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View Full Version : what fin size for a 6.8m on a S type104


thewoomf
7th September 2006, 06:04 AM
I?ve just bought an S type 104 and it came with a 29cm fin, I recon that will be ok up to my 5.8m. What I?d like to know is, what would you recommend to go with my 6.8m?

Ian Fox
7th September 2006, 08:49 AM
Hi Woomf,

Depends a little on your intended sailing style on the ST104, and also your rider weight, but in general you can consider 36-38cm for light 6.8m, 34-36 for medium 6.8m, 34 for powered 6.8m and even a 32 if you are going for overpowered 6.8m speed in flatter water.

A 34cm is probably a good ST104 second fin option. In general.;)

Cheers ~ Ian

thewoomf
7th September 2006, 08:57 AM
Thanks, for quick reply, rever thought to mention my weight which is around 85kg.
I guess the 29cm would be subject to spin out with the 6.8?

Ian Fox
7th September 2006, 09:45 AM
Well, yes - but mainly as you'll most likely simply never get it going fast enough in 6.8 conditions (except speed trial) to generate enough lift to offset the sail/rider load.

Sailing the ST's in marginal conditions (for their board/sail size combo/s) you do need to rely more on the fin (size/area) due to the softer (bevelled) rail on the ST's (c/w say iSonic in same size). Of course, that ST bevel helps a lot at speed, in mid to high end and choppy conditions, but in marginal 6.8m/ST104/85kg conditions you need some more fin than 29cm.

Obviously that extra fin size/area helps the ST stay upwind (more efficently than dropping the windward rail) in marginal conditions too.

Cheers ~ Ian

Duracell
8th September 2006, 03:05 AM
hmm, I never used any other than the stock fin (290) for 4.2-6.8 sails and was always quite happy (alas only 80 Kg). I always used the board on flat water and in very very gusty winds 15-40kts.

Ian Fox
8th September 2006, 01:25 PM
Considering the rocker and basic layout of the ST104 is similar to the S100/S95 - except with even less "edge" on the ST because of the bevel, then it's logical that the ST follows similar to Sonic fin tuning, perhaps even a bit more fin on ST due to the bevel edge/increase width etc. OK, not identical but you get the idea. In "typical" 6.8 conditions (especially marginal 6.8m conditions) a bigger fin than the stock 29cm would offer some advantage (in general 6.8m sailing use).

It's also previous solid feedback from many ST customer users that they consider ST's do perform better in lighter conditions (bigger sail sizes) with more fin than specced.

BTW, did you see the ST104 fin spec for 2007 ?

Cheers ~ Ian

Phill104
8th September 2006, 02:09 PM
36cm, blimey. That seems huge to me as I mainly use the 104 for speed. I use a 33 for a 6.5 in marginal conditions then switch down to a 30 when I get well powered up. With 5.2-5.7 I use a 27cm fin and that combo works well for me at 82kg (depending on how many pies and cokes that week)

Apart from a new fin, has the stype range changed much this year?

Ian Fox
8th September 2006, 03:08 PM
Yeah, it's kinda big. But in reality the new fin tends to ride "small" for it's mechanical size, so a 34 really was more like a 32 etc. And yes, I am also the first to note you can also OVERfin an ST pretty easy.
I'm personally guilty of loading the stock05 / 32cm and 06/33 in the 115 and just leaving it at that for personal / fun use..

Although visually the 2007 ST's look similar to previous, the new ones have a lower nose, flatter and faster rockerline, basically derived from the S85.

Cheers ~ Ian

Dolf
8th September 2006, 07:59 PM
Hi Ian,

I wonder if Starboard published fin area and if you used my formula for required fin area for sail size and sailor weight, how much easier and shorter these discussions would be. But then that might eliminate the mistique which is part of the fun for the old die hards? But it would make life a lot easier for the 90% of your customers who are not advanced enough to partake in this mistique and are struggling with wrong fin sizing.

steveC
9th September 2006, 12:36 AM
Dolf raises a good point about identifying total fin area. Focusing on only fin length can result in quite a bit of confusion for many folks. Contrasting low and high aspect ratio fins can lead to some vastly different numbers with respect to length, yet the total area can be very similar. While we are accustomed to healthy sum of specifications to describe the physical characteristics of boards and sails, fins tend to be represented very one dimensionally.

