hey guys and gals, I am hoping someone here can help me...

I recently purchased a 2012 Starboard Quad IQ 74L and would like to know what the fin area is for the 2x11cm and 2x13cm Drake Natural Wave fins supplied with the board is. I would like to get the most possible range out of this board and without knowing the fin area I unfortunately have no starting point to add or subtract fin area from. Starboard has been pretty ****ty about answering this inquiry and since there is loads of information about starboard boards on this forum I was wondering if anybody has an idea? suggestions pertaining to fin combinations used and their positioning on this board would be greatly appreciated as well!

Cheers,
Tom?

Fin manufacturers are very protective of any info , you will be supplied with a fin size relavent to the board size and most common sail size for the board, eg 70l board with 4.7m , 80l with 5m etc, i have always thought it would be interesting to trace fins onto paper and work out total fin size per cm'2 or inch'2. , why dont u start with a few stats for us while i have a berr heh? Ps dont forget its four fins u r tracing and cutting a jigsaw to make it into a square u can measure eh?

some more than others though... almost all after-maker fin companies gladly offer the areas of their fins and provide suggestions as to appropriate sizing for conditions... its just a pitty to have to go through all this trouble knowing that starboard has a CAD drawing of these fins and could easily find the fin area from it..

MUF suggests this sort of method, but i put a little twist on it which makes it a bit easier and faster...
i traced the fin on graph paper with the grid lines .5cm apart (MUF suggest drawing them by hand horizontally over the traced image). i then measured the lengths of all the vertical lines in cm, added those numbers up and divided by two. this gives the rough area in cm squared. i then did the same thing with the horizontal lines. So this is much easier than cutting and measuring, its sort of like integration but largely simplified and quite easy (just time consuming) to do. each fin took my about 45 mins to do because I did this twice, once vertically and once horizontally.. both came out within 5% of each other in both cases and i took the average of the two areas so the resultant should be pretty accurate. if starboard ever gets back to me with the actual areas we will know how accurate this method is but it should be pretty darn close.

Excellent work , yeah i thought tracing onto graph paper would be the go. Can you write out simplified measurement , ie is that for one 11cm drake or two or two 11cm and two 13cm that you came up with 328cm 2? This is why i am guessing MFC have qs 250 for 75l with 4.7m sail, recommend qs300 for 90l with 5m and qs350 for 100 l with 5.7m cheers zac

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Wiindz said...
MUF suggests this sort of method, but i put a little twist on it which makes it a bit easier and faster...
i traced the fin on graph paper with the grid lines .5cm apart (MUF suggest drawing them by hand horizontally over the traced image). i then measured the lengths of all the vertical lines in cm, added those numbers up and divided by two. this gives the rough area in cm squared. i then did the same thing with the horizontal lines. So this is much easier than cutting and measuring, its sort of like integration but largely simplified and quite easy (just time consuming) to do. each fin took my about 45 mins to do because I did this twice, once vertically and once horizontally.. both came out within 5% of each other in both cases and i took the average of the two areas so the resultant should be pretty accurate. if starboard ever gets back to me with the actual areas we will know how accurate this method is but it should be pretty darn close.

Looks good. And as you say, a fairly simplified integration problem. Just wondering qhy you divided by two???

You coukd actually just plot some coordinates on any geometry program, get two functions and find the definite integral between the two curves.

^ totally sounded like a geek there. Sorry I'm a maths teacher.

Zachery, the figures I found are indicated inside the fins. so 1x 11cm fin (i measured 10.8) came out to about 68 cm2 and the 13 cm fin (i measured 12.9) was about 96cm2. the total for 2x11 + 2x13= 328 cm sqaured. my math teachers did always say they couldnt follow my work and to make it neater..

