# Rusty's Nose vector

Rusty says:

"Nose vector (line towards nose): I typically point all four fins
to approximately the same place, which depends on board length and type
of surf the board is intended for."

Any two lines (fin lines) that are in a plane MUST intersect (except when parrallel).  If two lines (fins) intersect with a third line (stringer), and then the first two lines (fins) are mirrored over the third line (stringer) then all five lines MUST intersect.  So the fact four fin lines intersects isn’t that interesting.

HOWEVER

What is really interesting to me (because it is ubiquitously practiced), is WHY the intersection of the rear fin and rail fin  lines are on the stringer (on both thrusters and quads).  Why can’t the intersection line be somewhere off in in space, or why can’t they not intersect at all.  As blakestah contends with his fins, the more parallel the fins are, the faster you go.  Since the thruster is supposed to work on both rails, you obviously can’t toe the fin in either direction, so by compromise it is straight.  However, with the quad, why wouldn’t you make the rail and tail fin parallel (both would have the same toe-in angle)?

As far as I know (I could be wrong), on most boards the intersection of the “fin vector” (for fins on opposite sides) is off in space in front of the board, and for quads the fins on the same side intersect (unless parallel) somewhere behind the nose.

I don’t agree that “the more parallel your fins are, the faster you go”, unless you don’t turn your surfboard.

I don’t understand why you would want the rail and tail fin to be parallel, because the hull changes the direction of the flow and the further back the fin on the board the more the flow direction has been changed, decreasing the AOA. Furthermore, the front fin will change the direction of the flow further, lowering the effective AOA for the back fin.

Note: The above is just conjecture on my part. I reserve the right to be incorrect, but would like to be proven otherwise.