A GUIDE TO WINDSURFING FIN TYPES
Glossary - Fin Terms and Definitions Explained
Lift - Lift is the equivalent of power a fin is able to generate given the speed and direction of your board. More board speed and more fin angle generates more power. The moment you ask too much power from your fin is the moment you will 'spin-out'. E.g. at low speeds don’t push your board tail too hard!
Length - The length of a fin is measured from the bottom of your board to the tip end. Normally the length of a fin is the only figure used to discuss suitability for a certain type of board and sail. However keep in mind that most mentioned parameters below will also influence the fin behaviour.
Foil – the wing-like shape of the fin front-to-back (like a plane’s wing). From a foil the place of the widest point and the ratio of the width over the thickness are the most important parameters. The widest point further forward and larger ratio’s are most suitable for free ride sailing.
Plan shape – the fin outline. E.g., long, upright and narrow - or swept back and curved like dolphin fin. Fins with a little curvature are reccomended for free-ride use.
Area – the surface area of a fin. More area generates more lift.
Trailing edge – the aft edge nearest the board’s tail. Always quite sharp for a clean, efficient release.
Leading edge – the edge facing the boards nose and direction of travel. The edge should be nicely rounded off for free-ride use.
Flex – sideways movement of the fin under load.
Twist – side-to-side vertical plane movement in the fin’s construction. Both flex and twist can vary considerably pending on fin material and construction. For high performance [race] fins flex and twist are critical parameters. For free-ride fins some twist and flex will add to easier riding.
Rake – the degree of angle that the fin slopes backwards. Traditionally more rake has been associated with shorter fins and more maneuverability in waves and/or higher wind and more upright, deeper fins with more lift and power in lighter air. These are not hard-and-fast rules and there are exceptions.
Windsurfing Fin Box Types
Power Box – a strong head with a single bolt tightened from the deck of the board. Can handle forces from recreational fins of up to around 50-cm. depth.
Slot Box – lightweight surfing-style box with screws recessed into the underside of the hull securing fins at a diagonal angle popular on wave boards/multi-fin boards. Allows fin to partially pop out of the box in the event of grounding on rocks etc. while still giving a good chance of that fin being retrieved/still attached to the board. Popular on modern wave, freestyle and freestyle/wave boards sailed with shorter fins in shallower water. Usable length up to around 19 cm.
Tuttle Box – the standard method for performance fins on slalom/race/freerace boards to be secured. Two screws – front (fore) and back (aft) - are tightened from from the deck. Standard for fins of up to around 45-cm. deep.
Deep Tuttle Box – a similar head shape to Tuttle but with longer screws to facilitate the thicker deck and higher forces of longer fins as used on many much wider, ticker, higher-volume boards - such as light-wind slalom and Formula racing models. Accommodates fins from 45-cm. up to 70-cm depth.
Fin Construction and Material Types
Glassfiber / Vinylester - offers good durability and knock resistance at a decent price. Easy to repair.
G10 – usually a CNC machined block of resin sculpted into a hard-wearing and fairly high performance shape. G10 is easy to repair and delivers a good balance between price and performance – although it can be a little heavy, especially in larger sizes 45-cm. plus.
G10’s nature is also forgiving, so the levels of twist and flex help when overpowered and deliver good control, while speed freaks and experienced racers might find the slightly flexy nature a little ‘soggy’ and inefficient for their needs.
Carbon – the ultimate for stiffness and light weight performance, but with high price tags to match. Carbon delivers awesome lift and the lower levels of flex/twist that racers crave.
Not all carbon fins are hard to control though and many can be easy to sail - but are more sensitive to knocks.
Less experienced riders can experiment using slightly smaller carbon fins with performance equipment to get used to the added lift and ‘flight’ over swells and chop and then work their way up to larger sizes.
Often a smaller carbon fin can be as powerful as or deliver even more lift than a larger, equivalent shape G10 fin.
Shallow-Water Windsurfing and Weed Fins
Read more about anti-weed and low-water solutions.
How to Match Fin and Board
Most modern boards come with a suitable fin that’s had a lot of testing to make sure it will match that board and the type of sailing it’s designed to do. So, when replacing those fins, try and keep the original plan shape and size in mind. If you struggle with the supplied fin a board it can be because of the conditions or the sail you’re using on it. That said, many board brands supply a fin at the higher end or even slightly larger than the 'ideal' so as to prevent negative feedback on low-end/early planing or upwind performance from the more critical magazine testers, or customers with limited technique.
Here’s some examples of how to deal with certain fin behaviors during a session:
(Advanced wave, freeride or slalom sailors will have their own expertise to know when to change fins for purpose. These pointers are intended for intermediate riders in planing conditions.)
Spinning out too much – you may be either a fin smaller than the recommended size for your chosen board – or need to change down in sail size.
Can’t point downwind – you maybe too overpowered or have a fin that is too upright to feel comfortable.
Difficulty gybing – you may have a fin that is either too deep and/or too upright in shape. Experiment with smaller and more swept-back models to find extra comfort.
Difficulty planing – if you feel enough power in your sail but cannot plane, maybe the fin is too small for the day’s conditions – such as with strong sideshore currents.
Cannot point upwind – if the wind is at the lighter end of the scale your fin may be too small and require extra depth to allow you to head into the wind more efficiently.
Feel too much lift – if you do not have or cannot change to a smaller fin easily, this may be countered quickly in the water by either moving your mast-foot further forward and/or lowering your boom. Taking power out of your sail with extra downhaul can also help.) If those do not work, change down a sail size.
Fin Size Calculation
As mentioned it’s best to stick with the recommended size, shape and material of fin that your board was supplied with new. (Racing boards are supplied without as advanced riders like to choose their own favorites and experiment and switch fins frequently.)
One rule of thumb for single-fin freeride/freerace and even some freestyle-wave boards that can be an approximate guide is to halve the width of the board and/or ‘half’ the sail area. (This ‘scale’ only really applies to sails from 7.8 or below to 5.8 on boards down to approx.. 60-cm. wide.)
40-cm. fin on an 80-cm.-wide hull and/or ‘half’ the sail area - so a 7.8 sail is considered as ‘78’, divided by 2 = 39 cm. to get your ‘ballpark’ 39-40 cm fin estimation.
80-wide board (80/2=40) with a 8.4 (84/2=42) pick 40-42-cm.
80-wide board (80/2=40) with a 7.8 (78/2=39) pick 39-40-cm.
65-wide board (64/2=32) with a 7.2 (72/2=36) pick 32-36-cm.
65-wide board (64/2=32) with a 6.0 (60/2=30) pick 30-32-cm.
58-wide board (58/2=29) with a 5.4 (54/2=27) pick 27-29-cm.
All of the above can be adjusted according to ability, sailor weight and water state and you can confidently '+ 2' most of these, especially in the larger board widths and sail sizes for freeride equipment and '- 2' for wave/freewave sailing.
Specialist disciplines such as freestyle, racing, speed and wave-sailing require different, dedicated considerations and are much more a subject of preference based on experience.
If you have a ‘quiver’ of fins for each board, try not to have the sizes too close or far apart. So for freeride sailing as an example, 4-10-cm. gaps are about the minimum and maximum gaps respectively.
Here's a chart outlining our fins' features and benefits to help you pick the right one for you. For more information on selecting windsurfing equipment for your individual needs, please visit our Knowledge Section.