Trailer Fins

A trailer (or center trailer) sits in the tail's center fin box, behind the side fins. It stabilizes the tail, adds hold through turns, and gives the board more directional drive. As one experienced Swaylocks builder puts it: "how much different the board feels moving the trailer fin fore or aft 1/4 inch or less" — the placement sensitivity is dramatic.

Trailer size changes everything. Nubsters (1"–1.5") add just enough resistance to prevent full tail slide — a safety net. Small trailers (~40% of twin height) maintain twin character with some hold. Medium trailers (~50%) start to feel like a "twin-plus." Large trailers (60%+) shift toward thruster territory — "you get lots of hold and vertical ability, but you lose the twin character."

The core tradeoff is honest: you're trading speed and freedom for control and hold. Wider-based trailers add drive; narrower trailers add pivot. Start with something in the 4"–5" range, and have a few sizes on hand — go bigger and rakier as the waves get more powerful.