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Old 18th September 2006, 07:29 PM   #31
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Default RE: what fin size for a 6.8m on a S type104

Hi Dolf,
i am a recreational sailor that is at a skill level of planing out of some of my gybes. I just want you to know that your formula (as simple as it is) works perfectly for me and my boards. i am 84kg and use trueames fins and starboard boards. when i apply your formula to come up with the smallest area fin that is usabe and then take the next size up it seems to be right on. i applied your formula for my stype 126and 104and kombat 106 (used in freeride mode).


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Old 18th September 2006, 09:21 PM   #32
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Default RE: what fin size for a 6.8m on a S type104

Hi Paulc,

Thank you so very much for putting in writing what I have been told so often on the beach.

I am finding it apparently impossible to make my point to Ian and Ola that you see so clearly. Perhaps your input will allow them to get out of their expert position and see my suggestion from our shoes.

I am surprised that you found this discussion buried in the Ask Team section under a different heading, but I appreciate your support.

By the way the formula works just as well for wave fins as long as you are using a full size fin that allows you to fully power it up like an average wave sailor needs.
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Old 18th September 2006, 10:24 PM   #33
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Default RE: what fin size for a 6.8m on a S type104

Hi again Ola,

I am starting to find this very frustrating, as perhaps you and Ian are finding as well from your perspective. From your last post it is obvious to me that we are on different pages and you do not understand my fundamental point. I am running out of ways to express myself and I wonder if you are just so far ahead of the rest of us that you just can not walk in our shoes? I have a tremendous respect for both of your abilities and terrific assistance on the forum that I myself have found very useful. I can not figure out why you do not understand my point.

To specifically respond: I threw out all my notes of accumulated data and the spread sheet. It was so consistent that it seemed redundant to me to save it at the time. All I have left is a summary sheet of fin sizes relative to sails and boards and an area calculation chart. I will e-mail it to you but I am sure that this will not add any enlightenment to our discussion.

You can "look at your fin sizes for a while" and it will lead you to a more complex matrix than my formula. I imagine that it is quite normal for you to use a terribly small wave fin that I would spin out like crazy, to get out to the waves in light wind conditions, because that is the size that is ideal for surfing in, because you size your wave fin for the board and waves, not the wind. Or you use a mini fin for speed sailing where you have to bear off until you have sufficient speed to load the fin. These situations would result in different coefficients. They would certainly be consistent for you for that application, but you would have a different coefficient than the 0.53 and you might even have 2 or 3 different coefficients for different applications. And again the formula can be adjusted to cover those expert situations as I tried to say in my last post to Ian, but it becomes more complex for those few sailors who do not need a formula: probably redundant. But I maintain that you would find a linear relationship as long as you kept some applications separate.

This does not apply to the vast majority of us. We need a fin that gives us full lateral resistance regardless of our mode of sailing, hence one simple coefficient. It is remotely possible that some of us have sufficient different sailing style that we might need our own coefficient, but it would be close and it would be consistent.

Which leads us to our fundamental disagreement: it is indeed possible to develop an empirical formula that is indeed straightforward and is simple and effective to use for the vast majority of windsurfers. As long as we continue to argue about the exceptions that apply only to a very small segment of expert windsurfers we are never going to communicate.

Perhaps the disagreement is centered on your premise that I should use more advanced sailing techniques to adjust for more advanced sailing conditions rather than keep my fins consistent to allow me to sail my own comfortable way whatever the circumstances? I don?t know, but if that is the situation then it is just not realistic for the majority of us who do not have those skills or in my case don?t even want them.

Perhaps this part of this thread should be moved under its own heading in the bulletin board so that we can have a discussion outside of the elite few who this forum is focused on. I don?t know.

