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304 | | THE Marine REVIEW | - September, 1909 . is no barrier of any account to the em- ployment on ocean-going sailing vessels of even larger auxiliary powers. It is not known yet what it costs to run the Modwena, but it seems to be established that what the steam engine gains in economy as the power is increased, the oil engine does not. 'There is nothing to be gained, therefore, by going beyond a certain limit, and in the absence of an inducement of that kind makers are naturally disinclined to try to go beyond it. Inside the limit, however, the oil engine maker has it all his own way, and he is not absolutely hope- less of sooner or later gaining econ- omy by going to larger powers. NEW WHITE STAR LINERS OLYMPIC AND TITANIC. In the evolution of the modern liner there are well-defined stages of con- struction besides the five familiar stages of the laying of the keel, framing, plating, launching and completion. These S. S. Orympic. View or Tank Top LooKING Art SHowING WING TANK FLoors. are the terms used to denote the main TAKEN Juty 30, 1909. stages of construction, but in the larger and more complicated structures of the present day there are many intermediate stages that have an interest of their own, and afford an indication of the progress of the work. This, of course, is especially the case in such gigantic vessels as the new White Star liners Olympic and Titanic, now under con- struction at Belfast, and the reports that have already appeared describing one of these intermediate stages, viz., the construction of the cellular double bottom, have dealt with a number of interesting points regarding the keel, center p'ate (or inner vertical keel), floors and other parts forming this por- tion of the ship, special attention having been directed to the large amount of hydraulic riveting and the appliances for carrying on this work. The double bottom (which in these vessels is more extensive than usual, be- ing carried round the bilge), as is well known, serves several purposes. It pro- vides space for water ballast, which, being so far down in the ship, has an important influence on the stability, which can thereby be regulated as de- sired under certain conditions. Then, while contributing greatly to the strength of the whole structure, it forms an im- portant e'ement of safety in the event of the vessel grounding at any time, the ship, in fact, having, as the term im- plies, a double bottom. It will be seen from the accompany- ing illustrations that the tank top plating is now well advanced, and that the next important stage is being proceeded with, S. S. Otympic. View From CorrerpAm SHowinc Frames. TAKEN Juty 30, 1909 ? .