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Another pow wow on the 'ol muti fin versus single
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Wind-NC-Hatteras



Joined: 28 Jun 2008
Posts: 777
Location: Cape Hatteras, NC

PostPosted: Thu Feb 20, 2014 10:44 am    Post subject: Reply with quote

Well, NOW we're getting WAY deep into the personal preference side of things. There is no right or wrong, no better or worse, just personal preference. Here's what I noticed when messing around with toe-in:

1) Less drag in a straight line. The water flow is actually squirting out the side just that little bit when you're cruising around. I didn't believe it would have an effect until I tried it myself. Yes, we're going relatively straight, but the little bit of displaced water right around the planing surface area is getting squirted, hence the little mini wake that we make. Less drag makes the board feel lighter and faster.

So, if you're planning on using a multi fin for bump and jump, you may very well like the extra speed and light feeling associated with using toe-in.

2) The "hook" in bottom turns that xander mentioned was sort of apparent to me. More apparent, was the light feeling.

3) Top turns are where things get weird, and become purely personal preference. Power steering with a very fluid and smooth arc is how I'd describe the effect of toe-in. I went back to straight fins, because I like how they hook up and allow you to pivot in a top turn, rather than absolutely requiring a smooth rail based arc. I don't always want power steering, sometimes I want to hoark on the wheel. With toe-in, the fins weren't grabbing, and I felt like I needed to use the rail more to define the turn, and couldn't push on the fins as much... Which is fine, rail turns are really fun and feel awesome, but just not what I'm always looking for.

so yeah, at that point it's really just "what do you want to feel?"

In the long run, though, it's pretty crazy how different you can make one board feel, just by messing with the fins. Obviously, we're all used to that with single fins, but you are seriously magnifying the effect by playing with multi fins. Shameless plug: I absolutely LOVE having the ability to go back and forth between quad and thruster and single and twin fin on my Tabou DaCurve. And while the endless possibilities can seem confusing, what I've found is that even when I "mess up" and would have preferred using a different set up on any given day, it's still an awesome ride... We're talking about seriously fine tuning here. It's ALWAYs a sweet ride, messing with the fins is just a matter of squeezing that last 2% of personal preference potential out of it.

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U2U2U2



Joined: 06 Jul 2001
Posts: 3056
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Thu Feb 20, 2014 10:53 am    Post subject: Reply with quote

great perspective

from someone who has tried some variations. The part I like best is NR1



" I didn't believe would have an effect until I tried it myself"

agree probably too in depth for some, too geek,
for those that want to install the fins and ride.

I want to hear about the Plymouth posi traction.......YMMV

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scottwerden



Joined: 11 Jul 1999
Posts: 213

PostPosted: Thu Feb 20, 2014 3:22 pm    Post subject: Reply with quote

U2U2U2 wrote:
It seems that no amount of discussion would change you mind anyway.


That is an odd thing to say. Not sure where that is coming from.

I surf more than windsurf these days (very little wind here on Maui this winter, but plenty of waves) and my SUP surf board has thrusters, with yes, toe-in. I cannot change that as the fin slot is fixed. I think my board is a tad sluggish, which may be me or a variety of things. All I am saying is that toe-in defies engineering logic. But I would like to test other toe-in angles holding everything else constant.
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isobars



Joined: 12 Dec 1999
Posts: 14164

PostPosted: Thu Feb 20, 2014 3:38 pm    Post subject: Reply with quote

hodad.andy wrote:
messing with the fins is just a matter of squeezing that last 2% of personal preference potential out of it.

I wouldn't even move or change one fin, let alone 3 or 5, to gain 2%. It's blowin', and I enjoy sailing more than dweebing. But that's just me.
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Bullroarer_Took



Joined: 10 Apr 2000
Posts: 22

PostPosted: Thu Feb 20, 2014 3:48 pm    Post subject: Reply with quote

It doesn't defy engineering logic.

The following has been shown by computational fluid dynamics and by experimental flow tanks. When the water comes underneath the front of the board it is forced down. This increases the pressure in the water under the board and so it tries to flow to a region of less pressure which is directly perpendicular to the board direction. However, this flow velocity is small in general compared to the speed of the board and so the flow vector is still predominantly towards the back of the board, but it includes a little bit of outward velocity. In order to not be draggy at speed the designers add toe in. It has also been argued that at different depths there is a different outward velocity. (Btw, I'm certainly not saying that all designers do CFD analysis in their board design, but some of them do.)