If I could understand what is behind your disagreement then perhaps I could communicate from your perspective. Barring that I think that I am just guessing and I am stuck.
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Old 19th September 2006, 09:15 PM   #34
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Default RE: what fin size for a 6.8m on a S type104


I agree with Phil and think your formulae (not just for fin area, but for sail size also) are vague, and of limited practical value. Some examples from my experience, tried and tested, confirmed by other (non pro) sailors:

-kombat86 + 6.0 -formula gives fin area of 270sq.cm, while I've found I'm using that combo with max. 230sq.cm, more often with 203sq.cm
-kombat86 + 5.0 -formula gives 225sq.cm, while I use it with 203 or (often) less.
-now an interesting example: formula gives me 328sq.cm for a 7.3 sail, and I regularly use 320 (41cm slalom fin). Fine, right? But that's a cambered sail on a wide slalom with chunky, blocky tail, so hardly relevant for recreational use.
-sail size formula tells me I need an 10.4-11.4 (!!!) sail for 10-11 knots of wind. 1.34x85kgx10knots=11.39 (I usually plane on a 9.0 in that wind.) If we take light (but planing) 7-8knots winds for example, sail size results would be even more ridiculous.

Now I'm not "poking holes" in the formula using "extremes and exceptions", but giving real world examples for others to take into consideration. I'll say again, I'm far from expert, just your ordinary sailor well beyond tuning "elite" you refer to so often.
These things (sail and fin choice) can be a nightmare for the inexperienced sailors, but over-simplifications will not help. A little bit of experience and advice (and hit&miss, yes) will usually take care of the problem. You said yourself everybody can adjust the coefficient to their needs, so what's the point of a formula, when it's always different?
Let me add that I don't dismiss your efforts and I've found your contributions valuable before (mostly re. aero and sails/fins for it). But I can't help noticing you're taking issues with anyone who dare to question your findings, you almost demand of *board team to adopt them, and there is a certain bitter, condescending tone in your postings.

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Old 19th September 2006, 11:51 PM   #35
Join Date: Aug 2006
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Default RE: what fin size for a 6.8m on a S type104

Hi Screamer,

Thank you for your feedback.

You correctly pointed out my inappropriate tone. I let my frustration come out that these formulas, while simple, represented a huge amount of work in years of gathering data, analyzing the data to find the relationships, and then distilling them to make user friendly formulas (the focus was for my wife). I think that my objectives are not clearly understood by the team and I feel dismissed with data that is on a tangent and gut feel. I have further found it difficult that Starboard does not have sufficient support for the average sailor in terms of a simple "research" section on their website and my previous suggestions seem to have fallen on deaf ears. I had to learn too much the hard way. My motivator for my work was to make the learning curve for my wife a lot easier than it was for me and it grew from there. But that is arrogant on my part and it is all no excuse. I have taken a deep breath, put this in perspective, and I will chill out. I appologize if I have offended anyone. Thanks for your heads up.

As regards your data, I am stumped. You are indeed the base that the formula was derived from. I checked your calculations which seem right on. I even checked the conversions to knots as I never use them and could find no errors there. My experience is specifically that cambered sails or not and different tail shapes made no difference in the formula, so I can not see that as an explanation. And yet I have too much consistent data to not believe that I can somehow rationalize this. If you are willing to help me out, do you have any other information that relates and could shed some light on this? How did you measure wind speed? (That was one of my most difficult obstacles as even iwindsurf uses algorithms). I assume when you say planning, you mean your normal planning speed, not just planning. Any other relevant data would be appreciated. If this is going too far off the topic of this thread please feel free to e-mail me.

Re your comment "You said yourself everybody can adjust the coefficient to their needs, so what's the point of a formula, when it's always different?" Until your data, I had not come across any need to vary the coefficient for a wide variety of sailors in a wide variety of conditions. But if someone, for whatever reason, needed a different coefficient it should still be a valuable formula as it should be consistent, even if unique, for that person. But your data on fin sizing is even raising a question on linearity there.

Thanks again for commenting in a very positive and constructive manner and I look forward to possibly hearing from you.

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