Twin Fins and the Trailer Question: What Adding a Third Fin Actually Does

Pemulis Water & Power
2026-02-11T13:19:15-08:00

Twin fins are the most fun fin setup in surfing. They're also the most misunderstood. And the question that won't die: should you add a trailer fin?

Here's how they actually work, and what the trailer changes.

How Twin Fins Work

Two fins. No center fin. Nothing in the middle of the board creating drag.

Each fin sits near the rail, toed in (angled slightly toward the nose) and canted out (tilted away from the center). When you go straight, both fins push water inward and back, generating drive. When you turn, the inside fin disengages and the outside fin loads up, pushing you through the arc.

The thing that makes twins feel different from everything else: there's nothing in the middle slowing you down or creating a pivot point. The board planes across the water instead of cutting through it. Speed comes easy. Turns are wide and drawn out. The tail is free to slide and release whenever you shift your weight.

This is why people describe twins as "skatey" or "loose." The back of the board has no anchor. It goes where your weight tells it to go, immediately, with no resistance.

The Twin Fin Sweet Spot

Twins work best when the wave is doing most of the work for you.

Small to medium waves, clean faces, point breaks, beach breaks with open shoulders. This is twin fin paradise. You generate speed effortlessly because there's almost no drag. You can project down the line, do wide sweeping turns, pump through flat sections, and cover ground that a thruster would bog down in.

Fish, eggs, wide-tailed mid-lengths, retro shapes. The board matters as much as the fins. Twin fins work best on boards with width through the tail—swallow tails, wide squash tails, anything with enough planing surface to stay loose without a center fin holding it steady.

Where Twins Fall Apart

Steep, hollow waves. When the wave stands up and you need to set a hard rail line, twins can slide out. There's no center fin to catch you if the tail releases. This is where the "fun but unreliable" reputation comes from—twins are incredible until the wave gets serious, then they betray you.

Vertical surfing—on traditional twins. If you want to go straight up and come straight back down—hard snaps in the pocket, vertical reentries—classic keel twins fight you. The wide turning arc that feels so good on open faces becomes a liability when you need tight, vertical direction changes. Without a center fin to pivot around, the board wants to sweep, not snap. That said, modern performance twins have blown this door open. Guys like Mikey February and Mason Ho are doing legitimately vertical surfing on twins—boards like the Christenson Nautilus and CI Fish Beard paired with upright performance fin templates. The limitation is real on classic keels and retro fish shapes. On a modern performance twin, the ceiling is way higher than it used to be.

Late drops. When you're taking off late on a steep wave, you need the tail to hold. Twins let the tail slide at exactly the wrong moment. This is the situation where you eat it and wonder why you didn't bring your thruster.

The Trailer Fin: What It Changes

A trailer fin is a small center fin—roughly half the height of your twin fins or smaller—set behind the twins. It turns a twin into a twin + 1 (also called a 2+1, though that term usually refers to a longboard setup with a big center fin and small side bites—different animal).

What the trailer does:

Adds a pivot point. Now the board has something in the middle to rotate around. Turns get tighter. You can snap off the bottom instead of sweeping. The wide, drawn-out twin fin turn becomes shorter and more vertical.

Adds hold in steep surf. The trailer catches the tail when it would otherwise slide. It's not as much hold as a full thruster center fin, but it's enough to keep you in the wave on steeper drops and harder turns. This is the main reason most people add a trailer.

Reduces the slide. That loose, skatey feeling—the thing that makes twins fun—gets muted. Not eliminated, but tamed. The tail still moves more freely than a thruster, but it's not as willing to break loose on its own.

Adds drag. There's now a third fin in the water. You lose some of the effortless speed that makes twins special. On small, clean waves where you didn't need hold, the trailer is pure cost with no benefit.

The Tradeoff Is Real

Every trailer fin discussion comes down to this: you're trading speed and freedom for control and hold.

A twin with no trailer on a clean, head-high wave at your local point break is one of the best feelings in surfing. Pure speed, pure flow, the board does whatever you want.

That same twin on a hollow beach break overhead wave is terrifying. The tail slides on the drop, you can't set a rail, you eat it.

The trailer splits the difference. You can now surf both waves, but neither one feels as good as the dedicated setup would. The point break wave loses some magic. The hollow wave becomes manageable but not thrilling.

This is why a lot of serious twin fin riders own two setups: twins for good days, and a board with a trailer plug behind the twin boxes so they can add a small center fin when it gets heavy.

Trailer Fin Sizing

Smaller trailer = more twin feel. A trailer that's about 40% the height of your twins (roughly 2"–2.5" behind 4.5" twins) adds hold without dramatically changing the character. The board still feels like a twin that can handle more wave. This is the starting point for most people.

