Page 115 - Practical Ship Design

82 Chapter 4

The following items of steelwork which are more usually bought from a
subcontractor are generally included in the outfit weight and for consistency this
should remain so even if for a particular ship they have been fabricated by the
shipyard itself
- sternframe, rudder, rudderstock, shaft brackets and similar structures whether
these are castings or fabrications;
- steel hatch covers for cargo hatches (covers for access hatches are, however,
usually in the structural weight);
- bollards and fairleads.
Within the outfit weight, two other items which can cause demarcation diffi-
culties are plumberwork and electrical work -systems which are partly in and
partly out of the engine room. The demarcation here usually divides the systems at
the engine room bulkheads or engine casings. Everything outside the engine room
is taken as hull outfit and everything within as machinery weight, with the same
demarcation generally applied when writing the specifications of these systems.
There are a number of other items part of which is often fitted within the engine
room which for simplicity are usually dealt with wholly as hull items: refrigerating
machinery whether for cargo, stores or HVAC; sewage systems; watertight doors;
casing insulation and paint.

4.2 STRUCTURAL WEIGHT APPROXIMATIONS

4.2. I Lloyd’s equipment number method

In the author’s 1962 paper, the use of Lloyd’s equipment numeral was advocated
as a basis for estimating steel-weight in preference to the numerals L x B x D or
L(B + D) which were in common use at that time.
The reasons given for this were that the equipment number introduced allow-
ances of approximately the correct order for changes in draft and in the extent of
erections, and avoided making the choice of the deck to which D was measured as
critical as it is with both the other numerals.
The Lloyd’s equipment numeral (E) of 1962 is no longer in use for the
determination of ship’s anchors and cables, hawsers and warps; it was replaced in
1965 by a new numeral, which is now common to all classification societies having
been agreed to be a more rational measure of the wind, wave and current forces
which act on a vessel at anchor. The new numeral, however good it is for its
primary purpose, is not a suitable parameter against which to plot steel-weights,
but the reasons given for the use of the old numeral still stand. For those not
familiar with the old E number, the formula for this is as follows:
E 1 L(B + 7‘) + 0.85 L(D - 7‘) + 0.85( (E, . h,) + 0.75{ (E, . h2) (4.1)