In this interview:
Finn designers are sometimes real tinkering nerds. Do you also have a background in this area?
Yes, I come from a modelling background and always have to build and tinker. In the case of the fins, the plan wasn't to build fins to begin with. I had built another CNC milling machine in autumn 2015 and wanted to learn how to design and mill something three-dimensional on the computer using CAD. And that became a negative mould for a fin: quite simply made from MDF, which was then coated.
What kind of Finn was that?
It was called S for slalom and was a size 44, a terrible piece - a bit crooked and not symmetrical.
Next, I built a frame to measure the flex and torsion of fins from various manufacturers and collect as much data as possible. The aim was to get a feel for a layer structure in order to achieve similar values. Only the fin blade is laminated, the tuttle box is moulded on at a later stage. This means that after the first test rides, I will be able to(Red.: inclination of the front edge of the fin to the rear) still have to be adapted. I build only one mould for different fin lengths, laminate the fin and shorten it from the base to the appropriate length.
So a 40 mm and a 44 mm fin are actually the same in the lower range?
In terms of profile, yes. It became difficult when I realised that I needed a harder ply structure for shorter fins. It saved me time because I already knew from the measurements whether it was worth going out on the water with a fin.
What happened after the "crooked thing"?
It was surprisingly easy at first. It only took three or four attempts to build a 44 mm fin with values comparable to those of other manufacturers.
But do you follow your own ideas for your profiles? With thickness and profile shape, for example.
In aeromodelling or when you start with fin profiles, you usually use profiles from NACA. This is the predecessor of Nasa. That was okay for a start. However, fins don't work in the air, but in water, which is incompressible. So you have to look for profiles from the aero sector for supersonic. It took me a while to come up with the idea of making the airfoils as sharp and aggressive as jet fighters. A visit to Flugwerft Schleißheim helped me with this.
I then completely sharpened a fin at the front and rear. It was clear that it couldn't work like that. I then sharpened the fin back on the beach until it ran safely. That was an incredible aha effect, the fin initially had extremely low resistance - but was incredibly sensitive to ride. Basically, this way I understood how resistance and grip are connected.
What have you learnt from this for your Finns?
I avoid thick profiles and get the lift and lift from the flex behaviour of the carbon structure.
Do you also vary the point of greatest profile thickness?
That came afterwards. I started with the NACA 009, which means a profile thickness of 9 per cent in relation to the profile length. In the aero sector, anything from nine and below is a fast profile. The thickness reserve is 33 per cent, i.e. relatively far ahead. If you now go more into a laminar profile, you push this further back, to between 40 and 45 per cent. That's where I ended up, with a thickness setback of around 40 per cent.
What does laminar mean?
Laminar profiles have less resistance, but also less lift(Red.: The current is, popularly explained, smooth on the surface for a longer period of time before it continues to flow turbulently, i.e. in a swirling manner). If you move the profile thickness forwards, you have more lift, but also more drag.
Buoyancy of the fin - what's behind it?
I'd like to ask what the buoyancy of a fin is? In which direction does it work?
With a standard fin with a relatively thick profile, the profile itself generates a lot of lift due to the angle of attack. Angle of attack means that the nose of the surfboard does not point exactly in the direction you are travelling, but slightly upwind. This allows you to hold your course. If the board is tilted onto the leeward edge, the upwind tilt of the fin generates additional lift.
With a custom fin, you can adjust the flex behaviour so that the fin bends more to windward, making it easier to generate additional lift. I use a so-called soft tip for this. This means that the fin is very stiff at the base - and becomes increasingly softer towards the tip.
With a carbon fin, you can also consider in which area the fin should bend specifically to windward. I call this a soft tip. If you bend this fin over your knee, it is very stiff at the base, can hardly move and becomes more and more crescent-shaped towards the tip. On the water, the tip will bend more and more to windward under the right pressure, creating additional lift.
So there is a force component that acts vertically upwards?
Exactly. This has the advantage that you can reduce the resistance of the board with the lift. In difficult waters like Lake Garda, the board is supported from below and doesn't fall into the wave troughs as much. The board flies better over the waves. A thin carbon fin therefore not only has less resistance, but also reduces the resistance of the board thanks to the lift.
A thin carbon fibre fin not only has less resistance, but also reduces the resistance of the board due to the lift"
In other words: more flex for more lift?
Finns used to be relatively hard on flex. But on torsion they opened up relatively quickly like a flag in the wind - and thus let out excess pressure. I have reversed the principle: I build the soft tip with a progressive bending curve, but it is very stiff in torsion.
You laminated fins right from the start. Simply milling from G10 out of the solid was out of the question?
No!
What materials do you use?
carbon. The construction is very different. I realised this at the latest when I made shorter slalom fins. You can't just cut the 44s down to 36.
Hardness and flex - the decisive factors for a fin
How do you control hardness and flex? The thickness is predetermined.