Ian Fox
11th September 2006, 09:07 AM
For sure the whole thing is a complex area, mystique and not.

It's pretty clear that (for many years) I have been laboring the point that even amonst "similar" fins (ie: slalom) that typeX 32cm does not equal typeY 32 cm, and that in the end it comes down to a significant number of variables (inc rider style, as well as sail tuning, local conditions) that really make the difference between good and great.
Yes, agree, these are the micro level details - but what most here want.

Granted, there are some customers who simply require the macro knowledge (29 vs 36 etc) - although on average the guys looking for fin tuning info on these forums are more often seeking the micro tuning aspects (the "pro" level details found only by endless hours of on water time, racing, testing and comparing - something that is difficult for many normal customers to achieve but likewise welcome knowledge to share.) Yes, to some extent adding area specs to the dimensions could help (although a quick test of a Drake70NR with a similar area Drake40 Shallow will demostrate that area alone does also not do it). OK, macro example, but you got the idea. FW fins for F160? all 70cm, all similar area -but performance differences are quantum. Undertsanding could easily be described by non pros as mystique. Next one can be wave fin vs slalom (such as are both possible on say ST104..)

For the discussion, we had some years ago a very detailed "fin matrix" in preparation, it became a bit of an obsession to deliver the info accurately. In the end, it became too complex to be practical and precise, and, well, here we are..

No, doesn't mean it was a failure. More a work in progress;) .

Cheers ~ Ian

Dolf
13th September 2006, 03:29 AM
Ian,

We seem to have some disagreements, some misunderstandings and some agreements that you seem to see as disagreements. I will try to group my response accordingly.

First of all you say that most forum users want ?micro level details?pro level details? I am not in that category. My objective is to make my ?good? level of wave sailing look the best that it can, given my advancing years, heavier weight and limited skills. I have until now found this forum an excellent medium for my objective and until recently Starboard had equipment that was perfect for me. It seems that Starboard?s gear is becoming more technical and advanced and specialized which I would have thought is away from the major market of guys like me. If the forum is also shifting to the ?pro? level then perhaps I should shift to the Hot Sails Maui Forum. It is your forum, but for now I will continue.

I agree that fin design, manufacturing, and selection is a complex area. I personally know that, as I had the assistance of some terrific experts to help me design and build my own line of Aero big wave fins. Within this complex field there are some basic, simple and straightforward scientific based principles. Let?s compare it to boards. It is a basic decision if I want a wave board, a formula board or a speed board. The same goes for the basic shape of a fin. I do not use my engineering degree to sort that out. Secondly I make a basic decision on what size of board I want. This used to be measured in cm of length and Starboard changed the industry by switching to litres of displacement. (The two are generally related but ?scientifically? this is more accurate.) This is perhaps a slightly less basic but still not a terribly hard to understand decision based on flotation and resistance. The same goes for fins. To prevent spin out for a given sailor weight, sail size and average anticipated speed, one needs a proportional fin area. Any more than that area gives unnecessary drag and, after a point, instability of the set up.

I have a simple guide to required area which is not as you state ?macro knowledge (29 vs 36 etc)?. It is NOT based on fin LENGTH, that is my whole point; it is based on fin AREA. And the answer is simple. Minimum required fin area (cm2) = 0.53 x sail size (m2) x sailor weight (kg.). It covers 95% of your market. The additional 5% ?pro? market could be covered by adjusting the 0.53 constant to suit the individual and speed if they wanted to. It is my experience that by far most fin issues are spin out caused by insufficient fin area, typically for heavier guy on bigger sails in lighter winds; and secondly by instability caused by oversized fins, typically for lighter guys on smaller sails in higher winds. I am convinced, based on significant personal experience that starboard would significantly enhance the sailing pleasure of a huge segment of their market by helping these people.

