THE DIOLKOS ON THE ISTHMUS OF CORINTH
DIMENSIONS, CAPACITIES AND OTHER CHARACTERISTICS OF SHIPS
The placement of the ships’ hull on the carriages in such a way as to achieve
balance and equilibrium was always a skilled operation of fundamental importance.
This could be reality done only in standard ways and by simple means.
To understand the methods of loading [ships on carriages] that were most
likely used, it is essential to know the geometric characteristics
(capacities, dimensions shapes, weight distribution) of the ships, at least in so far
as there is evidence that they were pulled over the D across the Isthmus.
These ships were the Liburnians, trieres and drowous.
The diagram, drawn by John Coates, gives evidence of some characteristics
of ancient ships. We shall begin with the first ship in the table, the Liburnian,
the main type in the fleet of Mark Anthony, shich, pursued by Octavian’s fleet,
and was transported across the Isthmus.
Luburnian:
From the geometric characteristics, which are given in fig. 118/146 we see that:
The distance of the center of gravity G from the bottom of the keel H=3.0 m.
The distance of the center of buoyancy M from the bottom of the keel H=4.5 m.
The meta centric height MG = 1.5 m
The hull’s length at the water’s surface is LWL = 18.0 m
The hull’s beam at the water’s surface is BWL = 5.5 m
The length and beam at the level of the steering
oar are L (1) = 17.25 m and B (1) = 5.15 m.
Correspondingly at the Line 2 they are L (2) = 16.50 m and B (2) = 3.30 m
The straight part of the keel ahs a length LK = 8.0; the curved part
of it forward toward the kell l= 6.5 m and that of and of it toward
the stern is L = 5.5 m. This means the ship can be set upon “vasa”
with the length L = 8.0 m, and the comparison of this system gives a doubly
projecting beam with overhangs of 6.5 and 5.5 m and a length between
supports of 8.0 m.
Trireme:
As an example, we may take a Greek trireme as its character became
standardized in the 4th cent AD.
The total weight of the trires comes to 45 tons.
This can be broken down into the following partial weights:
Lull 21 tuns, fitting (rig) 3.8 tons, crew 15 tons, ballast 5 tons.
For this trireme weighing 45 tons and 36.8 m long,
we have the following geometric characteristics:
Height of center of gravity G above bottom of kell is H = 2.20
Height of center of buoyancy M above bottom of kell is H = 2.80
Meta centric height MG = 0.60 – 0.75 m.
Length of trireme at rea’s surface (waterline) LWL =32.20 m
Beam of trireme at rea’s surface (waterline) BWL = 3.62 m
The length and width at line 1, the level of the top of the steering oar,
is one respectively L, = 31.0 and B = 3.30 m
Correspondingly values at line 2 are L2 = 26.0 and B2 =3.0m
The straight part of the kell LK = 20.20m; the inclined portion
forward is L = 10.80m and aft is L=8.0m
The draft d = 1.10m for a trirme of 45 tons, moreover… … … per ton of weight.
Hypozomata:
Special mention must be made of the hypozomata [undergirdigs],
so that one can understand their function.
Our knowledge of these is derived indirectly and is based chifly
on references in ancient writers and poets, whose works describe their use.
“… after they had girdled with laid ropes the tricky
horse – like the black hull of a ship – the hypozomas [girdling lines] were ropes
tied in pairs along the hull’s length, form stain to stern, below the deck
in the middle of the ship cross section.
They were due to the need to curtail the surrounding tensions which develop
at the joints of the hulls planking, especially in its middle thratining
of local disconnection of its wooden members.
These ensions were aggravated if the ship while under way in the sea
encountered wave action, in which the wave length was the same
as the ship’s length at the water line and the ship was supported on the wave crest.
In this situation the hull may be thought of as a kolloms beam projecting
at both ends and supported in between only at the paint of the wave crest.
The greatest stress that develops at height, amidships and the middle
of the ship’s length, is about 1.1 N/m2.
These stresses are apportioned linearly over the height and decrease
to zones at the keel. Thus, to avoid possible damages to the hull,
recourse was had to.
The hypozomata were used.
These were strong heavy ropes 40 mm in diameter and somewhat longer
than twice the length of the hull. They ran trough the interior of the hull,
a little below the deck beams and about 0.5m above the neutral line representing
the apportionment surrounding stresses over the depth of the hull.
The hypozome rope began at the stern and extended o the bow, where
it made a loop and returned to the stern, where it was again tied.
And these 2 parts of the rope, once they were securely fastened
stretched from stern to bow with a tensional force of 13.5 tons.
This tensional stress was produced by a mechanism in the middle
of the length of the double line, such that the two parts of the same rope,
twisted end to end, have been wound together into a single cable.
This single unified twisted cable moreover was under tension and took up part
of the stresses that developed in the hull of the ship under way in the sea,
like a Spanish windlass.
We do not know exactly how thin ropes was fastened to the hull or how
it was kept under tension and slashed off when necessary.
Nor do we know the kind of rope fiber or how it was made.
The trireme Olympias, which was built on the basis of an organized
project by the Greek Navy with the aid of prominent shipbuilders,
naval architects and nautical scholars such as john Marrison, john Coates,
Demetrios Papadas and others, experts in ancient Greek shipbuilding,
encountered many practical problems associated with the trireme.
These had to do with the materials, the methods of design and building,
of sailing and navigation, maintenance, etc. Despite the significant progress
that was made, many unsolved problems remain that require further research.
In the transport of treremes on a carriage, over the D across the Corinthian Isthmus,
we must assume that the hypozomes of these ships’ hulls remained in place
in a state of tension, and also because their slacking off would have taken much time.
Moreover the Hypozomes would have prevented possible deformations
from the forward movements, chiefly during the placement of the ship’s hull
on the carriage and its movements on it.
Likewise the ship’s ballast remained within it. This would have made for balance
and equilibrium of the ship upon the carriage.
Bibliography: "THE DIOLKOS ON THE ISTHMUS OF CORINTH"
by Apostolos E. Papafotiou, Civil Engineer N.T.U.A.
(National Technical University of Athens).
Foreword by Theodosius P. Tasios, Prof. at N.T.U.A.
(National Technical University of Athens).
Animation film "Diolkos for 1500 years": https://youtu.be/3GtE0kfWDuU
Dr. Apostolos E. Papafotiou
Civil Engineer N.T.U.A.
Economist N.K.U.A.
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