Page images
PDF
EPUB

THE TECHNICAL WORLD MAGAZINE

the water. Of course, this slicing in twain of the cradle has been prearranged, the ribs forming the structure being so dovetailed together that they require but the almost instantaneous manipulation of key-pins to disconnect them.

As a final touch in the construction of the raft, bulkheads of heavy timber are placed at either end of the structure; and a six- or eight-inch hawser is attached, by means of which the unwieldy mass is towed out of the river where it was built and along the coast. All the giant rafts thus far built have been constructed at Stella, Washington, or some other point. on the Oregon or Washington shore of the Columbia river, and have been towed to San Francisco, where they are broken. up and sold, mainly to shipbuilders, for use as spars, or to contractors, for use as piling in railroad construction, etc.

In making the trip down the Columbia river, a giant raft is usually towed by a powerful tug, with a stern-wheel steamer at the after end of the log mass, for steering purposes; for this waterway is shoal in many places, and a raft drawing 222 feet of water is likely to go aground unless guided with great care. For the

ocean voyage, the raft is usually taken in tow by two big tugs. For the journey from San Francisco to Shanghai with posed that the two tugboats shall be acthe pioneer trans-oceanic raft, it is prorying fuel for the little fleet, which could companied by a collier or oil steamer caralso assist in the towing if necessary.

Considering the number of rafts which have been built, and the severity of the storms encountered on the misnamed Pacific, there has been a surprisingly small percentage of loss in transporting logs by this method. To be sure, one or two of the earlier rafts launched on the Pacific by Mr. Robertson did break away and go to pieces, stray logs being cast up as far away as the shores of Hawaii and Mexico; but latterly, practically no losses have been sustained.

For all that, marine underwriters look upon the log rafts as rather undesirable risks; so much so that they usually charge premiums of ten per cent or more for insuring these craft. The conseif ever insure a raft for more than onequence is that the raft companies seldom third of its value. They insure merely to the extent of guaranteeing reimburse

[graphic]

ONE OF THE GIANT LOG RAFTS OF THE PACIFIC.
Showing binding chains.

[graphic][merged small]

ment for the actual cost of constructing the raft, and without reference to the probable selling price, which in most instances includes a profit of $20,000 or more-a margin of gain that explains why great risks are taken in shipping spars and piling by means of rafts.

In raft construction, as in regular shipbuilding, there is a constant tendency toward increase in size. The earlier rafts did not exceed 300 feet in length, a representative raft of that period containing 450,000 linear feet of piling and spar timbers, valued at $45,000. One of the most recent of the giant log rafts was over 700 feet long and 50 feet wide; was bound together by 120 tons of iron chain, and contained 600,000 linear feet of piling, equivalent to 8,000,000 feet of lumber, board measure. And now it is announced that the raft which is to be sent to the Orient will contain no less than ten million feet of lumber.

The success of log rafting on a colossal scale on the Pacific, is in marked contrast to the failure that has attended efforts to raft sawed lumber by the same method. Several years ago, an immense

raft of sawed material was constructed at Portland, Oregon, the component parts being held in place by a rather elaborate steel framework; but when a storm was encountered, the immense mass went to pieces in short order, and no effort has been made to repeat the experiment. This mishap, and the occasional loss of a log raft in the early days, laid the foundation of a spirit of opposition, and certain shipping men are yet loud in their denunciation of the giant rafts as menaces to navigation.

In explanation of the demand for the red and yellow firs of the Northwest, it may be noted that these trees rival pine in lightness, and oak in strength and durability. They have nearly twice the strength under pressure of Eastern oaks, and nearly three times that of pine. Moreover, they grow very straight. Shipbuilders universally recognize the wonderful durability of these firs; and it is claimed that, until the steel mast was invented, no yacht ever defended the America's Cup that did not shake her sails to the breeze from sticks that came from the forests of the Northwest.

THE TECHNICAL WORLD MAGAZINE

[graphic]

COMING OF THE WHITE MAN.

Group presented to the City of Portland, Oregon, by the family of David P. Thompson.

[graphic][merged small][graphic][merged small]
[graphic]

LAKE VIEW TERRACE, LEWIS AND CLARK CENTENNIAL EXPOSITION, PORTLAND, OREGON.

Showing part of Agricultural Palace (at left) and Foreign Exhibits Palace (central background).-Fir-covered hills in background.

« PreviousContinue »