to be dangerous during bad weather, a defect that could only be
removed by the construction of sheltering breakwaters; and as in
doing this it was possible, at the same time, to create a large outer
WORKS FOR IMPROVING THE BILBAO RIVER. 81
harbour for the use of steamers at all states of the tide, the
following plan was adopted.
This outer harbour is enclosed by two breakwaters (i) The
west breakwater, 1450 metres (4757 feet) long, running out from
the coast at right angles to the north-west; (2) the eastern break-
water, running out in a westerly direction, is uoo metres (3610
feet) long. Between them there is an entrance 600 metres
(1970 feet) wide, facing the north-east. The area protected by
the two breakwaters is 741 acres, with a maximum depth of 46 feet
at low water of spring tides. The first breakwater is the more
important of the two, and rests on a bottom of mud and sand,
except near the coast, where the rock is uncovered.
As there were few days in the year during which it would be
possible to work with divers, it was decider! to build the super-
structure from the level of low water, and to let it rest on a large
mound of concrete blocks, of 30 to 50 cubic metres (39^ to 65^
cubic yards), which in turn would rest on a large mound of sorted
rubble. The building of the superstructure was begun in 1891,
and was damaged in 1893 and 1894, when the superstructure built
on the concrete blocks and rubble mound had a length of 127
metres (417 feet).
As it would have been very hazardous to persevere in building
the superstructure on the foundation of loose blocks already laid,
the solution that appeared the wisest to adopt was to leave all that
part as an outer protection, and to build the superstructure further
back under its shelter.
It was decided to build the superstructure upon large steel caissons
filled with concrete, and resting 5 metres (16 feet 5 inches) below
low water a system that was accepted by the Government in 1895.
The caissons are 13 metres by 7 metres by 7 metres 637 cubic
metres (833 cubic yards) so that when placed at a depth of
5 metres below low water of equinoctial spring tides, they would
emerge 2 metres (6J feet), as it was necessary that the top of the
caissons should be above the water-level at every low tide, to
enable the work to be carried on inside. As it was necessary to
fill these caissons rapidly, so that the sea might not break them,
we decided to ballast them with a layer of concrete 1.50 metre (5 ft.)
thick before they were floated out to their place, and afterwards
to deposit inside them, by means of a Titan, 12 blocks of 30 cubic
metres (39^ cubic yards) each. At the next low tide, the water
is pumped out from between the blocks, and concrete run into the
interstices, and lastly a layer an the top of them 0.50 metre (if feet)
thick, so as to make one monolithic block of 637 cubic metres
(833 cubic yards).
The superstructure is built upon this foundation, formed by two
face walls made with concrete blocks of 30 cubic metres (39^ cubic
82 WORKS FOR IMPROVING THE BILBAO RIVER.
yards) each, and a hearting of rapidly setting concrete. This
brings the work up to 7 metres (23 feet) above low tide, and it is
protected on the sea sicb by a strong parapet.
The system of construction explained has, in addition, the very-
great advantage of allowing the superstructure to be built in
separate lengths of 7 metres (23 feet), so that they can settle quite
independently on the mound.
Up to 3ist December last 150 caissons had been placed in five
and a half years, without the slightest mishap; and the system
can safely be adopted for seas as violent as those of the Bay ot
After two winters have elapsed it is considered that the caissons
have settled down to their full extent, and the joints between them,
and between the superstructure sections built upon the.n, which
are about 12 inches wide, are filled with concrete; and the parapet
wall is subsequently built.
The construction of tne east breakwater calls for no special
remarks, because the sea waves run nearly parallel to it. It is
built on a foundation of concrete bags, which, in their turn, rest
on a rubble mouncl protected uy large concrete blocks.
The Discussion was combined with the Discussion on the Zee-
brugge Harbour Works (see p. 84). The author replied.
On the motion of the Chairman a vote of thanks was accorded
to the author.
" ZEEBRUGGE HARBOUR WORKS."
Paper by J. NYSSENS HART and L. VAN GANSBERGHE.
