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Over or under finned
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DanWeiss



Joined: 24 Jun 2008
Posts: 2287
Location: Connecticut, USA

PostPosted: Fri Mar 23, 2018 2:06 pm    Post subject: Reply with quote

Outside of the nuances of fin selection, fin size is probably defined in your mind as fin depth. In other words, what is the distance at 90 degrees from the board's bottom to the fin's farthest point.

Using depth alone misleads because fin outline, area, foil shape and location and mounting location in the box contribute far more than merely considering the fin depth.

A basic summary goes like this:

All other things being equal, the location of the fin in the fin box tends to be the most controlling factor. A forward location will cause the board to power-up earlier and overpower earlier than a location closer to the back of the box. Actually, its the the location of the fin's center of lift.

A more upright and narrow fin probably will plane up faster than a more swept fin of similar area. This represents the efficiency of high aspect foils. This is not to say that a higher aspect foil therefore would overpower more easily. That factor comes down to how you tune all the gear together.

You will recognize "too much fin" by the situation where the board begins to behave oddly. Depending on the board, too much fin will lift the tail and push the board's nose down into the water, or, depending on the basic tuning of rig and board, will cause the nose to rise dramatically and lift the windward rail from the water rapidly.

Several techniques exist to help tame an apparently overpowered fin. The two basic ones are moving the fin back in the box if you can and/or moving the mast base forward 1/2" (you likely will need to raise your boom about 1/2 the distance you move your mast base forward in order to keep your booms "level". However, many boards that use a high aspect planing surface (like wide, formula-style boards) benefit from moving the mast base back rather than forward to counteract the fin's power and keep the nose from sticking.

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dmilovich



Joined: 19 Jul 2009
Posts: 95

PostPosted: Fri Mar 23, 2018 3:15 pm    Post subject: Reply with quote

Great set of comments, DanWeiss. I've just been wondering about some of those specifics while reading this thread. Thanks for the perspective and clarity.
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boardsurfr



Joined: 23 Aug 2001
Posts: 1245

PostPosted: Fri Mar 23, 2018 9:23 pm    Post subject: Reply with quote

If you're having problems with spinout or going upwind that make you think about switching to a larger fin, also consider a different type of the same size instead. Quality and behavior vary quite a bit between different brands, and also between different models from the same brand. Some boards are also quite "picky" about fins, and work much better with some kinds than with others (which may work perfectly well in other boards); that's more pronounced in slalom boards, though.

If a fin does not work well for you in a given set of conditions (board, sail size, wind strength, and chop), that does not necessarily mean the fin is bad. For example, I really did not care for one of my slalom fins until I realized that it needs at least 25 knots board speed before it "grips" well. Material and manufacturing-wise, it's probably the best fin I have, but I'm just too slow a lot of the time for it too work well. The profile is only about 10% thinner than other fins of similar size who are much easier to sail at low speeds. PWA sailors have won slalom races on the same fin. Bottom line: take the time to try different fins and see which one works well for you. For the price of one sail, you can get quite a few decent fins that may make your sailing much more pleasant, and give your board(s) a wider range.
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ss59



Joined: 10 Nov 2016
Posts: 92

PostPosted: Sat Mar 24, 2018 7:45 am    Post subject: Reply with quote

presumably, you ask the question because you have had some issue(s) commonly related to being under/over finned??

In windsurfing, as with so many things, start with the problem and try and solve it by working through..... technique - tuning - tools(kit) in that order.

spinout
technique - are you pushing too hard with your back foot? or more likely, is the pressure from your back foot on-off on-off, is all your weight on your back foot, can you move your back foot?

if that doesn't work
tuning - is the back strap properly aligned with the fin? is the sail downhauled enough? are your harness lines in the right place? is the fin damaged? is the fin in the box correctly? is the fin too far back in the (US) box?

if that doesn't work (and only then)
tools - is the fin upto the job? is the fin too small?

the same principle would apply to an uncontrollable board, getting upwind, getting planning etc.

In response to your other question, at times I sail with less fin than others of a similar weight because I prefer a looser feel and getting the tail to slide - other times I have bigger fins because I want more drive, normally to get out on onshore days. Compared to others my fins may be bigger or smaller but it isn't under or over finned, it is the right sized fins for me and my style of sailing on that day.
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techno900



Joined: 28 Mar 2001
Posts: 3879

PostPosted: Sat Mar 24, 2018 8:03 am    Post subject: Reply with quote

With fin costs roughly between $100 and $200, and a few much more, the average novice/intermediate won't be testing out too many options. Fins can make a big difference in performance, but to recognize the shortcomings of a particular fin or it's benefits, takes a fair amount of experience.

