How to choose fins for your twin fin surfboard, by tail width
Updated 2026-09-19
Change the fins on a twin fin board and you change the board. The rule I use to pick a starting point is simple: the wider the tail and the further apart the fin boxes sit, the more fin you need; the narrower and closer together they are, the less fin does the job. Everything else is fine-tuning from there.
Why Futures single tab over FCS for twin fins
Nearly every fin I own for twin fins runs on the Futures single tab system rather than FCS. With only two fins doing the work of three, I want them strong, and the single tab boxes hold up under load in a way FCS boxes do not. The range of twin-specific fins available in Futures is also far larger. The one exception is a Mark Richards board, which takes FCS, and in that system the useful options are the Channel Islands twin (comes with a small trailer, good for smaller or more performance-focused riders), the MR twin for FCS II boards (needs a trailer), the Power Twin (a larger, driving fin for a heavier rider that does not need a trailer), the Christenson (more laid back, suits a wider tail), and the FCS II Modern Keel for a very wide swallowtail.
Keel fins: for short, wide swallowtails
A Lis-style fish with a wide swallowtail and fin boxes set further apart wants a keel fin for drive and control. A handmade Soar keel from Australia, full of surface area, is a good example, and it gives real drive on a board that is short and wide.
Upright fins: for a more pulled-in, performance tail
Mark Richards rode upright fins, some of which he shaped himself out of skateboard decks, on his more pulled-in, flyer-and-swallowtail boards. That combination is squirrely and demands real balance, which is why riders like Richards moved toward pairing uprights with a small trailer fin instead.
Half keels: the category that works in the most boards
Between the two extremes sits the half keel, and it is the category I reach for most because it works across the widest range of twin fins. On a modern diamond tail board built with Exo Flex and a small acceleration channel, a half keel like the NVS Apex Series Ono, made from G10 fiberglass, gives maximum drive without needing a trailer fin. On a longer 7'4 board with four channels and a pin tail, where the channels already act like a third of a fin, an Ellis hybrid fin from Alkali works well because it has a long base for drive but a thin, upright top for pivot with less drag. On a wider, thicker 7'4 EPS board where the fins sit further forward and further apart, a bigger option like the Futures BMT twin, an upright keel raked back for more surface area than a standard upright, gives the extra hold that board needs. And on a long, wide 7'8 board with glassed-on keels, that fixed fin setup trades some turning ability for point-break drive and speed.
For a smaller rider, an Akila keel is a good half-keel starting point; for a larger rider, an EN fin with more surface area does the same job. Channel Islands' small trailer-equipped 2+1 setup has also worked well for me on a performance twin, and alternative options like a fiberglass Chippa Wilson trailer fin, or an S-Wings Twin 520 for bigger waves, are worth experimenting with if you want more power out of your turns.
Bigger keels: for very wide tails or maximum drive
A Futures Dave Rastovich keel, raked well back, is a widely stocked option that works reliably. A True Ames Hobie Keel is taller and longer again, a strong starting point for a very wide swallowtail or a large board. My own favorite in this larger category is the Mikey February Captain Fins keel, less drivey and a little more upright, sitting between a half keel and a full keel; it works particularly well in an 8'2 diamond tail channel bottom board, though the same board in a swallowtail outline needs the extra surface area because its fins sit further apart. An S-Wings keel, made from Volan, sits further back again for a slingshot style of drive with a little less turning area.
The fin I would start with
If I could only keep one set of twin fins, it would be a Chris Christenson half keel in honeycomb construction, set slightly forward of the base for an upright pivot with a longer base underneath for drive. Chris Christenson rates these as 30 percent lighter than a comparable fiberglass fin and prefers under-finning for less drag. It works in a wide swallowtail and just as well in a more performance-oriented board, even when it looks like more fin than the board needs.
A practical tip: sanding and reshaping fiberglass fins
New fiberglass fins, especially thinly foiled ones, often arrive sharp enough to cut your ankle, which matters on a twin fin because the fins sit wide. Sanding them down slightly blunts the edge. Some manufacturers, including Alkali, explicitly allow reshaping, and I have shaved one fin from a matched pair down to compare two profiles side by side in the same board.
Questions people ask
What is the single most important rule for twin fin fin choice?
Match fin size and rake to how wide the tail is and how far apart the fin boxes sit. Wide and far apart wants more fin; narrow and close together wants less.
Should I use FCS or Futures for a twin fin?
Futures single tab, in almost every case. The boxes are stronger with only two fins doing the work, and the range of twin-specific fins is larger.
What is a half keel fin good for?
A half keel is the most broadly useful twin fin category. It works across channel bottoms, pin tails and wider EPS boards without the drag of a full keel or the twitchiness of a small upright.
Is a bigger fin always more stable?
No. A fin sized to a wide, far-apart tail will feel sluggish on a narrower, more pulled-in board, and a small upright on a wide tail will feel loose and hard to control.
Can I reshape fiberglass twin fins myself?
Yes, with care. Sanding down a sharp edge is routine, and some manufacturers explicitly permit reshaping a fin's profile if you want to compare two setups from one pair.
Pair this with which type of twin fin suits you to match a shape to a fin family, and see more hybrid options tested board by board in 8 hybrid fins for your twin fin surfboard. For the fin shapes on their own terms, start at twin fin fins explained and keels or upright twin fins. The boards mentioned here sit across my current quiver and boards I have sold.