Whether in the Baltic Sea or the south of France, the weed fin is in constant use at many of Europe's top spots between June and October. Due to the flat angle of inclination ("rake") of 40-50 degrees, seaweed is left behind. The problem is that the flatter angle also shifts the centre of effort of the fin several centimetres further back, sometimes even to behind the tail. A less free ride and poorer upwind performance are the problems that amateur surfers have to deal with during the seaweed season. It's not uncommon to wonder which is actually worse: the grass or the weed fin?
To ensure that the board with the seaweed track holder does not mutate completely into a lame cucumber, the size must be right, which depends on several factors:
- Board volume and width
- Type and quality of the weed fin
- Skiing ability or loop position
Board volume and width
Some time ago, we carried out tests with a representative of the classic stretched freeride boards, a Tabou Rocket 135 with a 44 mm standard fin, as well as a representative of the short and wide freeriders, a JP Magic Ride 119 with a then standard 40 mm track holder. Both boards were tested with different weed fins.
A 1:1 swap, e.g. swapping the Magic Ride's standard 40 mm fin for a grass fin with the same draught, makes no sense under any circumstances, because the shallow angle of inclination means that an average grass fin has 40 to 55 per cent more surface area. Because this large surface area is also further aft, the turning characteristics are reduced, the speed is noticeably reduced and the sailing resistance and sail draft increase. Switching to a smaller weed fin with a draft of 32 to 34 centimetres turned out to be ideal - the fins still provided enough lift to allow the board to run reasonably freely. If you go even shorter, for example to a grass fin with a length of only 30 centimetres, you increasingly surf on the windward edge and it is difficult to let the board fly freely over the choppy waves in wind holes and on the cross.
The Rocket 135 made it clear that the classically stretched freeride boards can also tolerate a few centimetres more draft with the weed fin - 35 to 37 centimetres draft offered the best possible compromise between planing performance, speed and turning characteristics with the grass fins.
How to determine the right length for a weed fin
You can find the right grass fin length for your board in the graphic:
One example: Your board has a width of 75 centimetres, so draw a vertical line (1). The intersections with the straight lines give you the appropriate fin lengths. If you are surfing on a classic freeride board, your board should be equipped with a fin length of between 44 and 46 centimetres as standard (2). If you are looking for a weed fin for this board, those between 34 and 38 centimetres offer the best combination of planing performance, speed and turning characteristics (4). If, on the other hand, you are surfing on one of the wide and short shapes in the "Freeride Wide" category, you can swap your 40 to 42 centimetre long standard fin (3) for a weed fin with a draft of 32 to 34 centimetres (5).
Whether the choice of weed fin is orientated towards the lower or upper edge of the recommended range depends on the type of fin and your riding ability.
Weed fins with a stem have an advantage
It was particularly exciting for us to compare "normal" weed fins with models that are offset forwards on the base, such as the Lessacher Duo Bull Weed, the MFC Weed Burner or the Unifiber Anti Weed FWD. On these models, the fin protrudes several centimetres forwards over the base and fin box and is designed to keep the centre of effort of the fin further forwards.
The decisive factor with weed fins is the surface area rather than the pure draught
Our test rides showed a clear picture - compared to the "normal" models with the same draft, the forward offset weed fins had noticeable advantages in terms of the lift generated. Both test boards ran more freely over the chop on half-wind and upwind courses, it was possible to keep the pressure on the fin longer even in wind holes and thus run upwind better overall. Overall, these models only had minor disadvantages when it came to the feeling of speed on a downwind course - a little more drag was noticeable here, which is probably a result of the wider fin bases. If you opt for one of the forward offset models, you get more planing performance for the same length, or you can choose fins that are one to two centimetres shorter for the same performance, which can be an advantage for extreme shallow water areas. In our example, you can then orientate yourself towards the lower end of the recommended range (34/32).
Influence of driving skills on a weed fin
Riding ability and strap setup also have an influence on how big the weed fin should be: We simulated both types of rider during our tests: On one side of our test boards the straps were mounted in a climber-friendly inside position, on the other side we chose a far outside position for heating. The differences were noticeable here too: standing further out on the edge automatically increases the pressure on the upwind edge due to a larger body lever, the board no longer flies freely and sticks to the water with the upwind edge.
The bottom line here is that riders who usually surf their board with three straps and prefer relaxed uncruising instead of going full throttle with maximum sails should orientate themselves towards the lower end of the recommendation range in our graphic. Those who like to ride at top speed and with the straps mounted far out should orientate themselves towards the upper end of the recommended range.
Freeride Classic and Freeride Wide - that's what it's all about:
- Freeride Classic: The classic freeride boards are characterised by a slightly more elongated outline - narrower in the middle section, longer overall and with larger fin spacing on average.
- Freeride Wide: This shape concept has increasingly found new fans in recent years - with the same volume, these boards are five to ten (!) centimetres wider in the middle area than the classic shapes, thinner overall, but narrower in the tail area and equipped with shorter standard fins.
