want to modify, such as stability and resistance. But also the behavior in special conditions can be changed, such as neutral conditions in crosswinds, short turning radius for turns, or protection against seaweed. Many parameters can work together for one characteristic but give varying results for other characteristics. For example, both length and surface area affect course stability, but resistance is affected mostly by length and only to a small extent by surface area.
Length
More length gives more course stability
More length gives more stability
less length gives less resistance
Minor length gives a smaller risk of grounding
Surface
More surface provides more course stability
More surface provides more stability
Smaller surface provides better turning radius
smaller surface makes the board relate more neutrally in side winds
Shape
Straight shape provides more responsiveness (turns)
backward inclined shape is better against seagrass
backward inclined form protects better at grounding
Width
A thinner fin gives less resistance
Other factors
Heavy and stronger paddlers need bigger fins
the further forward fin-box, the larger fin is needed for the same traction