The Mediterranean and its weather placed severe restrictions on any seafaring, particularly under sail. Having no magnetic compass, Greek and Roman sailors navigated by the stars at night, and by landmarks in daylight, and so, in anything less than 'very good' visibility, they were very much at risk. Storms are more frequent and severe in winter, but keeping to the summer season does not remove that danger altogether. The earliest Greek lore, preserved by Hesiod, recommended that voyages should be made between June 21st and August 10th ― a very curtailed season, even allowing for the fact that he was a farmer, who had made only one short voyage (which he had not enjoyed) and had all the pessimism of his profession. More adventurous seafarers regarded late March or early April as 'a bit risky, but possible', from the beginning of June to mid-September as 'safe', from then until early November as 'doubtful' and the rest of the year 'definitely out', except for dire emergencies. The Garrulous Man, number 3 of Theophrastus' Characters, among various other platitudes about rising prices and the weather, is wont to say 'Just fancy ― the sea was navigable from the Dionysia (late March) onwards!' For most of five months in every year, the entire commercial life of trading ports effectively closed down.
The later developments in the design of merchant ships show two or more auxiliary sails ― a small square one on a sort of bowsprit projecting beyond the bow (called artemon in Greek) and a triangular one above the mainsail ('topsail', in Latin siparum). But at all times the main propelling force came from the single, big, square mainsail. The performance of a vessel with this type of rig in various wind conditions has been the subject of a good deal of argument, and it would seem that some practical experiments, which could be carried out without great difficulty or expense, might enable us to get a more accurate picture.
It is generally agreed that Greek and Roman sailing vessels, given a good following wind, could make speeds of about 4-5 knots, with 6 knots being exceptional, but not impossible in ideal conditions. It should be remembered, however, that such evidence as we have tells us the average speed over quite a long voyage ― of the order of 300 nautical miles or more ― and may conceal a wide variation of speed between spurts and lulls. A square-rigged vessel could sail quite effectively, though not so fast, with the wind on either beam (at right-angles to the desired course, Fig. 54a). This was achieved by using the devices described earlier. The yard was braced around aslant to the wind, and the 'sheet' on the windward side was let out so that the wind carried it forward of the mast. The other ('lee') sheet was drawn tighter (a winch would have been used for this on the bigger ships) and used to control the sail in such a way that the main thrust on the mast was forward.
But however well this was done, two side-effects were inevitable. The vessel would drift sideways through the water, off course to some extent, and would also 'head into the wind' ― that is, turn clockwise if the wind was on the starboard beam ― and correcting this by the steering oars would not be easy. In fact, the ancient remedy is described in the Mechanical Problems attributed to Aristotle. Apparently the brails were used to shorten up the leeward half of the sail (the part astern of the mast) thus reducing the area of sail directly confronting the wind, and enabling the forward half, which tends to turn the ship in the opposite direction, to counteract the 'heading' tendency.
The brails were also used when the wind was extra strong. If it was due astern, the middle of the sail was brailed up, leaving only a small area spread at each end of the yard. If a really sharp squall blew up suddenly, the whole sail could be furled quite quickly, leaving only the mast and yard to catch the wind, and this could be done from the deck, without any of the crew having to 'go aloft', as they had to in later sailing ships. Alternatively, it is sometimes said that the yard itself was lowered part-way down the mast, but this seems a clumsy and slow manoeuvre by comparison.
So far we have dealt with conditions in which the wind was 'following', or on the beam. When it blew from ahead of the beam, things became more difficult. The action described above, of swinging the yard around and adjusting the sheets, could be carried a little further, so that the ship actually sailed slightly into the wind, but how far this could be taken is a matter of doubt and guesswork. The usual approach to the question is to start from the capabilities of square-rigged vessels of the eighteenth and nineteenth centuries. These are known to have sailed, with some difficulty, what is variously called 'six points off the wind' or 'two points into the wind' ― that is, at the angle shown in Fig. 54b. On the assumption that Greek and Roman seamen were less competent, it is usually said that they could only manage 'one point into the wind' ― that is, with the wind just over 11° forward of a line at right-angles to the keel (Fig. 54c). It would be difficult to challenge this assertion without experimental evidence. What is certain is that they would have tried their utmost to improve the performance of their ships in this respect, for reasons which will become clear.
What happened when the wind was too far ahead for the braces and sheets to cope is very obvious from a number of passages in Greek and Roman authors. The ships resorted, as sailing ships have done ever since, to 'tacking', which involves setting a course alternately to the left and right of the destination (the 'port tack' and 'starboard tack' respectively). If the wind is dead ahead. this means a symmetrical zig-zag course, and it is at once obvious that here is a very slow way of travelling. Even in a fair breeze, a ship sailing close to its maximum angle into wind cannot make its full speed, and it has to cover more than five times the direct linear distance. In theory, geometrically speaking, it makes no difference how many tacks are made ― four short tacks from A to B cover the same distance as two long ones, but in practice there are a number of other considerations. The business of changing from one tack to another is hard work, and involves a lot of organization, and the vessel slows down and loses time during the manoeuvre; naturally, therefore, the tendency is to make as few tacks as possible. But the room may be limited in a channel or strait, or if the ship is following a coastline, and the helmsman does not wish to lose sight of land. Again, it is difficult to make changes of tack in darkness or poor visibility. It is also unwise to go out to sea on a long tack if there is a likelihood of the wind changing before the completion of the second tack. All these considerations have to be weighed against each other, and in the ancient world, without even a compass or rudimentary charts, it must have required great skill and long experience to make correct decisions on the best course.
