TRIBAL WEED FINS
Seaweed and algae are common in many good windsurfing locations - often catching on traditional upright fins and causing a sudden drop in performance. When debris is stuck to the fin, it effectively changes its profile and significantly reduces performance - reducing lift, increasing drag, and creating opportunities for air to leak down to the fin from the surface, causing spinout.
TRIBAL has developed specialised fins that are designed to avoid, or significantly reduce the chance of catching any seaweed, reducing the effects of seaweed if it is caught and making it easier to shed without getting off the board.
One thing all weed fins have in common is increased rake angle of the leading edge to allow the weed to slide down and off the tip. The greater the angle, the greater the force that pulls the weed towards the tip. It does come at a cost - of reduced lift for a given angle, and also the balance point shifts backward (due to the lifting surface being further back). The longer the fin, the worse the imbalance becomes.
Common Weed fin terminology
Length/Depth - this is the vertical depth of the fin. Blade length has little direct effect on the apparent size of the fin since the rake negates the effect of increased surface area. It is not comparable to measure the fin from base to tip along the leading or thickest section and compare it to an upright fin. This is because the balance of heel side load, to board roll (to balance heel weight), is dependent on the vertical depth of the fin and not on the angled blade length or surface area. It is the reason for the rule-of-thumb that approximates fin depth to board tail width.
Rake - the rake angle is usually specified as the angle between an imaginary vertical line, perpendicular to the board’s bottom surface and the leading edge of the fin where it connects to the fin “head” or “base”. Most slalom fins set this angle between 8 and 14 degrees. Weed fins 35 to 60 degrees.
The more rake, the less lift for a given fin area. This is because lift on a raked fin is determined by the velocity of water perpendicular to the leading edge. Water flowing along the leading edge to the tip creates no lift. So if we break the flow down into these perpendicular components, we can see that the spanwise flow (along the leading edge) increases as we increase rake, and consequently the chordwise flow is reduced- thus reducing lift. The result is that the fin behaves as though we are going slower. For a given force, surface area, and speed, the increasing rake angle results in higher fin angle of attack- ie it feels like its going more sideways. This is normal and expected. One benefit of extreme rake is that the flow becomes turbulent much earlier, and is thus more able to stick to the surface- especially when the profile is engineered to encourage this. The result is the ability to hold very high angles of attack without spinout.
Additionally for longer fins, the lift is centred further back as the rake angle is increased. This will upset the balance of the back foot position, with the ideal position for the foot ending up right at the back of the board. To compensate for this, fins are often offset in the base in a forward, and even overlapping position. The longer the fin, the harder it is to compensate.
WEED SOLUTION WITH A TWIST
We have introduced a totally new concept in weed fin design. The TRIBAL line looks unconventional due to the large curvature on the blade leading edge.
The TRIBAL line solves this problem with a more upright base region, which helps to keep the centre of pressure forward, giving more of the same feeling on the water as an upright fin. Weed is accelerated down the leading edge as the curvature increases, leading to a much better matched set-up than conventional weed fins. We also used some techniques to control mechanically-induced twist, so that the fin doesn’t lose power as you load it hard and try to bend it.
WEEDSPEED VS SUPERWEED
Besides our regular WeedSpeed fins, we have added the SuperWeed to our range for special use in those areas where extreme “sticky” weed growth occurs and our regular Weed fin does not quite cut it anymore… The SuperWeed’s rake is set up at a more extreme angle than the WeedSpeed to shed weed. It does have a straighter leading edge due to the need to keep the centre of pressure as far forward as possible, whilst maintaining an increased minimum rake angle at the head.
DELTA & DELTA SYM
From the instant classic Weed Speed Series, we have developed the specialised shallow water range for our riders who are gifted with access to dead flat water afforded by shallow seaweed beds, or areas where sandbars can have shallow spots that would cause other fins to dig in and cause a crash.
SHALLOW WATER WEED CHALLENGE
We looked at the locations, and the requirements to suit this style of sailing afforded by shallow seaweed beds. The challenges include the extra drag and erosion when cutting through surface type seaweed, starting in shallow water where the fin is likely to drag along the bottom, and the extreme rake causing problems with balance and power. We engineered the fin to simultaneously consider these constraints, and the design shape is unique as a result.
OUTSTANDING LOW-END POWER & RESISTANCE TO SPIN-OUTS
The designed-for-purpose foil profiles deliver outstanding low end power and resistance to spin-out, with unmatched recovery behaviour. This means you can run a much shorter fin for the same amount of power, but with drastically reduced drag and increased confidence to push at speed. We have achieved this despite running extreme rake angles towards the tip - higher than with other brands - to give you more weed penetration capability and efficiency where it counts, with a tip shape that doesn’t dig into the ground when you have to start really shallow.
Delta VS Delta Sym
The original Delta offers the highest resilience to debris of any of the Tribal range, with extreme tip rake, thickness for both durability and stiffness, and surface area to increase usability at lower speeds (upwind, or in lulls).
The Delta Sym was developed for similar conditions, but with slightly less rake- so we could reduce the surface area and decrease drag as a result.
For locations with thick and heavy weed, where getting started is potentially an issue or leading edge drag is substantial, the Delta is the one to go for. If you are confident in starting, and going upwind with slightly less powerful fins, and the weed is not always covering the surface, the Delta Sym has the potential to hit top speeds with less drag. Both designs have been successfully tested in moderate conditions to >45kts.