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PUBLIC RECORD OFFICE

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Reference :-

C.O. 885

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ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO

PUBLIC RECORD OFFICE, LONDON

24 November 1896.]

Chairman-continued.

Mr. PREECE.

a deep water cable is almost a guarantee of

security.

1330. What are the main dangers the cable has to fear? The principal danger is uneven ground. This has been brought before you by several of the witnesses who have pointed out that if you come across banks or ridges, owing to the fact of such a very long length of cable being suspended from the stern of the ship, a cable meeting a ridge would be suspended in the form of a catenary. If I had a bit of string I could almost show you. Assuming a cable falling from the stern of a ship falls in a per- fectly straight line, there is a little curve, which is on the upper portion of the water, and there is also a curve down at the bottom; but they are both so small that they may be neglected, and that cable as it falls to the bottom is supported at every inch of its length by the water. It falls with a uniform velocity; it falls at the rate of something between one and two feet a second, and as it falls it is really suspen- ded or supported by the water. Now when you come to rest--when the cable comes to rest or to rest-this support when the ship comes cesses, the cable gradually takes the form called a catenary. The weight or strain on the cable is simply dependent upon the length of the cable that forms the catenary. If the cable were laid in 3,000 fathome, the probability is that be something like 10 the catenary would miles, that is above the strength of the cable, which must absolutely break. So if you are paying out a cable in a straight line and then you come to a rock of that kind (pointing), the cable would become fixed there and the length behind would slack in one direction, and running over here it would take this catenary, and then you would have at the point where it is supported a strain upon it greater than the cable could pos- sibly stand. The result is it would break, which has happened over and over again; and that is why it is absolutely casential that we should know the position of these ridges, so as to be prepared to meet them when the ship gets over the spot.

1331. And after uneven ground, what other special dangers ?-In the Atlantic there is very great danger arising from banks, due to the deposit of great blocks of rock brought down by the iceberge, the icebergs straying from Green- land. They come laden with the rocks and the stones and the dirt; as they pass Newfoundland they get into warmer water; they dissolve, and there for hundreds of miles you have a new country being formed a new Ireland really being formed by icebergs almost in the same way; and this débris being deposited there is an tremely awkward place for cables to cross. Most of the cable companies have made detours to the south to avoid this rough ground. That we should not meet with in the Pacific; in the Pacific there are only two possible causes of danger, one is the coral reefs, and the other is the possibility of volcanic action.

ex-

1332. I presume that the coral reef is a very well-known difficulty, and therefore complete provision can be made to meet it?-I do not think that may be considered; a coral reef in

Chairman-continued.

[Continued.

are

On all these

itself may not be considered a danger except in a case where a cable has to cross a coral reef subject to great swell and breakers. As a rule, these coral islands, or these atolls, have an opening to the leeward side that enables hoats to go in and lay the cable in smooth water, so that, per se, a coral reef in the form of an atoll or in the form of a reef is really not a danger: it is only a sign of danger

these because

atolly

reefs UT coral existence of volcanic an indication of the action at some prehistoric time or other; how long ago it is impossible to say. coral islands the only rocks met with are lavas and volcanic tufas, and it is almost certain that every coral island has originated with some volcanic action. The only place where we have evidence of volcanic action going on at the present moment is in the neighbourhood of the Fiji Islands; but I think on this question you will find Admiral Wharton will give you very useful information. I do not quite remember who it was that reported on that point, but when I went into this part of the business connected with the Pacific Ocean, I found a report from somebody on this very point, and it is a very important point, because it is the only possible danger that we have to anticipate in crossing the Pacific. At the present moment we do not know where this volcanic action may be found, nor where there may be what they call earth- quakes, or landquakes, due to the existence of these volcanoes. Still it is a risk we must bear in mind.

1333. Not much is known about this South l'acific, even when you get beyond Fanning Island, is it? No, we know very little about the bottom between New South Wales and New Zealand Perhaps the Eastern Telegraph ('om- pany may give you some information about that, but there is a cable laid between Queensland and New Caledonia. I happen to have a report of the laying of that cable, and I have made a short ex- tract from it :-"The cable is a very good one, and “is laid in 1,150 fathoms all through except one big hole of 65 miles broad, which went as deep as 2,330 fathoms. The bed of the ocean is soft petrified shell (almost pure lime), and the cable is laid in an excellent resting place right through, where it is not likely ever to be dis- turbed." I think that corroborates Mr. Lucas's evidence in favour of the ooze being of a lime character and having a great preservative effect.

"

4

1334. Now I should like to take you to the

question of slack, which of course comes into immediate consideration. After you have ascer- tained the exact nautical mileage, what slack would you allow for the deep and the long section-I allowed in the estimate I have made, and I should allow under any circumstances, a slack of 20 per cent. It is made in this way: Slack when laid, 12 per cent.; slack due to the possible deviation of route, which would result, of course, from the survey, and also which would result probably from accident, if an accident happened, 5 per cent.; slack or spare due for maintenance purposes, which would have to be left on the different islands for repairs, 2.5 per cent.; so that the total of slack would be 20 per cent.