THE port of call of Zeebrugge is formed by a curved breakwater
extending out to sea, and consisting of a sea wall and harbour
wall, with filling between, forming a quay. It is also provided with
an entrance channel and lock, which connect the roadstead,
sheltered by the breakwater, with an inner basin in communication
with the Bruges ship-canal. The breakwater consists of three
portions. The first portion on the beach is a solid embankment;
the second portion, which is a continuation of the first, is an open-
work viaduct 400 metres (1312 feet) long; the third portion is a
solid breakwater and quay, 1605 metres (5264 feet) long. The third
or solid portion of the breakwater comprises two parts. The first
part consists of a quay with a sea wall on the outside, which
protects the filling between the sea wall and the harbour wall,
forming the quay; and alongside the quay or harbour wall,
1271.40 metres (4170 feet) long, there is a general depth of 8
metres (26.24 feet) at low water of spring tides, for a width of
300 metres (984 feet). The second part is a straight length of
solid sea wall, 340 metres (1115 feet) long, which constitutes an
The base of the sea wall protecting the quay of the third or
solid portion of the breakwater, consists of monolithic concrete
blocks weighing 3000 tons; these are 25 metres (82 feet) long, by
7.5 metres (24.6 feet) wide, and their height varies according to the
depth of the sea, so that the top of all the blocks may be i metre
(3.28 feet) above low-water level.
The straight length of sea wall constituting the outer breakwater
beyond the quay is larger, the foundation blocks being 9 metres
(29.52 feet) wide. The main body of the sea wall consists of
55-ton blocks laid upon the foundation blocks, up to a level of
7 metres (22.96 feet) above low water of spring tides. Upon
these is built a sheltering wall 4.80 metres (15.74 feet) high, and a
parapet 1.20 metres (3.94 ftet) high; the summit of the latter
being thus 13 metres (42.64 feet) above low water. The toe of the
sea face of the breakwater is protected from undermining by a
mound of large blocks of rubble stone, weighing from 300 to 2000
kilogrammes (5.9 cwt. to 39.36 cwt.).
The quay wall which protects the embanked portion of the
breakwater on the harbour side is built on foundation blocks
84 ZEEBRUGGE HARBOUR WORKS.
25 metres (82 feet) long, laid on the sea bottom, which has b,tn
previously dredged to a level of 8 metres (26.24 f eet ) below low
water, for a length of 876.41 metres (2876.6 feet), and to a level
of 9.5 metres (37.16 feet) below low water for a length of 393
metres (1289 feet). These blocks are 9 metres (29.52 feet) wide at
the base, and 6m.2o (20.34 feet) wide at the top. Upon these
are laid the courses of 55-ton concrete blocks, up to a level of
7.30 metres (23.94 feet) above low water.
The space between the sea wall of the breakwater and the
quay or harbour wall is filled in with earth, and covered with
stone pitching. This quay space carries the sheds, buildings, lines
of railways, cranes, etc.
The foundation blocks are built of concrete in iron caissons,
which remain part of the blocks. These concrete blocks have
large cavities in the first instance, providing sufficient displacement,
in comparison with their weight, to enable them to be towed out
floating into position, without danger of sinking during the voyage ;
and they are then sunk and filled up with concrete. These blocks
are made in the basin forming the inner harbour, just above the
sea lock. Four sizes of blocks are employed. Those used for
the outer solid breakwater beyond the quay are 25 metres (82 feet)
long, 9 metres (29.52 feet) wide, and 8.75 metres (28.72 feet) high,
which represents a cubic capacity of nearly 2000 cubic metres
(2616 cubic yards), and a weight of about 4400 tons. The lower
part of the caissons has a cutting edge to enable it to penetrate
into the ground, which consists of clayey sand. When the sea
bottom upon which the block is to be founded is uneven, it is
levelled by means of rubble deposited by hopper barges. Orifices
are provided in the shell of the hollow block for letting in the
water to sink it. When the block has been deposited upon its
foundation, it is filled with concrete by means of skips of TO cubic
metres (13.08 cubic yards) capacity, which open at the bottom
directly they begin to be drawn up.
Up to the present time, four caissons have already been
deposited; these form the starting point on the sea side of the
solid portion of the breakwater.
The Discussion was combined with that on the preceding paper.
The following members took part in the Discussion: Prof.
Vernon-Harcourt, Mr. P. A. Fraser. the Chairman, Mr. J. R.
Baterden, M. Mendes Guerreiro, Mr. de Charruca, and Mr. W. H.
Hunter; and M. Van Gansberghe replied.
On the motion of the Chairman a vote of thanks was accorded
to the authors.
