By the kindness of the Elder Brethren of the Corporation of Trinity House of Deptford Strond, I am enabled to give the following brief sketch of the nature and peculiarities of Floating Lights which was communicated to me by Mr Herbert, the secretary of the Corporation:—
“The annual expense of maintaining a Floating Light, including the wages and victualling of the crew, who are eleven in number, is, on an average, L.1000; and the first cost of such a vessel, fitted complete with lantern and lighting apparatus, anchors, cables, &c., is nearly L.5000. The lanterns are octagonal in form, 5 feet 6 inches in diameter; and, where fixed lights are exhibited, they are fitted with eight Argand lamps, each in the focus of a parabolic reflector of twelve inches diameter; but, in the revolving lights, four lamps and reflectors only are fitted. The greatest depth of water in which any light-vessel belonging to the Corporation of Trinity House of Deptford Strond at present rides, is about 40 fathoms (which is at the station of the Seven Stones between the Scilly Islands and the coast of Cornwall).
“The Corporation’s light-vessels are moored with chain-cables of 1¹⁄₂ inch diameter, and a single mushroom anchor of 32 cwt., in which cases the chain-cables are 200 fathoms in length; some of the said vessels are moored to span-ground moorings, consisting of 100 fathoms of chain to each arm, and a mushroom anchor of similar weight at the end of each; a riding cable of 150 fathoms being in such cases attached to the centre ring of the ground chain. The tonnage and general dimensions of the light-vessel are given on the drawing of the lines.” (See [Plate XXIX.])
Still lower in the scale of “signs and marks of the sea,” are Beacons and Buoys. Beacons and Buoys, which are used to point out those dangers which, either owing to the difficulty and expense that would attend the placing of more efficient marks to serve by night as well as by day, are necessarily left without lights, or which, from the peculiarity of their position, in passages too intricate for navigation by night, are, in practice, considered to be sufficiently indicated by day-marks alone. Beacons, as being more permanent, are preferred to Buoys; but they are generally placed only on rocks or banks which are dry at some period of the tide. On rocks, in exposed situations, the kind of Beacon used is generally that of squared masonry, secured by numerous joggles (as shewn at [Plate XXXII.]); and in situations difficult of access, and in which works of uncompleted masonry could not be safely left during the winter season, an open framework of cast-iron pipes, firmly trussed and braced, and secured to the rock with strong louis-bats, is preferred. The details of this framework are shewn at [Plates XXX.] and [XXXI.] A stone Beacon of the form and dimensions shewn in [Plate XXXII.], may be erected for about L.700, and the iron Beacon shewn at [Plate XXX.], for about L.640. In less exposed places, where the bottom is gravel or hard sand, a conical form of Beacon, composed of cast-iron plates, united with flanges and screws, with rust-joints between them, is sometimes used. A Beacon of this kind is shewn at [Plate XXXII.], which can be erected for about L.400.
Lastly, Buoys, which may be regarded as the least efficient kind of mark, and as bearing the same relation to a Beacon that a Floating-light does to a Lighthouse, are used to mark by day dangers which are always covered even at low water, and also to line out the fair-ways of channels. They are, for the most part, of one of the three forms shewn in [Plate XXXIII.], viz., the Nun-buoy, in the form of a parabolic spindle, generally truncated at one end, so as to carry a mast or frame of cage-work, and loaded at the other end, so as to float in a vertical position; the Can-buoy, which is a conoid floating on its side; and, lastly, the Cask-buoy, which is a short frustum of a spindle truncated at both ends, but almost exclusively used for carrying the warps of vessels riding at moorings. Those buoys are of various sizes and differ in cost. Mast-buoys, from 10 to 15 feet in length, cost from L.23, 15s. to L.48; and those of the Ribble and the Tay, which are 21 and 24 feet long, cost respectively L.105 and L.79; the Can-buoys are from 5 to 8 feet long, and cost from L.13, 13s. to L.20, 5s. Large buoys are often built on kneed frames resembling the timbers of vessels. The Cask-buoy is generally 6 feet long, and costs L.22, 15s. All these buoys are formed of strong oaken barrel-staves, well hooped with iron rings, and shielded with soft timber; and the nozzle-pieces at the small end of the Nun and Can buoys are generally solid quoins of oak, formed with a raglet or groove to receive the ends of the staves. Much skill, on the part of the cooper, is required in heating and moulding the staves to the required form; and great care must be taken that they be of well-seasoned timber. Buoys are not caulked with oakum, but with dry flags closely compressed between the edges of the staves, which swell on being wet; and they are carefully proved by steaming them like barrels, to see if they be quite tight. Buoys are also formed of sheet-iron, in which case they are sometimes protected with fenders of timber; but they have been found more troublesome for transport, and, for most situations, are considered less convenient than those of timber.
In the beginning of 1845, I suggested the idea of rendering Beacons and Buoys useful during night, by coating them with some phosphorescent substance, or surmounting them with a globe of strong glass filled with such a preparation, whose combustion is very slow, and emits a dull whitish light and little heat. Some experiments were accordingly made by my suggestion; but I cannot add that any practically useful result has been obtained.
In laying down Beacons or Buoys, their position is fixed, as may be seen in the [Table] in the Appendix, either by the intersection of two lines drawn through two leading objects on the shore (the magnetic bearings of which are given for the sake of easy reference on the spot, in finding out the marks), or by means of the angles contained between lines drawn to various objects on the shore, which meet at the Beacon or Buoy from which they are measured by means of a sextant. In the latter case, the angles are always measured around the whole horizon, thus affording a check by the difference of their sum from 360°. The magnetic bearing of one of those lines is afterwards carefully ascertained, by means of the prismatic compass (if possible from one of the objects on shore, and if not, conversely from the Beacon or Buoy), so as to afford the means of translating the whole into magnetic bearings for the use of seamen. The buoys are moored, as shewn in [Plate XXXIII.], by means of chains and iron sinkers, with a sufficient allowance in the length of the chain to permit them to ride easily.