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All about SUP fins | McConks SUP

Focus on iSUP fins

Most people know that fins are essential on surfboards and paddleboards, but most people don’t really know why.  Everyone has a vague understanding that they help SUP go in a straight line and give control when surfing, but scratch much deeper, and most don’t understand how fins work.  So, we thought we’d put this blog together to help.

First up, there’s some jargon you need to get your head around, about the fin itself, and about how the fin is positioned on the board.

Base: The base is the top section of the fin when your board is in the water, so closest to the board when installed. It is nearly always the widest part of the fin and it’s this section in particular that helps to stabilize the board and affects tracking.

Tip: The tip is the other end of the fin that’s furthest away from your board. The tip also affects tracking and speed.

Leading Edge: The leading edge is the front part of the fin the bit that hits the water first, and the angle is the called rake or sweep. The leading edge affects how the board turns and pivots and also how fast it releases water.

Trailing Edge: The trailing edge is the back of the fin and it affects how easily, or not, a board turns and pivots. Trailing edges aid in releasing water to greater or lesser extent, which affects speed.

Cant: Cant refers to the angle of the fin in relation to the bottom of the board. Fins that point straight up have no cant.  These are faster than fins where the tips point outwards towards the rail of the board, which are said to have cant. Fins with cant are more responsive when turning, but create more drag.

Flex: The stiffness or flex of a fin has a big impact on handling.  Stiffer fins give more stability, and more bite and control, but can make turns more difficult.  But stiff fins are also more brittle and more likely to be damaged on reefs or in rocky rivers.  Flexi fins make turning a little easier, and are more resistant to the knocks and snags you get on reefs or in shallow rivers.

Rake:  When you’re looking at the arc of the fin and how far back it tilts or sweeps from the front, you’re looking at the fin rake. The greater the rake, the slower the turn, the lower the rake, the more pivot around the fin. For short boards, less rake is great for junkier days, and more rake is good for walls.  For longer SUP we should be looking at a more relaxed rake for more drawn out turns.

The rake also allows the fin to release any weeds that may get hung up on it.

Toe: Toe is the angle at which the fins point relative to the centreline of the board.  Typically the side fins of a 2+1 or thruster set up point towards the nose of the board (known as toe-in). The greater the toe, the greater the grip.

Foil:  The foil is the curvature of the fins around the vertical.  Just as a wing uses its foil to create lift, so does the fin.  A cheap fin will have no foil, and will just have a sharp front edge and a parallel sides.  If the fin gets fatter towards the middle of the fin and then thinner at the back, then it has a foil.

Drag:  Drag is what slows you down and the force that decreases your speed.  The bigger the rake, the bigger the cant,  the bigger the surface area, the bigger the foil, the bigger the drag.  And dependent upon your paddling environment, drag can be a good or a bad thing.  When racing or touring, you want as little drag as possible slowing the board down.  When surfing it’s the drag that gives the bite that helps you turn.

The basics

So if you’ve ever lost a fin (and who hasn’t?), you’ll be aware that without your fin your board pivots from side to side and it’s extremely, difficult to paddle in a straight line. The reason for this is because the fin acts to prevent the tail of the board from slipping sideways as you put pressure on either side of the board as you go through your stroke. Without fins, it is theoretically possible to counter slipping sideways by controlling the trim of the board as you paddle, but this is an expert skill that most can’t master.

The design of the fin also affects speed, stability and how easily you can turn your board.

Some boards, especially inflatable boards, come with fixed fins.  These have the advantage of being simple to use, and cannot be lost.  However, by being fixed in position, if they get damaged, they’re next to impossible to replace, and you can’t change the shape, location or size of the fins to improve your ride. So we think removable, adjustable fins are a better bet.

There are many different kinds of fin box (the bit that the fins slide into) on the market, but there are three standard types.  Ideally, you want to choose a box that is standard, and that has stood the test of time in the surf world.  That way there’s a wide range of fins available from surf shops and online, and the box is robust and reliable having stood the test of time.  The three well know and reliable box types are

US box.  These have been used on longboards and windsurf boards for years.  Very reliable, and US box fins are very widely available.

FCS box.  FCS fins are the mainstay of surf boards.  Again, widely available and very reliable.  A recent addition to the FCS range is click fit fins that click into a standards FCS box.

