Assuming that Tean Mo (The human standing on the ship) is 177 cm:
He is 58 px.
1.7/58 = 0.03 m/px.
Distance between the ship and the center of the huge splash = 380 px = 11.4 m.
Panel Height = 699 px.
Splash Height = 677 px.
2atan(tan(70/2)*[677/699]) = 68.28784938 degrees.
Diameter of splash = 15.462 meters.
Radius of splash = 7.731 meters.
The splash area looks like a cone.
Volume of splash = 1271.1883027609 m^2.
Density of water = 997 kg/m^3.
Mass of splash = 1267374.738 kg.
Assuming 5 seconds as a timeframe:
Speed of creature that made the splash = 11.4/5 = 2.28 m/s.
E = 3.3e6 Joules = 0.001 Tons of TNT (Wall level+)
Huge Crab Splash = 0.001 Tons of TNT (Wall level+)