Longships were a type of specialised Viking warships that have a long history in Scandinavia, with their existence being archaeologically proven and documented from at least the fourth century BC. Originally invented and used by the Norsemen (commonly known as the Vikings) for commerce, exploration, and warfare during the Viking Age, many of the longship's characteristics were adopted by other cultures, like Anglo-Saxons and continued to influence shipbuilding for centuries. The longship's design evolved over many centuries, beginning in the Stone Age with the invention of the umiak and continuing up until the 6th century with clinker-built ships like Nydam and Kvalsund. The longship appeared in its complete form between the 9th and 13th centuries. The character and appearance of these ships have been reflected in Scandinavian boat-building traditions until today. The particular skills and methods employed in making longships are still used worldwide, often with modern adaptations. They were all made out of wood, with cloth sails (woven wool) and had numerous details and carvings on the hull.
The longships were characterized as a graceful, long, wide and light, with a shallow-draft hull designed for speed. The ship's shallow draft allowed navigation in waters only one meter deep and permitted arbitrary beach landings, while its light weight enabled it to be carried over portages or used bottom-up for shelter in camps. Longships were also double-ended, the symmetrical bow and stern allowing the ship to reverse direction quickly without a turn around; this trait proved particularly useful at northern latitudes, where icebergs and sea ice posed hazards to navigation. Longships were fitted with [oar]s along almost the entire length of the boat itself. Later versions had a rectangular sail on a single mast, which was used to replace or augment the effort of the rowers, particularly during long journeys.The average speed of Viking ships varied from ship to ship, but lay in the range of 5–10 knots (9.3–18.5 km/h) and the maximum speed of a longship under favourable conditions was around 15 knots (28 km/h).
The Viking longships were the type of naval power in their time and were highly valued possessions. Archaeological finds show that the Viking ships were by no means a standard type vessel. It demonstrated true individual designs with its designers' footprints and often had regional characteristics. For example, the choice of material was mostly dictated by the regional forests, that is pine from Norway and Sweden, and oak from Denmark. Moreover, each and every one of these Viking longships had particular features adjusted to the natural conditions, which they were exposed to.
They were often communally owned by coastal farmers and commissioned by kings in times of conflict, in order to quickly assemble a large and powerful naval force. While longships were used by the Norse in warfare, they were mostly used as troop transports, not warships. In the tenth century, longships would sometimes be tied together in offshore battles to form a steady platform for infantry warfare. During the 9th century peak of the Viking expansion, large fleets set out to attack the degrading Frankish empire by attacking up navigable rivers such as the Seine. Rouen was sacked in 841, the year after the death of Louis the Pious, a son of Charlemagne. Quentovic, near modern Etables, was attacked in 842 and 600 Danish ships attacked Hamburg in 845. In the same year, 129 ships returned to attack up the Seine.They were called "dragonships" by enemies such as the English because they had a dragon-shaped bow. The Norse had a strong sense of naval architecture, and during the early medieval period they were advanced for their time.
Keel, stems and hull
The Viking shipbuilders had no written diagrams or standard written design plan. The shipbuilder pictured the longship before its construction, based on previous builds, and the ship was then built from the keel up. The keel and stems were made first. The shape of the stem was based on segments of circles of varying sizes. The keel was an inverted T shape to accept the garboard planks. In the longships the keel was made up of several sections spliced together and fastened with treenails. The next step was building the strakes—the lines of planks joined endwise from stern to stern. Nearly all longships were clinker (also known as lapstrake) built, meaning that each hull plank overlapped the next. Each plank was hewn from an oak tree so that the finished plank was about 25 mm (0.98 inches) thick and tapered along each edge to a thickness of about 20 mm (0.79 inches). The planks were radially hewn so that the grain is approximately at right angles to the surface of the plank. This provides maximum strength, an even bend and an even rate of expansion and contraction in water. This is called in modern terms quartersawn timber, and has the least natural shrinkage of any cut section of wood. The plank above the turn of the bilge, the meginhufr, was about 37 mm (1.5 inches) thick on very long ships, but narrower to take the strain of the crossbeams. This was also the area subject to collisions. The planks overlapped by about 25–30 mm (0.98–1.18 in) and were joined by iron rivets. Each overlap was stuffed with wool or animal hair or sometimes hemp soaked in pine tar to ensure water tightness. Amidships, where the planks are straight, the rivets are about 170 mm (6.7 inches) apart, but they were closer together as the planks sweep up to the curved bow and stern. There is considerable twist and bend in the end planks. This was achieved by use of both thinner (by 50%) and narrower planks. In more sophisticated builds, forward planks were cut from natural curved trees called reaction wood. Planks were installed unseasoned or wet. Partly worked stems and sterns have been located in bogs. It has been suggested that they were stored there over winter to stop the wood from drying and cracking. The moisture in wet planks allowed the builder to force the planks into a more acute bend, if need be; once dry it would stay in the forced position. At the bow and the stern builders were able to create hollow sections, or compound bends, at the waterline, making the entry point very fine. In less sophisticated ships short and nearly straight planks were used at the bow and stern. Where long timber was not available or the ship was very long, the planks were butt-joined, although overlapping scarf joints fixed with nails were also used.
