Mr. Augustin Creuze has lately deduced from M. Marestier's drawings of the steam boat, the Chancel lor Livingston, and also from several English boats, and from two have been lately constructed in England for the service of the Norwegian Govern ment, by Lieut. A. G. Carlsund, of the Swedish Ro yal Naval Engineers, the exponents of their different elements, as recorded in the following table, accord ing to the parabolical method of Chapman, before al luded to.
The column devoted to the relation of the length to the breadth, was found by dividing the latter dimen sion by the former. The average length of these boats is 39.82 metres, or 130.64 English feet, and their average breadth 7.15 metres, or 23.46 English feet. The draughts of water, it will be observed, are very variable, arising necessarily from the particular purposes for which the vessels are destined. The Savannah is the steamer that first crossed the Atlan tic, and her draught of water, it will be perceived, is the greatest of the whole series. The Robert Fulton, which navigates the magnificent waters of the Mis sissippi, has a draught of 3.05 metres; whereas the Vesuvius, built for the purpose of navigating the same mighty stream, has only a draught of 1.8 metre, her It is of importance that the displacement and also the position of the centre of gravity should be accu rately determined, on account of the great and con stant weights on board a steam vessel being so consi derable. It is usual to distribute the coals as much about the centre as possible, and to adjust the posi tion of the centre of gravity of the engine, to the in tended purposes of the vessel. It would be proper also to form an estimate of the stability of a steamer with regard to its length, by calculating what effect the removal of a weight to a certain distance either be fore or aft the centre of gravity, will produce a given difference in the draught of water. This weight be ing known might be employed as a scale by which to regulate the disposition of other weights; and it is from a neglect of this important particular, that steam boats float at a different draught of water from what was intended.
Unless the displacement is correctly determined, and the area of the midship section also known, and limited moreover to a constant quantity, the power of the engine cannot be determined, so as to ensure a given velocity. Another necessary cause for accuracy
with regard to the displacement is, that any alteration from the water line, in relation to which the height of the axis of the paddle-wheels was determined, might materially affect the action of the paddles themselves; the height of the axis being adjusted in such a man ner, that the wheels having a specific diameter, the paddles may obtain such an immersion in the water, as shall cause their inner edge to have a velocity at least equal to that of the vessel, to ensure the absence of resistance on the fore side of the paddle. Hence it appears, that the depth of the paddle depends on the proportion of the velocity of the vessel to that of the velocity of the outer edge of the paddle wheel. It is, moreover, found in practice, that the paddles will not work well if immersed in the water more than eighteen inches or two feet. This circumstance ari ses from the great loss of power occasioned by the obliquity of Ihe stroke on their entrance into the fluid, and also on their leaving it, and the great quantity of water, moreover, they will lift.
The breadth of the paddle must be regulated by lo cal circumstances, attending to the condition, that the greater the arc of the paddle, the less is the loss of power occasioned by the motion it communicates to the fluid. 13ernouilli estimates this loss for the common oar to be 297 of the whole force applied. 1000 Sea-going boats should in general have their paddles narrower than boats intended for smooth water.
The number of paddies on a wheel is at present wholly determined by practice. One paddle for every root the wheel is in diameter, is the general rule fol lowed. If they are too near each other, they do not meet the water with all the advantage they ought; and if too far apart, the motion which their succes sive and distinct impact with the water communicates to the vessel is unpleasant.
Neither theory nor practice has yet determined where the axis of the paddle wheel should be placed with regard to the length of the vessel. M. Mares tier has given us the following of its situation in se veral American boats. Its position is, however, al ways very much limited by that of the engine.