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Old 18th September 2006, 02:07 PM   #30
Join Date: Aug 2006
Posts: 1,191
Default RE: what fin size for a 6.8m on a S type104

Hi again Dolf.

I will reply shortly to a few point below, but first I want to say that I think its good work with the formula and a strive for simplification. I have ablsolutely nothing against that, I'm only genuinly interested wether the formula actually holds or not and if not, if it will hold under some certain limitations.

Dolf wrote:

Now for the other 99% of us windsurfers: the formula was developed empirically using data from my friends with a range from beginner to very good (but I again emphasize not expert) with formula boards to wave boards and all kinds in between, with Drake formula fins and freeride fins to all kinds of brands of wave fins, from 9.8 to 3.7 sail sizes, over a 9 year period. I plotted the results and was astounded how consistent the data was given the huge range of parameters. That led to the formula, not the other way around.
If you want to share this data, you can post it to my email. I will then have a look at it and see if I also find a (bi-) linear relationship. Or maybe if would just be enough if you describe the method you used to find the relationship.

Dolf wrote:
It is easy to poke holes in any formula using extremes and exceptions, at the risk of loosing sight of the simple fact that this is a 9 year proven tool that provides excellent results for the vast majority of windsurfers in a huge range of applications. Again it would be fairly straightforward to extend the formula to cover the full range but that is not my intent The intent is to make life a lot easier for the huge majority of your customers and to keep it simple so that for those of us it is easy to use within our normal applications.

I could start poking holes in your arguments as it relates to my formula, but I think that it would be more effective if you kept track of the ?best? fin area for all your different conditions rather than looking at the possible ranges for the different set ups in conditions where you are not using your superior skills to make it work. An example is how you are able to use a terribly small wave fin that I would spin out like crazy, to get out to the waves, because that is the size that is ideal for surfing in, or in speed sailing when you bear off until you have sufficient speed to load the fin. Then if you find that there is not a consistent coefficient then we would genuinely have something to discuss. Or you could approach it from the other side and size the fins for your wife using the formula for a few months and see if she has any complaints.
The examples I used was not choosen specifically to poke holes in your formula and what is interesting about them is that both the freestyle and wave fins are predicted to hold much bigger sails than I think they do in practice. One of my points is that although I could maybe make them work (with a 6.0), I would not encourage any non expert to use such small fins. So, I don't think my level has much to do with this (like one could argue if the formula had predicted what I consider to be to big fins).

I will look at my fin sizes for a while and see what this leads me to. However, even the three mentioned examples indicates that any data set of mine will show quite a lot of deviation from a linear formula.

Dolf wrote:
Regarding your PS, this is relatively speaking what I did within my resources, so what is your point?
Well, my point was that I do think some kind of empirical derived formula is possible, but also that sometimes its not that straightforward to find.

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