Those of us that have been around for awhile can usually make good choices when trying something new, but it's still a gamble.

When I bought my last Starboad isonic 111, several years ago, it came with two Drake slalom fins . Both looked great, but turned out to be the worst fins I have ever used. Spin out was a given at every speed and I couldn't pull them back in until I was almost slogging. I bought a Tectonics fin that has been great ever since. The Drake and Tectonics look almost identical in design.

The point is that until you are on the water sailing your style, it's hard to know what will happen with your fin. Brand/model recommendations from experienced sailors can be a big benefit, but not a guarantee.

An has been mentioned above, you can have the perfect fin and it still can be a dog if everything isn't tuned correctly.
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akrausz



Joined: 19 Sep 2008
Posts: 145
Location: FL

PostPosted: Sat Mar 24, 2018 11:21 am    Post subject: Reply with quote

I appreciate the insights in this thread. I am always looking for ways to make windsurfing easier on my aging body, especially bouncing and pounding through chop, so I am particularly interested in this comment:

cgoudie1 wrote:
...if your fin is too big, you'll be running for a smaller board when the wind picks up due to control issues (bouncing and rodeo rides...).

I typically use mast foot position and mast foot pressure to smooth out my ride. I fully understand how a fin will affect the trim of a board from side to side. I document which fins work best with specific boards and sails. I tend to use larger fins, as I am heavy, but does the fin really affect unwanted fore-and-aft motion of the board?
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cgoudie1



Joined: 10 Apr 2006
Posts: 2377
Location: Killer Sturgeon Cove

PostPosted: Sat Mar 24, 2018 6:09 pm    Post subject: Reply with quote

Greeting Mr Kraus,

It's more of a control issue than just fore/aft. When you're over finned there
are times when your board will want to jump out of the water, and your
ankles will feel it, you may find it hard to go downwind also. Nothing
quiets a board down like quite like a smaller fin.......... but in the scheme
of things, a little rake doesn't hurt either when you're after control.

.02

-Craig

akrausz wrote:
I appreciate the insights in this thread. I am always looking for ways to make windsurfing easier on my aging body, especially bouncing and pounding through chop, so I am particularly interested in this comment:

cgoudie1 wrote:
...if your fin is too big, you'll be running for a smaller board when the wind picks up due to control issues (bouncing and rodeo rides...).

I typically use mast foot position and mast foot pressure to smooth out my ride. I fully understand how a fin will affect the trim of a board from side to side. I document which fins work best with specific boards and sails. I tend to use larger fins, as I am heavy, but does the fin really affect unwanted fore-and-aft motion of the board?
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U2U2U2



Joined: 06 Jul 2001
Posts: 5467
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sat Mar 24, 2018 8:04 pm    Post subject: Reply with quote

To help conserve your retirement K4 , offer fins that ARE still affordable , and easy to experiment yet.
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PeconicPuffin



Joined: 07 Jun 2004
Posts: 1799

PostPosted: Sun Mar 25, 2018 8:03 am    Post subject: Reply with quote

A situation in which an otherwise well-performing board might benefit from going with a smaller fin is learning to duck jibe. If you're finned for best upwind performance you'll find the board fighting the carve and trying to go straight as you duck the sail. To a lesser extent this is true with step jibes.

To tune for this I wouldn't go more than 1.5" shorter. 1" usually makes a meaningful difference.

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jingebritsen



Joined: 21 Aug 2002
Posts: 3347

PostPosted: Sun Mar 25, 2018 10:10 am    Post subject: Reply with quote

when trying different sized fins there are lots of variables:

material
foil
chord
length

G-10 has the same flex characteristics at any given thickness. but is very tough vs scrapes and such.

molded fin material has unlimited flex based on designers' goals. less tough, but can be oh so perfect, or not in flex dynamics.... or oh so wrong.

thicker foils allow max lift at low speeds, thinner, max control at high speeds.

chords, see foil, but materials complicate things

length, oh so tied into above parameters.

most ideal fin i have found for most free ride and blasting onshore surf conditions: hydrotech 32 cm free ride. works from 4.7 to 7.5 sail sizes

https://progressivesports.com/hydrotech-freeride-production

because of g-10, sizes smaller and larger aren't quite as perfect as the 32cm. still good, just not as perfect.

yup, fins can be expensive. try a few of what your buddies may like to help you find what you may like better, faster.

avoid weed fins. they suck.

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