Futures fins box.  Futures are the latest darlings of the surf world.  Again, widely available and very reliable.

There are other boxes available, many of which have a lower profile and a slide in key to keep the fins in place.  These have had issues with reliability, and the fins are not widely available if lost.  There is only a very narrow range of cheap fins available for these boxes.

So how do you decide what size fin you need?

  • If your priority is going in a straight line above all else, then you want a large surface area fin with a long base and long leading edge. This will help your board to track better (go straighter) and will also help stabilize the board making it feel less tippy side-to-side and make it more predictable in choppy water and swell. However, a larger fin can feel sluggish because it will not cut through the water as easily. It will also take more effort to turn and pivot the board since there will be more resistance to the flow of water around the fin. A strong paddler, or someone who likes to use a stiff paddle with a larger blade, may benefit from a fin that has a wider base and reaches deeper into the water. This type of fin will offer good resistance to t.he extra force exacted by the paddler, which will result in the board tracking better.
  • If you want more responsiveness and speed, then you should be looking at smaller surface area fins. However, a smaller fin will not track as well as a larger fin and it will be harder maintain stability in choppy water. A person who has a more fluid and slower stroke will benefit from a smaller fin as it will compensate for the lack of force by allowing the board to move more quickly through the water.
  • Paddleboard fins that are used for surf-specific SUPs will have a different shape than the fins used on touring, racing and all-around paddleboards. More on this later.

If you are looking to get more performance out of your board, then experimenting with different fins is good place to start. You can have several fins that you use for different applications, or you can find one that does a couple of things well, but may not be the best for any one situation. Either way, there are plenty of options to choose from and it will never hurt to try something new.

Fin arrangements

2+1

The most common removable 3 fin setup on a SUP is 2 + 1: i.e. two equally sized front fins (called sidebites) a few inches in front of, and either side of a larger rear fin.  For maximum flexibility, the front fins should be an FCS box or a Futures Fins box (the most common box types, allowing you to buy additional fins and different shape fins easily and cheaply). The purpose of the sidebites is to channel water through the configuration thereby compressing it and speeding up the flow. This gives the board more power which is essential for riding waves where you need speed to power through your bottom turn and hold the rail in tight against the face of the wave as you move across it. On the other hand, extra fins create more drag in the water, which will decrease your speed if you are not travelling on a wave, which is supplying you with power.

Though first designed for surfing on a SUP, the 3-fin setup is also good for tracking on flat water.   The twin front fins gives a little more protection against lateral drift (sliding slideways in crosswinds) than a single fin, and provide a little more bite in downwind runs.

To tweak this set up, you can reduce the size of the centre fin to something approaching a thruster size to create a traditional 3 fin setup. And the position of the rear fin can be tweaked. Back for better tracking and forward for more slide!

Twin

You can convert the 2+1 setup to a 2-fin setup just by removing the center fin. This leaves you with the two side fins, or “side bites” and really loosens up the tail and makes things lively when in surf.  This is also a great option for river running where the centre fin keeps scraping along the river bed, or catching and trying to throw you off!

Historically, many surfers moved from traditional single fins to two large fin setups when long boards started to become shorter. This, to some extent, paved the way for the aggressive hack and slash now common in surfing, and set up more progressive surfing such as 360’s.  Twin fins aren’t really the flavour of the month in surfing circles,  and a twin set up is very rarely seen on a SUP. However, sometimes it can be great when the surf is small to take out your rear fin and have some fun trying out 360’s in the mush.

Singlefin:

In surf, a single fin converts your SUP to a longboard setup ideal for long drawn out power turns or noseriding. Large single fins create a definite pivot point for your turn and tend to be preferred by exponents of drawing sweeping lines, and looking stylish on a board.

And outside of the surf and whitewater environments, singlefin is your most likely setup.   If you want speed and to paddle in a straight line, and you want stability, a large single fin is your partner in crime. Look for a fin that is between 8-10 inches in size, and make sure you put it as far back as you can in the centre box.

Fin placement can drastically affect the manoeuvrability of your surfSUP, the tracking of your race SUP and the stability of your flat water SUP. Although these are suggestions we recommend that you test the different placements for your own unique position as it really varies by board and rider.

