War at Sea – Northern Cog


After Roman hull-first construction techniques were abandoned and replaced with ribs-first construction, battering ram became useless as a weapon. As a result, naval action came to depend on missile exchange and boarding – only introduction of cannon saved galley as a ship of war in the Mediterranean (see “Galley vs sailing ship” post). In Atlantic, many battles were fought exclusively on cogs (e.g. Battle of Sluys), although war galley survived for purposes of raiding, anti-piracy and coastal patrol. Galley simply is not an effective seagoing weapon system: it has limited radius of action, endurance, and lacks seaworthiness to leave shore. Galley fleets were thus dependant on coastal stations (which is why Venice tried to conquer Croatian shore multiple times, succeeding after Croatian union with Hungary as latter didn’t care much about the sea). They were incapable of blockaing a port unless a friendly army held the shore, and navies operated as flanking forces of armies. As a result, all major world empires were land-based, and maritime empires only developed after sailing ships became effective warships.

Northern countries, facing harsh Atlantic ocean, never relied on galley as much as their Mediterranean counterparts. As a result, even in antiquity, most of the warships used there were of a sailing variety. In the Middle Ages, northerners quickly adopted improved roundships as war platforms, while Mediterranean peoples stuck to the galley. Roundship evolved into man-of-war, which then evolved into ship of the line after adoption of cheap iron cannon.

England was regional naval power between 13th and 15th centuries; its main enemies were France, as well as Scottish and Welsh princes. Consequently, operations of English ships were restricted to local waters. Royal ships formed the core of the naval expeditions, but majority of ships were invariably privately owned ships requisitioned for war. Lack of naval shipbuilding led to reliance on private shipyards to provide ships.

Oared warships formed the core of English fleet until 14th century, but their exact form is unknown. In late 13th century, ships started being fitted with stern rudder and fighting castles, though latter might have appeared earlier. From second half of 14th century, English warships were called balingers, and some could have more than 100 oars. In 1206., 47 galleys were on station to counter French attacks. By 15th century however growing size of sailing vessels and adoption of fighting castles meant that large sailing ships could only be defeated by ships of similar type. As a result, even in first decades of 15th century oared ships were used almost exclusively for scouting and patrol. Of Henry Vth’s fleet, oared ships accounted for 41% of ship numbers (11 out of 27) but only 10% of tonnage. They were thus likely only auxiliary craft, used in patrols, reconnaissance and amphibious assaults.

Fights typically developed into boarding actions and missile exchanges. Many ships were requisitioned merchant vessels. While galleys were more maneuverable, cogs had height, size, and greater numbers of marines. Reason why galleys remained so popular in Mediterranean likely had less to do with galley’s fighting power (cog and later caravel had significant advantage due to freeboard and general height advantage) and more with rowed ship’s innate superiority in amphibious and close-to-shore operations. Even so, sailing tall ships had been replacing galley even in the Mediterranean when introduction of cannon temporarily reversed the trend (see “Galley vs sailling ship“).

Northern Cog

Cog itself first appeared in nort-western Europe in 10th century and was widespread by 12th century. First mention of ship type is in 948 AD in Muiden near Amsterdam. Cog may have been developed in western Jutland to handle dangerous waters around Limfjord, but its origins lie with Romano-Celtic tradition of shipbuilding. Cog tradition of shipbuilding apparently comes from Frisian lands near the mouth of Rhine. Despite 1000 years difference, both traditions show ships designed for river or in tidal waters (and thus with either flat or round bottom) and for maximum room for cargo. Both types were built in “heavy” tradition of framing. Like early cogs, Romano-Celtic vessels had their mast steps well forward, and several were in floor timber. Some were also constructed with similar techniques, fastening together hull planking until floor timbers could be inserted.

Whatever its origins, it proved successful as an ocean-going ship. Its transformation into true seagoing trader came as an answer to closure of the western entrance to Limsfjord, which was blocked by sand in 12th century due to strong currents. This created a need for spacious and relatively inexpensive ships.

