Should you hold down the Attack Button while using your Cutlass, you will perform what is known as a Dash Attack. However, did you know you can use it to also slice through water as quickly as you can enemies? Usually, the Sword Dash allows a character to charge their Cutlass Attack before quickly moving a short distance forward while dealing massive damage. But if you position yourself just right, you are also able to use the Sword Dash to move across a great distance of water with incredible speed.
In order to properly execute this trick, you will need to either stand on a ledge (whether a rock or a cliff facing the ocean, or even the edge of your Ship) or in the shallow waters (literally one step before where you would enter the water to swim). From here, do as before and use a Sword Dash. Once you let go of the charged attack, you will automatically move forward. If done correctly, upon entering the water, the speed of the dash will carry onward for several moments. This is because the physics of water are different than that on the surface, where the velocity of an object will continue for a period after entering it.
With this trick, you will effectively be able to move to and from your Ship very, very quickly. However, do remember that if you don't execute it properly - whether by miss timing it or by doing it too far from the water - you will be stunned for several moments due to the Dash Attack. You will also be unable to anything while the trick is in the process of being used, so keep that in mind so you don't propel yourself right into your ship without being able to come aboard.