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.

The Jet tunnel finned semi gun wooden surfboard

Here's the latest progress on the Jet 7-8:

:

A number three elliptical pintail

Single concave through the nose and mid section, with soft rails. .  a favourite combination

Weathered  planks, no logo

The first resin coat

Shaping the Jet 7-8

 The Jet

 Length: 7'8"

Width: 21"

Thickness: 2.25"

Fins:  Tuberculed cutaway spitfire with tunnel

Construction: Hollow parallel profile 4 layer paulownia.

'Jet' 7'8" pintail wooden surfboard: laminating the panels together

Applying epoxx resin thickned with paulownia dust to the deck

The glue is squeezed on to the underneath of the deck where the frames will attach using a ziplock bag with the corner cut off

The first frame and rail panel is lowered into position

The next day the after the bricks which clamp the two panels together have been removed

Here the second frame panel is being clamped down

Adding the strategically placed vertical struts to some of  the frame junctions. This helps the board to resist any internal pressure which might build up due to temperature changes.

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'

'Jet' 7'8" pintail wooden surfboard

Here's the cutaway spitfire fin for the 7'8" 'Jet' being foiled today. The fin is 6 laminations of 3mm Paulownia.The 4 inch diameter tunnel fin will sit neatly inside the cutaway. My hand represents the bottom of the surfboardChord ratios will be 15% on the base, and 8% just above the cutaway. The complete fin system is 9 inches high and 9 inches long ( fore and aft ). It is a very powerful setup.

Building the 'Jet' 7'8" wooden surfboard

Here's the 4 inch diameter paulownia vort-x tunnel for the 7'8" Jet being foiledThe deck panel cut out and ready for gluing

'Jet' 7'8" pintail wooden surfboard

'Jet' 7'8" pintail wooden surfboard This board is a development of our original heart series 7'5" from 1995, and is powered with a cutaway spitfire plus tunnel fin.Construction is underway with the deck panel and fin panels made.