a great depth, for the purpose of getting our passengers berthed well out of the water; and as we had a large number of deck houses, it became an important thing to discover how we were to get a large amount of stability. You will see that the question was a difficult one, when you consider that the form of the midship-section of the ship is not a form conducive to stability, but one which tends to lower the metacentre very considerably, on account of the great ratio of the lower form to the upper breadth. I came to the conclusion that by driving the whole mass of the ship into the centre-by making a straight body and sharp ends-that, for the area of the load water-line, I should get the largest result in stability. This I was sure would answer satisfactorily, and I am certain that the cubes of the ordinates of the load water-line of the Merkara, massed together, are larger than the cubes of the ordinates of any other water-lines of the same area and proportions, worked out in a different way, the result of which would necessarily be to club the bow and stern. We did not attempt in this design to do what Mr. Froude says so many have attempted, to save resistance by a straight midship body, with the very faulty belief that a straight body amidships has no resistance, because that is a mistake; and I was sorry to hear Mr. Scott Russell speaking yesterday about adding 25 feet and 25 feet, without considering the augmented resistance from the skin surface, and also without considering the augmented weight, which would have reduced his coal, from the extra strength which Mr. Froude has spoken about, and which I am sorry to say at one time I contested. However, one can always acknowledge errors, and I acknowledge mine now. That is all I have to say. I merely wish to point out why the Merkara was designed on this principle. She came up to my expectations. She is a very stiff ship for her depth, and I do not think any other way than having a full water-line aft, which is apt to destroy the speed, would have been productive of such good results.

Mr. J. Scott RUSSELL, F.R.S.: I wish to correct a mistake. I hope I did not say that the lengthening of the middle body could be accomplished without any increase of resistance. Did I say so?

Mr. DENNY: You did not say that; but you led it to be inferred, because you added 25 feet and 25 feet to produce the amount of coal-carrying space. Your first 25 feet carried a certain amount of coal, your second 25 feet carried a certain amount of coal, and so on, but there was no allowance for the increased weight which would be required in the construction, nor, so far as I can see, the increased skin resistance.

Mr. J. SCOTT RUSSELL: Then I am very sorry that I was misunderstood, because the 25 per cent. contained a very large allowance for the additions which have been alluded to; and if Mr. Denny takes the trouble to find out, he will discover that all those additions were amply allowed for; and if I had no such additions I should not have added so much as the 25 per cent. Allow me therefore to correct what I said yesterday, only in this one respect, to prevent any error similar to that into which Mr. Denny has fallen. I correct it therefore by stating to you, that if you do not make these allowances you will find 20 feet added will do what I stated; but in order to be on the right side I gave you 25 feet. Allow me to sum up in one word what I meant to convey upon that subject; and I am sorry that, to a gentleman so intelligent as Mr. Denny, I utterly failed to make myself understood. That shows it was my fault; but to prevent the possibility of a misunderstanding, allow me to say simply this :-When you have fixed the dimensions and forms of a vessel for the purposes necessary to go at your speed through the water, you then have to prepare your ship for the length of voyage she has to make and the fuel she has to carry, in addition to what you have already obtained for the ship. When you have got to that point

in your calculations, what I say and repeat in the most distinct manner is this, that the additional length must be given to the central body of the ship in exact proportion to the length of voyage that the ship must go without coaling; and although it will require a separate minute calculation for each ship, I say that 20 feet and with a margin 25 feet of length must be added for each 1,000 miles of voyage which that ship has to perform. Permit me, therefore, to give a further explanation on that one point, in conformity with the request of a distinguished gentleman in the Admiralty who desires me particularly to call attention to the fact that the length given to the Warrior class of ship was the length given, by necessity, for the length of voyage for which that ship was built to carry fuel. Permit me to say, in justice to the original designers of that ship-who I am afraid have nearly all gone to the other world except myself and to your Lordship, an original promoter of that ship, that the original length of that ship would have given her all her speed, would have carried all her armour, and done all they wanted in the way of performing very short voyages. The additional feet added were precisely the number of additional feet added for the service for which the Admiralty, who superintended the design of that ship, intended her; and when I say to you, my Lord, that that ship was intended to steam more than 6,000 miles in any weather without coaling at high speed, I think, my Lord, I have shown any professional man here that that additional length was absolutely indispensable, along with the other qualities of the ship. There is one thing more which I think, also in justice to the original man responsible for the design of that ship, should be generally known. Admiral Eden was one of the men who gave the most professional thought, after Sir Baldwin Walker, to the construction of that ship; and Admiral Eden was the man who prescribed that she should at least have 4 inches of armour. He was the man who also stated that, confining the armour to the central citadel, he was willing that the ends should be left without armour.

The PRESIDENT: Admiral Eden was not in the Admiralty at that time.

Mr. J. SCOTT RUSSELL: Not when she was built, but when she was first proposed. I am talking now of the original proposition, which was made a year or two before. The construction was about two years after that. He then settled also another most important point, my Lord, which has been lost sight of—that in addition to the armour-protected battery in the inside of the armour, an equally powerful armour should cover the whole area of the vessel at both extremities. There was also an original element which has been perhaps since lost sight of, and I think you will see there was an amount of foresight in that which the designer ought to have full credit for. It was a forethought, because it was an understood arrangement in the construction of the Warrior class, that so soon as the weight of the armour and the power of the guns should have so increased that that armour was no longer able to protect the ship against the guns of the day, arrangements were made in the original design which rendered it perfectly easy to increase the armour at a very small cost and with no loss of time up to the point required.

