The Viking Ship Museum explains that longship hull design was largely determined by the **rowing requirement**, and experimental voyages investigate “the demands made by rowing and sailing a longship.” It notes that reconstructions are used to understand “how the combination of sail and oars functioned in practice” and why rowing remained so important even on sailing ships.

“The Viking ships' **square sail** was, in size and shape, developed together with the individual hull size and type of ship.” The museum notes that reconstruction of Viking Age sails is challenging because “there are but few traces preserved in the archaeological record,” but refers to “finds of rigging details, for example blocks, shroud pins, mast fragments, yard etc. from the Viking period and the Middle Ages,” which are associated with these square sails.

Square rigged; arguably the oldest sail type. Poor at sailing upwind. Good at sailing downwind. The document also identifies the Viking longship as square-rigged and contrasts square rigs with fore-and-aft sails.

The museum summarises reconstruction issues and states: "The Viking ships’ **square sail** was, in size and shape, developed together with the individual hull size and type of ship." It explains that Skuldelev 3 preserves mast traces plus "tacking holes for securing the sail forward at the rail, and sheet holes towards the stern to take the sheet," allowing the breadth of the square sail to be calculated precisely. It also notes finds of blocks, shroud pins, mast fragments and yards from the Viking period, which, together with oral tradition from later Nordic **square‑rigged boats**, are used to reconstruct the rigging.

The article discusses the long Nordic boatbuilding tradition and propulsion methods and notes that later large vessels included “a more narrow boat (type A), **propelled by a combination of oars and sails** that enabled it to move also when there was a lack of wind or when the wind direction was less favourable.” It also states that firm archaeological evidence for oars and sail “does not appear in the archaeological material until the Nydam and Oseberg ships of the 2nd and 9th c. AD,” linking the combination of rowing and sailing to the tradition that culminates in Viking-age ships.

The museum notes that sails and rigging are rarely preserved archaeologically, so reconstructions are based on ethnography and key ship finds like the 11th‑century merchant ship Skuldelev 3. It emphasises that "19th century Norwegian **square‑sail boats** have technological features in common with Viking ships with regard to both hull and to sail and rigging" and that these later square‑sail vessels play a primary role in reconstructing Viking Age sail and rigging. Viking Age images commonly show sails "twice as wide as they are high," whereas many modern reconstructions have more or less quadratic **square sails**.

Britannica describes the longship as a type of Norse ship used for raiding and exploration and notes that they were “**propelled by oars and a square sail** on a single mast.” It emphasizes their long, narrow form and shallow draft, and explains that the combination of rowing benches along the sides and a central mast with a **square sail** allowed both rowing and sailing depending on circumstances.

The article states: “The longships had **two methods of propulsion: oars and sail**. At sea, the sail enabled longships to travel faster than by oar… Oars were used when near the coast or in a river, to gain speed quickly, and when there was an adverse (or insufficient) wind.” It further explains that “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,” and that many Viking Age warships are depicted with **low, square sails** that are wider than they are high.

Warfare History Network notes explicitly that “**Viking longships used both sail and oars for propulsion**.” It adds that “When the weather did not cooperate or while they were in close-quarters in combat, the Vikings used oars,” and that “The Vikings lowered their masts and sails when approaching the coast… When maneuvering in the shallows along the coast, they used their oars.” The article also mentions that longships, once fitted with masts and sails, could rely on wind power but still kept oars for other conditions.

Discussing how Viking sails are reconstructed, ScienceNordic reports that there are no surviving Viking Age sails: "The fact is that we have never found any sails form the Viking Age, so we cannot know what they looked like." Archaeologists therefore use shipwrecks plus pictures and texts. It notes that the hulls of Viking ships share many features with 19th‑century Norwegian **square‑rigged vessels**, whose trapezoidal square sails inform reconstructions, although researchers at the Viking Ship Museum do not think Vikings used exactly that trapezoidal shape. The article confirms that "many reconstructed Viking ships have quadratic sails" and that all accessible material is used to reconstruct their **sails and rigs** as credibly as possible.

In its general article on Viking ships, Britannica states that these vessels typically had "a single mast with a **square sail**" and that on warships "a great many oars" were also carried. It describes how the combination of oars and square sail made Viking ships fast and versatile, able to cross open seas under sail but also to move up rivers and close to shore using **oars for propulsion** when needed.

Describing longships, the article notes: “In a sense, they were simply **overgrown rowboats equipped with sails**.” It explains that “longships featured sharp bows that could easily cut through the sea, thereby reducing resistance when motive force was applied to the hull **either through sails or oars**.” On usage, it states that “the **sail was the primary motive power for long-distance passages. The oars were ideal when raiding up shallow rivers**,” and that at short intervals “Viking ships could be rowed much faster than the typical two knots, but not for long.”

