The "hole in the sea" off East London is quite well-known to those sailing in that area. The weather conditions occasionally produce a hugh, deep trough into which the unfortunate ship plunges. Many years ago, the 27,000-ton Union-Castle passenger liner RMS Edinburgh Castle encountered it, and received quite a bit of superficial damage, but came nowhere near being sunk. I was not aboard at the time, but I was aboard the 36,000 ton RMS Windsor Castle when we "took the plunge!" Middle of the night, and I woke with a feeling of going down in a sloping lift. At the bottom, we fetched up with a tremendous crash, and then rose out of it with a lot of jerking and squeaking, and continued on our way. The expansion joint next to my cabin on the bridge deck had opened to such an extent that a lot of the looped electrical cables crossing it had broken. There were some broken portholes, windows and deck screens, but we wer OK. Rumours were that the Waratah was not as stable as she should have been!
Unfortunately, the plans seem to have fallen into the hands of the National Maritime Museum, so anyone wanting to purchase them will need a big bank balance. Expect them to cost well over £100!
In the early 70s, the cargo liner Bencruachan came into Durban with a broken back after having taken the plunge.
Bob