I don't understand how they get them on the beach. I'd think they'd bottom out well offshore, even at high tide.
Not that surprising really that the outcome is very different if the crew point the ship directly at the beach, try to arrive with as much momentum as possible and keep the engines at full power throughout while ignoring the various bumps and thumps.
All together that means the ship could potentially be significantly lighter than its usual unloaded weight let alone its weight when loaded.