Freeride, wave, freestyle: How to find the right weed fin for you

Even if it may seem absurd to those who count the Baltic Sea or the South of France among their favourite areas, seagrass is a great thing - whether as a nursery for fish and other creatures, for coastal protection or due to its ability to bind large amounts of CO2. So there are good reasons why seagrass meadows are being protected and even replanted. Seagrass grows in the Baltic Sea at depths of two to seven metres and is therefore inaccessible to fins and foils. While the roots remain in the ground for many years and give rise to new shoots, the leaves die off in late summer and come to the surface - where they sometimes drive windsurfers and foilers crazy.

• "The issue of seaweed was not taken into account for some boards" - Basti Wiepcke in an interview

At many spots, nothing works between June and November without weed fins. Special weed fins have a shallower angle of inclination ("rake") of 40 to 50 degrees, which allows the seaweed to be scraped off again. The reason why weed fins are still not particularly popular is that the flatter angle of inclination also shifts the centre of effort of the fin several centimetres further back, sometimes even behind the tail. The consequences: The board sticks more to the water, glides less freely over choppy waves and the performance when going upwind also suffers noticeably - at least when freeriding. Nevertheless, weed fins are the lesser evil, provided you use a suitable model of the right size.

The decisive factor is the area of the fin, not the length

A 1:1 exchange, for example swapping the 42 series fin of our Goya Carrera 127 test board for a grass fin with the same draught, makes no sense. Because the angle of inclination of the grass fin is flatter, it would have 45 to 55 per cent more surface area with the same length, depending on the model. Because this large surface area is also further back, the turning characteristics are reduced, the speed is noticeably reduced, and the drag and sail draft increase. Our test showed just how big the differences are. We replaced the 42 mm standard fin of our Goya Carrera 127 with a 40 mm weed fin as a test. Fuelled with the powered-up 6.9 GunRails Re-Zoom, we had to stop at just over 41 km/h in rough Baltic Sea conditions. After swapping it for a 34 weed fin, the speedometer needle hit just under 48 km/h. This example shows: In the freeride and freerace sector, the fin area is the decisive factor.

Some manufacturers try to minimise the other disadvantages of weed fins, i.e. poorer turning and upwind running, by moving the weed fin further forward on the base - a sensible measure in our test experience, which does not completely eliminate the disadvantages, but at least mitigates them.

The 20/10 rule for weed fins

But how do you know which seaweed fin length to replace the standard fin with? After all, the fin areas are not always specified. The 20/10 rule has proven to be a good guide for boards with a centre fin - these are freeride and freemove boards with a single fin, but also freewave boards with a thruster set-up. In other words, the weed fin should have ten to 20 per cent less draft than the standard fin. Whether you orientate yourself towards the lower end of the recommendation or the upper range depends primarily on the discipline, i.e. the board you are using. An example: Are you looking for weed fins to replace the small 10 mm side fin on your wave board? If you swap it 1:1 for a 10 mm weed fin, it would only have around five per cent more surface area. You can swap almost 1:1 or choose a seagrass side fin that is one centimetre, or ten per cent, shorter. If you were to replace a 42 mm standard fin on your freerider with a 42 mm weed fin, the latter would have around 50 per cent (!) more surface area. In this case, you can easily reduce the length by 20 per cent and choose a grass fin with a length of 32 to 34 centimetres. On the following pages, we will give you a size recommendation with a range of two centimetres for the freeride, wave and freestyle disciplines.

Size recommendation for freeride & freerace weed fins

The recommended length for the weed fins is a rough guide. If you weigh less than 75 kilos or surf on your freeride board with foot straps mounted on the inside, orientate yourself towards the lower end of the recommended range. If you weigh over 85 kilos, like to exert a lot of pressure on the fin and are travelling with large, powerful sails, you should ideally orientate yourself towards the upper end of the recommended range - then you will have enough counter-pressure from the fin and corresponding performance.

• Six freeride fins tested against seaweed

Size recommendation for wave weed fins

The recommended lengths for weed fins in the table are a rough guide. If you weigh less than 75 kilos and mainly surf with sails under 5.0 square metres, you can orientate yourself towards the lower end of the recommended range. Because the difference in surface area between standard and weed models is not as great in percentage terms with short wave fins as with freeride fins, you can sometimes use weed fins in the wave at almost the same length as the standard fins. However, the centre of effort of the fins shifts a little further back. While this has hardly any effect on planing characteristics, control and upwind performance, the turning characteristics of waveboards in particular are noticeably negatively affected. The radii in the bottom turn and cutback are limited and tight hooks are noticeably more difficult. In addition, the tail gains more grip, making it more difficult to let the tail break out in the cutback - the suitability for lipslides and takas is limited. For this reason, you should use the weed fins in the fin boxes. Mount about one to two centimetres further forwardto achieve comparable turning characteristics. However, if you make use of this small tuning measure, the perceived difference to standard fins is small, which is why many wave surfers simply continue to ride the weed fins even on trips to the weed-free North Sea.

• Four wave sets against seaweed in the test

Size recommendation for freestyle weed fins

If you are doing basic tricks such as Vulcan, Spock, Flaka or other slide moves, you should orientate yourself towards the upper end of the recommended range. The same applies if you weigh over 85 kilos and therefore want to do tricks with sails over five square metres. If, on the other hand, you surf at the level of double sliding moves and power moves, you can choose the lower end of the recommendation. The 20/10 rule can also be applied to freestyle boards, but for different reasons. As freestyle boards are ridden with comparatively short fins and more over the windward edge anyway, the loss of performance when switching to a weed fin in terms of top speed, levelling and planing is less than in freeriding, for example. Rather, the focus here is on the fact that the boards slide less easily due to the flatter angle of inclination of the weed fins. Germany's top freestyler Niclas Nebelung, who is involved in fin development at Maui Ultra Fins, explains: "Due to the larger surface area that weed fins naturally have, you have to make the weed fins a little smaller, because otherwise the sliding is too limited. Many production boards are equipped with a 20 mm production fin, so an 18 mm weed fin is a good alternative. The Pro version is thinner and faster - but you should be a little more careful in shallow water, because the thin fin blade is also less robust in the event of stone contact."

• Freestyle fins tested against seaweed