Allison SUP Race Fins and Probox retrofits are available at Abita Board Barn.

Tuning the Infinity Blackfish ST
By Marc Frechou of Abita Board Barn


    The 14’ Infinity Blackfish is the first board of its kind, setting the new trend in planing  hull race boards.  With its full nose and wide tail, it has a deep single concave that runs all the way to the tail.  The combination of these features makes it the most fin dependent board that we have ever paddled.  Our two 14’ Blackfish were ordered with the same fin box configurations, 1-10” center fin box, Pro Box twin fin boxes, and a Ventral fin box (10” fin box, 20” forward of the balance point).  The deep concave, wide tail and twin fins come from the Bob Simmons surfboards of the 60’s.  Dave Boehne of Infinity Surfboards, along with Larry Allison of Fibre Glas Fin Co. and Pro Box Fin Systems saw the advantages of this design and evolved this concept into a custom race board with no top speed limiter.  Unlike displacement hull boards that sit in the water and have a limit on the top speed that can be reached, planing hull boards quickly get on top of the water and have faster acceleration and no top speed governor! 

    The Pro Box twin fin set up on stand up paddle boards was pioneered by Larry Allison.  They started out as two rear fins, and quickly evolved into a triple fin rear system.  This should not be confused with the triple fins on surf SUP’s.  The Pro Box twins have a different foil, are angle adjustable with different inserts, and are designed to be faster and more stable than a single fin board.  The two outside fins work together to feed the center fin.  A single fin, by itself, acts as a pivot point, and has too many jobs to perform.  It is responsible for tracking, projection, the stability of the board, and that is a lot to ask of one fin.  The Pro Box twins are placed near the rail of the board, which gives a tremendous amount of stability to the board.  By doing this, they are removing some of the work from the center fin.  By taking away work that was previously required by the single fin, you can reduce the depth of the center fin.  Water recognizes depth as drag, so by doing this, you are reducing the overall drag of the board while at the same time increasing its stability.  

    The next fin that we are going to discuss is the ventral.  This is another fin concept that was developed by Larry Allison.  The ventral fin also plays a large part in side to side stability.  The other advantages of the ventral fin are projection, tracking, and removing some of the load from the center fin(remember that by taking away some of the work from the center fin, we can reduce its depth which in turn reduces the over all drag of the board).  Projection is turning the power from your paddle stroke into forward momentum.

    As I had mentioned earlier, the Blackfish is a new concept in race board design, so the proper fin setup was still unknown.  The board came to us with no ventral fins, Pro Box Stealth twins(the smallest of all the Pro Box twins), and a  Thresher keel kick fin(rear center fin).  The Thresher keel kick fin is also the smallest center fin in the Allison SUP Race fins line up.  The first time out on the boards, they felt very “slippery”, and fast to sprint, but we were unable to maintain these speeds for any distance.  We use the newest version of the NK Speedcoach 2 for all of our tests, so we have actual numbers, not just what “feels fast”.      Working closely with Larry Allison, the next step was to try all of the available ventral fins to solve this projection problem (unable to maintain speed).  The small ventral fin was better than no ventral fin, but was too small, with an underfinned feeling and still lacked projection.  The large ventral fin was too big.  You could feel the nose of the board rising, but it was no longer possible to reach the higher speeds that were previously attained.  The medium ventral fin was the perfect match to this rear fin combination, but we still felt that it could be better.  After trying nearly every fin that Larry has to offer, we settled on elliptical twins, a 6.25" (Rojas) kick fin, and a medium ventral.  With this combination, we now had a board that was stable enough for open ocean conditions, and on the flats was almost as fast as a flat water specific race board.

    Larry, being the perfectionist that he is, still thought he could come up with a better fin combination.  Like I had mentioned before, this is a new concept in board and fin design, and we had already tried every available fin.  This is when Larry went to work once again, and created a new prototype for us to test.  These new twin fins, combined with the Thresher keel kick fin and the small ventral fin are everything the board was missing!  These fins are a hybrid design, combining elements of the Stealth twins and the Elliptical twins that we had previously tested.  The result is an increase in the stability of the board over the elliptical fins, now rivaling the stability of recreational boards, while giving the board even more maintained speed, sprint speed, and unmatched tracking.  This new twin fin is now called the “Blackfish Twin”, and is the fin that completes the Infinity Blackfish.  We tested every combination that you can imagine, including single rear fins, twin fins with no kick fin, and all of these combinations with and without ventrals, so we can say with confidence that this is as good as it gets.  

    If you have any questions about tuning your board with the perfect fin combination, please feel free to call or email Abita Board Barn, and we can set you up with the best fins on the market. 

allisonsupracefins.com

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