Concise answer
Measure the physical dimensions where the sail or cover will sit, confirm material and hardware specifications, and record any relevant rigging or deck details so the maker can tailor the item to your boat. For sails you need luff, leech and foot lengths and details of spars and reefing; for covers you need measured points around the object including attachment style and clearance for fittings.
- For sails: luff (front edge), leech (aft edge), foot (bottom edge), halyard and tack attachment types, reefing system details, battens and batten pockets, cloth weight/oz (or fabric type), draft position and handedness (port/starboard).
- For covers/canvas: a measured plan of the object (dodger, cockpit cover, boom cover, winter cover) with multiple measured points (lengths, heights, widths), locations and sizes of fittings (cleats, stanchions, winches, hatches), preferred attachment method (zips, toggles, Velcro, straps) and allowance for retraction/clearance.
- General/specification items: boat make/model and year (if known), mast and boom section/profile or serial if unusual, sail number/registration (if relevant), whether you want UV or mildew-resistant treatment, and any colour or aesthetic preferences.
Why these measurements matter
A sail must match the rig geometry so it sets correctly, balances helm and fits with reefing and batten positions. A cover must fit the three‑dimensional shape and mate to deck hardware without chafing or leaving exposed gaps. Small errors in dimensions or ignored fittings lead to poor performance, water ingress or premature wear.
Common mistakes to avoid
- Sending only a single length (e.g. overall length) — covers and sails need multiple measured points and profiles.
- Not accounting for hardware or hatch clearance — cover panels that snag or sails that foul a winch are common.
- Forgetting attachment details — specifying “Velcro” when you need zips or toggles can make the product unusable.
- Using taped or worn measurements — take measurements on the actual structure, not an old or distorted template.
Terminology (plain English)
- Luff: the forward edge of the sail that runs against the mast or forestay.
- Leech: the back edge of the sail away from the wind.
- Foot: the bottom edge of the sail along the boom or deck.
- Draft: the depth of the sail’s curve (how full it is).
- Battens: stiff inserts that support the leech or shape of the sail.
Practical next step
Take a clear, labelled photo of the area and a short measurement sketch with at least three reference points; then contact the maker with those images plus your boat make/model and any rigging notes. If you’re unsure about any measurement, ask the seller for a measurement template or a phone/video call to confirm — many sailmakers and canvas workers will talk you through it.
If your query needs rules, class measurements or manufacturer limits that are specific to your boat or class, note the scope here and check the relevant class association, manufacturer documentation or the sailmaker’s instructions before ordering.