When the ship reaches the coordinates you specified, a hatch opens in the deck, and a giant treasure-crane emerges from somewhere belowdecks.
"Wow," you say, "that thing's pretty impressive."
"Yeah," says the navigator, "ever since aught three, all boats are required by law to have one. It's handy, though. Watch this!"
With a clanking of chains, the crane slowly descends into the water. After a few moments, the movement is reversed and the crane emerges from the ocean and swings back over the deck of the ship.
The crane opens, and a huge pile of foul-smelling wet sand plops onto the deck.
"Umm... great." you say.
The navigator shouts at some of the lower-ranking pirates, and they begin clawing through the nasty sand with their bare hands, until one of them exclaims "I found something! Here y'arrrre, Cap'm."
The crane opens, and a heavy object thuds to the deck.