Bigger trailer = more thruster feel. A trailer that's 60%+ the height of your twins starts to feel like a thruster with funny front fins. You get lots of hold and vertical ability, but you lose the twin character. At that point, ask yourself why you're not just riding a thruster.

Nubsters (1"–1.5") are even more subtle. They add just enough resistance to prevent full tail slide without meaningfully changing the twin feel. Think of them as a safety net, not a performance upgrade. Good for twin riders who are mostly happy but occasionally get caught out in bigger surf.

Keel Fins vs Upright Twins

Not all twin fins are the same, and the template matters as much as whether you add a trailer.

Keel fins: Wide base, lots of rake, big area. Classic fish fins. These generate drive through their base width and hold through their area. They're fast, drivey, and designed for wide sweeping turns. Keels on a fish with a swallow tail is the classic twin fin setup—fast, fun, lots of drawn-out carving speed. The Lovelace Keel, Hobie Fish, Gephart #2 Keels, and Tyler Warren Modern Keel are all in this family. Keels don't pair well with trailers because the base is already providing so much drive that the trailer just adds drag without improving much.

Upright twins: Narrower base, more upright stance, less rake. These are the modern performance twin fins. Less base drive, more pivot, tighter turns. They sacrifice some of the pure speed of keels for maneuverability. The TA Twin, Barrett Miller ʻIʻiwi, and Ryan Burch Twin fit here. Upright twins actually pair well with trailers because the narrow base leaves room for the trailer to contribute without overlapping.

Raked performance twins: Somewhere between keels and uprights. These are what most modern twin fin boards come with—enough rake for speed, enough height for hold, balanced template. The Stüssy Power Twin, Furrow High Aspect Twin, and Beamish Twin live in this space. These work both with and without trailers depending on conditions.

Twin + Trailer Sets

If you know you want the trailer option, several sets come packaged together so the sizing is already dialed. The True Ames High Pro Twin + Trailer is a solid all-around performance set. The Dice Twin + Trailer, Mackie Big Twin + Trailer, and Proctor Magnum Opus Twin + Trailer are other matched sets where the trailer is designed specifically for those twins—no guessing on sizing.

The Power Trailer + Twin-Fin Set is worth a look if you want a drive-oriented setup with the trailer built into the package.

Twinzers: The Other Way to Add Fins

A Twinzer isn't a twin + trailer—it's a twin with small canard fins mounted forward and outside the main twins. The canards break the water tension before it hits the main fins, creating lift and reducing drag. A Twinzer feels like a twin with more bite and control—somewhere between a twin and a quad. The TA Twinzer, Furrow Twinzer, and Lovelace FM Twinzer are designed as complete sets. These are specific to Twinzer boards—don't just stick canards in random boxes hoping for improvement.

Board Design Matters More Than You Think

A board shaped for twin fins has specific features that work with two fins and no center:

Wide tail. More planing surface compensates for no center fin hold. Flat to mild concave through the tail. Channels water to the fins without needing a center fin to organize flow. Swallow tail or wide squash. Gives the rail fins something to work with on both sides. Low to moderate rocker. Keeps the board planing and fast—twins need speed to work.

If your board was shaped for a thruster and you remove the center fin and call it a twin, it won't feel right. The tail is too narrow, the rocker is too much, and the whole board assumes there's a center fin providing hold that isn't there.

Similarly, if your board was designed as a convertible with 5-fin boxes, the shaper compromised—those boxes are set up for quad and thruster, not twin. The fin placement is different. A dedicated twin board has the boxes farther back and toed in at a different angle than a thruster's side fins. A 5-fin convertible ridden as a twin won't feel as good as a board shaped and glassed specifically for twins.

This isn't a reason to avoid convertible boards—they're great for versatility, especially if you want to switch between quad and thruster. Just know that a dedicated twin board with purpose-placed twin boxes will always feel better as a twin than a 5-fin convertible with the side fins repurposed.

The Call

Ride twins (no trailer) if: clean waves, small to head high, open faces, you want speed and flow and freedom, you're on a fish or wide-tailed board designed for twins, you're willing to accept that the tail might slide when it gets serious.

Add the trailer if: the waves are getting steep or hollow, you want to push harder into turns, you keep sliding out on drops and bottom turns, you want twin-ish feel with more safety margin.

Skip the trailer and ride a thruster if: you're surfing heavy waves consistently, you want vertical performance, you need maximum hold. There's no shame in this. The thruster exists because it works.

Start with: twins only. Learn what they feel like without the training wheel. Then add the trailer and feel what changes. You can't understand the tradeoff until you've surfed both.

We stock twin fins and trailers from True Ames in multiple templates. Come by the shop and we'll match the setup to your board.