As the pirate ship falls, its gravitational potential energy is transferred into kinetic energy. At the bottom of the swing it's travelling at its highest speed. As it swings back up the other side it slows down as its kinetic energy is transferred back into gravitational potential energy.
If the mass of the pirate ship is doubled, the kinetic energy also doubles, however if its speed is doubled its kinetic energy quadruples.
watch the learning pod and sketch a mind map