1. The definition of "vessel" used in Rule 3 would appear to encompass these
dynamically supported craft either in existence or envisaged in the
foreseeable future.
2. Where difficulty would be experienced in complying
completely with Rule 1(e) Administrations
have the right to decide upon the degree of exemption permitted.
3. The term "hearing" in Rule
5 may be impracticable for dynamically supported craft due
to their own high self-generated noise level and/or enclosed operating
positions. This also applies to Rule 19(e).
Because of this, Administrations should ensure that adequate compensatory
features are present on the craft (e.g. clear view from operating
position, carriage of radar, etc.).
4.
Rule 23(b) requires
an air-cushion vehicle to carry an all-round flashing light. As it
is accepted that the carriage of this light should be reserved for
craft capable of operating at high speed and whose aspect may not
necessarily indicate its true direction of travel, it may be necessary
at a future date to apply this section to other forms of dynamically
supported craft (e.g. ram-wing craft). Due care should be exercised
in the positioning of this light due to its possible cause of "stroboscopic"
sickness to operating crews.
5. The permanent fixture of a bell, and possibly
gong, required by Rule 33 is generally
impracticable when applied to dynamically supported craft. Such devices
should be portable and only fixed in position when required to be
used.
6. When there is a high self-generated noise level
of those dynamically supported craft propelled by airscrews, it should
be possible to conduct practical tests to ascertain the audibility
range. Where this is less than the figures given in Annex III, paragraph 1(c) then the craft's whistle
must be used under those circumstances stated in the Regulations.
7. The term "height above the hull" used in the
definition of Annex I may be difficult
to interpret for dynamically supported craft. In deciding what constitutes
such height, the datum so chosen should be clearly indicated on any
document issued by an Administration in respect of the navigation
lights.
8. The height of the white masthead light related
to beam as quoted in the Regulations is most probably based on normal
ship length/beam ratios of the order of 5 to 8. Whereas with dynamically
supported craft, especially air-cushion vehicles, the length/beam
ratio may be in the range of 1.5 to 2.5. As a result of this, for
ships, if the height of the white fore mast light is related to the
beam of the vessel as required by paragraph
2(a) (i) of Annex I and the side lights are placed at the maximum
height allowed by paragraph 2(g) of
that same Annex, the base angle of the isosceles triangle formed by
these lights when seen in end elevation will be approximately 27 degrees.
Whilst not explicit in the Rules, it is assumed that this is the minimum
angle desirable. For air-cushion vehicles, however, it would be possible
for this base angle to be 14 degrees or less. Consequently, it is
considered desirable that Administrations, by exercising the privilege
granted by Rule 1(e), allow relaxation
for dynamically supported craft from the height/breadth relationship
of the white masthead light given in paragraph
2(a) (i) of Annex I, providing:
- the height of the white masthead light gives the specified range;
- the base angle of the isosceles triangle formed by the white masthead
light and side lights, when seen in end elevation, is not less than
27 degrees;
- other Rules concerning lights are complied with as appropriate.
9. On dynamically supported craft of 50 metres
or more in length, the vertical separation between fore mast and main
mast light of 4.5 metres required by paragraph
2(a) (ii) of Annex I may be unduly onerous. It is suggested
that this figure may be modified by use of the following formula which
takes into account paragraph 2(b) of
Annex I:
where y is the height of the main mast light above the fore
mast light in metres;
|
a |
= |
is the height of the fore mast light
above the water surface in service condition in metres; |
|
ψ |
= |
is the trim in service condition
in degrees; |
|
C |
= |
is the horizontal separation of
masthead lights in metres. |