I will be conducting some underwater tow testing of some cylindrical
shaped components -- to record lift / drag data.
I would like to instrument the pieces under test such that I can
measure and record the tilt angle relative to tow direction using a
dual axis accelorometer.

1.  What is the best way to accomplish this (i.e. what sensor should I
use)?  I have a few Onset 4 channel external data loggers capable of
measuring voltage inputs (0-2.5 V) to log the data.

2.  I thought that I would mount the board on the bottom of the
cylinder and record pitch and roll; however orientation of the board
w.r.t. the yaw (z) axis will not be fixed necessarily (it could rotate
about z during the tow).  I need a resultant angle relative to flow
based on the pitch and roll from the accelerometer.  How do the pitch
and roll data output from the accelerometer relate to this resultant
angle?

Thanks