Editing Longship (section)

===Keel, stems and hull===

[[File:Sebbe Als 2.jpg|thumb|Schematic drawing of a longship construction representing the [[Sebbe Als]] ship. It is a reconstructed ''snekke'' from Denmark.]]
[[File:Immegram kyst.jpg|thumb|The ships' design gave both strength, agility and versatility. They could navigate the open ocean, coastal waters, fjords and many rivers and could be landed on a beach. The pictured ship is the reconstructed ''Imme Gram''.]]
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 stem to stern. 

Nearly all longships were [[clinker (boat building)|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 {{convert|25|mm|in|abbr=in|sigfig=1}} thick and tapered along each edge to a thickness of about {{convert|20|mm|in|abbr=in|sigfig=1}}. The planks were riven (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 {{convert|37|mm|in|abbr=in}} 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 {{convert|25|–|30|mm|in|abbr=on|1}} 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 {{convert|170|mm|in|abbr=in}} 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 {{convert|850|mm|in|abbr=in}}. 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 {{convert|700|kg|lb|abbr=in}} of iron nails in a {{convert|18|m|ft|abbr=in}} long ship. In some ships the gap between the lower uneven futtock and the lapstrake planks was filled with a spacer block about {{convert|200|mm|in|abbr=in|sigfig=1}} 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 ({{convert|90|cm|in|abbr=in|disp=or}}) of plank. In many early ships treenails (trenails, trunnels) were used to fasten large timbers. First, a hole about {{convert|20|mm|in|abbr=in|sigfig=1}} 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 {{convert|100|x|300|mm|in|abbr=in|sigfig=1}} 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 [[longboat]]s sailed in ice strewn water in spring. Hulls up to {{convert|5.60|m|ft|abbr=in}} 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 {{convert|1|m|ft|abbr=in|0}} 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&nbsp;AD and 400&nbsp;AD. Larger industrial scale tar pits, estimated to be capable of producing up to {{convert|300|l|USgal|sigfig=1}} of tar in a single firing have been dated to between 680&nbsp;AD and 900&nbsp;AD.<ref>{{Cite news|url=https://www.theguardian.com/science/2018/nov/04/viking-longboat-industrial-tar-pits-dominance-seas|title=The secret of Viking success? A good coat of tar…|last=McKie|first=Robin|date=4 November 2018|work=The Observer|access-date=3 November 2019|language=en-GB|issn=0029-7712|archive-date=2 November 2019|archive-url=https://web.archive.org/web/20191102220502/https://www.theguardian.com/science/2018/nov/04/viking-longboat-industrial-tar-pits-dominance-seas|url-status=live}}</ref> A drain plug hole about {{convert|25|mm|in|abbr=in|sigfig=1}} 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 {{convert|400|mm|in|abbr=in}} above the sheerline and was carved to retain anchor or mooring lines.