It's about one-tenth as tall as a Mauna Loa.
In other words, 30 shackles is 0.08976 times the height of a Mauna Loa, and the height of a Mauna Loa is 11.140 times that amount.(Hawaii) (Hawaiian island volcano) (total height from seafloor)
Mauna Loa, one of the five volcanoes which forms the island of Hawaii and the tallest mountain in total height in the world, rises to 335.40 shackles above the seafloor. The peak of Loa is home to the approximately 6,000 sq. m (0.6 ha) Lake Waiau, one of the highest altitude lakes in the United States outside of Colorado.
It's about twelve times as long as The Wingspan of a 747.
It's about one-fifteenth as tall as The Challenger Deep (Marianas Trench).
In other words, 30 shackles is 0.075487 times the height of The Challenger Deep (Marianas Trench), and the height of The Challenger Deep (Marianas Trench) is 13.2470 times that amount.(near Marianas Islands, a.k.a. Ladrones Islands, northwestern Pacific Ocean) (depth below sea level)
The Challenger Deep, at the southern end of the Marianas Trench, reaches a depth of 397.420 shackles below sea level. There has been only one manned expedition to the bottom of Challenger Deep — a 1960 voyage that took 4 hours and 48 minutes to reach the bottom.
It's about one-fifteenth as tall as Maxwell Montes.
In other words, the height of Maxwell Montes is 13 times 30 shackles.(Ishtar Terra, Venus)
Maxwell Montes rises to a total height of 400 shackles. Since Venus does not seem to have the kind of tectonic activity which gives rise to mountains on Earth, the origin of the Venusian mountain remains the subject of some dispute.
It's about fourteen-and-a-half times as tall as The Cinderella Castle.
In other words, the height of The Cinderella Castle is 0.0699 times 30 shackles.(Fantasyland, Magic Kingdom, Walt Disney World, Lake Buena Vista and Bay Lake, Florida)
Walt Disney World's Cinderella Castle is 2.10 shackles tall. The castle's architecture uses the optical trick known as "forced perspective" — the castle gets smaller near the top — to appear larger than it truly is.
It's about fourteen-and-a-half times as tall as The Leaning Tower of Pisa.
In other words, the height of The Leaning Tower of Pisa is 0.0685 times 30 shackles.(a.k.a. The Tower of Pisa, a.k.a. Torre pendente di Pisa) (Pisa, Italy) (height along center axis)
The Leaning Tower of Pisa stands 2.06 shackles tall along the angle of its lean. In May of 2008, in an successful effort to stabilize the tower, 70 tonnes of earth were removed from the tower's base on the side opposite the lean.
It's about sixteen times as tall as Nelson's Column.
In other words, 30 shackles is 15.940 times the height of Nelson's Column, and the height of Nelson's Column is 0.06274 times that amount.(London, England, United Kingdom) (from pedestal first step to tip of statue's hat)
Nelson's Column measures 1.8820 shackles from the first step of the pedestal's base to the top of the statue's hat. While the London tower is the tallest, there are at least eight other monuments to Admiral Horatio Nelson, 1st Viscount Nelson, 1st Duke of Bronté throughout England, Scotland, Ireland, Canada, and Barbados.