You own four fins. Three of them came in boards, chosen by whoever was assembling that model the month it was built, and the fourth you bought in a hurry after a session that went badly. You have never once put two of them in the same board on the same day.

Which means what you know is how four boards felt on four days in four different swells — real information, but not information about the fins, and it cannot be turned into that afterwards.

The problem is not the number of fins. It is that four points arrived by circumstance rather than by choice, so there is no particular reason any two of them are far enough apart to tell apart.

Three fins chosen deliberately cover more ground than six chosen by brand or by looks. This post ends by telling you to stop at three.

A quiver is a covering problem

Think of every fin you could buy as a point in a space, with axes for the things that change how a fin behaves — how much of it there is, how it is distributed, how it is foiled.

Two fins close together in that space feel the same in the water. Two far apart do not. A quiver is a few points spread out enough that anything you might want is near one of them.

There are two ways a quiver ends up clustered instead. Buying by brand stacks your points on top of each other: the Hobie Fish, the Tyler Warren Modern Keel and the Beatty Fish are three well-reviewed keels from three respected makers, and they sit inside 1.02 in² of one another. No session will separate them.

Buying by escalation does it more slowly — a slightly bigger fin every time you slide out, until you own a tight cluster at one end of one axis and nothing anywhere else.

Buying by coverage asks a different question about each fin: not "is this good," but "what does this reach that the ones I own do not." A fin that answers that badly adds little to the quiver even if it is excellent.

Two axes you can check, three you cannot

Fins vary on five properties, and only two of them come with numbers you can compare.

Area is how much fin there is. It is the gross control — more holds harder and drives harder, less releases earlier and accelerates in weaker water.

Base relative to depth is where that area sits. A wide base low down is drive; depth is hold when the tail goes light. Two fins of the same area with different proportions are not the same fin.

Rake, foil and flex are the other three. They change how a fin behaves as much as the first two do, and there is no figure published for any of them across a whole collection — so nobody, including us, can show you a quiver spread across them. What you get instead is the maker's description in words.

Which means the arithmetic below runs on area, in the collections that publish one, and stops where the numbers stop. On single fins you order by depth, the least informative of the three dimensions, so the same logic holds there and cannot be shown.

What the second fin buys, and the third, and the fourth

Read what follows as the shape of the curve, not a measurement of your quiver. Coverage can be computed only where areas are published, and twins are the deepest of those collections.

Single fins publish no area at all, so the same logic holds there and cannot be shown. And this is coverage of the catalog, not of conditions — the catalog is not a map of the ocean.

With that said, the arithmetic is ours, not True Ames'. For any set of fins you own, measure how far each template sits from the nearest fin you own, and average it — that average is the gap between what you own and what exists. Then find the best possible set of one fin, of two, of three.

Fins owned Best mean gap What that fin bought you
1 2.58 in² —
2 1.48 in² −1.11 in²
3 0.97 in² −0.51 in²
4 0.73 in² −0.24 in²
5 0.51 in² −0.22 in²
6 0.38 in² −0.13 in²

The second fin closes 1.11 in². The third closes 0.51. Then it flattens and stays flat: 0.24, 0.22, 0.13. The whole published twin range is 18.23 in² wide, so each fin after the third is buying you about 1% of the space — for $113.50, which is what a twin set costs on this page. Nobody has ever read 1% of the range in the water.

Every row in that table is the best set of its size, which is why six beats three in it. Run the same arithmetic on a quiver somebody actually ends up with and the order inverts:

Quiver Mean gap
Three chosen well 0.97 in²
One chosen well 2.58 in²
Three well-reviewed keels — 26.16, 25.25, 25.14 3.11 in²
The six biggest keels — 25.81 through 32.48 3.28 in²

Six fins spread along one axis cover less ground than three chosen across the range, by a factor of more than three.

That is the title of this post, and it is not a close thing: 29% of the six-fin sets you could assemble from the published twin catalog are worse than the best possible three. Buy only keels and the best six you can reach still falls short of the best three from the whole range.

That is the case for stopping at three, and also for choosing three properly. Two chosen well get almost everything: the pair below lands at a mean gap of 1.50 in² against a theoretical best of 1.48, the closest any pair whose areas are published can get. You cannot meaningfully beat that with two, so the third fin's job is not to subdivide the same axis. It is to add an axis you did not have.

Three quivers

Three fins each, with a total at prices taken on 7 August 2026. Every fin gets one line on what it covers that the other two do not. If you cannot say that line, the fin is not the one yet.

The one-board longboarder — $296.75

One log, one box, three fins that make it three boards.

Heritage at 9.75" — $103.50. True Ames' own summary: "full of area and minimal rake", "built for noseriders", and a fin that "provides stability and enables maximum tip time." Far end of the area axis, near end of the rake axis — True Ames' description restated on this post's axes, not a measurement. Neither of the other two fins in this quiver is described that way. It is the wrong fin the moment the wave has real push behind it; True Ames says knee to chest high and means it.

