Anchor Bottom Time Feet Calculator

How anchor descent time works

Drop an anchor and, once drag offsets its weight, it settles into a roughly constant terminal velocity on the way down. Rates usually land around 1-2 m/s. Weight, shape and hydrodynamics decide where in that range you sit. A heavy stockless or Bruce anchor sinks faster than a light Danforth, which tends to plane through the water. The math is just t = depth / velocity, with feet and feet per second. At 30 m (~98 ft) you're looking at roughly 15-30 seconds before it touches bottom.

Touching down is only half the job. Now you pay out cable. The usual scope ratio is 7:1 (cable length against water depth) for safe holding when it's calm, and you bump it to 10:1 in a storm. In 10 m of water that means letting out 70 m of rode, which keeps the pull on the anchor horizontal so the flukes bite into the seabed.

Real-world applications

Coastal navigators use it to plan where and how a vessel anchors. Marinas and yacht clubs lean on it to coordinate berthing manoeuvres. During regattas, committee boats have to deploy and retrieve marks fast, and the same estimate helps there too. Fishermen run the descent time to judge when the anchor has set, then reverse the engine for the bite test.

FAQ

Why doesn't the anchor accelerate forever? The moment water drag matches the submerged weight, net force drops to zero and the anchor keeps falling at terminal velocity. That usually happens inside the first few metres.

Does current affect descent time? The vertical time barely budges. What a strong current does is push the anchor sideways as it sinks, so it ends up landing further from where you dropped it.

What is scope and why 7:1? Scope just means how much rode you've let out relative to the water depth. Run it at 7:1 and the pull on the anchor stays nearly horizontal, and that horizontal pull is what makes the flukes dig in and hold.