Fin Forward: Placing your fin forward will put less pressure on the tail of the board which creates more manoeuvrability and a quicker turning radius. If you have a three fin set up (thruster) then having the middle fin placed forward will channel the water in a concentrated area and could potentially slow the board down while surfing. That said, if you are looking for less hold and a shorter turning radius then moving the center fin closer to the nose is the answer. 

Fin Far Back: Positioning the fin towards the back of the board will result in more stability, this is because the fin is rigid in its line. More importantly, the board will track better compared to the other placements because it gives more restraint to the tail.

The Happy Medium: The happy medium is always a good default position, it is a balance between control and stability. This placement is the most widely used because of its versatility between turning, tracking and steadiness. If you are surfing and using a thruster then you want the centre fin about 2 inches behind the side fins which allows enough spacing for water to flow around the fins.

The more flexible race fins do not offer the downwind performance benefits of the stiff ones, but you do not have to worry about face-planting if you hit a log or rock.

With the tail positioning mentioned above, you are all set for touring, racing or flat water paddling because the fin position makes the board track better.

For something different, slide that fin forward and position it at the nose of the box. This makes the board easier to turn, which is perfect for whitewater conditions and surfing.

As you shop, you will notice that some of these large fins feature leading edges that are sharper or serrated, which are designed to cut their way through weeds and kelp. Depending on where you do your paddleboarding, this could be a great feature for you.  Our carbon fin is a great example of a race fin with a weed shedding profile.

Zero: Recent proponents suggest that surfing was set back by the addition of fins and the purest form of surfing is still fin-free. With SUP however one has to consider that in effect a paddle can be used as a fin to steer the board as well. Save this one for those small mushy days and have a good laugh. Good luck with your tracking when paddling out!

So, if you haven’t done it yet, have a play around with your fins in the surf this year. Try out different fin set ups and fin sizes in different conditions. And get an understanding of how your fins change the feel and performance of your SUP. It’s one of those things that you just don’t know until you try. (And it will give you another excuse to go out for another cheeky session!)

5 thoughts on “All about SUP fins | McConks SUP

  1. Love this article Andy, great info and I totally agree with the lovely 2+1 setup as a great way to explore fins and fin setup. Quad fins? Fancy me a retro 70’s vibe! Next article on tail shape please just to fit in withmy retro vibe! Maybe a fish tail or wing tail next? Or how about a rails article! You know you want to…….

  2. Great article! This is the most info about fins and in one place that I’ve read to date. Thank you! I agree when you state that most people have only a vague idea about the differences in fins and why we should carefully choose them for our individual needs—all who SUP should read this!

  3. Great Article! thanks Andy!!i agree with you, fins are essential and can change your surfstyle! I ride my paddle board in single for cruising, trusther for waveriding or twin for staticwave. And the board is like a new one at each ride 😉

  4. This excellent article sums up exactly the conclusion I was coming to – that the larger the fin the better the tracking. I SUP flatwater rivers and lakes in the UK, using a 12’6” x 30” hard Swedish Yster nose displacement board. A single fin is all that’s used for this beautiful board.

    I pull the paddle towards myself, to counteract the boards tendency to turn away from my paddle side, and can paddle on one side for as long as I like. The line of the paddle stroke has to be in front of the fin which acts as a pivot, as you said. The smaller the fin, the larger the angle I have to pull my paddle. But this results in my board travelling partially sideways, at an angle to my direction of travel. This is because the displacement nose has significant resistance to sideways movement. The fin has to provide much larger resistance to sideways movement than the nose, if the fin is to stay in line with the nose.

    So, I increased my original dolphin fin from 45 to 75 sq. inches with a homemade extension of plastic sheet. Much better tracking, but this shape still picks up river weeds. So I bought the 10” straight-line tracking fin with an area of 60 sq. inches, and a very shallow rake that doesn’t pick up weeds. So far so good, but not quite as good as 75 sq. inches. Believe it or not, I’m now extended it to 85 sq. inches, and the tracking is superb. Obviously you wouldn’t need to do this with a planing hull, like my old board – the nose just slips around where I want. And of course, a narrow 14’ board will be better than my 12’6” one.

    1. Interesting insights Brian!

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