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Old 21st November 2006, 05:48 AM   #11
Roger
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Default RE: How to avoid "spin outs"?

Hi Bill,
If you look through the archives on the forums here, on each specific tuning option, I'm sure you would discover a wealth of information, but I think you are correct.
No one has "compiled" all the suggestions, and then gone out on the water and changed them one at a time (maybe with a training partner
to get some realtime change vs no change data) to determine what each change does, and how it affects the overall physics and balance.
It's something I've wanted to do, but to do it right I need alot better graphics skills as I think animations may be the best way to illustrate
the physics. I'm working in that direction with an online book and some other ideas.
As far as the 20 knot clause, I'm heading to the west coast of Florida tomorrow morning, so I'll be driving into the gale up the island and hoping to have it push all 7.5 tons over to and down I-95 to FL.
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Old 16th December 2006, 04:21 PM   #12
TomG
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Default RE: How to avoid "spin outs"?

Hi Roger,

I still don't have as many opportunities as I would like to get on the water. However, I think I start getting the "message". Although a number of other things (such as rig tuning to avoid unnecessary drag) may have an impact it seems to boil down to board control. Where I had the opportunity to sail more recently it was extremely gusty, wind speed ranging from ~10 kn well into the (mid) 20's and I battled with my 7 sqm sail, getting a bit better every time (better rig tuning has helped at least here - I have new sails, so another variable to get used to). This meant that I didn't have a lot of opportunities to watch the board (trying hard to stay on the aboard and some lack of confidence). Used my 129 l and 104 l boards.

Now I come more to the point. I recognised few times that the board was sort of dancing a bit, potentially allowing too much air to get under it. I also changed the straps to the outer positions while I used to use the inner ones (I focussed more on manoeuvre). The outer positions seem to have made it more difficult to control the board. I am not fully comfortable with this position when I get into what I consider as (well) overpowered conditions and struggle occasionally to quickly slip into the rear one (can't find it first time and then I struggle to stay control and have to stabilise first again). I had some good runs though where the board/fin started to howl/sing when I was on a slightly downwind course and the board control felt ok. Is this normal by the way (I think I have good qauality fins)?

Does the above (board control most important, outer strap positions can make it more difficult) make some sense or not?

Thomas
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Old 16th December 2006, 08:06 PM   #13
Roger
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Default RE: How to avoid "spin outs"?

Hi Thomas,
Yes, footstrap position (inboard or outboard) can affect your control, but not perhaps in the way you are thinking.
Moving the footstraps outboard does basically 2 things.
It gives your foot and ankle more "leverage" to control the attitude (side to side or "roll" angle) of your board and fin.
It places your weight more outboard off the centerline of the board and if you aren't getting your weight totally committed to the harness lines and rig, having the footstraps outboard can lead to some control issues. If you are getting all your weight off your feet and onto the rig, then it becomes pretty easy control the roll attitude of the board as you can do that with better leverage, and virtually no weight on the tail of the board, so your ankles have the ability to hold the board at the attitude that gives the best control, and when you get enough TOW (Time On the Water) you soon find the board's attitude can be controlled very precisely even over the chop.
Having the footstraps inboard kinda does the opposite, and for your smaller boards (esp. for chop hops and jumping maneuvers) having the footstraps in the center position can be used to minimize the "leverage" giving better control on the narrower board with the smaller fin. Landing a chop hop or other "jump" in the outboard footstraps, on a really small board with a very small fin can be more difficult because you don't need the extra leverage, and you also don't really want your weight applied very mch off the centerline.
So, you need to adjust the positions of your rear footstrap (s) to suit the conditions, the board, and what sort of sailing you intend to be doing.
The flatter the water and the more "back and forth" (B&F) slalom sailing you are doing, the more you need the footstraps outboard.
The rougher the water, the more you are jumping and landing, and the more B&J (Bump and Jump) type sailing you are doing, the more desireable it is to have a singe footstrap over the centerline.
It sounds like most of your "spinout" issues occur when you start to head upwind.
Be sure that when you change course to more upwind, you do so gradually and when you roll the board and apply more pressure that you do it smoothly and with a steadily increasing pressure until you get the course you want.
Also, more time on the water is going to "teach you" how to "feel the fin" and become much more sensitive to when it's beginning to let loose and "spin out". In essence, you learn when you have the max. pressure and angle the fin can withstand (at a given speed) vs when you've applied a bit too much and the fin begins to "let loose".
Then you can begin to "ease off" when you get near the max. load and angle and keep your fin solid, but right on the verge of spinning out.
Try different fins.
Some let go with a bang, all at once. Normally this would be with larger more vertical fins.
Some fins never really seem to "hook up" solidly, and are a bit "loose" all the time. These normally are smaller very curvy planform wave and bump and jump fins. The "looseness" has been designed into these fins on purpose, so the board will be very loose and slashy, but they don't work very well for B&F straightline slalom sailing or fast speed sailing.
Actually, when I read your reply and you said your board was "dancing" a bit, I found that very encouraging.
When the board "dances" a bit, that usually means it's sailing fast, and on the minimum sustainable waterline length.
Now we just need to send Thomas to "dance class" so he can learn to dance to the same tune.
That's probably the big "secret" to solving your spin out issues. More time on the water so you become more sensitive to when your fins are going to let loose, and how to moderate the pressure and angle (with your feet and ankles) to keep the fin "right on the edge".
Hope this helps,
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Old 16th December 2006, 11:29 PM   #14
TomG
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Default RE: How to avoid "spin outs"?

