fin spin

[Ken]

There are a lot of things that cause spin out, but what I have found on more than one occasion is that the foil shape or other subtle design differences between similar fins can have a huge impact on spin out.

For example, my iS 111 came with two Drake fins, a 38 and a 44, both with identical profiles and with rather thin/small foils. Both would spin out very easily. I also sanded them at Roger's suggestion with no improvement. So I bought a Tectonics Tomcat 42, that essentially had the same profile and rake as the Drakes, but a thicker/larger foil. The difference in spin out was HUGE and when I do push the Tectonics out, it will come back with very little effort. Getting the Drakes back in line after a spin out was significantly more difficult.

Lessacher
Aeration (pardon earlier spelling) could initiate at any point along length of fin totally dependant on route and where air is originating from.. Suspect its nearer base ???(ie its nearer surface) but this is only one aspect likely to cause spin out ; and the reason I mentioned it was to clear up the misuse of the term cavitation.. (Which IMO simply never happens on any wind driven craft.;Hydroptere whose fins and foils must operate at significantly higher pressure differentials than WS does not cavitate.) I`ve seen cavitation damage on stainless steel surface piuercing props; never seen anythiing similar on WS fins.. (spoken to a few who insist they`ve seen it tho ???)

A fin aerating is only one reason fins release but it is hard to seperate aeration from simple overloading or too high A0A.. Suspect in WS its probably a combination of all 3 to some extent.
ie) Any fin will spin out
a)if aerated. (chop; leaving water etc etc)
b ) if overloaded ,that is more load put into it than it can handle
c) if expected to operate at too high(or low? ) AoA (angle of attack) that is sailed too close to wind.
Fin design;shape; cord; thickness..will all effect when above will happen.

[Lessacher]

What could I see through the Acryl Bottum. The water goes behind the fin from the pressureside in an angle of sometimes 40° to the other side,where we have vacuum.Through the high pressure goes the water
(and air)on the vacuum side in front.The most time it stop in the middle and it is a brake.Now to the nose.
Is the nose thick and rounded ,lays the water good on the profile and all it works good. Is the nose thin
and sharp,there can it be that the water goes away from the profile , the water from the pressure side goes
on the other side to the nose,there to the pressure side and a rotation round the fin begin. Thats
spin out.My first idea was,the water should not go to the other side of the fin. So I worked leewards
behind the thickest point of the profile a concave 2-3mm deep from the base to the tip. Thats the
idea to work asymmetrical fins for one way. The water cannot go to the other side. But only with the concave.You can work sharp noses.No problems. Only for one way. Look please:
www.designlessacher.eu And for tour retour??????????

[Lessacher]

Please dont write over long or short fins. Flex or twist,Thick or thin fins. Sanded or not. G10 or carbon.
Please only what a spin out is, I wrote what I saw, and what I did to eleminate spin out.Sorry, that write I
tomorrow. Wolfgang

"Please dont write over long or short fins. Flex or twist,Thick or thin fins. Sanded or not. G10 or carbon.
Please only what a spin out is, I wrote what I saw, and what I did to eleminate spin out.Sorry, that write I
tomorrow. Wolfgang"

Think its good that we try and keep things simple butt all parameters you mention have influences on spin out.

Putting it simply though (IMO) spinout is what happens when fin stalls; ie when it stops opposing downwind force and lets board slip down wind.

Reason for stall are many fold and inter related and hence diiicult to quantify. Aeration is simply but one of them. (But cavitation is not)

If you are spinning out very early try a thicker fin.(It will work at higher AoA encountered at slow speeds.)
If you spin out at speed try a bigger fin but check you have not affected your Vmax. ???

