During the period of the great organized Christian crusades against the Muslims in the Holy Land, 1095 – ca. 1400, ships played a crucial role in both logistic and tactical efforts. Throughout the period, the Christian crusaders had a more effective navy, which would prove invaluable in maintaining supply lines and harassing Muslim troop movements. Due to a number of reasons, including both a cultural distrust of the ocean and the unfavorable prevailing current and wind conditions of Muslim-dominated areas, the Muslim forces did not make as effective use of the seas as did the crusader forces. This paper intends to compare and contrast the maritime technology available primarily to the Crusader forces, although some Muslim technology will be discussed, with an eye towards the implementation and effectiveness of such technology on both sides.
Susan Rose, in her article “Islam versus Christendom: the Naval Dimension,” refers to the “unchanging imperatives of the physical world”1 such as the lay of the landmasses and their effects on the currents and winds as a significant factor in Mediterranean maritime innovations of this time period. As J. H. Pryor pointed out in his book Geography, Technology, and War: Studies in the Maritime History of the Mediterranean, 649-1571, the prevailing Mediterranean currents and winds tend to run in patterns unfavorable to the Eastern (and in this period, Muslim-held) shores. Rose takes this a step further by theorizing that the predominant wind patterns act as a natural barrier to northern (i.e., upwind) navigation. The technological reasoning behind this impediment will be addressed further down.
The period of the Crusades is a time of interesting changes in maritime shipbuilding, tactics, and navigational techniques. Lawrence Mott, in his book The Development of the Rudder: A Technological Tale, asksif “radically new technologies arise from an innate human desire to experiment, or do they occur because technological crises force man to search for them?”2 The answer is not so cut-and-dried. Certainly, medieval seafarers were fiddling with new types of rudders, hull designs, and means of propulsions, but they were also at war throughout much of the period not only with the Muslim forces but also with each other. Naval architecture was significantly influenced by the Byzantine/Frankish/Muslim arms race. As Unger points out on page 237 of “Warships and Cargo Ships,” it was the “threat of Arab fleets after the middle of the 7th century and then the need to reconquer the strategically important island of Crete in the 10th century [which] led to the development of a large galley” capable of carrying over three hundred men.3 The Italian city-states were nearly constantly in strife (as seen by the disastrous side-trip undertaken by the Fourth Crusade), and since many of these cities were heavily involved in maritime trade, so too did their combat take a naval dimension.
Richard Unger, in his article “Warships and Cargo Ships in Medieval Europe,” traces the evolution of both the fighting ship and the cargo vessel as separate and distinct forms of naval architecture, a division dating back to Roman times. He argues that this distinction blurs and then nearly disappears for a time in the 10th through 12th centuries, as ship styles more traditionally used in cargo movement become the preferred platform for maritime warfare. The distinction between cargo carriers and warships was a constantly fluctuating boundary. Often cargo carriers would be hired into military service during periods of conflict, and then return to their mercantile duties upon truce.
Richard Unger categorizes the two major trends in Mediterranean shipbuilding into long ships, which he defines as those “with length-to-beam4 ratios in excess of 6:1,” and round ships, those with a ratio of 4:1 or less.5 Long ships tended to be used as warships, which stands to reason. A vessel which is narrow in its hull design is more hydrodynamic and thus likely to be faster, though its hull-based turning ratio is not as responsive. The short ships are likely to be slower, but they contain increased interior hull space suitable for cargo in comparison with longer vessels.
Throughout most of the period addressed in this paper, the primary warship was the galley. Powered by banks of oarsmen, these long, relatively narrow vessels were fast and maneuverable. However, as Unger mentions, the galley is a ship design peculiar to the Mediterranean – its low freeboard6 renders it very vulnerable in heavy swells such as those found in the Atlantic and Baltic seas. Byzantine dromons, or war galleys, developed in response to the need to reconquer Crete from the Muslims in the 10th century. These were capable of carrying 300 men, and of sufficient size to serve as cargo ships in peace time.7 However, the galley soon saw competition in the form of the round ship.
