Lecture 22: Machines at Sea – Ancient Ships
Understanding Greek and Roman Technology: From the Catapult to the Pantheon
Dr Stephen Ressler (2013)
As Romans weren’t a seafaring people, this lecture mainly focuses on Greek technology. To build a naval fleet during the first Punic War (264-241), the Romans merely copied the technology used by their Carthaginian enemies. By 200 BC, they had already abandoned it, relying on allies (mainly Persia) to defend their maritime interests. Once Augustus came to power (27 BC – 14 AD) he built the empire’s first commercial fleet to import wheat from Egypt.
Roman cargo ships were up to 60 feet long and 20 feet wide. Some carried 400 -1,000 tons of cargoes that included grain, wine, building stone, metal ingots, oil and looted art treasures. In their heyday, the Romans had a fleet of several hundred.
Grain ships to the Roman province of Egypt took 20 days to reach Alexandria. Owing to unfavorable winds, the return trip to 45-60 days. To avoid Mediterranean winter storms, they only sailed between April and September, which mean each ship took two trips a year.
By the 3rd millennium BC, the Minoans and early Greeks had developed two major sea goingl prototypes: the roundship and the longship. Both remained in use throughout the classical era and into the Middle Ages.
Roundships were merchant vessels powered mainly by sails though the sometimes carried supplemental oars. They had broad, rounded hulls (with a 4:1 length to width ratio) to maximize cargo capacity.
Longships were either naval or pirate vessels with a large crew of oarsmen that were built for speed. Most had one supplemental sail.
All classical ships used shell-first hull construction. More recent plank-on-frame construction originated in late antiquity in northern Europe and is still used today. With the latter approach, the inner skeleton is built first and the planks (connected to the shell rather than each other) are added later.
With early shell-first construction, the outer shell segments were sewn together with linen cord. This technology was eventually replaced with mortise and tenon joints along the length of each plank.
Because buoyancy* is distributed unequally in rough water, both the hull and the keel (the ship’s backbone) had to be reinforced to prevent sagging. Most keels required at least two lengths of timber connected by a locking scarf joint.
The square sail used by the Greeks required a sophisticated system of support and control. Mounted into a socket in the ship’s keel, the mast was held in place by standing (stationary) rigging: stays (ropes extending fore) and shrouds (ropes extending aft).
Running rigging (used to adjust the sail) consisted of a halyards that would raise or lower the yardarm, lifters that would move it from side to side and braces that would rotate it horizontally. Brails would rotate it horizontally.
The sail itself was controlled by sheets. The helmsman adjusted the leeward (downwind) sheet to control the speed of the vessel. Pulled taught, the sail caught the full force of the wind.
An extremely flexible steering system (based on two steering oars) combined with precise sail adjustment allowed Greek ships to tack 11 1/4% (ie sail against the the wind) for the first time in human history. The Greeks added a small sail in the front of the boat to prevent the ship listing to leeward when it tacked. This eventually led to the emergence of three masted Greek and Roman freighters.
*Discovered by Archimedes in his bathtub around 246 BC.