Fin dynamics

[coldsup]

At what stage does a centre fin (2plus1 set up or thruster) start to interfere with the flow of water from the front side fins? Is it when too close to the sides? And what does that do....slow it down make turning a bit off? Just interested.

[Dwight (DW)]

I can hear and feel the turbulence when the rear fin is in the back of the box. It goes away as the fin moves forward.

I run single fin back of box. 2+1 front of box.

[coldsup]

I can hear and feel the turbulence when the rear fin is in the back of the box. It goes away as the fin moves forward.

I run single fin back of box. 2+1 front of box.

That’s interesting....I always understood it to be the other way round on a 2 plus 1 set up eg. You move the fin too far up the box it interferes with the flow from the two sides.....however that always threw me as surely the fin would be out of the way of fast moving water. I’m no fin expert though.

[PonoBill]

Hopefully, water is rarely moving straight across the bottom of your board when you are in a wave. If you think about the water moving somewhat sideways across the foils of the fin then it helps with visualizing what the fins are doing.

[coldsup]

Is there a point where fin position becomes inefficient? Eg. If on a two plus one set up....all the fins are more or less in line?

[dingfix]

I've never seen a board where the centre finbox is far enough forward to allow that.  I've always run the centre fin about as far forward as it will go which is typically where the leading edge is just behind the side fins.

If the board feels like it is too loose and lacks drive, move the fin back in 1/4 or 1/2 inch increments. Stop when you get the balance right between looseness and drive.

[coldsup]

I've never seen a board where the centre finbox is far enough forward to allow that.  I've always run the centre fin about as far forward as it will go which is typically where the leading edge is just behind the side fins.

If the board feels like it is too loose and lacks drive, move the fin back in 1/4 or 1/2 inch increments. Stop when you get the balance right between looseness and drive.

Yup, I’ve never run a centre fin that far forward but I’m interested in whether doing that or near to that causes any water flow issues/inefficiency kind of thing.  . On surfing, it just makes boards squirrely Imho.

[tautologies]

At what stage does a centre fin (2plus1 set up or thruster) start to interfere with the flow of water from the front side fins? Is it when too close to the sides? And what does that do....slow it down make turning a bit off? Just interested.

Well it is also not as easy as saying a thruster will do this or that. For instance the toe and cant thruster boxes will also impact the speed in which it is ideal for use. Then add the type of fin you are using.

In normal waves you will not have enough speed for it to matter that much, but adjusting the lateral position of the back fin will probably help how fast you can turn...but I doubt it is related to inhibitions from the side fins. The is more a function of leverage. Shorter distances between side fins to back of center fins help make the board more turny. 

[Beasho]

Too much talk.

I made this video last year to show what is going on with fins.  Slow speed - Big Fins.  High Speed - Small Fins.  It's physics.

https://www.youtube.com/watch?v=C3z01EF80RE

[exiled]

Beasho, how small would you dare to go on a single fin gun?