When we first introduced the SP9 fin series, we mentioned that the intended construction methodology involved a combination of G10 and plywood.
This build technique allowed the fin's blade to flex torsionally, a feature that could not be achieved with a solid fiberglass version.
With its solid G10 base and a blade made from a combination of G10 and Baltic Birch plywood, this prototype served as a valuable learning experience. The insights gained from this prototype will be instrumental in the development of the next version. The main question was successfully answered. Building the fin this way allows the blade to flex torsionally. We measure between 5/8" and 3/4" of flex and a slight vertical flex. This torsional flex will provide an extra pop out of the turns and enhance the turning radius.
Initially, the plan was to add a layer of 4 oz over the wood to seal it. Instead, we have decided to give it a solid coat of epoxy to seal the wood. The main reason is that this will have less impact on the flex, and the wood will be sealed from water, so no glass is needed.
All of the parts were cut on the CNC machine before being assembled.
In case anyone is wondering what that RED dot is all about, it is a G10 rod used to keep all the pieces aligned during the gluing process. There was another one in the base where the pin was located.
Since the blade has a core of G10, we are not concerned about the wood being damaged in a collision. The primary change in the next iteration will be to change the transition area from the G10 base to the wood blade. This change will further enhance the torsional flex. But more importantly, it will simplify the gluing process when assembling the fin blank.
One of the reasons this construction method was selected is that it results in a much lighter fin. It is remarkable how much lighter it feels than the solid fiberglass version. We suspect it will float, but this has yet to be confirmed through testing.
We will provide more details once the next version is completed.