What type of wave shows wave-particle duality? Mechanical or Electromagnetic?

I would have have said electromagnetic. This is because visible light can have a calculable wavelength and frequency and can undergo diffraction patters as a wave, and yet can also be modelled as a particle called a photon which is used when describing how electrons jump between energy levels as it is a discrete packet of energy. It is not mechanical as they require a medium to travel through.

Because the dept in the ocean

The speed was not exceeded so it was slow