Backstaff

John Davis, English navigator and explorer (c.1550–1605), invented the backstaff around 1594, though it reached widespread use during the Golden Age of Piracy. Davis designed it to overcome the limitations of the cross-staff, which forced observers to stare directly into the sun. His innovation became standard equipment aboard pirate vessels, merchant ships, and naval vessels by the mid-seventeenth century. The instrument bore his name in some maritime circles—the 'Davis quadrant'—though 'backstaff' became the common term.

The backstaff operated on a geometric principle: the observer stood with his back to the sun and aligned two vanes—one casting a shadow, the other receiving it—along a single line of sight to the horizon. The main staff, graduated in degrees, carried a sliding cross-piece (the vane assembly). By positioning the shadow vane so its shadow fell precisely on the sight vane, and adjusting the sight vane until it aligned with the horizon, the navigator could read the sun's altitude directly from the staff's scale without looking at the sun. This eliminated eye damage and the difficulty of simultaneous observation inherent in the cross-staff. The instrument's accuracy depended on clear horizons, steady hands, and careful calibration of the vanes. Brass fittings reduced warping; bone or hardwood scales resisted wear. The geometry was elegant: the angle read on the staff equaled half the actual solar altitude, a relationship Davis exploited to keep the instrument compact.

The backstaff emerged from John Davis's refinement of earlier cross-staff designs in the 1590s and gained prominence during the seventeenth century as maritime commerce and naval power expanded. By the Golden Age of Piracy (c.1650–1725), it was the standard latitude-finding instrument aboard European and colonial vessels, including pirate ships. Unlike the cross-staff, which required the observer to face the sun and often resulted in damaged eyesight, the backstaff allowed safe, accurate solar observations. Pirate captains like Henry Morgan, Blackbeard (Edward Teach), and Captain Kidd relied on backstaffs to navigate to known hunting grounds and escape routes. The instrument's portability and relative ease of use made it ideal for vessels operating in distant waters where printed charts were scarce and dead reckoning alone was insufficient. By the early eighteenth century, the backstaff began to be superseded by the octant and sextant, which offered greater accuracy and ease of use, but it remained in service aboard many vessels well into the 1700s.

Determining latitude—the north-south position on the globe—was the fundamental problem of oceanic navigation. Medieval and early modern sailors used crude methods: observing the sun's noon altitude, the angle of the North Star, or dead reckoning (estimating position from speed and direction). The cross-staff, introduced in the thirteenth century, allowed measurement of celestial altitudes, but it forced observers to stare into the sun, causing eye strain and injury. John Davis's backstaff solved this problem by using a shadow-based method, allowing safe, repeatable measurements. For pirates, accurate latitude determination was essential: they needed to return to known anchorages, intercept merchant vessels along predictable routes, and navigate to remote islands where they could careen ships and hide from naval patrols. A pirate captain who could reliably determine his latitude had a decisive advantage in planning raids and evading pursuit. The backstaff thus became as vital to piracy as the cutlass or the cannon.

A navigator or master aboard a pirate vessel would use the backstaff during clear daylight, typically around solar noon when the sun reached its maximum altitude and latitude could be most accurately determined. The procedure was straightforward: stand on deck with the sun behind you, hold the staff vertically, and adjust the sliding vane until the shadow vane's shadow fell exactly on the sight vane's slit. Then adjust the sight vane until you could see the horizon through its peephole. Read the angle from the staff's scale. The entire operation took two to three minutes. On a pirate ship, the captain or sailing master performed this task; on larger vessels, a dedicated navigator might do so. Results were recorded in a log book or on a slate. In poor visibility—fog, heavy cloud, or rough seas—the backstaff was useless; navigators relied instead on compass bearings and dead reckoning. The instrument required regular maintenance: the vanes had to be kept clean, the scale markings checked for accuracy, and the brass fittings oiled to prevent corrosion. A damaged or warped backstaff could introduce errors of several degrees, potentially sending a ship miles off course.

A backstaff was handcrafted by a specialized instrument maker, a skill that took years to master. The main staff was turned from a single piece of hardwood (oak, lignum vitae, or boxwood), chosen for resistance to warping and splitting. The craftsman first shaped the staff to a rectangular cross-section, then carefully laid out and engraved the degree and minute scales using dividers and a scribe. The scales were often filled with ink or paint to make them visible. The shadow vane and sight vane were cut from thin wood or bone, fitted with slits or holes, and attached to the staff via brass collars or sockets. The brass fittings were cast or forged by a metalworker, then fitted and soldered to the wood. The entire assembly was tested against known altitudes (using a plumb bob and a protractor, or by comparison with another instrument) and adjusted if necessary. A well-made backstaff could take weeks to produce and cost as much as a skilled craftsman earned in a month. Cheaper versions, with less precise scales and simpler fittings, were available but less reliable. Pirate vessels sometimes carried captured or stolen instruments rather than commissioning new ones.

Backstaffs are rarely recovered from shipwrecks because wood and bone degrade in saltwater over centuries, and brass fittings are often corroded beyond recognition. However, fragments have been identified in a few contexts. The wreck of the *Queen Anne's Revenge* (Blackbeard's flagship, sunk 1718, discovered 1996 off North Carolina) yielded brass fittings and scale fragments consistent with navigational instruments of the period. The wreck of the *Whydah* (Captain Kidd's associate, sunk 1717, discovered 1984 off Massachusetts) contained navigational artifacts, though no complete backstaff. Land-based finds are more common: backstaffs have been recovered from colonial settlements and maritime museums, including examples from Port Royal, Jamaica (a major pirate haven), and from private collections in England and the Netherlands. Dendrochronology (tree-ring dating) and metallurgical analysis of brass fittings can help date recovered instruments. The rarity of archaeological backstaffs reflects both the fragility of the material and the fact that valuable instruments were typically salvaged from wrecks or removed before a ship sank.