Fifthly, the effect upon the steerage is singular, the mass of water put into motion by the thrust of the screw is thrown directly upon the rudder, and the consequence is not only that when the ship is going at any given rate, the rudder is passing through the water at a greater rate, and consequently is more sensible, and acts more powerfully upon the ship; but even when the ship has no way, but the screw is at work, the rudder is acted upon by water moving perhaps at two or three knots per hour, and the vessel is still under command—this must be a most important power to possess in a ship, and must materially diminish many of the greatest dangers arising from a strong head wind and sea, and at the same time and under the same circumstances must increase the speed by improving the steerage.
And lastly, her diminished breadth of beam. Important as this alteration would be to any vessel, it is peculiarly so as connected with Bristol; the total breadth, including paddle-boxes, would be at least 78 feet; with the screw, and taking all the increased beam that might be convenient, it would be under 50—very nearly 30 feet of difference. One of the principal objections to her coming up the river would be removed, and the dock gates might easily be made to receive her.[201]
There are many other points upon which comparisons may be drawn, but I am not aware that any very important differences exist.
As regards first cost I believe there would be little difference—if any, it would be in favour of the screw; as a reduction of ninety-five tons of iron can hardly fail to cause some saving, although some portion of the substituted machinery may be more costly per ton.
As regards wear and tear I can have no doubt that some considerable saving would be effected; the paddles are a constant source of trouble and expense, and seem never to be capable of being kept in good repair; indeed, they are huge and comparatively light frameworks subjected to extraordinary and constantly repeated shocks, each arm receiving direct about 260,000 very sharp blows per voyage, independently of the more violent shocks from heavy seas, while the screw can be subjected to no such constant source of mischief.
From all that I have said it must be evident to you, gentlemen, that my opinion is strong and decided in favour of the advantage of employing the screw in the new ship; it certainly is so. I am fully aware of the responsibility I take upon myself by giving this advice, I am also fully sensible of the large amount we have at stake, and I have not forgotten the nature and tone of the observations which have on more occasions than one been so freely made by individuals upon the course we have hitherto pursued; although, and I have pleasure in referring to the fact, this course has in every instance where results have been obtained proved successful; but my conviction of the wisdom, I may almost say the necessity, of our adopting the improvement I now recommend is too strong, and I feel it is too well founded, for me to hesitate or to shrink from the responsibility.
I think I have hardly advanced an opinion which I have not supported, and in most cases preceded, by a statement of facts, leaving no doubt as to the correctness and safety of relying on these opinions; still it would be too much to hope that my mode of laying before you these facts which I have collected and the opinions I have formed could produce as strong a conviction in your minds as the consideration of them has in my own; but if you bear in mind that the actual results of the fair and full trial of the ‘Archimedes’ for several months has completely established the fact of the efficiency of the screw as a propeller; that the experiments I have made, as well as the general and apparent results of her working, have equally satisfactorily explained the fact of the power required being no greater in proportion to the effect produced than in the ‘Great Western’ steam-ship, and many other good steamboats; and that these results are satisfactorily explained by theory, you cannot fail to draw the same conclusion that I have done as to the general question of at least the equal efficiency of the screw.
As to the comparisons I have drawn between the general and what I may call the indirect advantages of the one mode of propelling over the other, they seem to me so evident that I am disposed to apologise to you for having occupied your time in pointing them out, and we have the satisfaction of knowing that they are now very generally admitted, particularly by practical men.
In conclusion, I must observe that much more detailed information and recorded results than appear on the face of this Report have been required to enable me to form correct comparisons, and to reduce to calculation and to actual figures and amounts many results observed; and that it would have been impossible for me to have given you such clear and positive facts on many most important points without the very detailed observations made and recorded by Mr. Berkeley Claxton in the several voyages of the ‘Great Western,’ and also in one on board the ‘Archimedes.’
The information obtained from these logs has been, and may still be, of the greatest importance to us in our future working, and I have much pleasure in adding that the manner in which my directions were carried out was highly creditable to Mr. Berkeley Claxton, who, I think, has conferred a great benefit on the Company by his labours. I have to express also my thanks to my friends Captain Claxton and Mr. Guppy for their assistance in the various experiments which have been made, and in working out the results.