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dmilovich
Joined: 19 Jul 2009 Posts: 99
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Posted: Thu May 18, 2017 12:05 pm Post subject: |
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@U2U2U2:
Help me understand this - why would increased toe angle improve things when the upwind fin (only) is already ventilating at ~1 degree? Wouldn't it just increase the stall?
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U2U2U2
Joined: 06 Jul 2001 Posts: 5467 Location: Shipsterns Bluff, Tasmania. Colorado
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Posted: Thu May 18, 2017 12:25 pm Post subject: |
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The toe is only part of the fin, you are leaving off the asymmetrical inside part, they work together.
You think what, it's ventilating .. the fin could cavitate , or humm
To make it clear, I don't think you actually have a huge issue, and if the side fins don't fix it, then nothing will.
To think that using the center fin only , causes no trail leads me to think you need a lot of research to understand the hydro effects.
Initially no, and I mean NO, Cobra quads or tris had ANY toe, it's taken them about 10years to remotely come close to my 2009 Witchcraft, with 1.5 toe and very specialized fins.
You will find divided opinions on toe and asymmetrical fins.
The fins you are using may just need improved, like MUF BPF or K4s, to eliminate your 'streaming' _________________ K4 fins
4Boards....May the fours be with you
http://www.k4fins.com/fins.html
http://4boards.co.uk/ |
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dmilovich
Joined: 19 Jul 2009 Posts: 99
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Posted: Wed Jul 26, 2017 1:53 pm Post subject: Streamlines going away... |
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OK, here's an update on my "streamline" issue with my cool Fanatic FW STB 105. (CraigG pointed out that my streamline issue is really my issue of staring at the water behind me instead of in front of me.)
Got some K4 Ezzy asymmetric 1 degree fins. Tried them both ways, meaning set up to "neutralize" my ~1 degree toe-in, and also switched to accentuate the 1 degree toe-in. No real change, although the neutralize setup seemed a little better. Still strong streamlines evident. Not good upwind performance.
Got in touch with Keith at CNC fins, at U2U2U2's fine suggestion. Replaced my center fin with his Weed Demon 22 cm and two of his side biter 10 cm asym, twisted, curved beauties. (all of these are for weeds, BTW)
Last week got out for about 40 minutes mostly powered 5.3 planing. Problem virtually disappeared - magic! Glided through jibes like it had a little motor. Upwind was pretty good, too. Can't say enough about how nice the board felt, but again, only about 40 minutes of testing. More to come as soon as we get more wind. |
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hilton08
Joined: 02 Apr 2000 Posts: 505
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Posted: Thu Jul 27, 2017 12:31 am Post subject: |
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I had Art Colyer (North Pacific) add thruster fins to a couple of my older single fin wave boards. He uses Futures fin boxes for his side fins so many of the fins are asymmetric (stock surfboard fins) with some toe-in (on the boxes). His theory is that the more vee in the bottom of the board, the more toe in you need since the water isn't necessarily flowing straight off the tail. Instead it will be diverted slightly off the sides of the tail by the vee. Both boards worked better with the extra fins, and I don't recall any streamlining turbulence being visible from the new fins.
More recently, I have had newer Cobra built boards that came stock with US or slot boxes for the side fins. I haven't measured, but I assume no toe-in.
I have seen the streamline trails on these boards, but not worried too much about it. They do seem more pronounced with larger side fins, so I usually stick to 10cm or less for the thrusters to minimize drag. These are all symmetric foils since that is what is readily available.
I have been tempted to try the K4 asym fins on the newer boards since the thinner foils should also have less drag, but cost/availablility are limiting factors.
That is the problem with multi-fin boards, there are too many options and variables in the setup and it gets expensive to try too many different fin sets. |
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dmilovich
Joined: 19 Jul 2009 Posts: 99
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Posted: Thu Jul 27, 2017 1:58 pm Post subject: |
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Thanks for the info, hilton08.
Keith at CNC, whose brilliant fins solved my problem, suggested something similar, but also pointed out the flow direction changes as you go deeper into the water along the fin span (towards the fin tip).
I was focused on weed conditions and in flat water exclusively (SPI). I'd tried the K4 asym Ezzy fins primarily to see if the "switched" positioning would negate the toe-in (.86 degree per side on my FW STB, also Cobra-built). But that's backwards from their intended use. In big chop or waves, the streamlines wouldn't matter if you're going rail to rail more often. I'll be using them in small waves in September.
I agree on the too-many options, and having weed conditions just compounds the variables. But I'll echo the fine suggestion U2x3 made, that the K4 fins are relatively inexpensive compared to G10 and the shipping is also not much. Steve from K4 was very helpful and prompt. I got my fins in about a week or so (from UK to SPI) so that was pretty quick, too. So you may want to try those as well.
Once you get the right set up, it's worth all the hassle, I think. |
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U2U2U2
Joined: 06 Jul 2001 Posts: 5467 Location: Shipsterns Bluff, Tasmania. Colorado
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Posted: Thu Jul 27, 2017 8:27 pm Post subject: |
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Appreciate the reports and updates.
K4, are getting quite the following, with more to come.
Keith at CNC , great guy and sailor, and extremely knowledgeable. _________________ K4 fins
4Boards....May the fours be with you
http://www.k4fins.com/fins.html
http://4boards.co.uk/ |
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U2U2U2
Joined: 06 Jul 2001 Posts: 5467 Location: Shipsterns Bluff, Tasmania. Colorado
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Posted: Thu Jul 27, 2017 8:33 pm Post subject: |
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hilton08 wrote: | I had Art Colyer (North Pacific) add thruster fins to a couple of my older single fin wave boards. He uses Futures fin boxes for his side fins so many of the fins are asymmetric (stock surfboard fins) with some toe-in (on the boxes). His theory is that the more vee in the bottom of the board, the more toe in you need since the water isn't necessarily flowing straight off the tail. Instead it will be diverted slightly off the sides of the tail by the vee. Both boards worked better with the extra fins, and I don't recall any streamlining turbulence being visible from the new fins.
More recently, I have had newer Cobra built boards that came stock with US or slot boxes for the side fins. I haven't measured, but I assume no toe-in.
I have seen the streamline trails on these boards, but not worried too much about it. They do seem more pronounced with larger side fins, so I usually stick to 10cm or less for the thrusters to minimize drag. These are all symmetric foils since that is what is readily available.
I have been tempted to try the K4 asym fins on the newer boards since the thinner foils should also have less drag, but cost/availablility are limiting factors.
That is the problem with multi-fin boards, there are too many options and variables in the setup and it gets expensive to try too many different fin sets. |
I use ProBox surf fin boxes, unless I use slotboxes for sides or quads.Both ready availible in symmetrical or asymmetrical . I use 1.75 to 2 degree of toe in. FWIW FCS FINS install right into ProBox.
Most Cobra built tris or forward quads NOW have some toein, but only about .5
The K4 Ezzy or little sharks with toe are the way to go for many applications. _________________ K4 fins
4Boards....May the fours be with you
http://www.k4fins.com/fins.html
http://4boards.co.uk/ |
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