Blackbeard, Bannister, and Bernoulli

The Life of Crime

Golden Age pirates have inspired countless movies, books, and children’s birthday parties. We both commend and despise these sailors for blazing their own paths, establishing their own codes of conduct, and living each day as though it could be their last.

In the present, many of us are more familiar with captain Hook from Peter Pan or captain Jack Sparrow from Pirates of the Caribbean than we are with their historical inspirations. This is fitting; pirates reveled in their ability to blur the lines between fact and fiction [6, p 44,45]. Tangled webs of truth and legend were often their means of success in battle and escape from the gallows.

It was not, however, only the pirates who were inflating and distorting reality. Piracy itself went in and out of being considered a capital offense by the British Empire. An anti-piracy law from King Henry VIII defined piracy in deliberately vague language, and the ambiguity was exploited the by courts in political gambits [6, p 27]. The Crown liberally bestowed the label of piracy on many events, such as the Boston Tea Party, which we generally do not associate with piracy at all anymore. Defendants were called pirates so they might be subjected to more severe and public punishments. Embarrassing or threatening powerful people frequently doomed offenders to suffer greater recompense than justice demanded. Many of these scapegoats went to their graves believing themselves to be innocent, and denying that any of their actions constituted piracy. Ironically, even one of the most famous pirates in all history was one such example. Captain William Kidd’s execution served to quell social, economic, and foreign affairs. Though his actual culpability is not easily determined, his trial and sentencing were undeniably prejudiced.

It is reasonable to wonder how it is possible to murder or steal on the high seas and yet not see such actions as breaking the law. This confusion largely arose from the government- sanctioned occupation of privateering [6, p 25]. The daily practices of privateering and piracy were essentially identical, except that privateers possessed written documents granting them permission to attack and rob specific marks. Often commissioned during conflicts and wartime, privateers were simply another method to cripple the enemy by targeting their ships. Privateers, like pirates, earned their wages through the division of spoils. In stark contrast to merchant and naval careers which offered little opportunity for promotion and poor pay, successful privateers were able to accumulate a great deal of wealth very quickly. For those who could manage it, privateering was fantastic business.

However, this system had several flaws. When conflicts between nations resolved, the privateers were often immediately unemployed [6, p 26]. Having learned to scare, rob, and kill, piracy became a natural transition and, frankly, a better alternative to the poor pay and unhappy conditions on naval ships [6, p 34]. More dangerous, however, was a war ending while a privateer was still at sea and beyond the reach of news. Without the knowledge that his documents had been voided, the privateer was suddenly culpable for his acts as though he were a pirate.

This is how many pirate companies came into being. It is true that a few pirates were merely greedy, thrill-seeking, sadistic people, but a large number of them had deeper and more complex reasons for choosing a life of crime. Piracy was a strong tool used to express disdain for an unjust social system, and its efficacy was plainly evident. Countries tried to stomp out piracy through worldwide manhunts, expensive pardons, and brutal executions.

Limiting our pirate knowledge to tales of sword fights, burned ships, and lost treasure forfeits a great deal of richness in the characters who committed these acts. Most importantly, it blinds us to why they chose to live such wild, villainous, and irreverent lives. People who have happy lives do not typically trade peace, comfort, and governmental protection for certain death upon capture. Yet the Golden Age of piracy lasted eighty years.

The Vessel

Joseph Bannister was a respectable man who captained the square mast merchant ship the Golden Fleece [5]. Without warning and, seemingly, without motive, he abandoned a life of security and prosperity to turn pirate by stealing his own ship [5]. This dramatic and unforeseen behavior inspired many questions, but chief among them must be: was this ship quick and nimble enough to succeed in a life of crime? From the moment he turned pirate, British naval ships would

be hot on his trail, seeking to overpower and out-maneuver the Golden Fleece.

Figure 1: An English merchant ship similar to the Golden Fleece. Taken from the journal of Edward Barlow [1].

When looking at the puffy sails of these ships, it seems sensible to assume that a ship moves by putting the wind at it’s back. When the wind is pushing the boat forward by coming up the rear, this is called running [2, p 30]. Because of the resistive force caused by the bulky hull dragging through the water, the ship will not be able to move as fast as the wind, but it is one way to get the vessel moving.

Bernoulli

Far more efficient, is to make use of Bernoulli’s principle. At its heart, Bernoulli’s principle is a manifestation of the conservation of energy. Conservation of energy states that as the kinetic energy increases, the potential energy must decrease proportionally so that the total energy of the system remains constant. Applied to fluid dynamics, this relates the speed of a fluid (such as wind moving over a sail) to other key elements of a system, such as pressure and density.

