Minecraft wiki entry for Dolphin%27s_Grace, associated text: Dolphin's Grace significantly decreases the amount of "friction" from moving through water. This causes the player to swim significantly faster and lose speed at a slower rate, but also makes changing directions slower. Dolphin's Grace on its own allows you to travel 9.8 m/s underwater without Depth Strider, making it faster than a boat. Combining it with Depth Strider, players are able to travel at much higher speeds, adding 8.983 m/s per level. Potentially higher speeds are possible by adding soul soil underwater and using Soul Speed-enchanted boots, along with Speed II.