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Mooring Line Load Calculator

Work out mooring line load instantly with clear inputs, formula shown and shareable results.

About Mooring Line Load Calculator

Mooring lines only share load in proportion to the cosine of their angle to the applied force, and never perfectly because of stretch and tension differences — an 85% sharing efficiency is a common allowance. Industry guidance keeps working load below about 55% of minimum breaking load.

Formula

Mooring load

load per line = total force / (lines x cos(angle) x sharing efficiency)

Worked example

With the default values below, Mooring Line Load Calculator returns Load per line of 38.94. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total environmental force
180 kN
Lines sharing the load
6 lines
Average line angle to the force
25 °
Line minimum breaking load
90 kN

Results

Load per line
38.94 kN
Share of minimum breaking load
43.3% %
Effective lines allowing for angle
4.62 lines
Assessment
Acceptable but monitor

Step by step

  1. 1Values used
  2. 2Mooring load
  3. 3Load per line= 38.94 kN
  4. 4Share of minimum breaking load= 43.3 %
  5. 5Effective lines allowing for angle= 4.62 lines
  6. 6Assessment= Acceptable but monitor

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

Why not assume equal sharing?

Differences in line length, material and initial tension mean the tightest line takes far more than its nominal share, so an efficiency factor is applied.

Why is 55% of MBL the guideline?

It preserves margin against snap-back, wear, splice strength loss and dynamic surge loads, which can easily double a static tension.

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Mooring Line Load Calculator – Calculate Load per line