Water speeds are not usually measured with a pitot tube.  The reason a pitot is
needed in air (as I understand it) is that the pressure varies so greatly due to
the large range of operation.  In a boat you don't have that problem.

I've done pitot tubes for aircraft and they work fine.  This time it's going in
a boat.

The pitot project didn't need to know absolute speed, it needed to maintain a
setpoint (like a cruise control).

Andy