Anchor Rode Calculator

Determine safe anchor rode length, catenary chain requirements, and swing radius for peaceful and storm anchoring.

Water Depth (Feet) Sounder reading at high tide

Bow Freeboard (Feet) Waterline to bow roller

Boat Length Overall (LOA) Required for swing radius

Rode Type

Anchoring Conditions (Scope Ratio)

Required Rode to Deploy

115 Feet

23 ft total vertical height

Min. Chain Leader 32 Feet 1x Boat Length min

Total Swing Radius 145 Feet Rode + Boat Length

Crucial Freeboard Rule: Never calculate scope from sounder depth alone! The height of your bow roller above the water must be added to water depth. Overlooking a 5 ft freeboard turns an intended 5:1 scope into an unsafe 3.9:1 scope.

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Understanding Anchor Scope and Catenary Curve

Modern anchors (Rocna, Mantus, Manson Supreme, Fortress) hold by digging into the seabed horizontally. If an anchor is pulled upward at an angle exceeding 10 to 12 degrees, the fluke breaks out of the bottom and drags.

Total Vertical Height = Water Depth at High Tide + Bow Freeboard
Rode to Deploy = Total Vertical Height × Selected Scope Ratio
Max Swing Radius = Rode Deployed + Boat Length Overall (LOA)

Heavy chain provides catenary (a curved sag in the rode) that acts as a natural shock absorber, keeping the pull on the anchor shank completely horizontal.

Frequently Asked Questions

What scope ratio should I use for overnight anchoring?

The US Coast Guard and Chapman Piloting recommend a minimum 5:1 scope for all-chain rodes in calm anchorages, and 7:1 for rope-chain combinations or freshening winds.

How much chain should be on a rope rode?

A good rule of thumb is at least 1 foot of chain for every foot of boat length (e.g. 30 ft of chain on a 30 ft boat) to protect nylon rope from chafe on rocks and provide holding catenary.

Why must tidal rise be factored into anchoring depth?

If you anchor in 10 feet of water at low tide with a 6-foot tidal rise, your depth at high tide will be 16 feet. Calculate scope for the high tide depth to avoid dragging in the middle of the night.