Free Anchor Swinging Circle Calculator
The anchor swinging circle calculator determines the maximum radius and diameter your boat will cover as wind or tidal currents shift. It uses the Pythagorean theorem to calculate the horizontal distance of your set anchor, plus your boat's length, to ensure you maintain a safe distance from shores, reefs, and other vessels.
Understanding Your Swinging Circle
When you drop your anchor, your boat acts like a pendulum on a string. As the wind, current, or tide changes direction, your boat will pivot around the point where the anchor is buried. Knowing this total distance is vital for safety at crowded anchorages.
How It's Calculated
The simplest (and most conservative) method many boaters use is adding their total rode length to their boat length. However, this calculator uses the precise Pythagorean Theorem. Because your rode travels at a downward angle from the bow to the seabed, the actual horizontal distance the rode covers is shorter than the physical line paid out.
Swinging Radius = Horizontal Rode Distance + Boat Length Overall
Why High Tide Matters
You must always calculate your swinging circle based on the maximum expected high tide during your stay. If you anchor at low tide in 10 feet of water, and the tide rises another 8 feet overnight, your scope and your horizontal swinging distance will change dramatically.
Variables in the Real World
Keep in mind that boats do not always swing in perfect unison. A heavy cruising sailboat on an all-chain rode will hang differently than a light powerboat on a rope rode. When pulling into an anchorage, visually estimate the swinging circle of your neighbors and give them a wide berth.