BOAT HANDLING ARRANGEMENT.

The laws of the principal maritime nations require that not only shall a stated number and kind of boats, lifeboat and working, be installed on board ship, varying of course with the particular requirements of the vessel itself and the trade in which it is employed, but also that these boats shall be efficiently installed on board ship and conveniently arranged with proper boat handling appliances.* To comply with these enactments various arrangements are adopted suited to the special conditions which obtain in the particular vessel, ranging from the simple single davit handling a 10-foot dinghy slung on a single span, usual in harbor tugs and similar craft, to the row of lifeboats on a modern liner handled by steam or electric hoisters, while on the larger war vessels nests of boats are stowed and operated by special electric driven boat cranes or large derrick booms.

Before an arrangement of boat handling appliances can be laid out the special requirements governing the particular case as to number and type of boats must be considered and also the kind of davit decided upon. As already stated the rules and regulations of the hailing country and the trade will determine the former. The kind of davit suitable if the vessel be in the ocean passenger trade is restricted to two or three varieties as shown by the arrangements in the figures, these consisting of the ordinary rotating davit, the Mallory type or the Welin quadrant davit, the latter being an excellent davit but of course slightly more costly than the others, the cheapest and most convenient where there is room to install being that known as the Mallory davit.

Rotating Davits. This is the most common type of davit used on shipboard. The davit and method of installing are shown by Fig. 242, but, of course the heelstep and bearing are susceptible of many variations to suit individual cases or local conditions. The required diameter suitable for a given weight of boat may be calculated by the equation WX a= D3f; by transposing we get diameter,

Wa

π

32

D =

П

32

*For these requirements see "Inspectors of Steam Vessels, U. S.," "Board of Trade Rules and Regulations."

ROTATING DAVIT.

FIG. 242.

the lever a, or outreach of davit, being measured with the ship inclined 10 degrees. Where the ship is intended for Lloyd's classification the formula used as required by their Rules is practically similar to the foregoing, but is differently expressed to make it more convenient of application where actual weights of boats are not at hand and to ensure uniformity of requirements. Lloyd's formula is:

where L, B and D are the length, breadth and depth respectively of the boat, H is the height of the davit above its uppermost point of support, and S is the spread of the davit; each of these dimensions being in feet.

The value of the constant term C is to be as follows:

1. When the davit is to be of wrought iron and of sufficient strength to carry the boat, its equipment and a sufficient number of men to launch it, the value of C is to be 144.

2. When the davit referred to in (1) is to be of wrought ingot steel of from 28 to 32 tons per square inch tensile strength, the value of C is to be 174.

3. When the davit is to be of wrought iron and of sufficient strength to safely lower the boat fully equipped and carrying the maximum number of persons for which it is intended, the value of C is to be 82.

4. When the davit referred to in (3) is to be of wrought ingot steel of from 28 to 32 tons per square inch tensile strength, the value of C is to be 99.

The mountings on these davits comprise belay cleat, fairlead sheave, spectacles for span and guys, the span being clipped with sister hooks at one end and shackle on the other, and the guys shackled to spectacle and set up on deck with either lanyard or turnbuckle. On lifeboat davits, it is also obligatory to secure to davit head, lifelines of say 2-inch manila, long enough to reach to waterline and also a rope ladder from span. Where the davits operate the emergency boat (slung outboard at sea), a pudding boom should be lashed to davits suitably padded in wake of chafe to which the boat gripes are secured.

Suitable tackling for falls are readily determined from the weight of boat.*

In first class practice the cast-steel bearing is bushed with composition either gun metal or babbit and a conical disc of hard steel is inserted in the heelstep, these additions reducing the friction with a consequent acquisition to the ease of operation.

* For tackles see Knight's "Seamanship" or "The Naval Constructor."