A revival in round-ship construction and technology in the 11th and 12th centuries soon created a formidable threat to the galley’s alternate role as a trading vessel. Instead of the square sail, these round ships were two-masters, each carrying a lateen sail8. The lateen sail offers a vessel significantly increased maneuverability, among other advantages. The secret behind the benefit of a lateen sail versus a square sail9 lies in its bracing. A square sail hangs off a yardarm which is suspended perpendicularly to the centerline of the ship. They can be angled slightly, but not very far. Running downwind or on a broad reach, square sails are very fast. However, once the wind angle begins to get close to the bows, the vessel slows and must bear off, or risk being stopped altogether and pushed downwind. A lateen sail, on its diagonal suspension, can get much closer to the wind and thus offer more ranges of option in the vessel’s choice of course. A fleet of square-rigged vessels might have to wait for the wind to change before they could leave port, but lateen-rigged ships face no such difficulties. Lateen sails to make it more difficult to change direction relative to the wind, however – the yard must be manhandled around the mast in order to tack.
One intriguing theory mentioned by Lynn White, Jr. in his review of Richard Unger’s The Ship in the Medieval Economy is the idea that a change in loom designs (from the vertical, warp-weighted design to the larger horizontal heddle-treadle loom) resulted in sails being made up of larger pieces of cloth and thus less seams where two pieces join. Seams are the weakest part of any fabric construction, and so the use of these new looms would in turn also produce much stronger sails with longer working lives. White mentioned that this was not included in Unger’s book, but should be considered as a possible factor in sail design advances.10
White also mentions the fact that a change in hull construction itself accompanied the spread of the lateen rig. Up to this point, ships were built by fixing the hull planking together first, a process which required a significant amount of time and skill. At the same time as the increased popularity of the lateen rig, the shipbuilders shifted to a skeleton-first design, laying the keel and ribbing first and then affixing planking. This is markedly faster, and does not require the same level of master-craftsmen type work. White argues that the combination of lateen rigs and skeleton-first design were both ways of cutting corners in construction and voyage time and making voyages more profitable.
Regardless of whether it was faster to construct or not, the lateen rigged hull did provide other additional advantages. These lateen-rigged round vessels also were built with a deck above the hold, enabling them to widen their options when trading in bulk cargo. Heavy items went in the hold and had the additional bonus of acting as additional ballast, while lighter goods could go between decks. Unger states that by the 13th century, round ships dominated Mediterranean cargo transporting.
The distinction between cargo ship and warship, specifically between round ship and galley, was a very blurred line, as Unger points out. A few round ships could be found using oars to supplement their sails, but the major method of propulsion for these craft were their sails. Galleys carried masts and rigging, and often sailed most of the way to their destinations, using the oars only for combat maneuvering.11
While round ships became the workhorses of the Mediterranean fleet, galleys still were the warships of choice. However, the galleys too showed some evidence of similarities in design with round ships. The Venetians created their great galleys by increasing the size, while at the same time creating a beamier vessel. Despite its galley designation, these great galleys turned out to be more effective as cargo ships than fighting vessels.12 Richard Unger argues that these great galleys were faster than round ships, and were more efficient cargo transports than the light galleys, which had a lower ratio of hold space to rowers. Great galleys could be used for cargo or military purposes. Being so multipurpose, however, they were so versatile that the light galleys could not compete. In Unger’s opinion, it was this development that relegated the light galley solely to warfare.13
Thus excluded, many of these light galleys abandoned trade entirely and became strictly military enterprises. Now freed from cargo space constraints, many added a third rower at the end of each oar. This was a mixed blessing, however. The ships had more speed but were obliged to put into port more often for the additional supply stops necessitated by additional crewmen. This decreased their sea time (and thus their range of operations, with increased dependence upon friendly ports) even further.