What do you mean ?(although a quick test of a Drake70NR with a similar area Drake40 Shallow will demonstrate that area alone does also not do it)? What does it not do? Are you being silly about my first point of selecting a beginner fin vs. a racing fin? Is it not obvious that first you pick the appropriate type of fin. Then you need the right area. If these two fins have the same area then they both meet that criterion. Am I missing something or are you being sarcastic?

You are more knowledgeable than I on the micro level details on the next levels of fin selection which I will not even attempt to go into. With the exception of some very poor design and manufacturing that I have found on too many fins on the market, it is beyond my interest, needs and wants. If you want to design a complex ?fin matrix? to aid in fin selection for the ?pro level? of the windsurfing market I wish you luck on such a daunting task.

Ian Fox
13th September 2006, 08:41 AM
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

steveC
13th September 2006, 11:54 AM
Boy things appear to be heated a bit!

Really, I think that Dolf has raised a vaiid point about fin area. Apart from recommendations, it would be good to better appreciate fin area, and particular, its planform when talking about fins. Depending on use, the shape of things can be varied. Information is power, so let's invest a bit more sensibily. And that should include the "Team" too.

Ian Fox
13th September 2006, 01:05 PM
No emotive heat from my side, all pretty clear logic.

But no shortage of investment from my side either.

I agree, it should all be simple. In theory. In practice, maybe not.

Area and formulas are great things - when they are used correctly and when they work.

Above is a good example. Take it as just that. Not more.

As we knew from our fin matrix project (itself just a series of factors, variables and formulae),
to do it properly truly is a complex or daunting task.

An accurate fin formula would indeed be a welcome attribute ~ for all of us.

So yeah, let's go for it. Who's up for the challenge ?

Cheers ~ Ian

Dolf
14th September 2006, 04:37 AM
Hi Ian,

I have seen you sailing and from my perspective your idea of ?just good pure sport sailing? is high speed blasting and running circles around everyone else on the ocean. Is it fair to say that you are not just good but unbelievably fast; can we say a difference of ?quantum?, in the top 1% of the windsurfing elite? If I (or the other 99 or 95 or 80 or whatever % of us windsurfing mortals) used your set up, I would be spun out and lying in the ocean as I would not have the fin area for my skill level to get me up to speed.

We know that required fin area is inversely proportional to the square of the speed. If you go twice as fast you can use a fin up to one quarter the area. Conversely if you go twice as slow you need four times the fin area. This is why so much of the forum discusses techniques to get up to speed before loading up the fin. So for you the coefficient seems to be 0.36 rather than my ?normal? 0.53. (As an aside it seems that you are sailing 21% faster than me which is the square root of the ratio of coefficients) But your specific coefficient should hold for your different combinations of sail sizes, boards etc. So if you did not have your vast experience and intuitive sense you could use your specific coefficient in the formula to pick equivalent fin sizes for all your different gear combinations. Also the few other sailors in your league or race could use the same coefficient as they are in the same speed range. So the formula works even for the advanced users of the AskTeam forum, but I concede that it would not be as valuable a tool for this level of sailor. It is the other 95% of your total market that I often see struggling with grossly incorrect fin sizing that would benefit immensely from some initiative with basic guidance from Starboard and that is where the formula is easy with a constant coefficient and a complex matrix project is overkill.

Have a great day.