"RECENT IMPROVEMENTS IN THE LIGHTING AND
BUOYING, ETC., OF THE SCOTTISH AND ISLE OI-
Paper by DAVID A. STEVENSON.
A GLANCE at a chart of Scotland shows that, owing to its exception-
ally rugged coast-line, and numerous outlying islands and dangers,
the task of lighting and otherwise guarding it effectually for the
purposes of navigation, is an interesting and difficult problem for
the lighthouse engineer.
Owing to the want of funds, little was done up till 1854 to light
the Sounds and Kyles on the West Coast, between the outlying
islands and the mainland, and the coasts of the Orkney and Shetland
Islands, and of the Western and Northern shores of' the mainland.
The war of 1854, however, made it necessary that something should
be done to enable the fleet to navigate the' Northern seas at least
with some degree of safety, and the advantage of lighting the West
Coast sounds came also about the same time to be appreciated.
Since that period good progress has been made, and in 1875 there
were 60 lighthouses. 98 buoys, 49 beacons, and 2 fog signals on the
coast. Druing the last twenty-five years (since 1875) there have
^een erected on the coasts under the jurisdiction of the Com-
r-ss : oners of Northern Lighthouses, 16 lighthouses, 21 fog signals,
and cC lighted beacons ; and there have been laid down i lightship
equip,.e i with a fog-signal, 15 lighted buoys and 9 unlighted buoys!
and i vnlighted beacons have been erected.
The course of a seaman making for and navigating the Scottish
coast bus thus been much facilitated, though no doubt much
remains to be done, for there are still many outlying dangers
unf.nar'jed, and stretches of coast line with 50 or even 100 miles
between the lights, while the range of our most powerful lights in
weather when they are most required does not exceed 9 or 10 miles
The characteristics of the lights on the Scottish coast have also
been much improved as regards their distinctive character, which
next to the existence of a light at all, is the most important factor
in its usefulness. It has been the policy of the Northern Light-
house Board to gradually alter the old fixed lights which are liable
to be mistaken, or, at all events, not so readily recognised and
identified, and give them a definite character. ' Durin<r the last
twenty-five years eight fixed lights on the coast of Scotland have
been altered to flashing or occulting lights. The introduction bv
Messrs. Chance in 1874 of the group-flashing characteristic, pro'-
86 RECENT IMPROVEMENTS IN THE LIGHTING AND BUOYING
posed by the late Dr. Hopkinson, put into the hands of the light-
house engineer the power of greatly varying the character of lights,
and many lights of this character have been installed on the coast.
Further, the periods of many of the lights have been shortened as
much as possible, consistently with other considerations. Not
only has the number of the lights been increased and the characters
improved, but the powers of the lights on the Scottish coast have
been greatly increased. Thus, in 1875 the most powerful light on
the Scottish coast had a power equal to 44,500 candles ; now there
are several over 100,000 candles, and the Isle of May electric light
has a power which is calculated is equal to 3,000,000 candles.
The limitation of the duration of flashes to about half a second,
and the reduction to a minimum of the number of faces of the
apparatus have long been recognised as leading principles, and
acted on in Scotland where consistent with producing the proper
characteristic, and a duration of flash of sufficient length. The
recent increase in the power of the apparatus has been effected by
the use of one or both of the following improvements in lighthouse
apparatus, which have been described by Messrs. Chance as " most
(i) The introduction of hyper-radiant or long focal distance
apparatus proposed by Messrs. Stevenson in 1869, designed and
experimented on by them in 1885, and introduced in many lights
since that date both at home and abroad. (2) The introduction
of Mr. Charles A. Stevenson's equiangular prisms, which effect a
saving of 15 per cent, of the light incident on them at 45 deg., and
26 per cent, at 40 deg., and which permit with efficiency of the
use of refractors of 80 deg. focal opening in place of only 60 deg.
with Fresnel elements. The adoption of flint glass to extend the
refracting portion to 80 deg. caused more loss of light than if
catadioptric prisms had been used for this portion; indeed, the
great divergence from the prisms, and the loss of light due to
using flint glass, rendered this portion of the apparatus practically
useless as a lighthouse agent.
