Start with data: record target true wind speed, apparent wind angle, sea state and crew for every current sail. A new sail should close a measured gap or replace one whose shape no longer supports the target numbers.
Build a crossover chart
Plot each sail against true wind speed and apparent wind angle, then annotate sea-state limits and handling cost. A nominal J1, J2 or A2 designation is less useful than knowing where the sail is fastest on this hull, under this rule and with this crew. Review racecourse format: harbour windward-leewards, passage races and offshore programs reward different inventories.
Mainsail, genoa and jib
The mainsail should be designed around rig bend, control range and the headsails it supports. Specify whether the boat needs power in chop, depowering in flat water or a broader compromise. Low-stretch construction keeps designed draft position repeatable, but batten, luff and reef details still determine reliability.
For overlapping genoas, define LP, clew height, track range and tacking clearance. For non-overlapping jibs, sheeting angle and leech control become especially important. A light-air genoa and working jib must have distinct crossover conditions; otherwise the second sail adds cost and crew work without enough speed difference.
Code sails and spinnakers
Code sails can bridge the gap between a jib and asymmetric, but designations vary. Specify target angles, mid-girth and measurement treatment. Downwind sails should be mapped by intended mode: VMG running, reaching, heavy-air stability or light-air acceleration. Fast boats sail at different apparent angles from displacement boats, so catalogue descriptions cannot replace polar and on-water evidence.
| Sail decision | Evidence to bring | Quote output |
|---|---|---|
| Upwind replacement | Draft photos, target speeds, trim limits | Flying shape, cloth, weight and range |
| New crossover sail | Inventory map and missing conditions | AWA/TWS envelope and adjacent sails |
| Rating-sensitive sail | Current certificate and rule objective | Measured dimensions and rating treatment |
| Offshore sail | Crew, course exposure and rules | Reinforcement, reefs and handling plan |
Performance per season
Race sails are often replaced for shape before structural failure. Define the expected competitive life, training use and rotation plan. A premium sail used outside its intended range can age faster than a slightly heavier sail that carries loads appropriately. Include recut potential, local service and downtime in the cost comparison.
- Confirm the governing rating or class rules before design
- Record finished weight and measured dimensions
- Define crossovers numerically, including sea state
- Agree draft-stripe locations for repeatable photography
- Commission on both tacks and save baseline trim settings
- Log hours, major loads, repairs and observed shape change
Reviewed 19 September 2026