The reason I divided by two bowsa is that the lines are .5 cm apart. I also jumped from cm to cm2 without multiplying. so what I was doing was i pretended every line was the length of a rectangle with .5cm as the width. so realistically i am not dividing by two but multiplying by .5cm. obviously this results in the same number, just throws the units off but since we what we looking for its not a huge deal ;) as far as plotting points on a program, that assumes that there is some fixed function for both lines and that my drawing is good enough to copy it! i have a feeling it might be multiple functions and i dont have said geometry program, but if you do that image is to scale, if you would like to try that it would be cool to see how far off i am! :)

Ah yep gotcha. Didn't realise you had smaller widths on rectangles

I used a relatively basic program called geogebra to simply plot the co-ordinates along the edge of the fin and make a polygon between the co-ordinates. This isn't as good as integration as it still doesn't make a smooth inference between each coordinate, however, i recon it'd be more accurate than the sum of all parallel lines / 2.
I only did the 11cm fin and it came out with an area of 64.91cm2. A bit less that your calculations Wiindz.

I had a think about this and if you were to model it and work it out properly with integration i recon you could fit three or four functions to the curve and work it out from there. It would give a slightly more accurate area but not sure if it'd be worth it as it may only be around 1cm2 off. Would still be interesting to play around with it and see the difference.

very cool! check this out, posted the same thing on I windsurf and this is what came up... www.iwindsurf.com/forums/viewtopic.php?t=27880
lots of bs and blah blah but some guy turned my tracing into a cad image and used it to get the area getting an area of 65.7 cm sqaured for the 11cm fin

cool, yeah a CAD program would be the most accurate i guess. I just was keen to play around with it and plot if out. I did that image with the details you had written on the image every 0.5cm. Obviously the more co-ordinates the better, reducing the length of straight lines between points. Just like with integration, the smaller the width, the more accurate the area.

How did you measure the widths of the fin, just by laying the fin on grid paper and measuring across the paper? What I'm trying to ask in a roundabout way is did you take into account the foil profile of the fin and the effect that the thickness of the fin has on the surface area?

haha I was wondering when that question would come up from a math teacher ;) no I did not find a way to account for the profile of the fin, i traced out the outline. I figure the fins are so thin that it cant add much and with only one set of hands I couldn't curve the paper around the profile and then trace the outline which theoretically should yield a more appropriate result! another way this can be done is by draping a rope over the fin x amount of times and using that as the length, but that would take forever and considering the margin of error we are dealing with by doing all of this manually I don't know if it would make a significantly more accurate result... any other ideas how this could be done without some fancy electronics and software?

by the way i was wondering how you would plot out the points and very nice, I wouldnt have thought of using the measurements that way!

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Wiindz said..

haha I was wondering when that question would come up from a math teacher ;) no I did not find a way to account for the profile of the fin, i traced out the outline. I figure the fins are so thin that it cant add much and with only one set of hands I couldn't curve the paper around the profile and then trace the outline which theoretically should yield a more appropriate result! another way this can be done is by draping a rope over the fin x amount of times and using that as the length, but that would take forever and considering the margin of error we are dealing with by doing all of this manually I don't know if it would make a significantly more accurate result... any other ideas how this could be done without some fancy electronics and software?

by the way i was wondering how you would plot out the points and very nice, I wouldnt have thought of using the measurements that way!

Hmmm, what you COULD do, given the time and the will to calculate it without the use of any 3D CAD software, is to use the width measures and measure the subsequent depth of the foil profile at each length. Using the assumption that the foil is two triangles creating the profiles (obviously a very simplified and incorrect assumption, but better than nothing) then you can use simple pythagoras to find the length across the surface of the fin and using that, find a ratio of width:length over the fin. If you did this a whole bunch of times, you could work out the average and then multiply the area we have calculated by the ratio and it would give a slightly larger area and i think, a slightly more accurate surface area for the fin.

I've tried to show this quickly in the pic below, obviously the more 'x' lengths you measured and used to find the average ratio of width to surface length the more accurate you'd be. Just an idea - i'm totally open to someone telling me this is bollocks haha

I think that makes a lot of sense, but think of it this way.. the average x for the 13cm fin is about 7.5. y ranges from .47 at the base to .15 at the base. lets assume y tapers down more or less evenly from base to tip making the average y about .31 . this is obviously an over simplification but if we do your calculation we get (skipping a couple mental calculations and steps): (7.5)^2 + (0.31)^2 = z^2 resulting in an average z of 7.507 and a fin area of 97.59 instead of the outline giving 97.03 ( I used the figures associated with the horizontal lines) and a difference of about 0.5%. correct me if I made a mistake above somewhere or if my line of thinking is flawed, but half a percent is meaningless with the kind of accuracy in measurement and tracing that we are dealing with here haha even if the foil was 1 cm thick all the way down, the area accounting for foil using this method would be .75% bigger than the original one... I think pain for gain in this method is just not worthwhile unfortunately

