Mooring example
Input
Mode = Mooring, Depth 8.5 m, Tide range 1.2 m, Wave/Wind factor 1.2, Scope 5:1, Extra allowance 2 m
Output
Minimum 50.5 m, Recommended 60.2 m, Purchase length 61 m or more
Important safety note
- This tool gives a general estimate only. Required length can change with wind, waves, current, vessel size, attachment height, bottom type, chafe, stretch, rope or chain type, and local rules.
- Stay conservative to avoid shortage, and make the final decision in the field.
Rope Length Calculator (Depth, Tide Range, Safety Factor)
Estimate minimum and recommended rope length for mooring, anchoring, and buoy lines from depth, tide range, scope, safety factor, and extra allowance.
Switch between m and ft, compare minimum versus conservative recommended length, and share the same setup by URL.
Modes for mooring, anchoring, buoy lines, and generic use
Shows minimum, recommended, range, and purchase-ready length
Metric/imperial switching with shareable URLs
How to use
- Choose the usage mode and unit, then enter depth and tide range. If you are unsure, use the deeper value and the larger tide range.
- Set the wave and wind factor, scope, and extra allowance with the presets or your own values.
- Review the recommended length, minimum length, and purchase length, then copy the result or share the URL if needed.
Examples
Buoy / drop line example
Input
Mode = Buoy / Drop Line, Depth 4.0 m, Tide range 0.6 m, Wave/Wind factor 1.1, Slack ratio 1.10, Extra allowance 1 m
Output
Minimum 6.1 m, Recommended 6.6 m, Purchase length 7.0 m or more
Glossary
Effective depth
The sum of depth and tide range. This is the depth used for the rope-length estimate.
Scope
The ratio of rope length to effective depth. Mooring and anchoring often use values like 3:1, 5:1, or 7:1.
Slack ratio
A multiplier used for buoy and drop-line setups. A value of 1.10 means 10% extra slack.
Formulas
- Effective depth D = depth + tide range
- Minimum length Lmin = D x scope + extra allowance
- Recommended length Lrec = D x scope x wave/wind factor + extra allowance
- Purchase length = round the recommended length up by the selected step
FAQ
Can I use it for more than mooring?
Yes. Switch the usage mode to anchoring or buoy/drop line to change the common ratios and help text for that use case.
Can I switch units?
Yes. Use the unit toggle to switch between m and ft. Inputs and results always stay in the same unit.
Which safety factor should I choose?
Start with the normal setting if you are unsure. Consider 1.4 to 1.6 when swell, gusts, or vessel movement are significant. Field conditions come first.
What is scope?
Scope is the ratio of rope length to effective depth. More rope lowers the angle and can soften shock loads, but the right ratio still depends on conditions.
What is the difference between minimum and recommended length?
Minimum length excludes the safety factor. Recommended length applies the wave and wind factor so you can see a more conservative working length.
Important notes
- This is a conservative general estimate. Actual needs change with wind, waves, current, vessel behavior, attachment height, bottom type, chafe, stretch, and rope or chain type.
- Decide conservatively to avoid shortage, and make the final decision in the field.
- Detailed anchor calculations with chain length or attachment height are outside the scope of version 1.