The major point here is that a particular toe in angle works best at a particular speed for a given board.

Enough with the science, now on to the art. What speed do you optimize the board for? On my board, with the stock thruster fins I find that at full speed it doesn't really seem to have much drag at all when on a beam reach. Below this speed, and especially below planning speed, I can definitely feel the drag. So, to me, my board is much slower to plane when used as a tri compared to a single. (And this is why I hate it on a flood. It's not the pointing ability, which is still not as good, it's the planning threshold.)

Your SUP was probably designed with surfing in mind and so the designer added the toe in assuming that you would be riding a wave of a given size and speed. In s straight line on flat water I would expect that you can feel the fins dragging.
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U2U2U2



Joined: 06 Jul 2001
Posts: 3056
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Thu Feb 20, 2014 3:50 pm    Post subject: Reply with quote

scottwerden wrote:
U2U2U2 wrote:
It seems that no amount of discussion would change you mind anyway.


That is an odd thing to say. Not sure where that is coming from.

I surf more than windsurf these days (very little wind here on Maui this winter, but plenty of waves) and my SUP surf board has thrusters, with yes, toe-in. I cannot change that as the fin slot is fixed. I think my board is a tad sluggish, which may be me or a variety of things. All I am saying is that toe-in defies engineering logic. But I would like to test other toe-in angles holding everything else constant.


Odd.... I read the below quote , ZERO. Certainly gives me the impression that you made up your mine, and it wont be changed.
I think Andys post may enlighten you some to the possibility , if you have such better knowledge than toe in on Cobra boards than them..good on you
Quote:
It makes zero sense (to me) for the thrusters to have toe-in, or toe-out. The primary purpose, and for BnJ, the only purpose, of fins is tracking - keeping the ass end of the board following the front end. Most of us point the nose where we want to go and expect the tail to follow.


the fin requirements for SUP or surf boards are different than a windsurf board .

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U2U2U2



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

PostPosted: Thu Feb 20, 2014 3:59 pm    Post subject: Reply with quote

isobars wrote:
hodad.andy wrote:
messing with the fins is just a matter of squeezing that last 2% of personal preference potential out of it.

I wouldn't even move or change one fin, let alone 3 or 5, to gain 2%. It's blowin', and I enjoy sailing more than dweebing. But that's just me.


fins , of course depending on the respective boxes can be moved fore or aft
to alter the character of the board results tighter or more drawn out turns.Not very time consuming and if you are handy with a screw driver not a major project, most can accomplish this when having a drink or small break then continue on their way.

Fin companies are now making fins with different toe in built into the base, so you dont HAVE to change the box, just the fin, same handly screwdriver.

if I could gain .5 MPG increase by dweebing ..would I ? But thats just me

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scottwerden



Joined: 11 Jul 1999
Posts: 213

PostPosted: Thu Feb 20, 2014 5:51 pm    Post subject: Reply with quote

derekcoon wrote:

The following has been shown by computational fluid dynamics and by experimental flow tanks. When the water comes underneath the front of the board it is forced down. This increases the pressure in the water under the board and so it tries to flow to a region of less pressure which is directly perpendicular to the board direction. However, this flow velocity is small in general compared to the speed of the board and so the flow vector is still predominantly towards the back of the board, but it includes a little bit of outward velocity. In order to not be draggy at speed the designers add toe in. It has also been argued that at different depths there is a different outward velocity. (Btw, I'm certainly not saying that all designers do CFD analysis in their board design, but some of them do.)


Thanks Derek, that makes sense. There does not seem to be a universal adoption of toe-in for thrusters, or for quads for that matter. The same rational would seem to apply to any outboard fin. But looking at what JP, Naish, RRD, Quatro, and Starboard are doing, the toe-in angle for similar type boards is very different from each vendor. Any idea which of those are doing CFD? That is not easy nor cheap.
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U2U2U2



Joined: 06 Jul 2001
Posts: 3056
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Thu Feb 20, 2014 8:48 pm    Post subject: Reply with quote

derek

you post does not address asymmetrical fins used in conjunction with toe in

they work in harmony

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Bullroarer_Took



Joined: 10 Apr 2000
Posts: 22

PostPosted: Fri Feb 21, 2014 6:40 pm    Post subject: Reply with quote

Scott - I know that Witchcraft does (or at least did) and some other fin manufacturers talk about it. I'm not sure about any others.

U2 - That exercise is left to the reader. In this case, you.
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