addition has been made to the internal metal air-cases. Most of the Class IIA lifeboats are now constructed on these lines.

The details of construction and method of obtaining the correct number of persons which can be allotted to this class of boat, are dealt with in Section D of Part IV.

Class IIB. Pontoon lifeboats having a well-deck and collapsible bulwarks.

The hull of this class of boat is constructed in the same way as a Class Ic lifeboat, the only difference being in the type of bulwark. To facilitate stowage the bulwarks of the Class IIB lifeboat hinge down on the deck.

FIG. 5.-Midship section of Class IIB pontoon lifeboat with well-deck and collapsible bulwarks.

Constructive details are dealt with in Section E of Part IV., and a midship section is illustrated in Fig. 5.

Class IIc. Pontoon lifeboats having a flush deck and collapsible bulwarks.

The general arrangement of construction is very similar to a Class IIB lifeboat, except that the latter possesses a well in the deck and the Class IIc has a flush deck. Efficient arrangements must be fitted for speedily clearing the deck of water. Two tons of water must be cleared from the deck of a boat 28 feet in length in 20 seconds, as compared with 60 seconds in a Class Ic or IIB lifeboat. Non-return valves or scuttles are fitted in the deck and bulwarks, the number of which depends on the experience gained from the flooding tests.

Details of construction are referred to in Section E of Part IV. Considerable care and oversight need to be exercised on the part of ships' officers and inspectors in keeping the pontoon lifeboats periodically under a close survey. Usually these boats are stowed in tiers, and very rarely come into the operation of boat drill. The influence of the weather has a detrimental effect on the watertightness of the hull, if the deck is of wood. Boats constructed of steel can more easily be divided and each compartment made independently watertight. Probably the decks of such boats are not subjected to the same damaging effect from the weather as the wooden boat, but the necessity of periodical survey for the prevention of corrosion is just as great in the steel boat.

FLUSH DECK

L.W.L

T

VERSE WATER TIGHT COMPARTMENT

FIG. 6.-Midship section of Class IIc pontoon lifeboat with flush deck and collapsible bulwarks.

The American Balsa Company, the successors to the Welin Marine Equipment Company, construct a large number of steel boats of this class, which are known as the "Lundin " Decked Lifeboat; Messrs. Mechan and Sons of Glasgow have also constructed boats of similar type for the Welin Davit Co.

Information dealing with freeboard and the method of obtaining the correct number of persons that can be assigned to a boat, is given in Section E of Part IV.

A midship section is shown in Fig. 6.

Class III.-Open boats which have not the buoyancy required for lifeboats of Class I.

The construction of this class of boat is identically the same as a Class IA lifeboat, with the one exception that buoyancy air-cases are not fitted. If it forms a part of the statutory

equipment of a vessel, it should be fully equipped in every detail as a Class IA lifeboat. This provision is often lost sight of by shipbuilders and boatbuilders.

THWART

FOOT SPAR (OR LOWER SCAT)

BILGE STRINGER

FIG. 7.-Midship section of Class III. open boat.

Further reference is made to this type of boat in Section C of Part IV.

A midship section is shown in Fig. 7.

SECTION C.-FORM, STABILITY, STRENGTH, AND CAPACITY, OF SHIPS' BOATS.

FORM.

It has been the aim of the author throughout the preparation of this text-book, to deal essentially with the practical application of the subject, and to avoid all abstruse theoretical considerations which would hinder the reader with a limited knowledge of the Science of Naval Architecture, from obtaining an intelligent grasp of the main features which have to be observed in determining a suitable form and general design, before commencing construction on a ship's boat which has to form part of the statutory equipment of a merchant vessel as a lifesaving appliance.

Practice and theory are inseparable, and both must be correlatively associated with any attempt to deal in detail with the present subject. It would be just as futile and useless to commence the building of a house, without previously taking the precaution of considering the suitability and strength of the foundation, as to discuss the practical details of ship or boat

building without due reference being given to the main theoretical investigations connected with the design.

Progress in all Engineering Science has been largely due to the personal initiative of the "investigator" who has given to the practical man in later years much financial advantage as one of the results of his work and devotion.

We should, therefore, not think lightly of theory in its relation to the subject of ships' boats, even if it can only be regarded as the "offspring" of the much larger and more important Science of Naval Architecture.

As far as this book is concerned theory has been given its . correct locus standi in the order of treatment.

During the past ten years there has been ample opportunity provided for students to become thoroughly acquainted with all the theoretical considerations associated with shipbuilding, through the medium of many excellent text-books written on the subject. The author has, therefore, kept this section of the treatise within defined limitations, with the exception of that portion which deals with initial stability and the influence of free water in a boat on its stability, and as these features have such a regulating influence on Form, the matter has been discussed at some length.

Form and Stability cannot actually be separated into two distinct sections for discussion: one is the outcome of the other.

Before determining the most suitable dimensions for a lifeboat in order that it may safely carry, in a seaway, the allotted number of persons, it is of importance that we should understand some of the salient features which influence the form of a

boat.

There has been too great a tendency in past years for certain boatbuilders to fine down the sections of their boats, in order to save material, and provide less work in the operation of planking. Keen competition in busy shipbuilding centres, without the existence of a recognised scheme of scantlings or minimum specification, has been responsible for many doubtful lifeboats being placed on board merchant vessels.

Very little consideration was given to the underwater form, and the common practice was to build the boat "to the eye without the use of even a midship section mould. A great deal depends on the way the garboards or sandstrakes and their adjacent strakes are worked, as to what measure of fullness the boat will take. If the rise of floor comes up too quickly to suit the breadth, or the bilge planking is worked in such a

manner as to narrow the beam of the boat, a too frequent use of shores has consequently to be made to preserve the form of the boat, to suit the specified dimensions. In the effort to save material and labour, suitability of form is often sacrificed for the convenience of working, and these objectionable practices make one often doubt the seaworthy qualities of the boat.

It is generally accepted among practical men, that in order to preserve efficient soleing of the plank landings, upon which the watertightness of a boat so much depends, and to maintain a parallel breadth for the landings, it is most essential that section moulds should be used at amidships and the quarter lengths.

The Life-saving Appliances Rules of 1913 insisted that in open lifeboats of Class I. (they were then known as Section A lifeboats) the boat's half-girth amidships, measured outside the planking from the centre line of the keel to the top of the gunwale, should be at least equal to eighty-eight hundredths of the sum of the boat's depth inside and half its maximum breadth amid3G ships, i.e. 88%, and that the mean of the half-girths B+ D measured in the same manner, at two points, one quarter of the length of the boat from the stem and sternpost respectively, should be at least equal to eight-tenths of the sum of the depth inside and half the maximum breadth amidships, i.e. G B+D

80%.

=

If a lifeboat did not comply with this girth rule, the number of persons to be carried was reduced, by dividing the capacity of the boat by the larger divisor 12 instead of 10, unless it was proved by actual test afloat, with the full equipment on board, that the boat had sufficient seating accommodation for the full number of persons, without interfering with the oarsmen.

With the 1914 issue of the Life-saving Appliances Rules, the girth rule was deleted, partly as a result of the recommendations of the Departmental Committee on Boats and Davits.

The girth rule, nevertheless, possessed an advantage which prevented the builder from fining away the ends of the boat after he had secured the correct depth and breadth at the midship section.

For some time there has been a unanimous expression of feeling among boatbuilders that there should be some definite rule or dimensions given, which would ensure a minimum fullness of form being maintained in open boats of Classes I. and III.