The end of the galley did not come until after this period, with the dawn of ship-borne artillery. The galley’s advantage in maneuverability was rendered moot by other warships’ ability to blow them out of the water from afar. Gradually, the galley took on guns and made the transition into a pure warship in the 16th century as the galleass.14
Meanwhile, while galleys were dividing and specializing, the round ship form created a new kind of vessel: the cog. These appeared in the Mediterranean in the 1300s, although their Northern European status as warships did not survive the transition. Cogs served in the Mediterranean primarily as cargo vessels, since the characteristics which made them so useful as a warship in the Atlantic and Baltic seas (namely, their ability to withstand heavy seas and strong winds) were rendered moot, as the Mediterranean is a significantly more placid body of water. In light winds, cogs were easily becalmed. Galleys, although capable of sailing, were much less vulnerable in calm weather, due to their ability to make headway via oars. The chronicler Ibn Shaddad, in his Rare and Excellent History of Saladin, mentions an occasion where a Muslim sailing vessel was sunk due to a sudden drop in the wind, allowing the Frankish galleys to surround her. The Muslims scuttled the vessel rather than allow her to be captured.15
Cogs were used during combat between Barcelona and Genoa, but for the most part remained out of warfare in an active role.16 They were, however, frequently used as transports due to their large carrying capacity. Even in this, though, they were superseded by galleys: galleys were often the preferred vessels for amphibious attacks, as they could get close to the beach in the manner of Viking raiders.17
One last improvement in hull design was the transition from quarter rudder to the sternpost or pintle and gudgeon rudder. The quarter rudder was the standard Mediterranean method of controlling a ship’s forwards motion, but as Lawrence Mott points out, it had a number of drawbacks. For one thing, the design itself (see Figure 1) was very high-turbulence, producing drag and thus slowing the vessel down. The quarter rudder was hung on one side of the ship’s stern, not amidships as modern rudders – the pintle and gudgeon rudder – do. A single quarter rudder was sufficient for small long-ships, but for the larger ones, two rudders were required. Quarter rudders also did not work well with the rounded sterns of the new kinds of ships.
The solution to this was the pintle and gudgeon rudder. The pintle and gudgeon rudder was fitted on a straight beam attached along the keel at the stern. These were significantly more efficient in their effect on turning rate and maneuverability. One drawback to the pintle and gudgeon rudder not found in the old design, however, was its vulnerability. A pintle and gudgeon rudder could be damaged by heavy following seas or enemy action, and once put out of order, they were both extremely difficult and dangerous to fix at sea. (And of course, with a broken rudder, a ship will be severely impaired in its ability to put into port – a catch 22.) The pintle and gudgeon design spread relatively quickly across the Mediterranean, although galleys continued to use the double quarter rudders.18
In addition to advances in ship construction, this period also saw the creation of new tools for ship-related skills (such as navigation) and the refinement of already-existing items. Francesco da Barberino, in his 1306-1313 work “Documenti d’Amore,” which is otherwise a book on the conduct of gentlemen, includes a chapter on shipboard life. One segment detailing shipboard equipment appears amongst the anecdotes and helpful hints. The three items he lists which are indispensable aboard ship are the lodestone and needle (used to determine north), the hourglass, and charts.19 As Kreutz points out in her article “Mediterranean Contributions to the Mariner’s Compass,” the fact that there is nothing to indicate the compass is a new invention suggests that they were in common usage by 1315.20
With that said, the compass is possibly the most crucial navigational tool aboard ship. Its invention is a cloudy issue. The Chinese are thought to have come up with it first, yet other authors claim the Chinese and Europeans both came up with the idea independently of one another. The major difference between the European and the Chinese compass is that the Chinese compass pointed south, a fact which is often referenced in support of this latter concept.21
Barbara Kreutz states that the first European literary mention of the compass dates to the 12th century, when an English monk “in two separate works… described a magnetized needle which he said sailors used for locating the North Star in bad weather.”22 This needle is elaborated in the 1205 statement by Guyot de Provins that sailors “touched the needle to the dark, ugly magnet stone, and then put the needle through a straw and floated the gadget in water.”23 Kreutz also provides the tantalizing fact that Guyot spent some time in the “Near East” during the Third Crusade. Guyot’s simple device would only work on land or in calm seas, however. This was a major drawback since vessels are most in danger during rough weather when they need to be able to plot a safe course away. The Muslims, too, were aware of the compass, and its first mention in an Arab chronicle occurs in the 1240s. The Muslim compass operated in the same fashion as the previously described needle in a bowl of water, and thus was subject to the same requirements for calm conditions. Clearly, some method of stabilizing the needle was required.