24 November 1896.]

Mr. PREECE.

Chairman-continued. 1335. What has been the practice as regards the percentage of slack?-I find that the first Atlantic cable was laid with a slack of 25 per cent, and that nearly all the Atlantic cables laid by the Telegraph Construction Company were laid with a slack varying from 12 to 15 per cent. I believe it is 14 per cent.: I do not know how that 15 came in. The present practice pursued by Siemens Brothers, who have laid four or five cables across the Atlantic, is 10 per cent., and less than this 1 should consider absolutely dangerous.

1336. But there is a wide margin between 10 per cent., which you say is the present practice, and 20 per cent., which you recommend for this special section ?-The difference between myself and Mr. Siemens, or between myself and the present practice, is only two and a half per cent., because in all the evidence given to you by Mr. Siemens, and by Mr. Matthew Gray, and by Mr. Lucas, and all of them, it was very explicit that the slack was the slack when laid. They also mentioned, I think nobody mentioned less than, 15 percent and Mr. Matthew Gray said he would not think of going to sea with less than 15 per cent. of slack; and Mr. Lucas said they never started with less than 20 per cent. of slack; 20 per cent. is the regular allowance the Telegraph Con- struction make, but I make the slack when laid in the Pacific 12 per cent. I think the depth of water does make a little difference.

1337. As against 10 per cent.? Ten per cent. in 2,000 fathoms.

1338. But I do not think any previous witness has ade any allowance of extra slack for deviation of route and accident?-Yes, I think Mr. Lucas did.

Sir Saul Samuel.

1339. Was the line to New Caledonia from Queensland surveyed before the cable was laid? -I do not know. It was laid by a French com- pany.

1340. Are you aware that they all at once found they had not sufficient slack ?—No.

1341. It was so.-On this I should like to

add; I Bay that less than 10 per cent. I regard

as dangerous.

Chairman.

1342. The difference really between yourself and most of the witnesses on this point amounts to this, that you would allow 2:5 more slack when laid, and you take in a larger insurance against accidents-Yes; and deviation of route.

1343. Which, if not used, would be all avail- able for maintenance?---Certainly,

1344. Now what are the records of the speed of laying the early Atlantic cables?-There is an extremely interesting paper published by Captain Trott of the steamship Minia," who is the man in charge of the repairs of the Anglo- American cables in the North Atlantic. He is a man who has had more experience in repairing deep-sea cables than, I think, anybody else, and I suppose he has repaired as many faults in deep

*

+

Chairman-continued.

[Continued.

water as all the other engineers put together, and he reports to this effect" The records of laying the early Atlantic cables show that the maximum speed was six knots, and that a percentage of from 11 to 13 was allowed for slack, yet they were "broken from suspension over inequalities of the "button." In his paper he refers to several cases where even with this slack he had come across breaka clearly due to suspension.

water.

1345. What does the slackness depend on?- Well, it depends on, first, the speed of the ship, and it also depends on the weight of the cable in Of course, if the cable weighed the same as the water it would not sink at all, and the rate at which it falls simply depends on the difference between its weight in water and its weight in air. Deep-sea cables weigh about 20 cwts.- 22 cwls, in water, and they fall with a velocity varying from somewhere about 15 to 2 feet in a second. Then it also depends upon the rough- ness of the exterior. There is a very curious fact in laying a cable. I am not sure if I can show it nicely, but I can show the same effect with a piece of paper in air-that we meet with in the water. The curious thing is this--that a cable, in falling to the bottom, not only talls in an inclined straight line to the bottom, but it slips down this incline of water. It is just the same in air.

This

Bea.

is a little heavier than air of paper course, if I crumple and crush it, it woul drop in a line like that (showing), but if I flatten it, it ought to slope off in that direction, but I have not made it very nicely. You see it slips down an incline of air. Well, that is exactly the same operation that takes place in the Captain The cable as it falls slides down. Goodall to-day gave an impression that you could lay a cable on even ground without any slack at all, but you cannot lay a cable without slack. This sliding down is a necessary consequence of the reaction of the sea and cable. Well, the rate at which it slides down is checked very much by the roughness of the surface. You will find by the sample cables that Mr. Siemens had here that some of the cables were rougher than others. In the early Atlantic cables the Telegraph Con- struction Company made the surface very rough indeed to check this falling down, but now they find they can regulate the slack so nicely that the sliding down adjusts itself independently of the roughness of the surface. Well, now, when you take a cable like this (referring to the string), supposing you want to lay it absolutely straight, it will be necessary that the length ou the ground should be exactly the same as the hypothenuse. To do this it would be necessary to force it through the water in the direction of the ship, and you

It is cannot do that. impossible to force a cable through the water, and the result is that in deep water slack is an essential feature of the laying of a cable, and you cannot lay a cable without slack unless you put upon it an infinite tension which would break it. You have these four conditions. You have the speed of the ship, the rate at which it falls down the water, the roughness of the sur- face, and you have the slipping action, and the result is that with your instruments on board

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