The layer structure is complex. My design allows a certain flex and torsional stiffness to be set at any point. It was also important to me to have a standardised structure across all fin lengths. This means that an MS fin always feels the same. No matter in which length it is used. A typical layer structure consists of twelve layers of carbon, two layers of glass and a core of epoxy and carbon. The fin is then laminated wet-on-wet, immediately pressed and tempered.
If you want to build two fins as identically as possible, what tolerances do you have to live with?
A numerical example: I clamp the blade for a 44 mm fin from 47.5 cm, load it at 7 cm with a weight of 15 kilos and measure at 5 cm from the tip. This gives me a spread of one to two millimetres, with a total bend of around 46 millimetres.
With masts, this hardly seems achievable.
I'm not a mast specialist, but I think these guys are familiar with prepreg carbon fibre.(Red.: fabric impregnated with resin in advance) some of which are much higher quality. I laminate wet on wet. If the first layer gets just a little too much resin, it floats slightly in the mould, the second layer perhaps also and they get a little further inside the fin body. It's only tenths of a millimetre, but that's where the fluctuations in hardness come from.
Have you thought about prepreg carbon?
No, not for long, because I don't think there are enough different types of carbon. That would massively restrict me in terms of layering.
How many types of carbon do you use?
Four. On the outside, a reasonably nice, visible carbon fibre fabric. With fins, you can often tell whether it's a torsion or tension layer. I then switch between torsion and tension layers. I do it in such a way that I support a strong tensile layer on the outside with a torsion layer.
How are they orientated?
45 degrees in the torsion position and the traction positions are uni-layers, i.e. a single layer that only runs in one direction. I work with the soft tip to get lift and smoothness into the fin, which all takes place in the lower area of the fin. You have to think carefully about the angles at which you place the layers so that the soft tip opens up in the desired direction. A tip that is too stiff will cause unsteadiness and you won't be able to control the power, but if it opens too early it will also cost you performance.
What exactly do you mean by power?
I've now made a power slalom, it's called the X7, a fin with which you can ride man-to-man on Lake Garda, you get out of the wake well with the other person, you have the power to ride better upwind. You can glide through better and the board is higher in the water in the jibe, you don't park so quickly. This fin is about four tenths of a millimetre thicker than my speed slalom fin. With a thickness of 9.7 mm at the base. However, this "poer fin" is still thinner than a NACA 009 profile.
High-performance model gliders have pointed tips, whereas the wing of a Cessna is "cut off" at an almost right angle
In difficult conditions, choppy waves, sometimes gusts, you need a more tolerant fin, which allows you to take advantage of the strong gusts and still put the board down cleanly. My fins have a slim tip for this, because you create a large edge vortex by using a lot of surface area. The vortex destroys lift area. High-performance model sailors have pointed tips.
On a Cessna, on the other hand, the wing is cut off almost at right angles. This creates a huge edge vortex and is certainly not fast, but the stall behaviour is very tolerant. It is assumed that an elliptical shape is almost the most favourable. I have extended this ellipse backwards to the height of the tear-off edge, because I want the tip to have a little more leverage for flexing, for opening. As always, this is a compromise.
How do you get to the primordial fins?
One fin always builds on top of the other. At first there was only the slalom fin. Then we wanted a fin that would be faster and more stable on a space sheet. The idea was to reduce the surface area in the tip. To do this, I first had to reshape a normal fin by hand. From the "Speed Slalom" to the power fin, I clamped something into the old mould and made several fins, each of which was slightly thicker. If that fits, I'll remove the mould from the final fin. When I make something completely new, I mill a raised half of the fin in acrylic. I can then laminate a mould half from this.
How the expert assesses series fins made from G10
Do you also ride freeride equipment?
No, not me. But I have customers who are very happy with the R2 slalom fin. In this case, the fin is not ground as sharply as in the slalom area and is therefore more tolerant. As a rule, however, these are power box fins and the power box is not particularly good in my opinion.
Series boards often come with milled fins made of G10, but also laminated carbon fins. Can you judge that?
I have already looked at fins milled from G10 material, which usually have a relatively thick profile. That's why it's easier to glide, you can run upwind well and the fin is more robust on the beach. If someone wants to handle their fin with confidence, this is perfect. But of course I can also see the disadvantage of the thick profile.
Why do milled fins have a thicker profile?
G10 requires a certain material thickness so that the fin is not at risk of breaking.
You test yourself and have your drivers who are also successful in the Speed Kini. It's all about hard numbers. What's the benefit of a top fin compared to an average series fin?
The difference in speed is huge. With a speed slalom fin, we are in the 55 to 65 km/h range. With the Speedkini, the speed goes up to 70 km/h, which even a hobby racer can manage. A standard G10 rider is probably happy to get up to 45 or 50 km/h. However, a fin should not be reduced to speed alone. A custom fin not only gives you more speed, but also smoother running, which makes you faster again.