[Lessacher]

Only nose and what at the end of the fin happend,that should we see. Why work I cut outs at the base.I saw that water and air from the bottum of the board want to go down at the end of the fin to the tip of the fin. The bubbles are a little brake. We go with an angle of 10-15° through the water..The water must go through the cut out and in the same angle behind the fin and cannot go down.So you make jumps and
nothing can go down at the fin. Wolfgang

Ken

A thicker foil does have a wider tolerance with respect to varying angles of attack. (a thicker leading edge will be less critical to changes in AoA) so like I said earlier a thicker foil will initially give beter results and feel less prone to spin out(and recover more easily) but like many things in life its at a cost somewhere else. Might well be you are actually a bit slower with your new fin and other sailors might find the drakes spin out less when fully maxed ??? It all depends on the sailors ability;conditions and what they want to achieve. V max. Vmg.playful feeling.. control ???


Very often a fin that has to be coaxed initially (ie bear away; accelerate and gradually increase load) will give higher Vmax but not everybody wants to sail like that and in some situations you simply cant..

Thats why its very difficult to give broad assumptive answers.. We all give answers based on our own circumstances and limitations..
Basically (IMO) if you want to go really fast fit smallest thinnest fin you can just cope with at slow speed; coaxing into life slowly... When its up and running it will be great. (Highest Vmax)
If you want to simply go and arent concerned about Vmax fit largest fattest fin that you can cope with at highest speed you are likely to achieve.(Highest VMG)
Somewhere between the two is freeriding. (and wave sailing ???)

[Ken]

Lessacher and unregistered,

Both of you make good points and I think my issue with the Drakes is the exactly Lessacher's point regarding the thick/thin nose. The Drakes have a thin nose and in a speed trial, probably are a bit faster than a fin with a thicker nose. However, a faster fin that spins out frequently is not a faster fin, it's a pain in the ass. In chop, the Drakes were particularly bad. My skills are pretty good having windsurfed for the last 28 years and have raced the entire time, but on average only 3-6 regattas per year. Last year, I had 89 days of windsurfing.

The other side of this issue is the type of sailing one does. 95% of my windsurfing is freesailing where I most commonly head up and bare off rather than just reaching. Since I try to point as high as I can on my slalom board about 1/3 of the time, I am pushing the fin to it's limits. I typically am in gusty conditions where staying on plane is ALWAYS an issue even on very windy days, so a larger fin with a little more lift helps keep things going. If I sacrifice some speed, so be it, it's worth it.

[Lessacher]

The asymm. fin was for one way over 1km. 20m in front.But retour slowlier. So I said,okay,to be the half
of 20m in front, that are 10m in front,so or so, I am the first. But how. The conave only to the half,from the base to the middle,and for retour on the other side from the middle to the tip. But what happend?
I made not 10m, always 20m,but why? It works always the concave leewards, the concave on the other side shell work retour. The concave on the vacuum side reduce the vacuum,that could I not know, but it was so.The concaves reduce good 5% of a normal profil. A thinner profil is faster.But I work the nose
thicker, thats better for upwind. Through the concaves is a speefin 2 knots faster. That works at all fins.
But nobody want to know that. A assym.fin for one way is leewards thinner than on the other side,
And the nose? Leewards is the angle sharper, there the profil is thinner,thats better for speed. On the other side is the profil normal,the nose angle is not so sharp than on the otherside.There you can nothing reduce on the vacuum side,is such a fin a little slowlier.than my fins. Wolfgang

[Lessacher]

When I work speedfins between 18 to 28cm i work they very stiff so they cannot produce a lot of
twist and flex. When,than a little flex for lift and not 2 things ,flex and twist at the same time ,one works against the other. A twisting fin need more power for flexing. That reduce the speed. I worked a fin with
20cm for one way. The idea is, to work flex in the fin,for a little lift of the end of the board.The fin stay
in an angle of 10° to the left or right side.So you need only the half power for to get flex and later the lift.
The power you need for flex ,reduce the speed a little. I work only 100% carbon fins,the reaction of
carbon is the shortest,I know,( bending and back). I worked a fin inside only with rowings.I lay the rowings
in epoxy and do powder of ceramic around the rowings. that makes the fin stiffer than all the other things.
So I try and try. Wolfgang