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Over or under finned
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swchandler



Joined: 08 Nov 1993
Posts: 9987

PostPosted: Mon Mar 26, 2018 5:54 pm    Post subject: Reply with quote

"I find vert fins plenty stable , until they aren't, when they do spin out, they're hard to get to reattach. Raked fins are really easy to get to reattach."


Sorry Craig, I have to disagree. I find that high aspect slalom fins rarely spin-out, yet if they do, they are very easy to reattach. I can't say the same for my low aspect wave style fins sailing out and about in faster conditions.

Of course not all fins, irrespective of planform, are created equal. As pointed out earlier, two fins can look very much the same, but their respective real world performance can be worlds apart. Overall though, I think it's safe to say that you often get what you pay for. Cheap fins usually fall very short on the performance scale, and I would avoid them like the plague.
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grantmac017



Joined: 04 Aug 2016
Posts: 920

PostPosted: Mon Mar 26, 2018 11:58 pm    Post subject: Reply with quote

If sweep adds stability, then why are turny wave fins swept?

I have my own theories but I'd like to see if any actual documentation exists.
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Brian_S



Joined: 11 Jun 2005
Posts: 234
Location: SE Michigan

PostPosted: Tue Mar 27, 2018 7:27 am    Post subject: Reply with quote

grantmac017 wrote:
If sweep adds stability, then why are turny wave fins swept?


Too bad we don't have any fin designers here. I hate to speculate, but I brought up the swept fin issue, so that's what I'll do. Wave fins are slightly swept, with a turned tip. The turned tip probably forces the fin to bend and twist a little to maintain its lift while the board rolls and turns.

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Brian_S



Joined: 11 Jun 2005
Posts: 234
Location: SE Michigan

PostPosted: Tue Mar 27, 2018 7:45 am    Post subject: Reply with quote

swchandler wrote:

Sorry Craig, I have to disagree. I find that high aspect slalom fins rarely spin-out, yet if they do, they are very easy to reattach. I can't say the same for my low aspect wave style fins sailing out and about in faster conditions.

I have a feeling that it's more about the specific fins as you mentioned - some fins just seem to spin out more. Some of the slalom fins are thinner and designed with the wide point farther back (see the red profile below).

This can reduce the drag and allow lift at higher speeds, but often limits the angle of attack. The thicker, wide point more forward foils, allow lift at lower speeds and often tolerate a higher angle of attack at those lower speeds. BTW, 'thinner' is relative to length, since the longer fins have to be thicker to be strong enough.

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skyking1231



Joined: 10 Jul 2000
Posts: 260

PostPosted: Tue Mar 27, 2018 8:02 am    Post subject: Reply with quote

When looking at wave fins with the rake or swept back tip. Swept back fins allows for more broader turns one the waves....opposed to a move upright wave fin gives move pivoting turning ability. The drawn out sweep acts like a keel so to speak. Think of a gondola in Venice. If the big long oar went straight down....moving side to side would not move the gondola forwards, the rear would just move side to side. But straight out the back gives leverage to propel the gondola forward . This how it was explained to me my a fin designer. FWIW.
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techno900



Joined: 28 Mar 2001
Posts: 3879

PostPosted: Tue Mar 27, 2018 8:05 am    Post subject: Reply with quote

Fin discussions are always interesting because, at best, there are only a few generalizations that are true. There are just too many variables such that it's pretty hard to know what will happen on the water, until you get on the water. Variables meaning: fin design, type of sailing, water state, board speed, board used, sailor skill and sailor opinion, etc. etc. Fin design by itself must have a few dozen different variables.

Point is - it's always somewhat of a gamble when considering and buying a new fin.

However, there is always something to be learned in these discussions, so don't be shy about sharing.
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swchandler



Joined: 08 Nov 1993
Posts: 9987

PostPosted: Tue Mar 27, 2018 1:36 pm    Post subject: Reply with quote

If a drawn out sweep acts like a keel and provides more power, one would think that weedfins would come out on top, especially moving to windward. But, I think that most of us that have to use them know that highly swept weedfins come up a bit short in quite a few performance characteristics.
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