Ramius-II wrote:I was thinking of this more like a venturi than a pitot or it does not make any difference?
It's all about the geometry of your pick-up.
If your pressure sensor connects to a tube that sticks straight out of the front of your boat and has negligible flow within that tube you have a pitot and my original answer stands. (This arrangement will see a pressure increase
as speed builds.)
If on the other hand you've got a device that the water flows through and you're measuring pressure off the sidewall of that flow-through tube, then you have a venturi and smooth tapers are what you need. (This arrangement will see a pressure decrease
as speed builds.) That said, the only place I can think of that I've seen that kind of structure is the vacuum source on an aircraft. (For running vacuum driven instruments, not measuring speed.) See below.