Kneeboard Surfing USA Community Forum

Hi all,

I like the looseness I get when I have my shorter fins in front and the larger ones in the back. However, I like the speed I get out of my Y2K Blast which has the smaller fins in back. I'd love to hear the reasoning behind selecting fin size and location/placement.

Thanks for your input,
Mike

Good question. I'd like to hear some responses also.
To expand on this, if one were to use FCS curved fin or H2 (foiled on both sides), should these specialty fins be in front or back of quad set up? Why?

nutshell answer - all related to my surfing, milage may vary (love that expression)

big fin in front: reasoning:

at the beginning of turn (which is the hardest driving part of my turns) you lock in the rail just in front of the front fin. At this point the front fin and the part of the rail you have locked in become the main pivot point (area) which you are driving off.

(assuming you drive off your rail) then at this point:

if the back fin is too far away it becomes like a rudder and not part of the fin cluster. - ie causes drag rather then drive.

or: if the back fin is too big or has too much rake it fights against the front fin.. Causing both drag and stiffness.


-moral:if you want to use the rail to drive off and get the board more on the rail, you work with a smaller back fin.

if you want to drive off the tail, then you could probably have the back fin bigger. But this means you use a lot of the advantages of using your rail. And maybe you will end up surfing a stabilised twinnie rather than a quad.- which is probably why it could feel looose.

getting back to the turn:

in the latter part of the turn, you have moved your weight back towards the back fin - but because you (I) are unweighting in preperation for the next turn you don't need as much fin area to push against. Consequently the back fin can be smaller.

If its too big then in this part of the turn it will also make the board too stiff..

coming out of a cutty ready to hit the foam coming the other way the smaller fin in the back can be a disadvantage cause you want to lift the nose of the board up onto the foam and you can't do it like a tri by weighting the tail and using the rocker - so small back fin in quad gives nothing to push against here.

For all my quads I (usually) have a box in the front and fcs in the back. Cause the position of the front fiin is what can lead to a dynamic board or a crap board.


flex is an important factor too - if you use a big fin at the front get some flex in the rake. But keep the flex out of the back fin.


btw steen has said that he uses a larger fin MR in back for fullish waves - didn't work for me tho.

sorry mik911 don't know answer to yours

as I said, these things work for me, maybe not for anyone else on the planet

Quote Headwax - "nutshell answer - all related to my surfing, milage may vary (love that expression)

big fin in front: reasoning:

at the beginning of turn (which is the hardest driving part of my turns) you lock in the rail just in front of the front fin. At this point the front fin and the part of the rail you have locked in become the main pivot point (area) which you are driving off.

(assuming you drive off your rail) then at this point:

if the back fin is too far away it becomes like a rudder and not part of the fin cluster. - ie causes drag rather then drive.

or: if the back fin is too big or has too much rake it fights against the front fin.. Causing both drag and stiffness.


-moral:if you want to use the rail to drive off and get the board more on the rail, you work with a smaller back fin."

Spot on answer Headwax

& if you want power & fluidity through all your moves...you've gotta use that rail pivot point.

ahhh Crox

at least two people on the planet

cheers from Oz land.

Thanks Headwax!!!

So, should the size of the front (& back) fin be based on the distance from the rail &/or the distance from the tail?

Mike

hello Mike

pleasure

the only one of the two variables (distance from rail or tail) I've been able to play with are distance from tail (and probably just as importantly "longitudinal" fin seperation) via fin box and using different tabs on the fcs fitting fins

but I guess distance from rail will have less effect on the fin size - can't give you any feedback tho . Then you run into fin cant and "toe in" as variables also. also no need to have same cant and toe in on front and back fins but that's just another variable to screw our minds with

on individual fin seperation: the interesting thing is that, in some sceneraios, if you push the front fin further back (and don't move the back fin) there comes a point where the board becomes LOOSER - rather than tighter as you would expect

emptybarrels explains it as unifying the fulcrum point

on the other hand, as you seperate the fins you increase the drive until the point where the back fin becomes a rudder and just drags through the turn.Similar thing happens when you leave the fins in place and change the rake.

flex in the front fin rake means that the board gets a boost halfway through the turn - not in the end of the turn as it would, for example, in a single fin

I've played with a set of fins where the fins "twist" so the cant and toe in varies (increase) as you go up the fin - but I couldn't get my head around whether it made any difference or not

just my personal observations over the last three years. (before that I rode tris) I'm sure Bud/ Parkes have tried all the variables would be the chaps to talk to.

Headwax,

It's imput like yours, that keeps me reading these threads!!! It seems that we have got a couple of similar threads going on now regarding how fins, rails and edges effect the way our boards react. Thanks for contributing to all of these!

Mike

Mike glad to pass on what I think I've learnt

lot of fun playing round with boards; my main problem is I'm never happy

I get a board tuned and then get another idea and order another one..... and start the process again

and then realise from what I learnt in the new board that I can go back and retune the old board

one day I'll be in the old people's home taking wheels (or brakes?) off wheel chairs to see if they go faster (heh)

(mind you, they'll be other people's wheel chairs)

cheers

HW