The thirteenth century would bring the most innovative uses of the proto-compass. Peter of Maricourt idly theorized a dry, pivot-point magnetized compass needle in a monograph in 1269.24 In the 1280s, a navigator is mentioned as having “established his position in relation to his course through the use of the needle in conjunction with charts and mathematical tables.”25 This suggests two things: first, that the compass was reliable enough for use in port-to-port navigation, and second, that the charts were accurate enough (one hopes) to plot a course upon. For the compass to become reliable enough for use in charting, it has to have become self-contained by that point. [This paper on maritime technology during the Crusades was written by Sarah O’Connor in 2005 and appears online at strangewayes.wordpress.com. If you’re reading this as part of someone else’s term paper, there’s been some plagiarism.] However, even the self-contained compass would have been a primitive affair. The compass card does not appear until 1380. Most likely, those Crusader vessels which were equipped with compasses were still utilizing handheld, rudimentary means of simply determining north. Experienced navigators could then extrapolate the vessel’s approximate heading, but even then, reliability would likely have been an issue.26
The second item on da Barberino’s list, the hourglass, is an item which is very useful for several shipboard needs. However, like the compass, the hourglass too was still in its infancy in terms of accuracy. The first physical appearance of the sand clock occurs in a late 1330s fresco in Siena, although da Barberino’s manuscript was written between 1306 and 1311.27 The simplest use of the hourglass (and the one least necessitating precision of measurement) is to tell the mate on duty when a given watch is over. For this paper, information on the medieval watch-standing system was not readily available, but aboard most modern vessels it is the practice to divide the crew up into 4-hour watches. These watches then perform all tasks of running the vessel during their shift, after which they get to go back to sleep. It is a relatively simple matter to have an hourglass set for a specific length of time.
The second, and more vital use of the hourglass, is in conjunction with navigation techniques. Assuming an hourglass could be kept precisely (i.e., turning it back over immediately), knowing the exact time is a crucial part of determining position. If a navigator knows the exact time, he can then calculate when the sun’s apparent position will cross his meridian, and thus have a better idea of his latitude when the North Star is not visible.28 However, as Balmer points out, the issues with keeping exact time at sea render doing so nearly impossible. Even assuming the watch was diligent about turning it over, the motion of the waves affects the fall rate of the sand particles, the moisture can cause the sand to coagulate, and the inexact graduation of the timepiece itself can all add up with dangerous results. An inaccurate timepiece can not be used for navigation: every degree of error comes out to approximately 60 nautical miles. Nevertheless, the medieval hourglass transitioned to the nautical world successfully enough, and it was useful in assisting with navigation.29
One later use of the hourglass was in combination with the chip log, a piece of wood on a line which would be tossed overboard at the bow and timed until it passed the stern. The result could then be calculated to produce a more exact definition of the ship’s speed. However, the chip log does not show up until the 16th century.30 It is possible to do the same thing without knowing the exact amount of elapsed time. Another method of determining ship’s speed, used by both medieval and modern sailors alike, is to lean over the side and watch the ship’s bow wake. With experience, surprisingly precise estimates can be obtained.31
With all this discussion of various items’ usefulness in navigation, some explanation of medieval navigation practices must be discussed. The simplest form of navigation, and probably the most common on short coastal voyages, was and remains dead reckoning. “Dead reckoning” refers to an almost intuitive form of navigation which is done by estimating the ship’s mileage and noting the vessel’s course, and simply progressing a bearing line ahead on a chart by the number of miles sailed. It is not especially accurate, as it fails to compensate for set and drift – the forces of the wind and current pushing the vessel ahead of or off of its intended course. Measuring mileage is currently done by measuring the flow of water through a taffrail log, a spinner-like device trailing over the stern, and then converting that to mileage. However, since the taffrail log is a post-medieval invention, medieval sailors likely estimated their ship’s speed using the aforesaid methods of observation of either the ship’s wake or a drifting object and then determined the amount of time elapsed. However, one issue with this form of navigation is that it can be significantly in error. Currents flowing with the vessel give the appearance that a ship is moving at a slow pace, while head-on currents make it seem the vessel is traveling significantly faster than it is. Dead reckoning is safe for short parts of offshore voyages, but in order to ensure landfall at the correct destination, a more reliable method of determining position is necessary.32
A simple and effective, if primitive, solution to that problem was to measure the altitude of the North Star upon leaving port, often using fingers at arm’s length. To return to that port, a navigator would sail north or south until the fingers lines up again, and then sail east or west until things started to look familiar. While this was sufficient for short trips, something more accurate was needed. The answer was the quadrant.
