The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

b2 MARINE REVIEW. [February 28, CONSTRUCTION OF TORPEDO BOATS AND DESTROYERS. BY GEORGE HERBERT WILSON. LONGITUDINALS. _ To continue along the line of longitudinal stiffness, the longitudinals or keelsons of a boat will bear a certain amount of inspection to decide upon the best mode of construction and to locate them at that part of the ship from which will be derived the greatest benefits. The principal keel- son or longitudinal—the vertical keel—has already been discussed and it remains for this portion of the work to demonstrate the value of the addi- tional strength gained and the functions performed by the longitudinals. The condition of the ship when under a “hogging” or “sagging” strain being two of the worst, will be taken in connection with the above values. To arrive at the proper decision as to their best disposition will require a full knowledge of the functions they will be called upon to perform ‘when in such conditions. Like the vertical keel, the longitudinal is required to give a certain amount of local strength; to act as it were as a “strong-back” for that part of the structure which it traverses and to distribute and take upon itself the various strains which are constantly occurring in its vicinity. As a strong-back or back-bone, as the keelsons are called, the longitu- dinals are of necessity an important factor, and to consider it at all, it must be under the worst circumstances. This is undoubtedly true when the boat is at an angle of heel sufficient to bring the longitudinal in question in a vertical plane, this being the plane at right angles to the water line—the position previously occupied by the vertical keel. Assum- ing this change of position, and regarding the boat as on the crest or in the hollow of a wave, it follows that its functions are practically those of the vertical keel which it has displaced. It must not be presumed from this condition of affairs, however, that the longitudinals should equal the strength of the displaced keel, else would result the ridiculous display of several vertical keels located along the transverse section. In addition to the support given by this longitu- dinal must be considered the partial aid gained by the keel in its new position. The keel’s line of greatest efficiency being destroyed it is not to be presumed that it is useless as a factor in resisting longitudinal stresses. Though the strains must act upon it in an oblique plane it still retains a great amount of resistance to bending. This is mostly effected by its strong connections to the adjacent structure and by the rigidity of the keel itself, _ Thus it will be seen that the longitudinals can be diminished in scantlings from that of the keel. This decrease is to a marked degree proportional to the distance of the same from the center line of the boat, measuring along the girth. The proportionate decrease can readily be accounted for when the conditions dependent upon the various longitu- dinals are taken into consideration. Relying upon the longitudinals to act as partial keels when in a heeled condition, it follows that those longitu~ dinals lying within the limit of the “probable heel” will require greater strength than those outside of this limit. The angle of probable heel has a maximum of about 25°. The exception is the case when a greater angle of heel occurs, and in such an instance the nearest deck or longitudinal bulkhead can be relied upon to assist in resisting the strains. Longi- tudinals lying without the limit of “probable heel” are generally of smaller proportions. Their functions are to resist the crushing strains of huge waves hurled against the structure and those incident to coming alongside of docks, ships, ete. But it is not in resisting the longitudinal strains alone that the side keelsons are important. In addition to these duties, they are depended upon for a great amount of local stiffness and for transmitting the strains and vibrations through the structure. As a part of the equivalent girder for a boat in the upright position the longitudinal is not as important as the shell plating or inner bottom (very few boats of this class have the latter except in wake of tanks), but it tends to thicken up the vertical web connecting these two members. In some of the later boats, built and now building, the longitudinals have entered largely into the construction of the engine and boiler foundations and tank sides. With the general char- acteristics and duties of the longitudinals outlined, an investigation into the practical methods of meeting these is pertinent. Longitudinals, like the vertical keel, should in some manner maintain a continuity of metal in some or part of some of its members. This is effected in various ways and along different lines. The manifold construc- tions of this portion of the hull structure are governed by the type of boat, her use and service, by the surrounding structure and by the question of economy. It will aid to enumerate them as follows: 1. In some cases the floors are cut entirely, allowing of an entire continuous longitudinal with continuous double angles at the top and clips at the bottom for shell connections. The longitudinal plate is scored out over the frames and is secured to the floor plates by two or four ver- tical clips as the strength requires. 2. In others the floor is scored out at the top to receive the longi- tudinal plate, and the longitudinal is scored out at the bottom to let down over the floor plate, thus insuring partial continuity in each. Con- tinuous angles at the top and clips to the shell and floor plates are features of nearly all longitudinals. __8. This method consists of making the longitudinal plate intercostal with continuous angles at the top and bottom. This requires the cutting