Ola_H
14th September 2006, 04:09 PM
Dolf, we have been discussing this before and I can see your point: I promised once to measure my fins and start to take notes of what sizes I used for different sails, but haven't gotten around to do it. In any case I'm sort of with Ian here from personal experience with wave and crossover boards. My main argument why I think (bi-) linear formula (even with a "personal coefficiant) is to simply is that in by definition locks the fin size to the sail size. I tend to look at sail-board-fin as a kind of holy trinity and I reguarly trim the feel (and performance) od a certain board-sail combo by changing fins (both fin type but also fin size). If we accept your formula as a basis, anyone who want to take full advantage of a boards "crossover appearance" will still have to have a set of coefficients for different types of sailing and then we're allready on our way into matrix land.

Actually, while I'm a fairly competent sailor on wave baords, I'm totally new to slalom boards and even with my new iSonic 101 and (my only) freeride sail of 7.5 sqm, I've so far have had equally fun experineces with the Slalom pro 40 and 34 cm fins. The choice for me depends on if I want to go for max downwind speed, and struggle a bit more upwind or just enjoy the (for me) fantastic upwind capability of the 40cm fin but loose a tad of top end speed maybe. I don't think this is an elitist way of thinking from my side, I think even many "casual users" wants to have the chance to use their boards to the fullest and fin choice is a part of this.

In any case, publishing the area of the Drake fins can't be a bad idea. Then people can do with this information what they want.

Dolf
14th September 2006, 08:02 PM
Ian and Ola,

I understand your points and do not think that you are looking at this in an elitist way, rather from the perspective of very advanced sailors who are having some memory lapses of your struggles before you joined the ranks of the super elite of windsurfing. You can turn my formula into a matrix indeed for the expert sailors if you like, that is if the experts would bother because by and large they don?t need a formula. (But it would work if they did. Every expert can develop his own coefficient and they could go to the extreme of having 2 or 3 coefficients for different aspects of windsurfing). It is the rest of us struggling mortals, the vast majority of your customers, who would benefit tremendously from a guideline. Once they advance from the point of needing to turn the guideline into a matrix they can do so or throw the formula away.

I use myself as a measure. I do not deviate from my formula as I am simply not good enough to appreciate the benefits of doing so when I have so many more urgent issues to deal with on the water. I consider myself a good sailor, maybe in Maui slightly less than that, but probably in the top 10%. Frankly Ola, casual users don?t often change fin sizes for a given sail, they are lucky if they have one fin per sail in their quiver. More often they are grouping sails around one fin size. I am rare amongst casual sailors to have 11 fins for my 11 sails. And even if they did, it does not change the benefit of the formula as providing a personal standard around which modifications could be made to suit unique situations.

I know that there is no disrespect from either side and we are all genuine in our efforts to promote our sport but I hope that you can walk in my shoes and appreciate that I see your position on this issue as stubborn to the point of being insensitive.

I am off for a few days but I think that I have said all that I can say.

Have a terrific day.

Del Carpenter
15th September 2006, 11:43 AM
Thanks to each of you for the good discussion. I'm one of those average (or less) skilled guys with quite a few more sails than fins. Dolf's formula interests me as a general guideline. It was presented as a formula for determing the "minimum required fin area" needed. Dolf, do you have a formula for determining the maximum useful fin area? And does the length of the board change either formula? My knowledge of the physics involved is minimal. My intuition tells me there are formulas that apply. And my intuition also says the differences between my 372 cm long Equipe and my much shorter X-186 should mean there are significant differences in the formula's I should apply to each board. (I don't remember the X-186 length, I think its about 270-280 cm.) Maybe overall length doesn't change the formula but planing surface length would? And wouldn't the board width in the fin area also change the formula? Again this is just my intuition, I have no theoretical or applied experiments to back up those ideas.

Ola_H
15th September 2006, 05:30 PM
Dolf,

I'm trying not to be insensitive since I'm a mathemathician and hence I like both numbers and structure. I would love a formula to help me understand these thing better and to give better advice. However, there has always been something about your linear formula that has been bugging me. Often when I see a formula or some other type of "explanation" I get this feeling "right - thats it". Since I've had no record of the areas of my fins I have not been able to "see though" your formula from an experience point of view and I neither really see why it would hold theoretically (maybe it does (within limits) but I just do see why).

