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Old 13th September 2006, 08:41 AM   #13
Ian Fox
Join Date: Aug 2006
Posts: 533
Default RE: what fin size for a 6.8m on a S type104

Hi Dolf,

It's a nice windy day today, just about to start a fun session with my friends. (true, so I'll be brief..) The wind is blowing 15-20 with gusts to 25, the water is moderate chop, the sailing style is fun B&J blasting, a few fun moves and a few straight line drags when it's on. It's not "pro" stuff, just good pure "sport" sailing.

I'm fully intending to use the funnest gear I can choose for the session, from what I know works, based on numerous previous sessions in such conditions.

My equipment selection, (and not modified in any way prior to any fin size formula debate) is :

ST93 / NC-X 6.5m / Freeride 280 (it's the one jammed in the board)
(aprox fin area = 220cm /or equiv performance size to a moderate AR 30-31cm slalom)

Using the Dolf formula, my "minimum fin size requirement" will be :

"Minimum required fin area : 327cm2 = 0.53 x sail size (6.5m2) x sailor weight (95kg.)"

So according to the minimum formula I would need to take a minimum of 320+ cm2.
That's equivalent (in relating measured area) to a 37cm slalom in moderate aspect ratio - or even longer in higher AR race/slalom designs. (i've a moderate 37cm race/slalom with 11cm base chord right here - actual surface area 316cm2/49sq")

I've been easy on your numbers, and not tweaked area/s, AR etc on my side.

The difference in the result is (with respect to your contributions, and no sarcasm) : quantum.

30/31 vs 37/38cm. (~220cm2 vs ~320cm2 in same style/AR etc)

In fact, as far as most of this Forum's users are concerned, that's the whole game plus change.

I haven't run the numbers on a bunch of other combos, simply what I'm going to use today in "normal" conditions - and surprisingly close to the subject example of this thread (fin size for ST~6.5m).

We do run a number of Forums, with the subtle but logical intent of offering different levels of information/discussion. This one happens to be in the AskTeam section, so the majority of the readers/questions/answers are intended to be of an advanced level, the target audience in AskTeam is unlikely to be your 95% market figure. It's far more likely (on average) to be our advanced sport/intermediate/local/national racer types guys (far less than 95% of market) but also short of the Pro level (as pros simply know they have to test for themselves, on their gear, in their conditions to get their optimal individual tuning edge). In most cases, our users are appreciative of being able to access (somewhat) personalised product specific and accurate detailed, info and advice. Especially with boards like ST that subtly deviate from "typical" sail/fin capacity vs board volume/dimension parameters (as explained in earlier posts in this thread and elsewhere).

Anyway, the wind is up and I'm outta here. Hope you have a great day.

Cheers ~ Ian
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