National Museums Scotland describes Viking longships as "long, narrow, light boats" that were "powered by **oars and a square sail**." It notes that the mast was set roughly amidships and carried a large square woollen sail, while multiple oars along each side allowed the crew to row when there was no wind or when navigating inshore waters.

The V&A Museum entry for a model Viking ship describes it as having “a central mast with a **square sail** and multiple **oar ports** along the hull.” The descriptive text explains that the original ships that inspired such models “were sea-going vessels that could be driven by **sail on long sea crossings** and by **oars inshore and on rivers**,” highlighting the dual-propulsion design.

A specialist retailer’s historical overview explains that archaeologists identify a ‘true Longship’ when it is “at least five times as long as it is wide and has **both a mast to mount a sail and rows of benches for a team of oarsmen**.” It contrasts earlier Scandinavian boats, which “didn’t **combine the use of wind and oar power**,” with Viking-age longships, where “Combining two methods of propulsion, wind and manpower, meant that a longship could travel at 5–10 knots in average conditions, and could even reach speeds of up to 15 knots in favourable conditions.”

The official page for the experimental-archaeology project Draken Harald Hårfagre describes the vessel as a “clinker-built Viking longship” reconstructed from archaeological evidence and saga descriptions. It specifies that “Draken Harald Hårfagre is a **square sailed, open wooden ship**, 35 meters long,” and that “She can be **rowed by one hundred oarsmen**. The ship is equipped with 25 pairs of oars – each oar powered by two men.” Although a modern reconstruction, it is explicitly designed to mimic an ocean-going Viking **longship combining a large square sail with extensive oar power**.

This specialist group focused on Viking ship reconstructions states: "A large single **square rigged sail** on a mast set mid-ship is one of the defining visual elements of a classic ‘Viking’ ship." It describes typical Viking ship rigging as including forestay, backstay and shrouds, plus halyards, braces and sheets to control the loose‑footed **square sail**. It further notes that the keel running the full length of a Viking ship "was well suited to, and undoubtedly developed due to the use of, the **square-rig sail**," and discusses how the keel helped convert lateral wind force into forward motion.

Hurstwic, a site focused on Viking-age research, writes that “Most Viking ships were equipped with **both oars and a sail**.” It notes that warships were “long and narrow, with many oars” and “a single mast carrying a **square woolen sail**,” and that the sail was typically taken down and rowing used when sailing conditions were poor or when maneuvering was required.

Reporting on a modern reconstruction, the article notes that the ship is built on Viking models with "a single mast and a **square sail**, complemented by multiple oar stations along the sides." It explains that, like the original Viking longships it imitates, the vessel is designed to be "propelled by sail on long voyages" while "the **oars provide auxiliary propulsion and manoeuvrability** in harbors and when there is little wind."

An educational summary for schools notes that “Longships were clever in that they **used both wind propulsion and rowing power**. They had a **sail and a mast**, but also had **oars for rowing in case the wind disappeared**.” It further explains that chants and songs helped maintain rowing rhythm “up rivers and in places where their sails could not be used,” indicating that oars and sails were used in different conditions on the same longship.

This historical overview notes: “The classic Viking longship had a **single mast with a large square sail** and a row of oars along each side.” It adds that longships “could be propelled by sail on the open sea, but the **oars were crucial for maneuvering in narrow fjords, rivers, and during raids**,” underlining the dual-propulsion design.

Modern maritime historians commonly describe Viking longships as clinker-built warships with **a large, roughly square sail on a single mast** combined with banks of oars along the sides. Academic syntheses emphasize that by the height of the Viking Age, longships routinely used the sail for open-sea voyages and oars for coastal work, rivers, battle maneuvering, and when wind conditions were unfavorable, reflecting a deliberate design for combined propulsion.

Discussing the Roskilde reconstruction ‘Havhingsten fra Glendalough’, a contributor describes performance under different propulsion: “The ship does **3 knots when rowing and easily 8 knots when the sail is up**.” The thread explains that the reconstruction is based on archaeological finds and equipped with a single mast and a large square sail plus multiple rowing positions, illustrating in practice the combination of oars and sail seen in Viking longships.

The Vikings, whose longships were also equipped with square sails, introduced the use of a bowline, enabling the sail to be trimmed sideways and thus allowing limited upwind sailing. When sailing against the wind, propulsion was supplemented by oars.

The square sail is fastened to two yards. The page describes square sails as a distinct rig type and gives construction details consistent with a square-rigged vessel.

Archaeologists made replica Viking sails out of Gotland wool, and their ships sank, and then they made them out of Gute wool, and the ships sailed. This is a discussion of Viking sail material and reconstruction experiments rather than a primary historical source.