The evolution of the Laird tunnel finned surfboard

Here are the original 11'8" 'Laird' prototypes. We built two identical prototypes at the same time ( 2004) , one equipped as a singlefin and the other with a 6 inch diameter tunnel fin



 The singlefinned version, which rode well.

The tunnel finned version, which rode amazingly well:

The first fin setup, with a very thin 12 inch base bulb tipped keel fin  , and only 6 inches deep. The entire fin system was 16 inches long foreand aft. This combination resulted in one of the fastest boards I've ever ridden, a ridiculously fast section making rocket. Turns were easy and precise, but restricted to very long arcs. Shorter radius turns could be accomplished with a lot of effort, but were only required if paddlers got in the way.

Here's the second fin used for the MkII prototype, which was a great all round fin, many waves were ridden with this one in conjunction with the 6 inch tunnel and I was very happy with it. 

MkIII sporting a new bulb tipped flex fin with carbon fibre upstand, which is still on the board today.

The JET tunnel fin setting

Today the tunnel fin for the JET 7-8 was set into place.

  

The angle of attack of the tunnel is at one degree of lift greater than that of the hull adjacent to the fins.

Even though such a low difference in the angle of attack between the annular wing tunnel and the hull means that the tunnel is essentially a slave foil, in practice the effective difference in the angles of attack is greater than one degree, especially at low speeds. This is because the annular wing is a good lift producer at low angles of attack, even at low speed, whereas the surfboard  hull in the fin area is relatively narrow and  soft railed, thus producing very little lift at the low angles of attack in which the annular wing works efficiently. As speed increases the hull and the tunnel work together more harmoniously, partly because the tunnel dominates in the lift department thus taking load off the hull, and partly because the efficiency of the hull increases with greater speed.

Building the 'Jet' 7'8" wooden surfboard: The tunnel fin

Foiling tunnel fins can be very tricky, especially on the inside of the fin.This setup makes the job easy, hopefully it is self explanatory. The fin is of course the 4 inch diameter tunnel for the 7'8" Jet ' semi gun'