Fluids possess something called ‘flow energy’. This is a kind of potential energy, which captures the work (joules) needed to move the fluid a distance against the system’s pressure [3]. The formula for this is

where FE is the flow energy, P is the pressure, A is the cross sectional area, and d is the distance over which the work is done. Remember that pressure is simply a force distributed over an area, which is why a needle prick will pop a balloon more readily than squeezing the balloon with your hands.

Just like a ball or particle, when the speed of a fluid increases, its kinetic energy increases. In a system that conserves energy, this means that the potential energy must decrease to maintain a constant total energy. As we see from our equation, if the cross sectional area and distance over which work is done remain constant, then that means our pressure has to decrease for the potential energy to decrease.

Figure 2: A diagram showing the Bernoulli principle when applied to an airfoil on a plane. A sail possesses a similar shape when viewed from above.

For wind flowing over a sail, this creates a low pressure front on the side of the sail which has wind moving faster over the surface. This may not initially seem to follow, but it is because the air molecules which move faster are actually farther apart, creating a sort of semi-vacuum. It might help to think of a conveyor belt carrying widgets. If I have a conveyor belt moving at a set speed, and widgets are placed on it at some uniform distance, then as this conveyor belt moves, there is no change in the distance between the widgets. For every meter that widget one moves, widget two has also moved in the same time frame. Then, if that initial conveyor belt connects to a new belt which is moving faster, there is a time when widget one has passed onto a faster moving belt while widget two is still on the slower belt. The distance between them increases, until widget two is on the faster belt, and then the distance between the two widgets becomes fixed once again, except that the new distance between them is greater than the initial distance.

Figure 3: A demonstration of how switching from moving slower to moving faster can spread out the molecules of air and create a partial vacuum, which results in a lower pressure.

Even if you believe that this creates a low pressure front, it might be difficult to believe that this actually produces an appreciable lift or pulling force which could actually move a ship. To you, dear skeptic, I say this: take a single slip of paper (light, not card-stock) and hold it by one end in front of your mouth. Due to its own weight, the paper will curve up briefly, and then droop towards the floor. Give a good strong blow across the top of the paper, and watch what it does. If it does nothing, your paper might be too heavy, but if not, you should see a rather dramatic display of the force due to low pressure.

Back to the Ships

The merchant ships and sloops-of-war from the mid 1600’s to 1700’s were largely powered by this one principle. On the ships, there would be at least one jib, and many sails. The jib is on the very front of the ship, and is the first sail to make use of Bernoulli’s principle.

Figure 4: The basic anatomy of a simple sailboat. (A sloop, to be precise [2, p 3].)

When a sail has wind pass over it, the low pressure actually pulls the boat along through the suction effect. As the air comes off the end of the jib, the flow direction has changed slightly [4][2, p 49]. This increases the airspeed falling on the back of the next sail, which in turn increases the suction effect of that sail. It is called the ‘slot effect’, which refers to the space between each successive sail. By layering many sails on a ship, the boost from each sail (apart from the initial jib) is increased. The square mast merchant ships, with their many sails, were able to move faster through the water than the speed of the wind (unlike running the ship).

Bannister

Joseph Bannister was the captain of a transatlantic merchant ship, responsible for transporting valuable cargo from London to Jamaica [5, p 5]. His vessel was fitted with artillery precisely for the purpose of fending off pirate attacks, and was both large and powerful for a merchant ship [5, p 42]. Six weeks after stealing his own ship and embarking on a lifestyle of piracy, Bannister was captured and put on trial [5, p 49]. He bribed a witness to claim that he had purchased the boat and its cargo, and a jury of local business owners who appreciated pirates’ extravagant spending habits found Bannister ‘not guilty’ of piracy.

Bannister was arrested again and recharged, but after making bail, he snuck aboard the Golden Fleece in the dead of night and silently sailed for his life, stealing the boat a second time. It was not until he was passing the fourteenth cannon when he was sighted and the alarm sounded. Even as cannon balls ripped into the Golden Fleece, she sailed on until she reached the open seas.

Bannister then proceeded to have an excellent run of piracy, capturing prizes and slipping away [5, p 53,54]. He was an extremely elusive pirate, causing great distress and rousing deep anger. Upon learning that Bannister was set to careen his ship, governor Molesworth issued orders for two powerful navy warships to kill the pirate captain.

