🔍 Key Concepts

• Elevated coastal driller (jack-up rig) – how it operates and why it raises its hull • Difference between chart datum / charted depth, tide, and wave action • Meaning of still water level versus the effects of waves

💭 Think About

• Ask yourself: What exactly threatens the safety of a raised hull – is it long‑term water level, or short‑term motion on the surface? • When a jack‑up rig sets its leg length, what changing vertical factors must it account for over the entire period it will be on location? • Which option best represents the maximum vertical reach of the sea that could hit the hull under worst expected conditions?

✅ Before You Answer

• Be clear on the difference between charted water depth and actual water depth at a given time. • Consider whether tide alone is enough, or whether short‑term surface motions must also be included. • Check which choice describes the combined effect that could physically contact the underside of the hull.