A full-rigged ship has three or more masts carrying square rig. On a three-masted example these are the foremast, mainmast and mizzenmast. Braces turn the yards in the horizontal plane so the crew can change the orientation of the square sails. Use the animation to follow that movement and compare the geometry of two selected yard angles.
Full-rigged Ship Interactive Calculator
Choose a reference brace angle, a second brace angle, a comparison allowance and a yard span. Zero degrees places the yard across the vessel. The calculator measures angles and endpoint movement, not sail performance.
Equation Used
The yard is a straight rigid spar rotating about its midpoint. End travel is the straight-line distance between the two endpoint positions, not the arc length or brace-rope travel. The allowance is your comparison value, not a luffing or safety threshold. No optimum sailing angle, driving force or luff probability is calculated.
Three masts, square sails and braces
The foremast is forward, the mainmast is near the middle and the mizzenmast is aft. Yards carry square sails at several levels. Headsails occupy the stays toward the bowsprit, while a fore-and-aft spanker sits aft. The number and names of upper sails vary with the ship; three tiers in the illustration keep the main arrangement visible.
Each yard is supported near its middle at the mast. Brace lines act at its ends to change its horizontal angle. The animation moves the yards slowly between the two selected angles and back. A separate plan view shows one rigid yard pivoting about its midpoint, with the reference and second positions marked. The entered span applies to that isolated yard; the ship’s overall proportions remain illustrative. Both directions of travel are an explanatory cycle, not a sailing maneuver.
The simplified rig rotates its yards together. A real crew can trim yards separately, and standing rigging and other spars limit their travel. The two lines drawn from the plan-view yard ends to fixed points illustrate the purpose of braces; their routing and lengths are not a particular ship’s rigging plan.
A familiar arrangement on tall ships
Royal Museums Greenwich holds G. F. Campbell’s rigging plan for the three-masted clipper Cutty Sark. It shows the many levels of yards, standing rigging and running lines that a small schematic necessarily simplifies. The modern Stad Amsterdam also uses a three-masted square rig, as described by its operator.
A three-masted barque has a fore-and-aft rig on its aftmost mast, whereas a full-rigged ship carries square rig there too. A brig has two square-rigged masts. These names describe the rig arrangement; they do not by themselves establish speed, crew requirements or a safe sail-carrying limit.
Calculate the motion of a yard end
Let L be the full yard span and let theta1 and theta2 be its two angles from the transverse position. The absolute angular difference is e = |theta2 − theta1|. One end lies at radius L/2 from the pivot. The straight chord between its two positions is therefore d = 2(L/2) sin(e/2) = L sin(e/2).
The signed fore-and-aft offset of the highlighted end at the second angle is x = (L/2) sin(theta2). The opposite end has offset −x. In the plan view the bow is up, and a positive angle moves the highlighted right-hand end toward the stern. The animated rig and the plan use this same angle convention.
Margin = comparison allowance − e. A positive margin means the two angles lie within your selected allowance; a negative margin means they differ by more than it. The calculation has no information about apparent wind, sail camber, sail interaction or separation of airflow, so that margin is not a luffing prediction.
Yard-end chord distance differs from arc travel, which would be (L/2)e with e in radians. It also differs from rope hauled at a brace: the latter depends on lead positions, blocks and purchase.
Example: a 12-metre yard
For a 12 m yard moving from 0° to 25°, the angle difference is 25°. One end moves through a straight chord of 12 sin(12.5°), or about 2.60 m. At the second position its fore-and-aft offset is 6 sin(25°), or about 2.54 m.
With a selected allowance of 5°, the margin is 5° − 25° = −20°. That reports only the comparison you entered. It does not mean the sail will luff, that its drive falls by a known percentage, or that the rig is overloaded.
If the two angles are equal, endpoint movement is zero and the animation holds the yard in that position. Increasing yard span increases the distances in metres in direct proportion while leaving the angles and allowance margin unchanged.
What a bracing sketch leaves out
A square sail is flexible, and its aerodynamic force depends on apparent wind and its three-dimensional shape. Different sails interact with one another and with the hull’s motion. A universal five-degree luff limit or a cosine-squared force rule cannot be established from yard angle alone.
The spar support, lifts, braces, sheets and standing rigging form a load-carrying system. This animation explains its arrangement and one rotation, but does not size ropes, blocks, spars or powered handling equipment. Use vessel-specific plans and operating procedures for those decisions.
Frequently asked questions
How does a full-rigged ship differ from a brig?
A full-rigged ship has three or more square-rigged masts. A brig has two. The illustration shows a three-masted ship with foremast, mainmast and mizzenmast.
What do the braces do?
They act at the yard ends to turn the yard around the mast. Actual line leads and purchases depend on the vessel.
Does the reference angle mean the best sailing angle?
No. It is a position you choose for comparison. The calculator does not use wind or aerodynamic data to find an optimum.
What does a negative allowance margin mean?
The selected angles differ by more than your entered allowance. It is an angular comparison, not a measure of sail luffing, structural load or safety.
Is yard-end movement the amount of brace rope to haul?
No. The output is the straight chord between two positions of one yard end. Rope travel also depends on the geometry of its leads and any block purchase.
Why do the yards move back and forth?
The slow cycle illustrates rotation between the reference and second positions. It is not an automatic sail-control strategy or a simulation of a vessel maneuver.
Why does the animation stop when both angles are equal?
There is no angle change to illustrate. Change either angle to give the yard a range of movement, or use the motion-position control to inspect a pose.
Can every yard on a ship use the same brace angle?
Not necessarily. Sail interaction, rig geometry and sailing conditions can require different trim. The grouped movement keeps this schematic easy to follow.
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