Mr. FROUDE: I think I have very little to say upon the point. There is one thing in reference to the value of long ships, which I omitted to mention in the Paper, and therefore I mention it verbally, and that is their unquestionable advantages in a sea-way. A very long ship will seldom meet a sea that will make her pitch. It is undoubtedly easier for a ship, if she has height enough, to go straight through the waves than to be set dancing upon them, first plunging her head downward into each wave, and then lifting her head high above it. I believe very often these long ships, in moderate weather, get along very much more smoothly, and with less strain on their engines, because they escape the bobbing up and

down they would experience if shorter. That is an advantage on the side of very long ships which we ought to give them credit for, but which I think ought not to make us forget the fact that increased breadth with diminished length will very often produce a diminution of resistance.

Mr. J. SCOTT RUSSELL: I am not an advocate for having a foot added to the length of any ship which it is possible to dispense with.

The PRESIDENT: I am sure every one will agree with me in saying that we are very much indebted to Mr. Froude for his two very able Papers which have undoubtedly contributed very much to the value of this Session of the Institution. I have to add it is with great regret that I must intimate to you the clock opposite warns me. I am so situated that I must request you to be kind enough to release me from my duties at this moment, as I have a good deal of other business to attend to, but as Sir Frederick Nicolson has kindly consented to take the Chair this evening, perhaps he will do so now. I hope it will be understood that I have not the least desire to offer any impediment to the Discussion on the next Paper, "On Raising Sunken Ships," which Paper I am very sorry I am not able to stay and hear, as I think it is upon a most interesting subject.

[Sir FREDERICK W. E. NICOLSON, Bart., C.B., Vice-Admiral, then took the Chair.]

The CHAIRMAN: As Lord Hampton has called upon me to take the Chair, I do so in obedience to his desire, but I do not think the noble Lord's logic is very good. He says because I have consented to take the Chair in the evening that therefore I am bound to take it now, after a very long sitting; however, I will do what I can.

ON RECOVERING SUNKEN AND STRANDED VESSELS.*

By HENRY F. KNAPP, Esq., C.E.

[Read at the Seventeenth Session of the Institution of Naval Architects, 7th April, 1876; Vice-Admiral Sir F. W. E. NICOLSON, Bart., C.B., Vice-President, in the Chair.]

THE immense amount of wealth continually being lost in all parts of the world by sunken and stranded vessels being abandoned, because of the considered impracticability or impossibility of attempting to save them by any previous known method, or if attempted afterwards abandoned, because of their destruction by the action of the sea before salvage is effected, mainly because of the improper appliances and consequent slow manner of working a wreck, renders any improvement in means for saving maritime property a question of national as well as local or individual interest.

Though some wonderful and great improvements have been and are continually being made in all branches of arts and manufactures, the art of recovering sunken and stranded vessels seems to have remained to this day the same that it was centuries ago, excepting incidental improvements to pumps, diving apparatus, &c., which, though valuable in themselves, have not been of sufficient importance to produce any radical change in the old style of doing such work, but are merely adjuncts to the style; and the art as worked to-day is the same "heave-and-haul" arrangement, as regards taking off stranded vessels, that it has always been, while the idea of attempting to raise a vessel of any size and weight, sunk in 40 to 100 feet of water on the open coast, has always been regarded by practical people as too absurd to be thought of. That the backward state of this art should always continue would be unreasonable to suppose, and the fact that it has continued so long is probably largely due to the contempt naval people have to any theory not fully and successfully demonstrated, thus nipping in its infancy all attempts at progress.

As regards the recovery of the Vanguard, theoretical ship-raisers have had complete and unlimited possession of the field; as all practical ship-raisers-viz., old hands

* Received 7th March, 1876.

at such work-have stood in the background and condemned as impracticable any attempt at her recovery.

As the public in general have but a faint idea of what is practicable, and practical ship-raisers have not a thorough idea of what is impracticable in raising sunken vessels, it may not be out of place to refer superficially to some of the many plans proposed, as well as plans practised for accomplishing such work.

As regards pumping out a deeply-submerged vessel for effecting her flotation, it is impracticable for the following reasons:—

1.-On account of the immense and costly difficulty of making her decks, hatches, &c., water-tight.

2. If the vessel could be made water-tight, water will not lift on suction more than 25 to 28 feet high, and a force pump could not well be arranged to work under water.

3.—Allowing these two insurmountable difficulties to be overcome, the pressure of water being ths of a pound to each vertical foot, would give a pressure in an ordinary case of fire of 10 to 50 pounds per square inch on her decks and hull, which would quickly collapse the entire fabric.

4.-Removing all these difficulties, the vessel, having no controlling buoyancy to keep her upright, would turn over in any shape in her upward movement, which would generally be the cause of her going immediately to the bottom again, provided the operation took place in deep water.

Another plan proposed is forcing air below decks, and thus displacing the water. The first and fourth named difficulties of the previous plan pertain to this plan also; besides which, if sufficient displacement were created to lift the vessel, the decks would have to sustain the entire dead weight of the ship, and as no decks were ever put in sufficiently strong for that purpose, this plan may be considered impracticable.

As some people have claimed that ships have been lifted in this manner, it is well to cite a case :—Take a ship submerged to the very ordinary depth of 50 feet, air is forced into her, and one end is seen to come up before the other, provided the previous-named troubles are overcome: then one end is afloat and the other end is submerged 50 feet; it requires more air to displace the water from the submerged end before it will come up. Under these circumstances the pressure of the entire body of air within the vessel is co-equal with the pressure due to the depth of water at the point of impingement of the air and water-say at the depth of 40 feet-in which case the pressure inside the vessel would equal 18 pounds per square inch, counterbalanced at the upper end by