Yes. I'm sure about that.
You are correct. A sinking ship landing on the seafloor invokes ordinary collision mechanics. This is governed by kinetic energy, a concept Vixen has previously grappled with and lost. Kinetic energy is reckoned from mass and velocity. Here the mass is more than just the ship's displacement, but I'm not going to tangentially explain the inertial factors in this post. Velocity depends on the downward gravity force—which operates the same underwater as it does above the surface—residual buoyancy, and hydrodynamic effects.
A ship founders the moment it exhibits negative buoyancy. Initially this can be a comparatively small force, but it generally increases during the sinking progression as flooding increases and air departs. This part of the computation is relatively straightforward. The mass of the flooded ship results in an easily computed downward gravitational force. Buoyancy is reckoned from the average density of the flooded ship (obviously much greater than the average density of the healthy ship) and the portion of it that is submerged—in the case of a foundered vessel, all of it. The force vectors are defined to be in opposite directions, so the final computation is simple arithmetic. That's the only accelerative force acting on the sinking ship. To correct Zooterkin: Earth's gravitational acceleration is 9.81 m·s
-2 in a vacuum.
Hydrodynamic effects are vastly more complicated. Two locomotives colliding—such as in the staged wrecks of the late 19th century—get to ignore aerodynamics. Both vehicles are moving through a fluid, but the dynamic effects of that fluid are negligible compared to the other factors. But an airplane wing falling from the site aloft of a midair collision will incur enough air resistance that we need to account for it in the dynamics computations. It will likely reach terminal velocity, and this is the velocity we have to use when figuring the kinetic energy of the wing's impact on the ground.
A ship that sinks in sufficiently deep water will also likely reach terminal velocity. And terminal velocities for objects sinking in water is much slower than for the same object in air because the water is obviously much more dense. It is the density of the fluid that factors into hydrodynamic resistance.
Static
pressure of the seawater is utterly irrelevant.
In any case, water is dense enough that even without contemplating terminal velocity we have to consider the hydrodynamics in order to determine any sort of velocity accurately—including the directional component of contact with the seafloor. Fluid resistance depends, as I said, on density, but more importantly on the area of the aspect of the object at right angles to the object's path. This changes as the ship rotates while underwater. And the resulting planing forces in turn change the direction of motion. Ships are meant to be hydrodynamic in part, and often aerodynamic in part. So a sinking ship hull will tend to align with its intended fluid flow as the velocity becomes high enough. (Fluid resistance is proportional in magnitude to the square of the velocity.)
The resulting damage to the vessel and the seafloor depends on the elasticity of the collision, which would have to be another post.
No, what Vixen posted has a nothing to do with how to solve the problem. It appears to be a pastiche of generally valid (but unrelated) physics principles thrown together in the vague hope that it looks like something.