Careening is the process of grounding a ship so that it may be repaired. Due to the nature of piracy, there were often holes to calk, and in an era where ships were crafted from wood, shipworms could destroy a boat if not dried out periodically. Bannister and his men had beached the Golden Fleece on an island when two warships from the most powerful empire on Earth approached. Naturally, surrender was expected.

But Bannister didn’t surrender. From the trees, the pirates launched an attack, firing cannons and muskets. The naval ships returned fire for two days until their ammunition ran out and they had to retreat. Bannister burned the Golden Fleece and escaped in a smaller vessel. He was later captured and executed without a trial, but it cannot be doubted that he was an exceptionally skilled leader and sailor, and that his vessel, though a merchant ship, was more than up to the task of piracy.

The Loss of Blackbeard’s Jib

For the amount of fame (or infamy) that the pirate Edward Teach amassed, his piracy career was short, ranging from about 1716-1718 [7, p 145,282]. Over his career, he made several remarkable captures and robberies, and earned the name Blackbeard from his... black beard. He was exceptionally skilled at inspiring fear in the hearts of those he robbed by cultivating an untamed and unafraid demeanor. Interestingly, however, he was generally opposed to violence, and relied primarily on scare tactics. He flew black and bloody flags, put burning fuses in his hat, and screamed curses of damnation on his enemies.

Blackbeard’s final ship, the Adventure, was a fast sloop, capable of executing narrow escapes [7, p 283]. The governor of Virginia, Alexander Spotswood, made it his mission to stamp out Blackbeard’s pirating operation. This was largely done to divert attention from his own corruption, as he was known to have spent inordinate sums of the country’s money on his own private residence. The death of a sensational pirate was expected to cause a positive shift in Spotswood’s image.

Governor Spotswood hired lieutenant Robert Maynard to hunt down and capture or kill Blackbeard and his crew [7, p 289]. At the time, Blackbeard had settled himself into the seas around North Carolina, and set up a pirate rendezvous on Ocracoke island. Maynard’s men discovered Blackbeard’s sloop there, along with another merchant ship captained by Samuel Odell. The friends were drinking late into the night, so when Maynard’s ships finally freed themselves from sandbars the following morning and approached Blackbeard’s Adventure, the drunken pirates were a little slow to the draw. They unfurled the sails, but the Adventure did not have enough time to distance itself from Maynard’s Ranger and the Jane, which were in hot pursuit. The pirates and naval officers fired muskets and cannons, which immediately took an immense toll on Maynard’s men.

By an incredible stroke of luck, however, one of the musket balls from Maynard’s ship snapped the jib halyard [7, p 239]. This rendered the jib unusable, and the loss of that single sail crippled the Adventure. Unable to sail with nearly enough speed to escape, the pirates were forced to fight. Soon the pirates boarded the Jane thinking they had won the battle, only to be ambushed by Maynard’s men [7, p 294]. A vicious six-minute battle ensued. Maynard lost fingers, and Blackbeard lost his head.

Ultimately, the loss of a single, small sail significantly reduced the ‘Bernoulli power’ of the ship, resulting in Blackbeard suffering five gunshot wounds, many deep cuts, and decapitation.

References

[1] Edward Barlow. Journal of edward barlow, 1656-1703.: Royal museums greenwich. URL: https://www.rmg.co.uk/collections/objects/rmgc-object-505786.

[2] Stephen Colgate. Manual of “Basic sailing theory.”. Offshore Sailing School, 1972.

[3] NICOLAE CRACIUNOIU and BOGDAN O. CIOCIRLAN. 8 - fluid dynamics. In Dan B. Marghitu, editor, Mechanical Engineer’s Handbook, Academic Press Series in Engineering, pages 559–610. Academic Press, San Diego, 2001. URL: https://www.sciencedirect.com/science/article/pii/B9780124713703500097,doi:10.1016/B978-012471370-3/50009-7.

[4] Spinnaker-Sailing San Francisco. Sailing upwind,

2022. URL: https://www.spinnaker-sailing.com/online-courses/lesson-1/sailing-upwind#:~:text=The%20jib%20in%20the%20illustration,is%20called%20the%20slot%20effect.

[5] Robert Kurson. Pirate hunters: Treasure, obsession, and the search for a legendary pirate ship. Random House, 2016.

[6] Rebecca Simon. Why we love pirates: The hunt for captain Kidd and how he changed piracy forever. Mango Publishing, 2020.

[7] Colin Woodward. The Republic of Pirates: Being the true and surprising story of the Caribbean pirates and the man who brought them down. Pan Books, 2014.