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.