Do fins actually make a difference? Same board, different fins

Updated 2026-09-19

Yes. The same board, unchanged, surfed differently depending on which fins were in it, in every test run across a thruster, a quad and several twin fins. The difference was not subtle: boards described as squirrely, stiff or benign with one fin set felt controlled, fast or lively with another.

Measuring a thruster and a quad toward a twin feel

Fin box position, not the board itself, decides whether a thruster or quad can be made to feel like a twin. Measuring from the back of the fin to the back of the board on a standard thruster with upright twin fins fitted gave about 10 7/8 inches, against about 9 3/4 inches on a true Mark Richards-style twin fin board, a difference of about an inch. Swapping the upright twin fins for an NVS Apex Ono keel, a hybrid keel that sits further back in the box than an upright, brought that measurement to 10 3/8 inches on the same thruster. Switching again to the Ono convertible, a version of the same fin built to sit even further back, brought it to 9 1/2 inches, matching the Mark Richards board almost exactly, on the identical thruster with nothing else changed.

Surfed in one to two foot waves, that thruster with the convertible keel felt stable and responsive, close to a genuine twin fin feel, purely from the fin change. The same convertible keel improved the feel of several quads too: a small-wave quad specialist measured at 9 1/4 inches back and 13 1/2 inches apart surfed particularly well with the change, including one of the best waves caught in a cyclone swell. A quad with fins measured 10 inches back and 12 1/4 inches apart, close together by quad standards, worked so well with the convertible keel that it handled anything up to chest to head high as a twin, matching the rounded tail pin tested with the same fin at 9 1/2 inches back.

Not every board responded the same way. A very wide volcanic groveler board, with the same convertible keel measuring 8 7/8 inches back but 14 1/2 inches apart between the fins, felt too loose on takeoff and through turns; the width between the fin boxes was too much for that fin's surface area to control, and a larger keel fin was recommended for that board instead if run as a twin at all. A widowmaker setup, with fin boxes measuring almost 13 inches from the tail, was judged too far forward to work as a twin before it was even tried, since a board balanced that precisely was not worth disturbing.

Same keel, two versions, three boards

Testing two versions of the same hybrid keel side by side across three twin fin boards produced three different verdicts from the identical pair of fins. On a six-foot fish with thin, knifey rails and small tail channels, whose own shaper had recommended upright fins, both the older and newer version of the keel gripped too hard and felt clumsy, with no meaningful difference noticed between the two versions. On a heavier six-foot fish with thicker rails and no channels, the older version worked with no complaints, while the newer version, lighter and with more curve built into the tail of the fin, was noticeably livelier and just as controlled even in chest-high waves. On an eight-foot-two diamond-tail board with channels, the newer version alone was tested and felt fast and alive from the first wave, clocking close to 42 km/h on the day it was tested, on what was already logged as the fastest board in the fleet.

What decides the outcome

Three factors kept showing up across these tests: how far forward or back the fin sits in the box, how much rake and curve is built into the fin itself, and how well the fin's surface area matches the width between the boxes. A fin that sits further back can shift a thruster or quad toward a twin fin feel more than swapping fin shape alone. A board with unusually thin rails or aggressive channels can override what a similar-looking board without those features would do with the same fin. And a fin with too little area for how far apart the boxes sit will feel loose no matter how well it performs on a narrower board.

Questions people ask

Can changing fins really transform a board that badly?

Yes, measured directly: the same thruster went from needing a trailer fin to feel stable with upright twin fins, to surfing like a genuine twin with nothing changed but the fin, once a keel set further back in the box was fitted.

Does a newer version of a fin always surf better than the old one?

Not automatically. Two versions of the same keel felt identical on a board that did not suit either of them, and only showed a real difference on boards that did suit that fin family in the first place.

How do I know if my board's fin boxes are too far forward for a twin conversion?

As a working guide from these tests, once the back-of-fin-to-back-of-board measurement passes about 10 to 11 inches, results get inconsistent; boards measured near 13 inches were not worth trying.

Is a bigger fin always a safer choice if I am unsure?

No. A board with wide-set fin boxes needs a bigger keel to avoid feeling loose, but a narrower board with the same big fin can end up over-gripped and clumsy, as happened on a thin-railed, channeled fish tested with two different keel sizes.

For the config-specific detail, see twin fin fins, quad fin sets and keels or upright twin fins. The two videos behind this page are Can You Turn A Thruster Or Quad Into A Twin Fin? and NEW Machado Too Fish Keels: Do They Really Work With Any Board?. Full board specs sit in the current quiver and sold list.