Improvement of the mouth of the Mississippi river.-Dredge-boat.-Proposed application of scrapers.

a, scrapers in position for deepest cutting; a', position for less depth of cutting; a", position of scrapers raised clear of bottom passing up stream across bar; b,

Partial section of
up-stream end
of boat.

2'

NOTE.-Scrapers to be applied to up-stream end of boat
only, and to work only when the boat's course is down
stream, and she propelled by the down-stream or forward
propeller.

cast-iron shaft for scrapers; c, chains holding scrapers in position; d, chains attached to washers on ends of shaft, holding scrapers and shaft against any tendency to motion in direction of axis of shaft; e, windlasses on deck for holding and adjusting scraper-chains; g, hawser-holes through which scraper-chains

pass.

Improvement of the mouth of the Mississippi river.-Plan of proposed dredge

boat.

The dredge-boat to be a "double-ender" of like shape and construction at both ends, provided with two strongly built four-bladed propellers, one at each end, on separate shafts, powerfully driven by separate engines, or sets of engines, and with compartments or tanks, such that when they are empty and the coalbunkers full the boat will draw fourteen feet, and when full twenty-two feet.

The distance between the spar deck and bottom of the keel to be about 24 feet, so that the former will be about two feet above the water-line at deepest draught.

The extremities of the propeller blades to describe circles of 16 feet diameter; their shaft centres to be six feet above the bottom of the keel, and directly over it, so that the ends of the blades will pass two feet below the bottom of the keel, and at minimum draught (coal-bunkers full) tangent to the water surface.

Length and beam to depend mainly upon the space and flotation required for boilers, engines, pumps, and other machinery, coal storage, quarters for crew, and the consideration of a good model. The beam can probably be safely assumed at 30 feet, and a well-proportioned length would probably be at least 150 feet.

SPECIFICATIONS.

Hull. Of wood, constructed with as much strength throughout as is possessed by first-class Atlantic steamers, and, moreover, to be re-enforced at both ends in the most practicable manner to the extent of affording complete security against injury from shocks occasioned by the propeller blades striking the tough clay incrustations covering portions of the Mississippi river bars. Dead-wood to be built in at the stems, so as to increase their stability and steadiness against shocks. The model to be so formed as to give the least practicable resistance, consistent with strength and other primary considerations, to progress through the water, and to speed. The bottom to be covered with yellow metal to the water-line at 18 feet draught. Cut-waters to be inclined near the keel, so as to clear well the space about the propellers at that point.

Spar deck. To be flat as possible consistent with adequate drainage; surrounded with a substantial railing, and as clear as possible of obstructions, especially from the stems to distances of 40 or 45 feet towards midships.

Propellers and shafts.-These to be, say, twenty-five per cent. heavier and stronger than would be necessary for ordinary sea-going steamers. The pitch of the blades to be that which is most approved for speed and efficiency in water. The ends of the blades, and the edges for a distance of two feet from the ends, to be given well-defined edges, the angles of which being, say, 25 degrees. Shafts to be confined by means of bearings of unusually great numbers and strength, (to avoid as much as possible vibrations caused by impact of the propeller blades against hard or tough substances,) and to be provided with shoulders of sufficient number and strength to prevent the possibility of any longitudinal motion by the unusual strain in that direction to which they will be subjected.

Rudders and rudder-posts-All these to be wrought iron. Posts to extend to within, say, two feet of the bottom of the keel; to be well secured to the ends of the propeller shafts, resting against these and held there firmly by means of bolts or journals in prolongation of the axis of the shafts, the journals passing through the posts and taking keys or heads on the outside. So much of the posts as interfere with unshipping the propellers to be movable. Rudders to admit of being unshipped, of course. Rudders to be so arranged as to be fixed at will in positions parallel to the keel.

Water tanks for regulating draught.-These to be arranged in sets running fore and aft; each set to be equally distributed on both sides of the keel, to have the areas of its cross-sections perpendicular to keel, proportional to the areas of the corresponding cross-sections of the hull from stem to stem, and to be subdivided in such a manner as to confine the contained water and prevent its following any motion of the boat, for the purpose of obviating as far as practicable any tendency to "shift cargo." The tanks or compartments of each set to be connected by apertures; these to be fitted with convenient devices for firmly closing and opening them at will. Each tank to have a manhole, admitting of the re

moval of sand and mud (precipitated by the contained water) when pumped dry. The tanks to be filled by means of scuttles placed just below water-line for minimum draught when the coal-bunkers are empty, and emptied through scuttles placed just above water-line for maximum draught, by means of pumps driven by donkey engines.

The capacity of these scuttles and pumps to be sufficient to fill all the tanks within, say, thirty minutes, and to empty them in a like space of time.

All scuttles to be fitted with convenient devices for securely closing them, and those admitting water to the tanks to be also fitted with substantial strainers. Propeller engines.-Each propeller to be driven by a power, say, twenty-five per cent. greater than would be required for a like propeller in an ordinary sea-going steamer. This to be accomplished by means of two cylinders placed base to base, with their axes in the same right line perpendicular to the shaft, the common base of the two cylinders being directly over the prolongation of the shaft; each piston-rod being connected with the crank-pin by means of two short connecting rods and a rock-shaft with two arms strongly made and mounted, an arrangement adopted generally on sea-going monitors, giving great simplicity and compactness while obviating all dead points.

Boilers.-The two sets of engines driving the two propellers should be supplied by steam from separate boilers, or sets of boilers, so arranged, however, as to be all connected together, and disconnected at will.

The several donkey engines ought also to have separate boilers.
Furnaces. These to be adapted for burning soft coal.

Storage for coal-Sufficient coal storage to be provided to supply the furnaces of all the engines on board one hundred consecutive hours of uninterrupted running.

Anchors and cables.-Three anchors, each capable of holding the boat against the Mississippi river current, and five chain cables of weight and strength to correspond to the anchors, of the length usually provided for sea-going ships.

Masts and sails.-One short mast rigged for a fore-and-aft sail, with sail and rigging all complete; and the gaff fitted completely for hoisting coal on board. Quarters. To be provided below spar deck for thirty men, and a house, say fifty feet long by eight feet wide, running fore and aft amidships on the spar deck, to be fitted up for an office and quarters for six persons, (one officer, ship's captain, mate, purser, and two steersmen.)

Pilot-house-One pilot-house amidships on top of officers' quarters.

Pumps.-An ample supply of steam and hand pumps for putting out accidental fires, washing decks and other necessary purposes, with full supply of hose to lead to every part of the boat; steam pumps to be worked by steam from the main boilers.

Arrangement for attaching two scrapers, one each side the keel at either end of the boat, at will.-At a point near each stem, say twelve feet distant from it, and five feet above bottom of keel, a cylindrical tube of boiler iron five inches interior diameter (a, see sketch) to be inserted, running from out to out of the hull, athwart ships or at right angles to the keel, and projecting far enough on either side to take a large and strong wrought iron washer which is to be accurately fitted and strongly bolted to the ship's side, and to present a shoulder three inches wide around the aperture of the tube, the plane surface of the shoulder being perpendicular to its axis.

At points at least twenty-four feet from these tubes or apertures (measured parallel to the keel and towards midships,) and eight feet (measured horizontally) from the middle of the keel, hawser-holes to be inserted (four in all) through the boat's sides, connecting with the spar deck by means of strong cast iron tubes extending up obliquely towards midships, large enough to admit shortlinked three-fourth inch chains, (b, see sketch.)

Should the iron in contact with the yellow metal sheathing give rise to too rapid oxidization, any other equally strong metal can be substituted.