The quadrant came into widespread navigational use around 1450, although it probably was used aboard ships as early as the 1200s. An ancestor of the modern sextant, the quadrant offered both increased accuracy and a built-in database of ports’ locations. As the name suggests, quadrants were quarter-circle pieces of wood or metal. The navigator would take the altitude of the North Star above the horizon by sighting Polaris through the two brass eyes on the side, which would be on top when held in the correct position. 33The weight and string will show the angle. Its reading is the vessel’s latitude. I built the quadrant in Figure 3 from a late medieval design out of pine, paper, a lead musket ball, 2 brass eyes, and some woollen yarn. It was not uncommon for medieval European navigators to write the names of important ports at their latitudes – all the navigator needs to do is line up the string with the name, and then sail east or west as necessary.34
The Muslims had a similar device, called the kamal. The kamal was a small piece of wood with a knotted string attached. The string was held between the teeth, with the wood at arm’s length. The goal was to line the edge of the wood up between the North Star and the horizon; the length of string indicated the altitude. Like European mariners’ quadrants, Arab navigators put knots in the string at the latitude of given ports. By biting a knot for a given port, a Muslim captain would sail until the wood touched both the North Star and the horizon, and then sail east or west accordingly. Arab inventors also created the astrolabe, a device used to determine the time of sunrise and sunset, as well as to calculate the altitude of the sun and selected stars. However, this did not make the transition from astronomy to seafaring usage until after the scope of this paper.35
The result of all these ferocious advances in maritime technology was a navy that was vastly improved by the end of the period over the comparatively simple vessels at the beginning. To defend against attacks by sea, many ports strung heavy chains across the entrance to their harbors. Hanging at or just below the waterline, these chains would do considerable damage to any vessel attempting to enter. A lucky ship would merely have her rudder torn off; unlucky ships could spring planks or stave in their bows. The chronicles of the Crusades are filled with accounts of ships attacking other ships, fleets, and even taking entire cities.36 The advances in maritime technology made during the period 1095 – ca. 1400 were both fuelled by the constant conflicts and a major contributor to the warfare.
- Bachrach, David. “Medieval Siege Warfare: A Reconnaissance,” in The Journal of Military History, Vol. 58, No. 1. (Jan., 1994), pp. 119-133.
- Balmer, R. T. “The Operation of Sand Clocks and Their Medieval Development,” in Technology and Culture, Vol. 19, No. 4. (Oct., 1978), pp. 615-632.
- Boas, Adrian J. “Archaeological Sources for the History of Palestine: The Frankish Period: A Unique Medieval Society Emerges,” in Near Eastern Archaeology, Vol. 61, No. 3, The Frankish Period: A Unique Medieval Society Emerges. (Sep., 1998), pp. 138-173.
- Eickhoff, Ekkehard, Seekrieg und Seepolitik zwischen Islam und Abendland. Berlin: Walter de Gruyter & Co., 1966.
- Fisher, Dennis. Latitude Hooks and Azimuth Rings. International Marine: Camden, ME. 1995.
- Hourani, George Fadlo, Arab Seafaring. Beirut: Khayats, 1963.
- Ibn Shaddad, Baha’ al-Din. (trans. D. S. Richards). Rare and Excellent History of Saladin. Burlington: Ashgate Publishing, 2002.
- Kreutz, Barbara M. “Mediterranean Contributions to the Medieval Mariner’s Compass,” in Technology and Culture, Vol. 14, No. 3 (July, 1973), 367-383.
- Lewis, Archibald R., and Runyan, Timothy J., European Naval and Maritime History, 300-1500. Bloomington: Indiana University Press, 1985.
- Mott, Lawrence. The Development of the Rudder: A Technological Tale. College Station: Texas A&M University Press, 1997.
- Nicholson, Helen J. The Chronicle of the Third Crusade. Burlington: Ashgate Publishing, 1997.
- Nicolle, David. “Medieval Warfare: The Unfriendly Interface,” in The Journal of Military History, Vol. 63, No. 3. (Jul., 1999), pp. 579-599
- O’Connor, Sarah E. Sheet Anchor. Unpublished manuscript. Written in conjunction with Woods Hole SEA Semester, September – December 2004.
- Peters, Edward, ed., The First Crusade : the chronicle of Fulcher of Chartres and other source materials. Philadelphia : University of Pennsylvania Press, 1998.
- Pryor, John H., Geography, Technology, and War. New York: Cambridge University Press, 1988.
- Rose, Susan, Medieval Naval Warfare, 1000-1500. New York: Routledge, 2002.
- — “Islam Versus Christendom: The Naval Dimension, 1000-1600.” The Journal of Military History, Vol. 63, No. 3 (July 1999), 561-578.
