A triangular sail needs three edges. A four-sided sail needs five dimensions — four edges and a diagonal — because four points in space aren't fixed by their edges alone: the shape can still rack like a hinge. The diagonal is what pins it. These are the values on our four-sided form (CS-FS-01), in centimetres.
Before you put a tape on anything
First decide what you're describing: an existing sail, or a documented target dimension. Then mark your four corners — tack, throat, peak, clew — and here is the rule the whole form turns on: use the same marked point at each corner for every adjoining measurement. If the luff runs to one spot on the throat and the head runs to a spot 3 cm away, the sail you get back will not be the sail you drew.
The coded measurements
| Code | What it is, and where the tape goes | Where |
|---|---|---|
| LpLuff | Tack up to the throat. | |
| LgHead | Throat out to the peak — the edge that rides the gaff, yard or sprit. | |
| LwLeech | Peak down to the clew. | |
| LdFoot | Tack aft to the clew. | |
| DDiagonal | Clew to throat. The one that stops the shape racking — without it, four edges describe infinitely many sails. |
Don't measure through the hardware
The form calls it the boundary check: “Do not infer a point through obscuring hardware.” If a jaw, a band or a fitting is in the way and you can't see the actual corner, leave the value blank and tell us which bearing was uncertain. We would far rather have four numbers and an honest note than five numbers where one is a guess — because we can't tell which one is the guess, and neither can you. The form also records your sail type (gaff, lug, sprit or gunter), whether it has battens, a boom, and how many reefs, plus the cloth colour: white, tan or beige.
The rule that runs through every form we print
If you aren’t sure of a bearing, leave it blank and tell us. Our forms say it on every page, and it isn’t politeness — it’s arithmetic. A blank is a question we can answer with one phone call. A guess is indistinguishable from a measurement, so it survives all the way to the cutting floor and comes back as a sail that doesn’t fit. We would rather have four honest numbers and a note than five numbers where one is fiction.
The words on this page, explained
Or don’t measure anything at all
The easiest measurement is the sail you already own. Bag it, send it, and we’ll do all of this on a flat loft floor with proper tension — then send you the production dimensions to approve before we cut.