HesapHanem

Anchor Rode Length Calculator

Enter the water depth, bow height above water and scope ratio to get the rode length to deploy.

Result

50.40

How it is calculated

The tool multiplies the vertical distance from the seabed to the bow roller by the scope ratio:

rode length = (depth + bow height) × scope

depth is the water depth at the anchoring spot, bow height is how far the bow roller (or the point where the rode leaves the boat) sits above the water, and scope is the ratio of rode let out to that vertical distance, so 7 means 7:1. The answer carries no unit: it is in whatever length unit you used for depth and bow height, so use metres for both or feet for both. Depth and scope must be above 0, and an empty bow height is treated as 0. The tool does not check whether your scope value is sensible, so choose it for your anchor, rode type and conditions.

Worked example

You are anchoring in 6 m of water. The bow roller is 1.2 m above the water, and you want a 7:1 scope. Vertical distance: 6 + 1.2 = 7.2 m. Rode to deploy: 7.2 × 7 = 50.40, i.e. 50.40 m. With only 3:1 scope the same spot would need 21.6 m, which holds far less firmly because the pull on the anchor is at a steeper upward angle.

Try this example →

Common mistakes

  • Leaving out the bow height. Rode runs from the bow roller, not from the water surface, so using depth alone, 6 × 7 = 42, gives you 8.4 m too little.
  • Measuring depth at low tide and ignoring the rise to come. At high water the depth is larger, so enter the depth you expect at the highest tide before you leave the boat.
  • Mixing units, such as depth in metres and bow height in feet. The result has no unit, so a mix gives a wrong length without warning.
  • Typing the rode length you already own into the scope field. Scope is a ratio like 5 or 7, not a distance.
  • Counting a short length of chain only. If part of the rode is chain and the rest is rope, the formula gives the total length to pay out, not the length of each part.

About this calculator

This calculator determines how much anchor rode — chain, rope, or a combination of the two — to let out using the standard boating formula: rode length = (water depth + bow height above the waterline) × scope ratio. Measuring depth from the bottom to the bow roller, not just to the surface, matters because that's where the rode actually starts.

Scope is the ratio of rode length to that total vertical distance; a typical overnight anchorage uses a 5:1 to 7:1 scope for adequate holding, while a low-angle pull in storm conditions calls for 8:1 or even 10:1 to keep the anchor shank pulling nearly horizontal instead of yanking it up out of the seabed. Sailors and boat owners use this to avoid the two failure modes of anchoring: dragging from too little scope, or swinging into neighbours from too much.

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Comments (1)

  • Editorial team

    Plug in the depth you expect at high tide, not the depth you see when you arrive, because the water can rise while you are at anchor. The result is the total rode that must be paid out, so mark your line or chain at known intervals to measure it. It also gives no unit of its own and says nothing about swinging room. What conditions do you usually anchor in?

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