What is anchor scope?
Scope is the ratio of chain paid out to the depth of water from the hawse pipe to the seabed. More scope lays more chain on the bottom, so the pull on the anchor stays more horizontal and the anchor holds better. Too little scope can break the anchor out. Too much scope increases the swinging circle and can put the ship too close to other vessels or shallow water.
How this calculator works
Required chain (m) = (Water depth + Height of hawse above water) × Scope ratio. One shackle of cable is taken as 27.5 metres (15 fathoms). The result is rounded up to the next quarter shackle as a practical guide. In good weather many ships use about 4 to 5 times the depth. In strong wind or current, 6 to 8 times is more common. Always follow the Master’s order and the company’s anchoring procedure.
Who should use it
Useful for bridge officers preparing an anchoring plan. Check swinging circle, holding ground, wind, current and nearby ships before deciding the final amount of cable.