So, I just took out a few fins and compared their area, the Slalom pro 34, Drake Natural 24 and Drake Style 20. They all pretty much have the same area (around 220cm2, +-2cm2 or so, the Style being a tad bigger).

I don't have very much experience with the slalom pro except that is worked pretty good with a powered up 7.5 freeride sail. OK, upwind was not excellet, but still oceans better than any wave board with any wave fin.

The Drake Natural 24 is a fin I use a lot, usually with 5.3 in onshore conditions or with 5.5-5.6. Its noth a nice wave fin but also a nice freeride/B&J fin for say a Kombat and 5.3. In that setting it could easily handle 4.5 too.

The Drake Style 20 can be used with 5.3 or even bigger, but it then feels very small and very freestyle specific. For general sailing (on freestyle, crossover or wave board), I would prefer the Style 22 for 5.3. With the style 20 you need a fair bit of technique to go upwind.

So, what's my point? Well, first, using the Style 20 would be totally useless with a 7.5. I would say its easier to get planing with the SlalomPro 34 and a 7.5 than with the Style 20 and a 5.3 (different winds and different boards, but you get the idea) and the difference would be even bigger if you less good a sailor.

Even if you compare the Style 20 and Natural 24 on the same board (Kombat, fx) with, say, a 5.3, I consider the Natural 24 to be very easy to use and friendly also to beginners with that sail size, while the Style 20 is demanding to sail and a beginner would not have a very good time on that fin.

Using the 0,53 coefficient with my 70 kilos puts the (max) sail size for both fins at just below 6.0. Thats "super expert freestyle only area" for the Style and personally, despite being quite good with small fins, I wouldn't be totally comfortable in most conditions on the Natural24 with a 6.0 either (confirming my thought that these wave fins sails small, not only given depth but also area).

So, whenever you don't stay with the same type of board, sail and fin, it seems to me it get kind of hard to use the formula to predict fin size. However, it may well be that the fomula is still excellet for predicting how much you shoul increase fin size when you get a new bigger sail (fin type, board and sail type staying fixed).

Best regards,

Ola H.

PS: The other day I read an article about scientists that had measured the activity level of each of the 30.000 humen genes on 100 patients with a certain form of cancer. By using mathematics, they could from this very sparse data get a relevant visual representation where you could indentify two discinct groups of gene expressions. This predicted that there was actually two distinct forms of cancer and htis turned out to be clinically relevant (one of the groups tunred out to live longer than the other, statistically speaking). My point with theis ps is that given enough data, it would be possible to come of with lots of results on which fin that works best. After all, we would be dealing with less than 30.000 variables and could probably fins more that 100 people willing to report data to us. Not sure I'm willing to coordinate this though...

DS

drzone
15th September 2006, 06:54 PM
Just like the Art and Science in medicine, fin making and tuning is just as much Art as it is science. In this case, probably more like magic. No one mentionned the thickness of the fin, the water state, how much foot pressure you intend to push on the fin, water temperature and salinity.
And it's not like medicine, which is already 'grey', where you either have cancer or you don't.
Here, you are trying to define what is the right fin...what is right.
May as well answer 'to be or not to be'.
Kills me when people introduce formulas like the gospel truth. Just like the gospel, it's only a guideline. I would agree that if SB wrote down the aspect ratio, fin length, thickness and surface area, it would be a good guideline for all.
Cheers.

steveC
16th September 2006, 01:48 AM
Hi Ola,

Earlier you made the following statement:

"In any case, publishing the area of the Drake fins can't be a bad idea. Then people can do with this information what they want."

This is getting to the heart of the matter that I commented on earlier. Information is a good thing, and it creates broader base or dimension that folks can reference. Like Del Carpenter, I'm not one with a scientific mind that gravitates to formulas to figure things out. Nonetheless, I still like specifications because they tell a story of sorts. A wealth of simple facts can help us ferret out a path. Personally, I find inituition one of my best guides, particularly when the visual shape of something is revealed. Still a lot of trial and error is possible in conclusions, but there are lessons in that.

