The Welin Quadrant Davit for Double-Banked Boats
Reprinted from the Weekly Journal "Engineering", July 1, 1910
| Editor's Note: The following article is presented in it's entirety. While only two or three paragraphs deal with the actual workings of the davit, I thought the reader would be interested in some of the background involved with the development of these davits, and the general attitude of the time regarding the emphasis on deck space over actual life-saving capacity. One gets the impression that the presence of lifeboats was almost considered a "nuisance". Of course, attitudes would change in just a couple of years...|
The last paragraph deals with the davits' installation on Olympic and Titanic. Some "specifications" obviously changed after this article was written, which will become clear.
While I realize that much of the material in the article and the accompanying scans are of little practical use to a modeler building a 1/350th model, it is always fun to know how these things worked. I for one have always wanted to know what the front of the davit looked like up close, and how the double sided davits were operated. All known photos only show a glimpse of that area. So I was thrilled to find the plans you are about to see.
Links are provided in the text when an illustration is referenced. Figures 4/5 and 7/8 are combined on their own pages.
|It is some years since we published particulars of the standard pattern of the Welin Quadrant davit for lowering boats on board ship.* The first trial set had just been fitted on board the cargo steamer Kortnaer. Since that date the advantages claimed for the gear have been so well substantiated in practice that at the present time some 3000 davits are in use.|
In addition to what may be termed the mechanical superiority of this type of davit over the older form, the use of this gear renders possible a considerable saving in deck space. To all familiar with the conditions of modern ocean travel, it will be patent what this really means. Nowadays the success of a line of passenger-carrying steamers depends (at least on certain routes) largely upon its popularity among the traveling public. Competition has in many instances afforded a wide choice of routes, and passenger lines must provide, at the present day, vessels not only as safe and well found as possible in all respects, but also boats which are attractive and offer special facilities for the pleasurable occupation of the long hours of enforced leisure. For these and other reasons saving in deck space is a distinct advantage, and it may be taken that any gear which renders this possible has much to recommend it.
Of the many propositions put forward from time to time whose objectives have lain in this direction, probably the most obvious is that of "double banking" the boats on convenient portions of the deck ; in other words, to carry them in a double row, one inboard of the other, on the less valuable part of the deck. Up till the present, any proposal embodying this arrangement has been checked by the fact that the Board of Trade has refused to recognize the inboard boat as fulfilling the clause in it's regulations, which requires a boat to be "under davits", as it is termed. Double-banking has, nevertheless, been practiced to some extent; but owing to the above clause, only in the case of such life-boats as have been carried over and above the regulation complement. Thus it has assisted in no way in reducing the long file of regulation boats to port and starboard, which obstruct a space that might otherwise be advantageously devoted to recreation, etc. The sea going public unquestionably thoroughly appreciates the advantages presented by clear deck space, as well as unrestricted view, and as both these are rendered more easily possible by double-banking of the boats, shipowners will doubtless not ignore a decision, recently reached by the Board of Trade, on this point. In conformity with this decision, the Board's rules have been amended in such a way that, in certain cases, the inboard boat of two double-banked boats shall now count as forming part of the regulation complement, when fitted in an efficient manner.
A modified pattern of davit, recently brought out by the Welin Quadrant Davit, of Hopetoun House, Lloyd's-avenue, E.C., complies with these new conditions. This gear we illustrate in Figs. 1 to 8 herewith. The new design of quadrant is similar in operation to the old, and there is no need, therefore, to enter into a description of the principles on which the system has been worked out. The general arrangement of the new form of gear is shown in Figs. 1 to 3. From Fig. 1 it will be seen that for this double gear the quadrant is a much larger sector than formerly. The davit arm practically bisects the angle formed. The travel for the screw block is much greater than in the orginal pattern and allows the davit-head to move from an extreme outboard position into an extreme inboard position, in which it stands plumb over the keel line of the inboard of the two double banked boats. The larger sector and the lengthened rack and screw are necessary, of course, to this greater travel. The extreme positions are shown in dotted outline in Fig. 1. The lead from the block is taken over and round a sheave shown on the inboard end of the frame, and thence to a bollard on deck, as may be seen in Figs. 1 to 3. This, when the boat is being swung out, tends to raise it and keep it clear of the deck. When swinging in, after a certain point, the weight exerted by the boat actually tends to raise the davit, while the falls are paid out at the same time.
