Wind Waker’s Great Sea conceals eight Triforce Charts — fragments of a map to the completed Triforce — distributed across the ocean floor in chests that require the Hookshot, Power Bracelets, and other late-game items to reach. Collecting all eight is the game’s most time-consuming non-combat challenge and the one most likely to produce what players call ‘the slog.’
The charts then must be deciphered by Tingle for 398 Rupees each — a total of 3,184 Rupees in translation fees before you can even begin collecting the Triforce shards the charts reveal. Rupees are scarce enough that this requires grinding. Nintendo acknowledged the issue in the HD remaster, which reduced the chart and deciphering requirements significantly.
What the ocean floor contains beyond the Triforce Charts: twelve Sunken Treasure chests that do not appear on any chart, accessible only after finding a specific Treasure Chart on a specific island and sailing to the marked location. Several of these contain the game’s rarest items. None require completion. All require the player to treat the ocean as an object of exploration rather than a travel medium.
Wind Waker’s sea is either the game’s greatest achievement or its greatest flaw depending on the player. The original’s ocean traversal is genuinely meditative if you allow it to be — the wind direction, the sails, the way islands appear on the horizon — and deeply tedious if you do not. The HD remaster’s Swift Sail removes most of the tedium and most of the meditation simultaneously.

Stumbled across this on a late-night session and couldn’t believe it. Your explanation finally made it click.
The attention to detail the developers put into this is insane. Most players will never see it but it makes the world feel so much richer.