Cog was primarily used for trade, especially by the Hanseanic League, but was also used for warfare as well. Cogs developed of an amalgman of Celtic boat-building practices and Roman river-boats. They had excellent stability, shallow draft and good carrying capacity. Ship itself was constructed of oak, and could be 15 to 25 meters in length, with carrying capacity of around 200 tons. While a round ship, it had flat bottom and overlapped strakes near posts. Unlike later caravel and carrack, it had clinker-built hull, though planks on bottom were laid side-to-side. Both stern and stem posts were straight and long. It had plank-keel twice the thickness of the garboards. Hull itself was open, and cog could be rowed for short distances, though hull shape and high freeboard made such manner of propulsion less than optimal.

Cog had single mast with a single square-rigged sail, wide beam, excellent carrying capacity and stability, shallow draft but low speed. Their square sail also limited ability to sail against the wind, while introduction of keels (and sternpost rudder) in thirteenth century led to increase in draft (and thus need for docks) but also reduced leeway. Mast step was well forward early on, at 29% of length of the ship, but moved backwards at later seagoing cogs – Kolding at 34%, Vejby at 42% and Bremen at 43%. For comparison, Dutch cogs which continued to be used primarily on rivers kept their masts well forward, at 24 – 34%. Sails were mostly square. Bremen cog had a windlass aft for hoisting yard and sail. Cogs from 1242. onward used median rudder with fore-and-aft tiller.

When used for warfare, cogs were modified with fore and stern castles, which could also be added as defense against pirates. Stern castle in particular was important for command and control purposes.

At least some cogs were built plank-first, as two wrecks show holes used to hold planks together until ribs and floors are fitted. No such evidence had been found in Bremen cog. Construction, as summarized in “Boats of the World”, is as follows:

  • plank-keel scarfed to the stern hooks, then hooks to the main posts
  • bottom planking fitted and fastened at the ends in overlap; central part temporarily fastened
  • floors fastened, fitted and fastened to bottom planking, keelson fastened to floors, temporary battens removed, bottom caulked
  • first five side strakes fitted overlapping, fastened together and caulked inboard
  • main crossbeams inserted and supported by knees
  • two more strakes, higher crossbeams and remaining futtocks inserted
  • two more strakes and the washstrake added, followed by the top timbers
  • great knees / half-bulkheads added
  • ceiling planking, longitudinal timbers and decking added
  • superstructure added

Based on full-scale reconstructions of Bremen cog, some performance parameters had been estimated. Hold index for cogs is 0,4 – 0,5, similar to contemporary Nordic cargo ships. Two cogs from inland waters could carry 9 and 24 tons (tonnes), while sea-going Krupp cog could carry 30 tons, and Bremen cog could carry 70 – 130 tons; Brandt and Hochkirch estimate its maximum useful cargo capacity as 87 tons at draft of 2,25 m. This cog could sail at 67° – 75° off the true wind, but could not achieve more than 1 knot to windward – 90° off the wind was best normally achievable. On broad reach and when running maximum speed was 8 knots. Lack of watertight weather deck also limited performance.

Cog is inextricably linked with Hanse, a federation of German merchants and towns from which they came. These merchants dominated long-distance trade within northern Europe between 1250 and 1450, and also established contacts in Mediterranean and Russia. While not the only, cogs were the most common large transport ship. Around 22 cogs had been excavated, dating from 1150 to 1425. Length of 24 meters with capacity of 40 lasts / 120 m3 (80 metric tons of rye) seems to be on a smaller side of cog size, with more typical size being 100 lasts, and cogs of over 150 lasts known by 15th century.


Sailing ships were, until early 15th century, single-masters. In 14th century carrack was created by addition of a foremast with a lanteen sail, and in 1410. English acquired a Genoese carrack which had been captured by pirates. After that, English crown started building two-masted vessels, and by 1430s three-masters as well. By 1450s thre-masted rig had spread across Europe. Portugese transferred southern skeleton-building technology to Northern Europe in 15th century, which English first utilized in a carrack in 1460s. Guns remained unimportant in warfare until 15th century.

Further reading


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