In parting, I think drzone is right on in suggesting that Starboard outline aspect ratio, fin length, thickness and surface area. The only other additions I would suggest would be fin material, to include photos/drawings.

Phill104
16th September 2006, 03:05 AM
Do you buy a board because of the fin supplied. The supplied fin shoud give a reference point as to where you should start to look when adding new fins to your quiver. If you spin out on a given sail/board/fin then try a different fin, if you feel over finned, change again. There is usually someone with similar kit around that will let you try a fin of theirs. This kind of trial and error teaches far more than any formula could. Starboard alread show a suggested fin range for each board so that also provides guidelines. On top of that the fin manufacturers are very helpfull when choosing a fin so an email to them also helps to make an informed decision far better than any formula could.

I did sit and think about the formula thing for quite a while a couple of years ago but there are just too many variables to get even close to a working system. Even trying to simplify it gives far to vague a system.

It would be good if starboard would state whether the supplied fin is intended for the top,mid or bottom of a boards sail range and each fin name/size in the boards descriptive data to link directly to the relavent fin on the drake site.

p.s. a list of fin manufacturers can be found here http://www.windsurf.me.uk/Links/links.html

Ola_H
16th September 2006, 04:39 AM
Phill104 and others:

I have actually not asked exactly how the stoch fin choice ot the different Starboards is made, but from my persoective it seems like each board get a fin which is in mid sail range for the "typical" user of that board. For example, the Kombat and Flare 97 comes with the same fin (Drake Crossover) but the Kombat comes with a much bigger fin (given boards size/sail range). This is (I think) because a Flare is intended fo Freestyle and a dedicated freestyle sailor will want a much smaller fin for a given sail size than a B&J sailor that uses the Kombat would feel comfotable on.

That said, both a Flare and a Kombat can be trimmed towards more B&j (Flare) or freestyle or wave (Kombat), but then you need to look at different sizes and/or different types of fins.

Dolf
17th September 2006, 10:34 PM
Hello Ian,
Following is my entry for your challenge to provide a formula. These should all be added to your new Windsurfing 101 section of your website. If my entry wins please send the prize c/o HSM, Maui. Thank you.

REQUIRED FIN AREA
A general guideline for required fin area in normal sailing conditions is:
Required fin area (cm2) = 0.53 x sail size (m2) x sailor weight (kg.)
A smaller fin will result in spinning out and difficulty to point upwind.
Larger fins are unnecessarily slower from additional drag and if much larger result in instability and lack of control.
You can modify the coefficient to make it suit your personal preferences, which will then give you a reference for different types of boards, sail sizes and conditions.
As fin area is very sensitive to speed, experts and racers can use smaller fin areas with a coefficient as low as 0.36*. (Ian please feel free to modify and add to.)

REQUIRED SAIL SIZE FOR WIND CONDITIONS
Your sail size for a given wind speed depends on the type of sail construction, your ability, preference to being over or under powered or if you are racing, but a good rule of thumb is:
Sail size (m2) = 2.47 x sailor weight (kg) / wind speed (kmph)
Sail size (m2) = 0.7 x sailor weight (lbs) / wind speed (mph)
Sail size (m2) = 1.34 x sailor weight (kg) / wind speed (knots)

REQUIRED BOARD SIZE TO FLOAT
For a board to float you in stagnant conditions your board volume (litres) needs to be your weight (kg) plus 25.
This allows 10kg for the board, 10 kg for your rig and 5 kg for your personal gear.
Any forward motion of the board will significantly aid in keeping you floating which allows you to reduce board size.

