re being
carried out with them to determine the most efficient system of mooring
in the open, which will be discussed at some length in the chapter
dealing with the airship of the future.

RIGID AIRSHIP 23 X CLASS

During the early days of building the airships of the 23 class, further
information was obtained relating to rigid airship construction in
Germany, which caused our designers to modify their views. It was
considered a wrong policy to continue the production of a fleet of
ships the design of which was becoming obsolete, and accordingly within
ten months of placing the order for this class a decision was reached
that the last four ships were to be altered to a modified design known
as the 23 X class. As was the case with the ships of the preceding
class when nearing completion, they were realized to be out of date,
and special efforts being required to complete the ships of the 33
class and to release building space for additional larger ships, the
construction of the second pair was abandoned.

The main modification in design was the abolition of the external keel,
and in this the later Zeppelin principles were adopted. This secured a
very considerable reduction in structural weight with a corresponding
large expansion of the effective capabilities of the ship.

It has been seen that the purpose of the keel in No. 9 was to provide a
structure sufficiently strong to support all the main vertical bending
moments and shearing forces, and that in No. 23 this principle was
somewhat different, in that the keel in this ship was primarily
intended to support the distributed weights of petrol, water, ballast,
etc., between the transverse frames.

In this later design, namely, the 23 X class, it was considered that
the weights could be concentrated and suspended from the radial wiring
of the transverse frames and that the keel, incorporated in the design
of the former ships, could be dispensed with.

For all practical purposes, apart from the absence of the keel, the 23
X class of airship may be regarded as a slightly varied model of the 23
class. The main dimensions are nearly the same, and the general
arrangement of the ship is but little changed. The loss of space owing
to the introduction of the internal corridor is compensated by a
modification of the shape of the bow, which was redesigned with a
deeper curve. The hull structure was also strengthened by utilizing a
stronger type of girder wherever the g