Spreaders are the horizontal struts that project from either side of a mast and hold the shrouds away from it. By pushing the wire outboard they widen the angle at which the shroud meets the mast, and that angle is what allows a relatively small wire to hold a tall mast upright without crushing it. A beginner sees them as the aluminium bars with the shroud tips on the end; an experienced sailor knows that spreader length, angle and sweep are design decisions that decide how much the mast can bend, where a genoa can be sheeted, and whether the rig will stay in column when the boat is pressed.
Why a mast needs spreaders
A shroud that runs straight from the masthead to the deck edge meets the mast at a very narrow angle, typically only a few degrees. The horizontal component of its pull – the part that actually holds the mast up – is tiny, so the wire would have to be tensioned enormously and would drive equally enormous compression down the mast. Spreaders solve this by dividing the mast into shorter panels and giving each panel a wider support angle at its top. Naval architects like to see the shroud leaving the spreader tip at an angle of at least 10 to 12 degrees from the mast; less than that and the compression climbs steeply.
The spreader itself is in compression. The upper shroud passes over its tip, and the cap shroud tension pushes the spreader inboard against the mast. For that to work the spreader must bisect the angle the shroud makes as it passes over the tip, which is why spreaders on a properly set up rig cock slightly upward rather than lying dead horizontal. A spreader that is allowed to droop is being pulled downward by the shroud and will eventually fail at the root.
Anatomy of a spreader
- Root: the fitting where the spreader meets the mast. It may be a fixed socket, a bar passing through the mast, or an articulating bracket that lets the spreader pivot in the vertical plane while resisting fore-and-aft movement.
- Tip: the outboard end, with a groove or clamp that captures the shroud. Seizing wire or a tip cup keeps the shroud from riding up or down.
- Section: usually an aerofoil-shaped aluminium extrusion, though carbon spreaders are common on racing boats and wooden ones survive on traditional yachts.
Swept spreaders and mast bend
On many modern boats the spreaders are angled aft, often by 15 to 30 degrees. Swept spreaders let the cap shrouds do some of the work of the backstay by pulling the middle of the mast aft, which pre-bends the spar and stiffens it fore and aft. Fractional rigs with swept spreaders can often dispense with running backstays altogether. The trade-off is that the mainsail cannot be squared right out on a run before the boom lands on the shroud, and the mast bend induced by the shrouds has to be designed into the mainsail luff curve. A sailmaker measuring for a new main will always ask about spreader sweep and rig tension because they determine how much luff round to cut in.
What spreaders mean for sail trim
Spreader length sets the sheeting limit for overlapping headsails. A genoa trimmed hard will lie against the spreader tips, and if the tips are sharp or the spreader angle is wrong the sail will chafe through in a season. UK Sailmakers reinforce headsails with spreader patches exactly where the tips touch, and on a new boat they will note the spreader positions during measurement so the patches land in the right place. Racing crews watch the gap between the leech and the spreader tip as a reference for genoa trim: a few centimetres off the tip upwind in moderate air, touching in flat water and light breeze, eased further as the boat becomes overpowered.
Inspection and common problems
Look up the mast every time you sail. Spreaders should be at matching angles port and starboard and cocked slightly upward. Check the roots for cracks, corrosion around fasteners and wear in articulating brackets, and the tips for a loose shroud or a broken seizing. A spreader that rattles in its socket when you shake the shroud is asking to fall out on the next tack, and if a spreader root fails the mast generally comes down with it.
Frequently Asked Questions about Spreaders
Should spreaders be horizontal?
No. Each spreader should bisect the angle the shroud makes as it passes over the tip, which puts the outer end slightly above the root. Drooping spreaders are a warning sign.
Why do racing boats have several sets of spreaders?
More spreaders divide a tall, slim mast into shorter panels, each supported at a good angle by a lighter wire. Two or three sets allow a lighter, more bendable section than a single-spreader rig.
Spreaders are easy to ignore because they sit high above the deck and do nothing visible. They are also the part of the rig most often found lying on the deck after a dismasting. Keep the angles right, keep the tips padded, and give them the same attention you give the wire they support.