Reefing is the process of reducing sail area to maintain control and safety when wind speeds increase. By lowering the centre of effort, a boat can avoid excessive heeling, weather helm, and potential structural damage to the rig.
The wind speed at which a sailor should reef depends on several vessel‑specific parameters: the sail‑area‑to‑displacement ratio, the length‑to‑beam ratio, and the desired safety margin. Larger, lighter boats with big rigs will reef earlier than heavy, low‑profile vessels.
This calculator combines those factors into a simple empirical formula, giving you a recommended reefing wind‑speed threshold. Compare the result with the current wind to decide whether to reef now or wait for conditions to change.
What is reefing in sailing?
How do I determine when to reef my boat?
Why is reefing important for a sailor?
What factors affect when a boat should reef?
How does reefing impact a boat’s performance?
Are there different types of reefing?
Can I reef my boat if it’s not designed for it?
Results are for informational purposes only and do not constitute professional advice.