According to our current understanding of physics, nothing can travel faster than the speed of light in a vacuum, which is approximately 299,792,458 meters per second (about 186,282 miles per second). When it comes to traveling through a dense medium like water, the speed of light is significantly reduced due to the higher refractive index of water compared to a vacuum.
In water, the speed of light is approximately 225,000 kilometers per second (about 140,000 miles per second). This is about 25% slower than the speed of light in a vacuum. However, it's important to note that even though light travels slower in water, it still remains the fastest thing in that medium.
In terms of other objects, such as a boat or a submarine, their speeds in water are limited by various factors such as drag, propulsion efficiency, and the capabilities of the vessel's design. The maximum speed achievable by these objects depends on their specific design, power, and other factors, but it will always be significantly lower than the speed of light in any medium.
It's worth mentioning that there have been claims of particles called neutrinos traveling faster than light in specific experiments, such as the OPERA experiment in 2011. However, these results were later found to be due to experimental errors, and no conclusive evidence of anything traveling faster than light has been observed to date.