Alcarondas, the Castle of the Sea was the golden-and-black flagship of Ar-Pharazôn, the last King of Númenor. It had many oars and many masts, upon which were sails of gold and sable. In this ship he sailed to the shores of Aman, leading the Great Armament to challenge the Valar, leading to the Downfall of his kingdom.
The name is not easily translated, but it obviously doesn't mean "Castle of the Sea". It contains alcar "glory", and no recognizable element for the word "sea" which in Quenya is eär.
 Other Versions of the Legendarium
In earlier versions of the story Ar-Pharazôn's ship was the Aglarrâma, a word in Adûnaic which seems to incorporate the Sindarin word for "glory", aglar, perhaps adapted in Adûnaic.
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Silmarillion, "Akallabêth: The Downfall of Númenor"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Peoples of Middle-earth, "The History of the Akallabêth", p.156