If the wind is not dead ahead, the tacks become asymmetrical and in some conditions the second tack actually takes the ship away from its destination, though this is more than offset by the fact that the first tack is longer.
So far, it has been assumed that one point (11°15') into the wind was the maximum capability of an ancient square-rigged ship. It is clear, however, that even a very slight improvement on that would make a marked difference to the distance travelled and the time taken. For instance, with the wind dead ahead an improvement of just one degree ― too small to be detected without quite sophisticated apparatus ― would shorten the total tack distance by 8%, and a further improvement of 1° would shorten it by 15% altogether. If the ancient navigators could have managed one and-a-half points into the wind, the total distance would have been shortened by ⅓, which would have made a big difference on a long voyage against the wind, when the ship was tacking for most of the time, and many such voyages were regularly made in the ancient world.
For example, from Italy (Brindisi or the Straits of Messina) to Alexandria was a 'downhill run'. The prevailing wind during the sailing season was (and still is) N.W., and, if it blew steadily, merchant ships could make the journey in 18-20 days, at an average speed of just over 2 knots. According to Pliny (Nat. Hist. 19, 3-4), a small, fast sailing boat could make it in 9 days, which represents an average of about 4½-5 knots. The return trip, however, was very different. They had to beat into the wind for almost the whole voyage, making it much longer in distance and time ― anything between 40 and 65 days, or even more. The longer times probably indicate a number of weather bound delays in harbour, rather than a very slow rate of sailing, but even so, a very slight improvement in tacking performance would have shortened such voyages by days, or even weeks.
An account of a voyage on precisely that run, made by an unusually large merchantship, is given in Lucian's dialogue The Ship or Human Wishes, written in the second century A.D. The opening passage is clearly intended as a parody of the opening of Plato's Republic, but the description of the ship and its voyage are introduced entirely for their own intrinsic interest, and the satirical genre does not call for any distortion or exaggeration in that part of the work.
The ship was named the 'Isis', and was normally on the grain run from Alexandria to Rome. Its measurements are given as:
length overall
182ft
55.5m
beam 'more than'
45ft
13.9m+
height from deck to bilges
44ft
13.4m
and from these its cargo capacity has been estimated at about 1200 tons. Even so, it was steered into port by 'a little old man, who turned the huge steering oars with a slender wooden rod; he had curly hair, receding at the front, and his name was Heron'. All this sounds (as Lucian intended) very circumstantial.
They had started from Alexandria in a light breeze ― apparently a little W of NW, and sailed roughly NNE, sighting Acamas (Cape Arnauti, the western tip of Cyprus) on the seventh day This is about 250 sea-miles, and represents a speed of about 1¾ knots―quite reasonable for a heavy vessel on a port tack in a light breeze. Then things went disastrously wrong. A westerly gale blew up. Though they would probably have been making for Anemourion ('Windy point', now Anamur on the S. coast of Turkey), they were instead carried 'aslant' (plagioi, at right-angles to their intended course) and ended up at Sidon (in the Lebanon, about 20 miles south of Beirut). The change of wind direction need not have caused this change of course, but presumably the gale caught them before they had rounded the tip of Cyprus, and was too strong for them to beat against. The captain (wisely, no doubt) ran eastwards before the gale, and perhaps went further south than he needed to (about ESE), because he could not navigate in the bad visibility. Then, still in rough weather, they went northwards around Cape St. Andrew and westwards between Cyprus and Turkey (this, to Greek sailors, was Aulon, 'The Channel') and got to 'Swallow Islands' (now Gelidonya) 10 days after leaving Sidon.
The coast in that region is very dangerous, with jagged rocks and big breakers. One of the earliest wrecks so far discovered, dating from the Bronze Age, was found there. In addition, they ran one of the gravest risks for ancient seamen ― they came on this coast in pitch darkness. But, for a change, they had some good luck. They sighted a fire (perhaps a lighthouse or warning beacon) which told them they were nearing land, and 'one of the Dioscuri (Castor and Pollux, the patron deities of mariners) set a bright star on the carchesion and steered the ship to port when it had been driven close to the cliff. This is an obvious reference to 'St. Elmo's Fire'―the static-electric brush discharge which appears on the tips of wooden masts and spars in an electric storm.
Carchesion in the context of a ship normally means 'masthead', but the phenomenon, wherever it may have appeared, was taken as a divine admonition to turn to port (out to sea) rather than stay on course or turn to starboard.
Then, when they had been blown so far off the normal course, the captain decided to give up the trip to Rome, and make for Athens instead. His reasons are not given ― perhaps the cargo had begun to deteriorate. Even then, the ship had to 'sail aslant into the Etesian wind' ― that is, tack up the Aegean heading against the seasonal Northerlies ― and it arrived in the Peiraeus 70 days after leaving Egypt. It should have 'gone to the south of Crete, to the west of Malea (a dangerous area then as now) and should have been in Italy (i.e. Ostia) by that time'.
