Reading the Water (Eyeball Navigation)

Definition

Interpreting water colour, surface texture and breaking patterns to identify shoals, coral heads and channels where charting is poor, standard practice in tropical waters. Deep water appears dark blue, sand shelves pale green or turquoise, coral heads brown or black, and overfalls or tide rips mark shallow patches and strong streams. It requires high sun behind the observer, good polarised glasses and an elevated viewpoint such as the spreaders. It fails with the sun ahead, in cloud or chop, and near sunset, so timing the approach matters.