and 560 ft., if measured by Stirling's Rule, and in that case the buoyancy air-cases would have to be 54 or 56 cub. ft. and not 50 cub. ft.

Full details are given in the Rules for Life-saving Appliances, as to the correct method of obtaining the cubic capacity of open boats of Class I., which are as follows:

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The cubic capacity shall be determined by the following "formula:

"I denotes the length of the boat in feet, from the inside of "the planking or plating at the stem, to the corresponding point "at the sternpost; in the case of a boat with a square stern the "length is measured to the inside of the transom.

"A, B, C denote respectively the areas of the cross-sections at the quarter length forward, amidships, and the quarter length aft, which correspond to the three points obtained by dividing "I into four equal parts (the areas corresponding to the two ends "of the boat are considered negligible).

"The areas A, B, C shall be deemed to be given in square feet "by the successive application of the following formula to each of the three cross-sections :

"h denotes the depth measured in feet inside the planking "or plating from the keel to the level of the gunwale, or, in "certain cases, to a lower level as determined hereafter.

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“a, b, c, d, e, denote the horizontal breadths of the boat, measured in feet, to the inside of the planking at the upper and "lower points of the depth and at the three points obtained by dividing hinto four equal parts (a and e being the breadths at "the extreme points and c at the middle point, of h).

"If the sheer of the gunwale, measured at the two points "situated at a quarter of the length of the boat from the ends, "exceeds 1 per cent. of the length of the boat, the depth "employed in calculating the area of the cross-sections A or C shall be deemed to be the depth amidships plus 1 per cent. of "the length of the boat."

There are certain limitations to the depth used for calculating the capacity of an open boat of Class 1A, but these would be unnecessary if the dimensions of boats indicated in Table VII.

G

were worked to, as anything approaching 45 per cent. of the breadth for the depth, is considered by practical boatbuilders to be unsuitable for a rowing boat. The limitations referred to are as follows:

(a)" If the depth of the boat amidships exceeds 45 per cent. "of the breadth, the depth employed in calculating the area of "the midship cross-section B, shall be deemed to be equal to 45 per "cent. of the breadth, and the depth employed in calculating the "areas of the quarter length sections A and C, shall be obtained by "increasing this last figure by an amount equal to 1 per cent. of "the length of the boat, provided that in no case shall the depths employed in the calculation exceed the actual depths at these points.

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(b)" If the depth of the boat is greater than 4 feet, the number persons given by the application of these General Rules, shall "be reduced in proportion to the ratio of 4 feet to the actual depth, until the boat has been tested afloat with that number "of persons on board, all wearing life jackets, and the test has "proved satisfactory."

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The details in calculating the internal cubic capacity of an open boat of Class IA with dimensions 28′0'x8'5'x3'5' are shown on p. 83, and it will be seen that if twenty boats in one boat-yard are to be measured by Stirling's Rule and calculations made from the results, the operation is one which entails a great deal of labour. Life is too short for this rule to be constantly in operation. If a coefficient of form is recognised and check dimensions be applied to the forward and after quarter cross-sections to enable the boatbuilders to make suitable moulds, there would be very few occasions when it would become necessary to use the exact method of obtaining the capacity. The following rule would, therefore, become operative, viz:

(c) "The cubic capacity of a boat may be assumed to be the "product of the length, the breadth, and the depth, multiplied by "06 in cases where it is clear that this formula does not give a "greater capacity than that obtained by the above method (at "(a) and (b)). The dimensions shall then be measured in the "following manner :

"Length: From the intersection of the outside of the planking "with the stem to the corresponding point at the sternpost, or, "in the case of a square-sterned boat, to the after side of the

"transom.

Breadth From the outside of the planking at the point "where the breadth of the boat is greatest.

"Depth: Amidships, inside the planking from the keel to "the level of the gunwale, but the depth used in calculating the "cubic capacity may not in any case exceed 45 per cent. of the "breadth.

"In all cases the shipowner shall have the right to require that the cubic capacity of the boat shall be determined by "the exact measurement.'

When referring to the specimen calculation of the capacity of an open boat by Stirling's Rule, attention should be directed to the section of Fig. 23.

CALCULATION FOR INTERNAL CAPACITY OF AN OPEN BOAT OF CLASS I. Dimensions: 28°0′ × 8·5′ × 3'5′.

PART III

SECTION A.-TIMBER: CONVERSION, SEASONING, DISEASES, SELECTION, STRENGTH, ETC.

THE first British writer to give the benefit of his investigations by publishing a treatise on the subject of "Timber" was in the year 1664; and since that date a great wealth of information has been collected, as a result of experimental and research work, by many eminent and distinguished experts.

In the days of wooden shipbuilding, the subject of timber was one that attracted the attention of some of the best scientists of that period, particularly with reference to its treatment in order to prevent decay, and to increase the lasting qualities of a vessel.

Of recent years valuable help has been given to shipbuilders and other traders associated with the use of wood, by the publication of text-books containing the results of the practical experience of such authors as Professor Marshall Ward, D.Sc., Mr. T. D. Laslett, Mr. J. R. Baterden, and, more recently, Mr. Webster who has devoted his attention to British home-grown timber.

If students wish to advance their knowledge of the subject, they are recommended to read the published works of these authors.

It is not the intention of the writer, in the present section, to enter into any great detail on the physiology of trees, but only to collect a few salient features of the subject, combined with the result of some practical experience, which may help in the investigation of the best methods to be used in selecting, preserving, and working timber into the construction of ships' boats.

As an Empire and a Nation the "Great War" has taught us many things, and the urgency of forestry development, as one of the problems in the national reconstruction scheme, is of the greatest importance.

In proportion to its size Great Britain has less woodland than

any other country in Europe with the exception of Portugal, and imports more timber than any other country in the world.

To increase our own national resources and make this country independent of such a volume of imported timber, it is considered by experts that it will be necessary to afforest at least 1,500,000 acres.

During the European War we felt the difficulty very acutely in not having sufficient seasoned material to meet one-twentieth of the demand. Substitutes have been found to meet the urgency, but the subject is one of the greatest importance for future.

consideration.

Growth of Timber. If we examine the cross-section of a balk of timber we see that it is made up of three distinct portions,

viz. the pith at the centre of the tree, the heartwood, and the sap. The tree appears to be bound together in its structure by a number of layers or annual rings, which vary in thickness, being narrower at the centre and becoming wider towards the outer surface. Each of these layers are made up of two distinct parts (see Fig. 24), the lighter and larger being the spring-grown wood and the darker being the autumn wood, the latter being much harder than the former.

We are thus able to approximate to the age of the tree by the number of annual rings. A layer may vary in thickness owing to one portion of the tree having a better situation than the other. Trees grown in high altitudes do not show such a distinct contrast between the spring and autumn wood, but where there are rapid changes in the seasons, the contrast is magnified. In tropical countries the rings appear to run into one another.