As the planks reached the desired height, the interior frame (futtocks) and cross beams were added. Frames were placed close together, which is an enduring feature of thin planked ships, still used today on some lightweight wooden racing craft such as those designed by Bruce Farr. Viking boat builders used a spacing of about 850 mm (33 inches). Part of the reason for this spacing was to achieve the correct distance between rowing stations and to create space for the chests used by Norse sailors as thwarts (seats). The bottom futtocks next to the keel were made from natural L-shaped crooks. The upper futtocks were usually not attached to the lower futtocks to allow some hull twist. The parts were held together with iron rivets, hammered in from the outside of the hull and fastened from the inside with a rove (washers). The surplus rivet was then cut off. A ship normally used about 700 kg (1,500 pounds) of iron nails in a 18 m (59 feet) long ship. In some ships the gap between the lower uneven futtock and the lapstrake planks was filled with a spacer block about 200 mm (7.9 inches) long. In later ships spruce stringers were fastened lengthwise to the futtocks roughly parallel to the keel. Longships had about five rivets for each yard (90 cm or 35 inches) of plank. In many early ships treenails (trenails, trunnels) were used to fasten large timbers. First, a hole about 20 mm (0.79 inches) wide hole was drilled through two adjoining timbers, a wooden pegs inserted which was split and a thin wedge inserted to expand the peg. Some treenails have been found with traces of linseed oil suggesting that treenails were soaked before the pegs were inserted. When dried the oil would act as a semi-waterproof weak filler/glue.
The longship's narrow deep keel provided strength beneath the waterline. A typical size keel of a longer ship was 100 mm × 300 mm (3.9 by 11.8 inches) amidships, tapering in width at the bow and stern. Sometimes there was a false outer keel to take the wear while being dragged up a beach. These large timbers were shaped with both adze and broadaxe. At the bow the cut water was especially strong, as longboats sailed in ice strewn water in spring. Hulls up to 560 cm (18.4 feet) wide gave stability, making the longship less likely to tip when sailed. The greater beam provided more moment of leverage by placing the crew or any other mobile weight on the windward side. Oceangoing longships had higher topsides about a 1 m (3.3 feet) high to keep out water. Higher topsides were supported with knees with the long axis fastened to the top of the crossbeams. The hull was waterproofed with animal hair, wool, hemp or moss drenched in pine tar. The ships would be tarred in the autumn and then left in a boathouse over the winter to allow time for the tar to dry. Evidence of small scale domestic tar production dates from between 100 AD and 400 AD. Larger industrial scale tar pits, estimated to be capable of producing up to 300 litres of tar in a single firing have been dated to between 680 AD and 900 AD. A drain plug hole about 25 mm (0.98 inches) was drilled in the garboard plank on one side to allow rain water drainage.
The oars did not use rowlocks or thole pins but holes cut below the gunwale line. To keep seawater out, these oar holes were sealed with wooden disks from the inside, when the oars were not in use. The holes were also used for belaying mooring lines and sail sheets. At the bow the forward upper futtock protruded about 400 mm (16 inches) above the sheerline and was carved to retain anchor or mooring lines.