Twin fin surfboards can feature either fins or keels.
While the term “keel fin” is sometimes used to describe any sort of fin on all sorts of watercraft, it describes a specific design for surfboards.
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What are Twin Fins?
A twin fin setup features two side fins that are similar in appearance to the side fins you’d find on a thruster or a quad – sometimes a little deeper.
Twin fins can comes in a variety of depth and rake, but often feature a narrow base and moderate to large rake/sweep.
These types of twin fins can be placed anywhere from 5″ to 12″ from the tail of the board and may feature a variety of cant and toe angles. The further up and more toe and cant the twin fins have, the loose and more maneuverable the board will surf.
Twin fin set ups like these are going to give you a lot of options as to how the board performs.
What are Keel Fins?
A twin keel describes a fin with a much longer base and much shorter depth.
These can sometimes appear as almost half-circles.
Keels provide a lot of drive, speed, and stability and are often found on classic fish or Mini Simmons surfboards.
Keel fins feature minimal or zero cant, minimal or zero (Parallel) toe, and are often positioned 5″ to 10″ from the tail.
On swallow tail fish, keels are often placed in line with or slightly in front of where the swallow tail meets in the middle anywhere from 1-2″ off the rail.
Keel fin setups are going to have a classic drivey and drawn-out feel.
What is surfing a twin fin like?
If you’ve never ridden a twin before, you’ve probably heard the standard: twins are fast and loose.
While that can certainly be true, there is a lot of variety in the world of twin fin setups.
How your twin fins will feel really depends on:
- The template and flex of the fin.
- The size and shape of your surfboard’s tail.
- The toe-in angle of the fins.
A shorter, wider twin fin or traditional keel is going to feel fast and drivey.
A more raked, narrow twin fin will have a little more versatility and control in turns and vertical maneuvers.
As you increase the toe angle of the twin fins, you’ll sacrifice some of their natural speed for a little more response in your turns.
If you’ve got a hybrid surfboard with a 5-fin set up you can add a rear trailer fin to add some stability to the twin fins.
You’ve really got to experiment!
How to Surf Your Quad as a Twin Fin
If you’ve got a quad surfboard that you’d like to experiment as a twin set up, you’ll keep the front fins in and remove the rear quads.
Depending on the board’s design, this may or may not work well.