- Roland, Alex. “Secrecy, Technology, and War: Greek Fire and the Defense of Byzantium, 678-1204,” Technology and Culture, Vol. 33, No. 4. (Oct., 1992), pp. 655-679.
- Unger, Richard W., The Ship and the Medieval Economy, 600-1600. Montreal: McGill-Queen’s University Press, 1980.
- — “Warships and Cargo Ships in Medieval Europe,” in Technology and Culture, Vol. 22, No. 2. (Apr., 1981), pp. 233-252.
- Villehardouin, Geoffroi de (Marzials, Frank, trans.), Villehardouin and de Joinville : Memoirs of the Crusades. New York: Dutton, 1955.
1 Susan Rose, “Islam Versus Christendom: The Naval Dimension, 1000-1600.” The Journal of Military History, Vol. 63, No. 3 (July 1999), 561-578. page 562.
2 Lawrence Mott, The Development of the Rudder: A Technological Tale. College Station: Texas A&M University Press, 1997. pg 156
3 Richard Unger, “Warships and Cargo Ships in Medieval Europe,” in Technology and Culture, Vol. 22, No. 2. (Apr., 1981), pp. 233-252. page 237
4 Beam is the width of a vessel at its widest point.
5 Unger, “Warships and Cargo Ships,” 236.
6 Freeboard is how much clearance a vessel has above the waterline. A low freeboard means a vessel is more easily swamped and thus sunk, whereas a high freeboard requires an equally high wave height for water to cross the decks.
7 Unger, “Warships and Cargo Ships,” 237
8 See Figure 1
9 See Figure 2
10 White, Lynn Jr. Review of Richard Unger’s The Ship in the Medieval Economy in Technology and Culture, Vol. 23, No. 2 (April, 1982), 223-227.
11 Unger, “Warships and Cargo Ships,” 237-238.
12 Unger, “Warships and Cargo Ships,” 238
13 ibid, 238
14 ibid, 240; Richard Unger, The Ship and the Medieval Economy, 600-1600. Montreal: McGill-Queen’s University Press, 1980.
15 Baha’ al-Din Ibn Shaddad, Rare and Excellent History of Saladin, trans. D. S. Richards. Burlington: Ashgate Publishing, 2002. pg 151
16 Unger, “Warships and Cargo Ships,” 246
17 Alan Ereira and Terry Jones, The Crusades (documentary). A&E/BBC Productions, 1995.
18Mott, Lawrence. The Development of the Rudder: A Technological Tale. College Station: Texas A&M University Press, 1997.
19 Balmer, R. T. “The Operation of Sand Clocks and Their Medieval Development,” in Technology and Culture, Vol. 19, No. 4. (Oct., 1978), pp. 615-632. page 616
20 Kreutz, Barbara M. “Mediterranean Contributions to the Medieval Mariner’s Compass,” in Technology and Culture, Vol. 14, No. 3 (July, 1973), 367-383. page 374
21 ibid 368
22 ibid 368-369.
23 ibid 369
24 Kreutz 371
25 ibid 371
26 ibid 371-3
27 Balmer 616
28 There is not sufficient space in this paper to explain the intricacies of celestial navigation; suffice it to say, celestial navigation requires a geocentric worldview. Imagine the heavenly bodies projected onto a crystal sphere around the earth. Drawing a line from the center of the earth to the star or planet in question, the point where it passes through the earth’s surface is called its Apparent Position. CN requires the navigator to calculate the ship’s position in relation to one or more celestial APs.
29 Balmer 621
30 Balmer 621
31 When I was aboard the brigantine SSV Corwith Cramer in Fall of 2004, we often had to reduce speed to 2 knots while under sail for oceanographic tests. Our estimate in this matter was to watch the wake going by and determine when it was approximately the speed of a person “walking to get a bagel on a Sunday morning. Fast enough that he really wants it, but slow enough because it’s a lovely day and he doesn’t want to rush.” Inexact, true, but it worked precisely every time.
32 O’Connor, Sheet Anchor, no pagination.
33 See Figure 3: Quadrant built by the author.
34 Fisher, Dennis. Latitude Hooks and Azimuth Rings. International Marine: Camden, ME. 1995. pgs 34-43.
35 Fisher 17-21
36 Roland, Alex. “Secrecy, Technology, and War: Greek Fire and the Defense of Byzantium, 678-1204,” Technology and Culture, Vol. 33, No. 4. (Oct., 1992), pp. 655-679.