Roger,

Thanks again for your elaborate response. With winter in the UK and some heavy work over the next few months it will be unlikely that I get much TOW (if any at all) - apart from a 1.5 week break at the beginning of next year on Bonaire where I also intend to hopp few times on a board. Unfortunately I will miss you by few day.

In the mean time I will attend a dance school .

Thomas
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Old 17th December 2006, 01:36 AM   #15
Roger
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Default RE: How to avoid "spin outs"?

Hi Thomas,
After you sail the boards with the "cut off to 33 cm" fins in Bonaire, NA
(if you sail in Lac Bay at "The Windsurf Place" or Jibe City) you may find that the fins on your boards at home in the UK are "rock solid" in the spring.
When will you be in Bonaire?
Sorry I'm going to miss you as I'd like to see what your stance is and how you are sailing to get a better idea if your "fin issues" are totally related to the fins, or if there are some technique issues mixed in there as well.
Enjoy Bonaire! B)
R
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Old 17th December 2006, 05:50 PM   #16
TomG
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Default RE: How to avoid "spin outs"?

Hi Roger,

I will be in Bonaire 3rd to 13th January, so will miss you. Windsurfing is not the main objective but still want to do some. I will be in Lac Bay - may be the short fins are the best training opportunity.

I am sure that the spin outs are a technique issue rather than a fin (equipment) issue. What helps I guess is largely TOW, means practicing.

Coming back to the unrelated observation from my last sailing, that the board/fin started to howl/whistle/sing (fits to the dancing) few times when I felt that I was goinf fast and reasonably controlled. Is it normal? As I mentioned earlier, I use only one of the stock fin, all other are added and as I believe of good quality (Select, GSport/Curtis). It happened this time with the 42cm JP stock fin on the 129 l board and a Select Eagle 35 on the 104 l board.

Appreciate your comments.

Thomas
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Old 17th December 2006, 08:09 PM   #17
Roger
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Default RE: How to avoid "spin outs"?

Hi Thomas,
The "howling/whistling" noise could very well be coming from the fin, and as you suggest it's almost an "audible knot meter" as it only occurs when you are really going very fast.
The most common reason this happens is that the trailing edge of your fin is "thinned out" a little too much, or sometimes there is a little "concave" area just ahead of the trailing edge that's too thin.
You can check for the "concaves" with a small hardened and ground dowel pin or a precision straight edge. Roll the pin or drag the straightedge down the foil of your fins perpendicular to the vertical axis.
If you see light coming between the pin/straightedge (now resting on the back half of the foil from the thicker part of the chord to the trailing edge) then you have some concaves and the best way to fix them is to get a flat sanding block and work down the fin to remove any "concavity" between the max. foil point and the trailing edge of the fin. This will "sharpen" the trailing edge, so when you have all the concaves worked out of your fin, you need to "blunt" the trailing edge slightly.
If you have no concaves, and the trailing edge is simply too thin and setting up a hydrodynamic "vibration" (the source of the noises) then you simply need to "blunt" the trailing edge.
To do this, take a sanding block and lay it perpendicular to the fore and aft axis through your fin's foil. With "smooth" (320 grit) abrasive cloth on your sanding block, run the block down the trailing edge of the fin 3 or 4 times. This will create a very tiny "flat" on the trailing edge that will be thick enough to eliminate the noise.
There will be very sharp edges at the sides of this tiny flat, so take your sanding block and put it at 45 deg. to the fore and aft axis of the fin and run it down the sharp edge once on each side to "chamfer" the very sharp edges slightly.
Try your fin on the water.
I'll bet the "howling/whisling/singing" will be eliminated. If it still sings, but at a lower pitch (your fin now "growls rather than howls" ) try the sanding block down the trailing edge a few more strokes and then the 45 deg. chamfers on the sides of the flat.
This should quiet your fin down so that you only have to learn to "dance" with your board and fin.
Don't think you could dance to the "howling fin serenade" anyway as the pitch is way to high. You'd shake yourself apart very quickly!
Hope this helps,
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