Haha, yep lets just ignore the effects on foil on fin surface area :)

I am not convinced that knowing fin area is much of an advantage as there are so many other variables....fins forward or back, fin stiffness and so on...
One of the upsides of single fin boards was the lesser expense in owning a variety of fins, however there's no going back now. It would be easier if there was more independent data out there on fins as there is with masts, regardless it's cool to see all the back of the envelope calculations.

On the contrary Al, I think area is super important to be able to establish how much you need approximately and then the shape and flex will be be the fine tuning of the characteristics of the board. obviously both of these factors effect area as well, but not to the degree that one would have to make huge changes in area to compensate.. as far as placement goes, my understanding is that the fins stay at pretty much the same spot where they feel the best to you, and you can finetune from there with spacing and position of the fin cluster. this is my understanding based on lots of reading of better sailors understandings of how these boards work

^^^ I am unsure that it is so important.
My 100L has 350cm2 and your 74L comes with 328cm2 (!!!!!) so obviously there is a lot of things going on.
I think maybe the Drake have a thin draft so they are faster but make up for the lack of lift by using more area?

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Wiindz said..

On the contrary Al, I think area is super important to be able to establish how much you need approximately and then the shape and flex will be be the fine tuning of the characteristics of the board. obviously both of these factors effect area as well, but not to the degree that one would have to make huge changes in area to compensate.. as far as placement goes, my understanding is that the fins stay at pretty much the same spot where they feel the best to you, and you can finetune from there with spacing and position of the fin cluster. this is my understanding based on lots of reading of better sailors understandings of how these boards work

It is definitely a starting point and a lot easier to think about than foil shape and thickness. Having been on the" boards" website and tried to follow a few discussions involving Ola and the Witchcraft crew about fin placement , toe in and other stuff it can get bull**** ridiculous (this is a subjective term) pretty quickly.

I guess the acid test is if you believe it is working better for you. When I see the investment that the GPS guys put into their fin quiver I am in awe. At least they can collect empirical data to measure improvement.

I guess that if I have a theory about wave fins ( and its more of a superstition) I will use smallest fins that my skills and the conditions will allow (it?s a lazy approach because usually it means that I leave things as they are).

@Mark actually I have a feeling that the Drake fins are pretty inefficient for their surface area, with a thick profile and a very raked back/ low aspect ratio outline.. ,my theory is that starboard "overfinned" the board surface area wise to compensate for this as pretty much every other board manufacturer/ fin maker suggest significantly less area than these fins.... BUT, this is all from speculations based on others' findings, I just got this board and its been too cold to sail it and try the stock drake fins it came with or the Black Project ones I got for it.. but the BP fins are narrower with a higher aspect ratio and about the same area so I would be able to get a nice comparison of what shape/ profile does in relation to surface area between these two sets :D

@ Al for my 85l and 68l single fin wave boards I just found a fin I liked, put it on all the way forward in the track. If I got overpowered (board wise) on the 85 I would change down to the 68 and not bother playing around with different fins and positions and all that fun stuff. My goal though is to get the most range possible out of this new quad (using different fin configurations) so I can hopefuly have a one waveboard solution paired with a 95-100l freestyle board. It seems to be a popular combination around here for people my size... worst case scenario i hold on to my 85l for float and ride waves and have a very functional 3 board quiver, it could be worse! haha I love the discussions Ola and the Witchcraft guys have, I am a big fan of all the nerdy part of windsurfing, and am super tweeky about my gear (other than fins until now haha!) so trying to soak it all in is my idea of a afternoon well used... pretty lame I know!

I've got Stoney 100l keel quad and have just bought some K4 stubbys (14cm as rear fins). My fronts are 9.5cm. Will try and caluclate the area of the fins as I've never used such small rear's in my big quad. Am keen to see how she goes. Anyone else tries such small rears in a big quad?