This increase in the power of the lights has not been effected by
increasing the size of the burners employed, as no burner of a
larger diameter than six wicks for hyper-radiant, and five wicks for
first-order flashing lights has been introduced, because, owing to
want of focal compactness, and the fact that little increase of
intensity is obtained, -larger burners are considered not to warrant
the additional consumption in oil and difficulty of management
they entail. Nor has the length of flashes been reduced below
four-tenths of a second, as anything less than about half a second
is considered too short to give, under practical conditions, full
With the exception of one electric light and five stations where
OF THE SCOTTISH AND ISLE OF MAN COASTS. 87
oil gas is employed, four of which are also incandescent, the
illuminant used in the Scottish lighthouses is paraffin. The
introduction of gas as the illuminant has permitted, at less important
stations, of dispensing with the attendance of one of the keepers,
reducing the staff to one, who is rung up should anything go wrong
with the light by an electric automatic alarum.
In the case of lights made by oversea vessels, and coast lights
which are intended to light long stretches of coast, it is necessary
that they should be of considerable power, and that they should be
constantly attended by keepers to ensure their due exhibition.
There are, however, many places on the Scottish coast, as in
sounds, lochs, and firths, where lights do not require to be seen at
a great distance, and where even the extinction of the light for a
time would only cause inconvenience to the sailor, not disaster.
In such cases the lights may obviously be of low power, and be
unattended continuously by keepers. Lighted beacons and buoys
have consequently been introduced at such places on the Scottish
coast, ro rhe great advantage of navigation, and at a very small
cost. Twenty-three of these beacons and buoys are lighted on
Pintsch's system of compressed oil gas, and have given complete
satisfaction. They require only to be visited once in six weeks
Originally the fixed-light character was all that was available, but,
on Messrs. Stevenson's suggestion, Messrs. Pintsch introduced a
method whereby they show one, two, or three flashes as desired, and
this has greatly increased their usefulness besides reducing the con-
sumption of gas. Twenty-one beacons are lighted with petroleum
burned in the Benson-Lee and Lee lamps, in which the wicks are
carbon-tipped, and require attention every four or five days, but are
an improvement, as regards safety and power, on the Norwegian
Trotter-Lindberg system which was first used in this way. When
these lights require to be made flashing, this is produced by
revolving shades driven by the current of heated air from the
The buoys in use on the Scottish coast have been increased in
size and improved in shape, so as to ride upright even in strong
tidal currents, and they are for these reasons more easily seen
and picked up by the sailor.
The Otter Rock light-vessel just launched will be unattended by
a crew, and has been designed to lie in a very exposed situation.
The lantern apparatus and glass-work were specially designed to
suit the circumstances, and made by Messrs. Chance. The gas
fittings are on Messrs. Pintsch's system, and they are the contractors
for the work.
Owing to the prevalence of fog and snow showers on the
Scottish coast, amounting to between 300 and 400 hours in the
88 RECENT IMPROVEMENTS IN THE LIGHTING AND BUOYING
year, and lasting occasionally for spells, without a break, of 36
hours, the question of fog signalling is very important. Fog signals
minister not only to the safety of navigation, but facilitate the
making of regular passages, and hence are greatly appreciated by
the sailor and the shipowner. The 24 fog signals erected on the
Scottish coast during the last 25 years have explosive cartridges at
two stations, and siren fog-horns actuated by compressed air at all
the rest. These tonite signals, which give a loud report, were
originated by the Elder Brethren of the Trinity House, and are
of great value in certain situations. They are only used on the
Scottish coast at rock stations, where the siren horn could not be
introduced except at a very large cost, as they are not so. efficient
and much more expensive to maintain than fog-horn signals.
For fog-horns the motive pOAver to compress the air used 25 years
ago was hot-air engines, which were excellent for the purpose, as they
did not require a supply of fresh water, which is not easilv obtained
at most lighthouse stations ; but, on the other hand, they took about
three-quarters of an hour to start, and were costly to keep in repair.
Messrs. Stevenson accordingly introduced in 1883 gas-engines driven
by oil gas. They require little water, and have not the drawbacks of
the hot-air engine ; and his having proved successful, they followed it
up by the introduction in 1889 of the oil engine, then just perfected.
Both of these improvements were first used for fog signalling
purposes in Scotland, and the oil engine is now almost invariably
so used. Steam engines have been introduced at two stations, in
one case because steam boilers were already at the station for the
electric light engine, and in the other because the oil engine had not
been introduced, and, being a lightship station, the choice lay
between hot-air and steam engines.
