You are describing a hydrofoil.
When a vessel travels through the water it raises or sinks slightly relative to when it is not moving. This change in how the vessel sits in the water at varying speeds is referred to as the Settlement and Squat.
The speed of light in water is less than the speed of light in space. Only light can travel at the speed of light.
Speed of light in water = speed of light in vacuum/refractive index of water
When light with wavelength of 589 nanometers moves through water at the temperature of 20° C, its speed is 75% of the speed of light in vacuum.
The maximum speed that a vessel will achieve relative to ground is its own maximum speed through water plus the speed of the the moving water downstream.
No, light does not speed up in water, it slows down.
No. Light slows down whenever it passes through water. Nothing is faster than the speed of light in a vaccum.
A water-going vessel, such as a boat or ship.
adding salt raises the boiling point of water which can help speed cooking time.
That would depend what it enters from. If the light is transitioning from air to water,its speed decreases. If it's going from jello to water, its speed increases.
No, it shouldn't. And it isn't.
You are seeing a vessel from the rear, or it is at anchor.