^^^ standard fins in my 100L are MFC QS350 (350cm2) which is 9cm and 15.5cm.

I am yet to try a set of 300cm2 that I have - which has 14.5cm rears.- but given how the board works when it is windier I reckon it will be fine.

But K4 are so damned flexy I don't rate your chances with 14cm rears. Unless you are pretty light I guess

have got em in the post now and have shaped em to fit stoney fin boxes so will let you know how i go. i dont really sail cross to cross on conditions anymore so being mostly sideshore, and this being my big board, it's quite often float and ride so early planing etc isnt an issue

am no, i'm not light, am 90kg

I would be interested to hear how that works for you bowsa as I would have to agree with mark that that sounds like an awfully small fin set with such flexy fins in the back for somebody of your size to be using on a big board. I think boards coming stock with MFC QS fins generally run a bit of a smaller area than the rest.. ex for a 74l board: jp= mufs? 316, sb= drake 328, quatro qs 250-300 (72l and 78l), rrd qs 300, f2 muf 294-312(72 and 77). the goyas who also run muf qs set up i believe seem to run the same area as the quatro boards... so maybe the qs setup provides lots of drive for its size?

@ www.k4fins.com/fin-specs/ they have all the specs and CM2 from the K4 fins including your Stubbys.Personal I think finsurface is a rather small factor in overall grip and performance. Stiffness,thickness, rake and toe-in are in my experience a much bigger factor.

I would imagine so, the problem is that testing all of those elements out and finding the ideal combination for you should prove to be not only expensive but quite time consuming as well... since it is very difficult to accurately manipulate only one of these variables at a time without a cnc machine its going to mean that one way or another you need to sail with lots and lots of different fins...

It takes a lot of time, but during the years you get each time an better idea of what works for you and what don,t.
Moneywise, I get a decent discount on K4, MFC and MUFin. Selling the fins aren't my cup of tea keeps it affordable.
That said, I think that at the moment I have 6 sets for my Quad that you can combine to other sets and 5 sets for my Trifin matching the conditions / my moodswings.

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Jeroensurf said..
@ www.k4fins.com/fin-specs/ they have all the specs and CM2 from the K4 fins including your Stubbys.Personal I think finsurface is a rather small factor in overall grip and performance. Stiffness,thickness, rake and toe-in are in my experience a much bigger factor.

All those things affect performance, yes. But simple fact is if you don't have enough fin size (area) it just ain't gonna work.

That is why a 30cm fin is no good on formula boards and 100cm2 is no good on wave boards, regardless of your rake and toe in and stuff.

Once you have enough lateral resistance (and only area can do that, maybe augmented by lift which is affected by draft)
then you can think about toe and rake etc.

True, there are limitations in how big or small you can go ( and I think nobody has written otherwise). That said, size and surface are often seen as one, and for sure that isnt (the MFC Quad set is one of the very few making point of that talking about surface instead of CM length.
Besides that, how do you determ working? For allround, most of the time planing and sailing upwind I love the Witchcraft flextail with its stiff pre-twisted 14.5front and 17cm customfins. At the same time I sail often the same board with 15cmStubby and 12cm Ezzy 2degree. With those small fins the board early planing is horrible and very quick of the plane, but I love this set in a turn on smallish waves because it can go unbelievable tight milking every bit out of the waves and serious extending the high-end range.



I know speedsailors sailing with a 32cm fin with a 7.8cm.As a former slalomsailor that is defintly NOT working and I would a 37-40cm but for there broad reach it seems to be enough as the got sailpower enough to lift the board anyway out of the water...

About the lateral resistance the shape of the board is there a big factor in as well. If you got a board with a longer as average sharper rail in the tail you simply need less fin surface for lateral resistance and so does Vee in the bottom.
You still got the limitations you named, but within those boundaries there is a LOT to gain with testing/trying/playing with different types of material, shapes and profiles. I have fins with 1.5cm shorther and less surface as the others butplaning earlier and having the same amount of grip due the fact the got less rake and the thickest part more forwarded...

For me things like that offer soo much variables to play with making me it for me really intersting. Even more so as it used to be with the single fins.