Where oil engines are used, a fog-horn can now be put in
operation in about eight minutes, even if there is no air stored,
which, however, is done in several cases, so that the signal can be
practically instantaneously started. In recent cases the engine
power introduced at fog-signal stations has been about 50 H.P.,
one-third of which is reserve. The working pressure used, as a
rule, is about 30 Ibs. per square inch, and about 46 cubic feet of
air per second of blowing is expended. The siren used is a
modification of Mr. Slight's cylindrical siren. By improving the
shape and enlarging the horn and air passages, opening out and
properly forming the air ports of the siren, driving the siren by an
air motor, and properly proportioning the storage to the air con-
sumption, Messrs. Stevenson have recently greatly increased the
efficiency of the siren fog-horn.
For the purposes of distinction, groups of blasts have been
introduced, two, three, and four blasts given in quick succession,
and these are still further differentiated by making the blasts of
OF THE SCOTTISH AND ISLE OF MAN COASTS. 89
different pitch when necessary. Their endeavour has been to make
these blasts as long in duration as possible, consistently with due
economy, their view and experience being that a long blast is more
effective than a short blast, and that no blast should be less than
three seconds, and that five seconds is what should be aimed at.
The periods of some recent signals have also been reduced to i^
minute, though this is, in their opinion, perhaps unnecessarily short",
as in most situations a two or even three minutes' period would
serve the sailor's requirements, permit of a great reduction of the
power, and therefore reduce the expense necessary to produce an
In spite of all that has been done to improve our fog-signals,
they are undoubtedly the weak point in the provision made for
leading and guiding the sailor. This is, it is to be feared, inherent
in the system of using the air as the carrier of fog-signal warnings,
for sound signals are uncertain both as to penetration and location,
and the solution of the difficulty will probably ultimately be found
in Mr. Charles A. Stevenson's proposal of 1892, of an electric cable
or conductor laid down off a coast or danger so as to act on an
instrument on board each vessel, and thus either warn the sailor of
his proximity to it, and therefore to a coast or danger, or act as a
lead along which vessels might sail, keeping, as it were, in touch with
Although not directly connected with the guarding of the coast,
the remoteness of many 'of the lighthouses on the Scottish coast
one of which is 40 miles from land, one 20, and several about 12
at a very early period caused consideration to be given to the
possibility of connecting them with the shore by electric telegraph.
The expense involved prohibited the adoption of electric cables;
and in 1894 the Commissioners of Northern Lighthouses made an
experiment of the wireless system of telegraphy proposed by Mr.
Charles A. Stevenson, on the scale and distance that was required
for one of the stations in the Northern Lighthouse Service. This
experiment, which was carried out with the assistance of the
General Post Office officials in Edinburgh, proved quite successful;
but the Board of Trade declined to sanction its adoption on the
ground that flag signals were sufficient. Since then many other
similar or cognate proposals have been suggested, but nothing
practical has yet been done.
The Discussion was combined with that on the papers by Baron
Quinette de Rochemont, Mr. Harding, and Mr. Brebner (see
p. 97). The author replied by correspondence.
On the motion of the Chairman a vote of thanks was accorded
to the author.
"RECENT IMPROVEMENTS IN THE LIGHTING AND
BUOYING OF THE COASTS OF FRANCE."
Paper by Baron QUINETTE DE ROCHEMONT.
Department of Lighthouses and Beacons in France, under
the able direction of the late and regretted M. Bourdelles, has
introduced many improvements in the lighting and buoying of
The illuminating power of lighthouses has been greatly increased
1. Increasing the intrinsic brightness of the luminous source.
2. Greater perfection in the manufacture of the optical apparatus.
3. Reducing the number of lenticular panels, and increasing
their surface and power by employing lightning lights.
The brightness of the beam from a lenticular panel is pro-
portionate to the intrinsic brightness of the luminous source at the
burner, and not to the luminous intensity. The mean intrinsic
brightness of flames, produced by oil lamps, increases only to a
slight extent with the size of the flames. The illuminating power
of lighthouses can, therefore, only be improved to a slight extent
by increasing the number of wicks. The adoption of Auer incan-
descent burners, for compressed gas and petroleum vapour, has