Anchor Rode Scope
Calculator
Results
- Rode length (m)
- 60.899999
- Rode length (ft)
- 199.803149
- Total depth used (m)
- 8.7
Aviation and marine results
| Rode length (m) | 60.899999 |
| Rode length (ft) | 199.803149 |
| Total depth used (m) | 8.7 |
formula-map diagram
- Rode length (m)
- 60.899999
- Rode length (ft)
- 199.803149
- Total depth used (m)
- 8.7
Aviation and marine relationship
Formula
Rode = (depth + bow height + tide rise) × scope ratio= 60.9
Note
This is a simplified model: it applies a standard navigation, performance or seamanship formula to the numbers you entered. True airspeed and density altitude use the ISA troposphere model for dry air and ignore humidity, compressibility and instrument or position error, so they are not a substitute for your aircraft's flight manual or an air data computer. Wind, climb, descent and fuel figures assume a steady wind and a constant speed and fuel flow for the whole leg; they ignore manoeuvring, holding, taxi and start-up fuel, terrain, turbulence and air traffic control routing. Takeoff distance scales an entered sea level figure by a rule-of-thumb percentage per 1000 ft of density altitude and is not a certified performance chart. Weight and balance results depend entirely on the arms and weights you enter and must be checked against the approved loading envelope. Hull speed is the classic 1.34 × √LWL displacement estimate, boat fuel burn is a horsepower-based approximation, anchor scope is a rule of thumb, and the rule of twelfths is a linear approximation of a sinusoidal tide that does not hold in all locations. Always use official charts, tide tables, the aircraft or vessel manuals and current weather, and treat these numbers as planning estimates only.
More in Aviation and marine
See all →Frequently asked questions
What does 'scope' mean in anchoring, and why does this calculator need water depth?+
Scope is the ratio of anchor rode (chain and/or line) length deployed to the total vertical distance from the bow to the seabed. Water depth is essential because scope is measured against total depth, not just the anchor's position, and a low scope ratio makes the anchor more likely to pull out under load.
Why is high tide range added to water depth in this calculation?+
You need to plan scope for the highest water level expected during your stay at anchor, not just the depth at the moment you drop the hook. If the tide rises after anchoring and you only accounted for low-tide depth, your effective scope ratio will drop below what's safe as the water rises.
Why is bow height above the waterline included in the scope calculation?+
Scope is measured from the bow roller (where the rode leaves the boat) down to the seabed, not just from the waterline, so the height of the bow above the water adds directly to the total vertical distance the rode must span.
What's a typical recommended scope ratio and why does it vary?+
A common range is 5:1 to 7:1 for typical overnight anchoring with all-chain or mixed rode, with more scope (7:1 or higher) recommended in heavier winds or an all-rope rode, since a lower angle of pull (more scope) keeps the anchor shank pulling more horizontally, which holds better than a steep vertical pull.
What's a common misconception about scope?+
That the ratio only needs to account for the anchor line's horizontal reach for swinging room, when in fact scope is fundamentally about the angle of pull on the anchor. Even in a tight anchorage, cutting scope too short to save swing space significantly increases the risk of the anchor dragging.