With a view to gaining further fore-and-aft deck space, twin-frames are sometimes employed for the gear, as shown to the right hand in Fig. 2 and Fig. 3 . Under these conditions a special driving gear is used, which is further shown in detail in Figs. 4 and 5. It will be seen from these latter figures that the driving-pinion for the screw gear is carried on a swinging frame, the lower end of which is forked. Between the limbs of the fork is an eccentric which can be thrown over by hand, so that the pinion will mesh with the gear of whichever screw it is desired to operate. This eccentric has a throw rather greater than that corresponding to it's maximum eccentricity, so that it remains automatically locked when thrown over one way or the other.
The first twelve sets of this type of gear have recently been fitted on the new boats of the Union-Castle Mail Steamship Company, but in this instance they were applied only to boats carried on the poop-deck, the remainder being fitted with standard Welin davits.Fig. 6 is a photograph taken on board the R.M.S. Balmoral Castle, of which we recently gave illustrations. The view we now give shows the outboard boat being handled in the davits.
A more extensive application of the new system is being made on the White Star liners Titanic and Olympic, now in course of construction at the yards of Messrs. Harland and Wolff, Belfast. These vessels are to be fitted throughout with double-banked boats operated by the new Welin gear. A plan of part of the boat-deck of these vessels is shown in Fig. 8, while Fig. 7 gives a section showing the position and handling of the boats. Half the number of the boats fitted on these ships will be in excess of the Board of Trade requirements. Adequate provision on this scale could only be rendered possible by the adoption of some such scheme as that now sanctioned by the Board. The outer boats will be provided with shifting chocks, and at sea will be carried at the half-outboard position, allowing ample gangway room between the two rows of boats. The inboard boats might, of course, also be provided with shifting chocks, and the gangway between the boats and the deck erections thus increased. It will be evident that this arrangement might, with convenience, be adopted in cases where at present boats have to be cleared for coaling operations. Double gear would obviate such inconveniences, and we understand that more than one company are considering the matter with this in view.
* Volume LXXI, page 815. [I have calculated this be the Jan to June 1901 volume]
Additional Reference and Comments
The design of the davit is quite elegant. To understand what happens as the arm is raised and lowered, extend the curve at the bottom of the arm (the quadrant) into a complete circle. You will find that the pivot point (screw block) is at the exact center of that circle. As the screw is turned, the screw block travels forward or backwards while always staying the same height, just as the axle of a car travels in a straight line as the wheel turns. To keep things from slipping, a rack (row of teeth) on the davit frame meshes with teeth on the inner edge of the quadrant as seen ---. The outer edge of the quadrant has a wider rim with no teeth. The weight of the boat forces the quadrant towards the centerline of the davit frame, ensuring the teeth always mesh, and the arm stays locked in position.
Note that all the diagrams only show a "half" chock, on the inboard side of the lifeboat, not an outboard one. This can be confirmed in most photos of Titanic.
There was a "sheath" covering the screws that can be seen on most photos and was obviously there to keep the screws as free from dirt and corrosion as possible. This appears to have been a permanent attachment, as photos show it in place in a variety of arm positions. There may have been a wire wound inside that kept it expanded throughout the arms' travel. You can make out a spiral structure in this photo.
The crank was stowed by removing it from the center drive shaft and turning it around backwards, so the end rested on one of the pulley mounts. The center of the crank was just a square hole that fit the square end of the shaft. It's unclear if the outer circular object opposite the handle is another hole for mounting the crank further from the center for more leverage or if it was a counterweight. To keep the crank from getting lost, there was a small chain connecting the crank to the davit frame as shown Figure 4 - 5 shows the ring. It may have turned with the drive shaft, eliminating the need to unclip it.
Finally, for those of you that have a hard time deciphering the diagram of the fork assembly on the davit end, I have removed all the extraneous lines from Fig 4/5 .