It will, I think, be useful to consider the principal factors that
govern the dimensions of boats forming part of the life-saving apparatus
in merchant ships.
The minimum number and capacity of boats are determined by the
regulations, and the capacity is determined by the product of the
length, breadth, and depth of the boats. As the space on the ship in
which to stow the boats is generally limited, it is generally found
easier to increase their depth than the length or breadth, and this is
further encouraged, I believe, by the cost of boats being quoted at so
much per foot in length. The builder or owner determines the dimensions
of the boat; the boatbuilder is concerned merely with the construction
and, in most cases, usually their form or lines.
Attention has been called by the mark lane surveyors to the form and
proportions of the boats used in the Royal navy. The proportion of depth
to breadth is greater than is apparent from the particulars given, as
all boats larger than a 30-foot gig have 6-1/2-inch washboards above the
gunwale, and even the gigs and many of the smaller boats have portable
washboards. It must also be remembered that all the navy boats are
square-sterned, except the whaleboat, and are designed with easy lines
so as to make good sailers; no air cases are fitted, and the seats are
kept very low. The boats are not provided simply as life-saving
appliances; as a matter of fact, the life-saving equipment of a warship
is extremely small. It is true that each type of boat is given a certain
"life-saving capacity," which is ascertained by crowding in as many men
as practicable with boat in still water and all equipment on board. This
number agrees closely with that obtained by the board's rule L × B × D ×
.6/8. These boats, moreover, have a much smaller freeboard than is
considered desirable in the merchant navy; but the occupants are all
under discipline and in charge of experienced seamen. In the mercantile
marine it may, and often does, happen, that the boats are crowded with
panic-stricken men, women, and children, and instances have occurred, I
believe, wherein there has not been a single man in the boat who has
ever handled an oar before. Having these points in view, I do not agree
that the navy type of boat is the most suitable for our purpose.
The chief desiderata in a ship's boat as a life-saving appliance are,
(1) to carry the maximum number of people without overcrowding; and with
(2) a reasonable amount of stability and freeboard; (3) and without
undue interference with the use of oars.
(1) Is almost wholly dependent on the length and breadth of the boat;
provided (2) is satisfied; depth has very little influence on it. For
example, take a boat 30 × 9 × 3.5, 567 cubic feet by our rule, as a
section (D) or (E) boat it should carry 567/8 = 72 people; such a boat
should allow 30 × 9 × 8/72 = 3 square feet of area per person at the
gunwale, which should be ample if all sit in the bottom who can not find
seating room on the side benches or thwarts.
(2) Stability and freeboard are dependent upon the boat's breadth,
depth, and form. The element of length does not enter into it, and it
would be most unreasonable to limit the ratio of length to breadth, as
suggested from Liverpool, or to limit the depth to the cube root of the
length, as proposed by one of the London surveyors. Mr. Gemmell gives
particulars, M. 26,298, of four boats tested, which proved to have ample
accommodation and stability for the complements allowed by the
regulations; the ratio of depth to breadth varied from 0.41 to 0.45.
Capt. O'Sullivan also reported five boats which he tested with ratios of
D to B, varying from 0.4 to 0.44, all except one being satisfactory, the
exception being rather tender and overcrowded, due to poor lines. The
freeboards of all these boats when loaded were, I think, sufficient.
The depth in no case exceeded 3.6, and only in one case did the ratio
exceed 0.44.
The surveyors, Liverpool, tested a boat 3.75 deep and having a ratio of
D/b = 0.41, which proved satisfactory.
Capt. Griffiths tested a boat 4.1 deep, having a ratio D/b = 0.455,
which he considered to be unsafe with the full complement on board.
The consensus of opinion is that the depth should not exceed 3 feet 5
inches or 3 feet 6 inches, and the ratio of D/b should not exceed 0.44.
This, however, is not sufficient to guarantee sufficient seating and
stability. Capt. Clarke tested a boat 24.4 × 6.55 × 2.45, which was very
unsafe with the rule complement on board. The ratio D/b is only 0.38 in
this case. It will be seen, however, that this craft has exceptionally
fine lines and is evidently quite unsuited to carry the rule complement.
It is quite evident that the form of the boat must be taken into
account.
The dimensions of boats vary so greatly that generally the boat builder
builds his boats "to the eye," using only a midship mold; it follows
that the forms of boats of the same dimensions will vary considerably
and with different workmen. Something more is required than a limitation
in the ratio of depth to breadth. It is desirable that the sheer should
be ample, and the form not unduly fined away within the midship half
length. From consideration of the particulars and lines of the boats
mentioned in the surveyor's reports, I think a simple rule to regulate
the form may be devised such as I will indicate later.
It is, I think, necessary to limit the depth as a factor for
ascertaining the number to be accommodated. The increase of depth beyond
a certain point, while unduly increasing the number of people that may
be carried, increases proportionately the required air case capacity, to
meet which the seats have to be raised with a corresponding increase in
the height of the center of gravity and decrease in the stability and
difficulty in rowing. A boat 3.6 deep would have the thwarts about 3
feet above the bottom, and any increase in this height makes it very
difficult for any ordinary man to row when sitting down. In rough sea
the men would have very little control over the oars if standing up. A
further objection to the very deep boat is its small stability in the
light condition. It is not, I believe, an unusual occurrence for such
boats to capsize in rough weather, before the passengers or crew can be
got into them, and I have myself seen such a boat capsize in dock with
only two men in it; due to lumpy water and a stiff breeze catching it on
the beam when coming out of the shelter afforded by the dock wall.
I do not think, however, any limit of depth should be imposed, except as
a measure of capacity. Any rules that may be devised should be such as
are of easy and ready application, and which will not bear harshly on
the boats that have already been accepted. I therefore suggest that the
present rules will sufficiently meet the case, with the following
modification.
In no case should the depth to be used in general rule (2) exceed 3.6
feet and 45 per cent of the breadth. In all cases where the actual depth
is 45 per cent of the breadth or less, the maximum number of persons, as
ascertained by rule (3) should not be allowed unless the boat has been
found capable of carrying that number by actual test in the water, or
unless the boat has at least 1/2 inch of sheer per foot of length, and
the half-girth amidships, measured outside the plank, from the side of
the keel to the top of the gunwale, is at least 90 per cent of the sum
of the depth and the half breadth, and the mean of the half girths as
similarly measured at one quarter the boat's length from the stem and
stern post are at least 80 per cent of the sum of the midship depth and
half breadth.
The thwarts and side benches should be kept as low as practicable, and
the bottom boards should be so fitted that the height of the thwarts
above them will not exceed 2 feet 9 inches.