: Hello John,

: One thing I would consider with the lexan is "flutter" at
: higher speeds. This is something I deal with a lot in designing
: paddle board and surfboard fins. They have to be very stiff or
: they start to vibrate at speed and sometimes you can even hear
: them hum. Have you thought about trying nylon sheet? It is
: friction reducing, very durable, and pretty darned stiff. The
: friction reduction may help solve your issue with rocks sticking
: in the slot.
: http://www.interstateplastics.com/plastic-sheets-details.php?sku=NYLNE&thickness=0.125&dim2=12&dim3=12&utm_source=froogle&utm_campaign=froogle&utm_medium=na&utm_content=sheet-NYLNE&gclid=COWQ9tbMsrECFSQDQAod_yAAvw

: Here is the latest fin I designed for a displacement hull
: paddleboard that is basically a "stand-up kayak" more
: than a SUP. The hull has a vee all the way down the keel so I
: don't need too much fin. The idea came from a tuna's fins that
: are narrow and swept back. The leading edge is at 30 degrees. I
: often paddle over shallow reefs and want a fin that will tend to
: deflect up rather than snag. Also it makes the fin weedless. We
: have this type of seaweed that floats on the surface in large
: groups and it tends to hang on fins. I am probably going to cut
: it off flat at the bottom, reducing that point at the end by
: about 1.5".

Um...high speed is maybe 7 mph :)

Bill H.