Choose genoa size by its job, not a percentage alone. Many short-handed cruisers start around a 105–120% working headsail, while lighter-wind or racing boats may justify more area. Confirm LP, finished area, clew height, shroud clearance, sheet-track range and useful reefing limits on the actual rig.
Understand LP and overlap
Luff perpendicular is the shortest distance from clew to luff, expressed against J when described as a percentage. It is useful but does not fully describe finished area, clew height, luff curve or shape. Two sails with the same LP can behave differently.
Start with the wind range
Record where the current headsail feels underpowered, balanced and overpowered. A large genoa may help a heavy boat in light air but create sheet load, visibility and tacking problems. A smaller working jib plus Code Zero can split the jobs more cleanly.
Check real sheeting geometry
The proposed clew must lead to an available track position without excessive shroud contact. High-clewed cruising sails improve visibility and clearance but change area and leech profile. Ask for a drawing with LP, area and lead location.
Do not design around deep furling
A luff pad can improve partially furled shape, but a rolled genoa is still a compromise. Define the acceptable reduction range and plan a smaller heavy-weather sail when the sailing program requires it.
Decision table
| Approximate range | Typical benefit | Watch for |
| 95–105% | Easy tacking and strong-wind control | Light-air power |
| 105–120% | Broad cruising working range | Track and reefed shape |
| 120–135% | More moderate/light-air area | Loads, visibility and shroud contact |
| 135%+ | Specialised light-air or rule-driven use | Handling and narrow crossover |
What to put in the brief
- I and J plus maximum hoist
- Target wind and angle range
- LP, finished area and clew height
- Sheet track and shroud clearance
- Furler, foil and luff tape
- Inventory crossover above and below
Frequently asked questions
Is a 150% genoa good for cruising?
It can suit some heavy boats and light-wind areas, but it increases handling, load and clearance demands.
Is a 100% jib too small?
Not necessarily. Modern fractional rigs and boats with separate reaching sails may be designed around non-overlapping headsails.
Can I calculate genoa area from LP?
You can estimate it, but luff, leech, foot and shape are needed for a reliable finished area.
Should the replacement match the old sail?
Only after deciding the old sail’s job and geometry are still right for the boat and crew.
Prepared from the Buy Sails Australia research library and checked against the site’s measurement, material and provider methodology. Final boat-specific specifications and safety decisions require qualified sailmaker and rigger verification.
How this guide is researched