SAIL QUIVER SIZING
There is no specific correct answer to the right sail spacing as it is a personal choice of the compromise between bigger gaps that give a wider overall range of sails for more time on the water or a narrower range so you can size more precisely for the wind speed.
Generally a ratio of sail sizes of less than 13% is not significant enough to justify the extra expense of having more sails. On the other hand a ratio of more than 20%* can make it difficult to pick the right size.
(*This is our preference but Ola seems to think this should be a bit larger, feel free to change it based on your real data.)

MAXIMUM SAIL SIZE FOR A BOARD SIZE (This is an iffy one)
There are too many factors such as board type, shape, width, tail width to provide a formula for the maximum sail size for a board volume. On average this may provide an estimate:
Max sail size (m2) = 5.9 x Board size (litres) / sailor weight (kg).
Or conversely:
Minimum Board size (litres) = .17 x sail size (m2) x sailor weight (kg).

FOOTSTRAP POSITIONING
Add the info from your catalogue

Dolf
17th September 2006, 11:14 PM
Hello Del,
?It was presented as a formula for determing the "minimum required fin area" needed. Dolf, do you have a formula for determining the maximum useful fin area??
Thanks for your comment which helped me change my wording as per the post to Ian above. The rational was that 0.53 is the magic threshold for my wife and I where spin out becomes unacceptable. Hence we pick the next larger fin above the 0.53 limit. There is not such a black and white threshold for maximum size, the performance just gets progressively worse as you go larger. And for a beginner at slow speeds there is no maximum.

?And does the length of the board change either formula??
For the 99% of us less than experts: No. This is based on empirical data that I will elaborate on to my future response to Ola when I get some more time.

?And wouldn't the board width in the fin area also change the formula??
No. The maximum fin size that a board can take is related to the tail width but that is beyond my expertise and it is a different subject than the strict determination of required fin area.

Please let me know how things work for you as my formulas are always a work in progress and can use meaningful feedback to keep improving them.

Thanks,

Dolf
18th September 2006, 10:37 AM
Hi Ola,

I will emphasize again that the formula is not intended for experts. They do not need it. They could use it but it would have to be extended to a more complex matrix. I think that your example points out that the formula would work for you and Ian if you were to take the time to record enough data so that you could make the adjustments that work for you.

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.

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.

You have also brought up a related but separate issue. A huge part of selecting a fin is deciding on the type of fin. And within that criteria there are a gigantic number of variables that are all very important on the performance. These issues are very well covered on some of the fin manufacturers? web sites and you have given some excellent examples. It is a related but discreetly separate issue from selecting the fin area. As my experience is that this is where most of us have the most trouble, this is what I have focused on.

Regarding your PS, this is relatively speaking what I did within my resources, so what is your point?

Now my PS, This has become the wrong place to discuss this and it is way off the original subject. It should have been under its own heading in the Bulletin board, but we have gotten to this point so we may as well finish it here unless you want to move it.

Dolf
18th September 2006, 10:42 AM
Hi drzone,

Other than the science of fluid dynamics has largely replaced the art of airplane wing design and behind magic there is usually a clever application of science or simply deceipt, I agree with you. So what is your beef against my formula?

Dolf
18th September 2006, 10:52 AM
Hi Phill104,

My experience with fin manufacturers has been at both extremes, so I think it is usefull to have some knowledge in addition to their advice.

I agree that there a too many variables in fin selection but a managable amount if you stick to just the area selection. I know my formula is simple, but how do you find it too vague for the purpose and parameters stated?

It seems to me that the formula and the publication of fin area achieves your stated objectives so we have the same desired objective. What is your exact concern with my method?

Ola_H
18th September 2006, 02:07 PM
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.


Cheers,

Paulc
18th September 2006, 07:29 PM
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).

regards

Dolf
18th September 2006, 09:21 PM
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.

Dolf
18th September 2006, 10:24 PM
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.

Screamer
19th September 2006, 09:15 PM
Dolf

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.

Regards

Dolf
19th September 2006, 11:51 PM
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.

Regards,