How can a customer recognise whether a series fin is already quite good?
If the profile is thicker overall, this can be easily compared with other fins at the base. If the leading edge and the front part of the profile are also somewhat rounder, you have to assume that the top speed is limited and the holding forces of the sail are higher.
If the fin is a little thicker, it "wears" more in the neck."
How much does a freerace or slalom fin influence the manoeuvring characteristics?
If the fins are too thin, you park faster in the jibe - you need a certain thickness of profile so that the lift supports the board. I don't really understand the typical outline of freeride fins, which is curved backwards. I assume this is supposed to make the fin a little softer overall and make it flex. It also shifts the pressure point of the fin slightly backwards, which could also be achieved with more rake. From an aerodynamic point of view, I would build the fin more straight.
How every windsurfer can optimise their fin
Can you tune a fin yourself by sanding the edges or something?
The first fin tuning starts with the mounting in the board. If the fin sits too low in the box, this can cause spin-out. If it sits slightly higher in the box, it is not quite as bad. If the fin does not sit flat in the board, this changes the rake and therefore also changes the riding characteristics.
It is also possible to sand the fin completely until the surface is completely matt. This reduces the resistance of the surface and can also prevent the fin from whistling. I recommend 800 grit wet sandpaper. It is possible to sand the fin thinner towards the front to reduce drag, but the profiles are usually too rounded and you would have to sand away a lot to reduce drag.
Sanded surfaces are always a must, clear top coats are not an option."
And simply sharpening the rear, does that help?
The risk of injury is of course high, but you can also prevent whistling.
How do you have to grind for this?
You sand at a 45 degree angle from both sides of the profile backwards "into the air" until you recognise an even sanding pattern.
What grain size do you use?
I have the feeling that a thicker profile can be sanded finer and a thinner profile somewhat coarser. What always works is 800-grit paper. I grind long slalom fins finer, short speed fins, where grip is important, a little coarser.
Some Finns do spin outs, why?
If the leading edge is poorly made or damaged, it will destroy the flow in this area. I would look at this first. The surface roughness in the front part of the profile also plays a role. If this is too fine, it is more critical. I would also perhaps defuse the leading edge a little. If the fin only makes spin outs on one side, you have to look at the underpressure side to see if there is a fine degree somewhere. Take 800-grit wet sandpaper and place the paper at different angles to the nose and drag it along the leading edge three or four times, each time at a different angle.
Do you have a team of testers to support you?
The test sequence is clear and has proven itself. I first test the long fins (44 centimetres), if they work, I build the medium ones (36-38 centimetres). Then come the fins with a length of 30 to 32 centimetres. The short fins are usually sent to mates in Holland. After the first successful trials, the fins are then tested by other MS riders ("the boys") to get feedback from them too. The intermediate lengths are then built and tested. MS Fins is based on the formula: Hobby racer builds for hobby racers.
And they also compete in speedkini. But if Andy(Editor: Laufer) with Finn in the Kini, then we have a professional with us, it's like football in the DFB Cup: professional versus amateur racer. Then it's all about who comes first behind Andy. Chris Hirschberg is not only the one who motivated me to build fins, he even came first in the Kini last year - and of course I also really enjoy the brand ranking: it's available for sails, boards and fins - it went to MS for the second time.
It's basically amazing how fast you can surf with quite large fins. What are the most important sizes for the Speed-Kini competition, for example?
With the Speed Kini, we are usually talking about fins around 32 to 37 centimetres. With sails of five to seven square metres. Which can be good for almost 70 km/h top speed. I like to ride with large material and, surprisingly, you're not significantly slower than with much smaller stuff. Riding over 60 km/h with nine square metres is no longer rocket science. In the speed range, we are currently at 80 to 85 km/h with the asymmetric fins - by hobby racers, mind you!
How do you get an MS fin?
You have to order them. I will then ask you in detail what exactly you need. And whether I might grind the fin sharper or less sharp. And which hardness value suits you.
What would a fin for Lake Garda look like for me (1.80 metres; 80 kilos) and which one would Andrea Cucchi get from you?
Andrea usually rides 8.6 with an 85 mm board. He wants power. I would have an X7 Power Slalom in 44 or 45 for him. You probably ride 7.8 on an 80 cm wide board. That leads to a 42 mm fin, the Speed Slalom X6, because the X7 might be too powerful for lighter riders. Maybe I would also give you two fins to try out.
That's absolute custom service from you.
Of course.
What does someone who comes from the north do?
He has to rely on what I say.
How many MS fins have been surfing around out there since 2015?
In any case, it's approaching four figures.
And finally, the question of the price of handcrafted work "made in Germany"?
A slalom fin costs around 300 euros, a speed fin 250 euros.
Contact:
Mail: ms.fins.munich@freenet.de
Instagram: ms.fins.munich
Facebook: Michael Still