Farberow Flex at 9.5" — $103.50. The California Classic template, foiled out "to give it a powerful and performance-oriented level of flex." Same rough size as the Heritage, opposite behavior — it bends and returns through a turn instead of planting. It covers the one axis you can only buy by template.

Cutaway at 7.5" — $89.75. Two inches shorter with a bite out of the trailing edge: a long step down the area axis, and a different board in small surf. True Ames calls 7", 7.5" and 8" "the most popular sizes for a 2+1 setup" and adds "for more radical fin experimentation, try the smaller sizes." As a straight single fin in a log this is the experiment, and it will slide in anything with size. That is what it is for.

None of the three publishes an area or a base; the depth on the box is all there is. That is the whole single-fin category, not this shop being cagey, and it means this quiver cannot borrow the arithmetic above — three is right here because the three fins are separated by argument, not because a number says so. For one template against another, the Greenough guide argues it properly.

The mid-length and shortboard rider — $294.25

Two boards, and the cheapest fin in this quiver is the one that does the most.

Greenough 4-A at 8" — $92.00. The size our mid-length guide gives for a 7'4"–7'10" egg. It covers the single-fin board entirely; nothing else in this quiver fits that box.

Channel Islands Tri Medium, Futures solid fiberglass — $128.50. It covers the shortboard in average surf and it is the only three-fin set in this quiver. Choosing between its three sizes is a longer argument than this post can carry.

If your shortboard takes FCS, the Medium in solid fiberglass is not an option — the only FCS-compatible CI Tri True Ames makes in solid fiberglass is the Large — so buy the True Ames Thruster at $128.50, which publishes the same per-fin area.

6-4 Rear Quad in Futures at $73.75, or the same pair in FCS at $73.75. Pull the center fin, keep the two fronts, drop these into the rear boxes and the shortboard is a quad — roughly 17% more fin in total, and all of the change is area moved off the centerline and out onto the rails.

A different board for $73.75, and nothing else here overlaps it, because nothing else changes the configuration at all. It needs five boxes, which is the board's doing.

If your shortboard has three and your mid-length has side-bite boxes, buy the mid-length a pair of 3.25 side bites in the system that board takes — Futures at $73.75, or FCS at $73.75 — so the quiver still totals $294.25, and read this first.

The twin and alternative rider — $262.00

The one quiver where every number is published, so this is where you can see coverage working.

Hobie Fish keel, $113.50. A base half again wider than the fin is deep, so the area lies along the board rather than reaching down. True Ames calls it "our most popular keel fin set" and points it at "down-the-line surfing." It owns the high-area, wide-base corner, and nothing else here goes near it. Not the fin for a board you want to turn tightly.

TA Twin, $113.50. 5.55" deep on a narrower base — a fifth less area than the keel, arranged the opposite way round. True Ames' own summary: "full area, upright profile, moderate rake, flat inside foil."

It reaches down into the water instead of along the board. Together, these two sit within 0.02 in² of the best coverage any pair in the published twin catalog can achieve.

Wayne Rich Trailer in FCS — $35.00. The point is not area — it is that neither of the other two can give you a third fin.

Behind the TA Twin it stands at 46.5% of the twin's height: above the "about 40%" our trailer post gives as the starting point for a trailer that "adds hold without dramatically changing the character," and well short of the "60%+" it says "starts to feel like a thruster with funny front fins." The Futures version is $39.00, taking the quiver to $266.00. Your board needs a trailer box, which is the board's business and not the fin's.

The honest weakness here: the keel and the upright twin go in the same boxes, and your board will still prefer one of them. Box position and toe are the shaper's decisions and no fin purchase changes them.

One board, one day, one variable

All of it depends on how you test. A comparison is only readable if everything else holds still: same board, same session, same sandbar, same tide window. Surf twenty minutes on the first fin, come in, change it, go back out. Not next weekend — the swell will have changed, and a week apart it is the swell you end up rating rather than the fin.

Change one thing. Change the fin and the board together and the session tells you nothing you can use — which is why a small quiver ridden carefully teaches you more than a large one ridden at random.

If you are only buying one fin

A five-box shortboard with thruster fins already in it. Buy the 6-4 Rear Quad in Futures at $73.75 or FCS at $73.75, whichever your board takes. It is the cheapest fin in the shortboard quiver and the only fin on this page that turns a thruster into a quad — a change of configuration, not of amount — and you will read it in the first three waves: the tail holds through the bottom turn where it used to break loose, because you have taken the area off the centerline and put it out on the rails.

Your one board is a log. Buy the 7.5" Cutaway at $89.75 and keep the fin that is in the board now. One session in small surf will tell you more about what your current fin does than any amount of reading, including this.

Related reading

Sources

Heights, bases and areas from True Ames product pages, retrieved 7 August 2026, via https://www.trueames.com/products.json?limit=250 (pages 1–2, 466 products) and the single-fins, twin-fins, quad-fins and side-bites collections. The rake figure from https://www.trueames.com/products/greenough-power-glide. Prices from our own catalog the same day. Set totals, base-to-depth ratios, percentages and the covering arithmetic are computed from those published areas and are not published by anyone. Full working, and the data errors found on True Ames' pages while checking, on file.