Our understanding is that the ocean engineering field uses computational fluid dynamics (CFD) to do the initial analysis of designs. The CFD codes are good, but they are unable to handle some of the more subtle issues related to fluid dynamics, so the ultimate test is to build a scale model and stuff it into a wave tank. Apparently, the scaling limitations are well understood and “workable”. A good wave tank is expensive to build and run, so it can cost upwards of $10K/day ($US) to rent a professional wave tank. Hence, the use of CFD models first.
Both 3 axis tilt sensors and 3 axis rate gyros are readily available from places like SparkFun . Melding the resulting data into something useful is actually a little tricky. Kalman filters are typically used. Rate gyros suffer from drift. Tilt sensors suffer from noise. Designing a Kalman filter to integrate the two sensors is not particularly easy.
An alternative that is used is to mount 3-LED’s on the platform and video tape it with a couple of cameras. There is software that can track the LED’s and figure out the angles and accelerations.
Better have your test protocols worked out precisely in advance at those prices, and some empirical testing in a cheaper (uncontrolled) environment (like a lake) would be a good idea too, just for simple “gotchas” even if the measurements are of only limited usefulness. This would give you a chance to practice setting up and tearing down your test model so you don’t waste the time that you’re paying big bucks for.