J. W. Robertson, addressed to you on the subject of the Alabama River obstruction and forwarded to me by you for my information. The colonel's system of triangular rafts is explained in so little detail that I should scarcely feel justified in expressing my opinion in regard to it. I am not surprised at the unfortunate result of the experiment on Captain Farrand's plan. The construction and maneuvering of his huge rafts was evidently an undertaking of excessive difficulty, of not entirely impracticable. Would it not be well to inform Governor Shorter that, if he is willing to turn over the whole question of river obstructions to the Engineer Corps of the Army, every exertion will be made to produce satisfactory results?
The anomalous arrangement of Captain Farrand for chief of engineer, with engineer officers under him, to carry out plans which they do not approve can never accomplish the desired work.
Understanding that 1,800 feet of very heavy chain cable has been furnished to Governor Shorter by the C. S. Navy, may it not be used Judiciously for obstruction in the following way?
Construct first two large cribs, with a passage-way for steamboats of about 60 feet between them, and then stretch from them on either hand to the shore a slack chain, supported at intervals on small floating rats, as own in the accompanying sketches. Any attempt to injure the cribs or beak the chain by ramming would probably fail if a proper system of construction were adopted. The cribs should be built up to low-water mark, with salient up and down stream. The buoyancy of the rafts at intermediate landing points, if any are selected, should be considerable. The supporting logs might be of round timber, 30 or 40 feet in length and not less than 12 inches mean diameter.
The portion of chain between fixed points, or rather points of attachment, might be supported, or buoyant masses placed at intervals of 10 feet and formed on three logs each, fastened together with two or three sets of bolts. By keeping a few row-boats well manned and a steamtug constantly ready in freshest to guide the larger drift and heavy floating bodies of every description through the pass-way it is thought that the above obstructions may be keep free. Lighter material, such as ordinary logs, would probably pass clear of the obstructions, as the chain will be sustained at a depth below the surface varying from 1 to 10 feet.
It has been suggested that a guide, composed of floating timbers, fastened end to end, as shown in the sketch, might obviate the necessity of keeping in readiness the row-boats and steam-tug.
Should the season of high water prevent the prompt execution of this plan or one of a similar character, yet if the suggestions herein contained meet with your approval material might be collected and framed for rapid construction when the river subsides. The timber collected for Captain Farrand's raft and still remaining may furnish a sufficient supply. If stone cannot be had for filling the cribs, if they are large enough and built with close joints earth would answer.
The foregoing views and also the appended sketches are respectfully submitted for your consideration to give them such trial as in your judgment they may merit.
J. F. GILMER,
Colonel, Engineer, and Chief of Bureau.