The main thing is how little is growing on it, since that makes invariably wrecks look unrecognisable, and usually hastens their degradation

(the Titanic isn't spectacularly rusting because it's sat in water with very low oxygen contect, it's spectacularly rusting because there's a microbe feeding on it. The well preserved wooden wrecks tend to be submerged in mud or in zones with relatively little life too)