At olosurfer we have been designing, building, and surfing tunnel fins with great success since 1997.
The tunnel above has leading edge channels which create drag reducing beneficial vortices. . . there's a lot of work in those leading edge channels
Tunnel fins have the lowest drag of all possible fin shapes, and our tunnel fin equipped boards have reached speeds up to 37 mph on waves of around head high.
The inline tunnel with centrally mounted planar fin is a tried and true setup which has enormous drive and holding power, as well as being one of the the fastest systems we have tested so far.
The 'Squidfish' with a ten inch pure tunnel
Tunnels must be designed as a whole with the surfboard, only certain kinds of board can be used successfully
Here's a ten inch tunnel with stainless steel FCS tabs made for a customer in Australia
And some pictures of tunnel finned boards being ridden:
