Collision Regulations - Clarification of the term “rigidly connected in a composite unit”
Table of Contents
Rule 24 – Towing and Pushing
- When a pushing vessel and a vessel being pushed ahead are rigidly connected
in a composite unit they shall be regarded as a power-driven vessel and exhibit
the lights prescribed in Rule 23.
Rule 35(f) - Sound Signals in Restricted Visibility
- Requires a pushing vessel and a vessel being pushed ahead, when rigidly
connected in a composite unit, to give the same signals as a power-driven
vessel instead of the signals of a vessel engaged in towing or pushing another
Collision Regulations (continued)
Responsibility Between Vessels:
- Under the Rule 18 of the Collision Regulations, there is no distinction
made between a power-driven vessel and a vessel pushing another
- Therefore the difference in light arrangements between a power-driven
vessel and a vessel pushing another vessel does not impact on one
vessel's responsibility to keep clear of the other.
Issue - What is Rigidly Connected?
- A Marine Safety Tug and Barge Working Group, formed to examine the
status of Tug and Barge operations and regulations in Canada reported in
“It is recommended by the WG that a common definition of terms
be used nationally. Such terms as articulated, integrated, combination,
rigidly connected etc has led to misunderstandings and confusion.”
- CMAC discussions on clarifying the term “rigidly connected in a
composite unit” dates back to 2006
- There is a wide variety of connection methods used for tug and barge
pushing operations, ranging from simple to very complex systems.
- Connection using winches, hawsers and/or chains.
- Some with a special bracket or designed with a stern notch to help hold the tug
- Notches vary considerably in their depth relative to the tug length and in their design.
- Mechanical means: use of clamps, hydraulic rams or pins that apply pressure,
engage holes, teeth or notches and various other solid mechanical connections.
- Almost all are designed to allow some relative movement between the tug
and the barge i.e., independent pitching.
- Without a common understanding, the navigation lights exhibited by vessel
engaged in pushing operations will continue to be inconsistent.
US - Interpretation
US Navigation Rules Interpretation:
- A “composite unit” is interpreted to be a pushing vessel that is rigidly
connected by mechanical means to a vessel being pushed so they
react to sea and swell as one vessel. “Mechanical means” does not
include the following: a) lines, b) hawsers; 3) wires; 4) chains.
Pushing vessel and vessel being pushed: Composite Unit:
- 33CFR 82.3. and 90.3.
Previous CMAC Proposal
Tug and Barge Working Group (April 2010)
- The term “rigidly connected” when determining whether or not an integrated
tug/barge unit is a “composite unit” means that, a Push mode or Dual Mode
Integrated Tug Barge, when manoeuvring, does so as a single vessel, without
“perceptible relative motion” between the tug and the barge.
- “Perceptible relative motion” should be read to mean relative between the tug
and barge in the athwartship direction of the horizontal plane such that a
meeting vessel would be mislead as to the relative heading between itself and
the approaching composite unit.
- To take into account practical and operational considerations, it would be
necessary to deviate from the regulations with respect to the placement of the
forward masthead light and sidelights.
Standing Committee on Navigation and Operations (November 2010)
Comments on the April 2010 T/B WG proposal:
- Interpretation may not provide sufficient clarity such as, the term
“perceptible”, leading to further inconsistencies
- Would not be consistent with U.S. interpretation for “composite unit”
- Most ATBs exhibit lights of a tug pushing a barge, not as “composite
- Proposal would require in many cases deviations from Collision
Regulations technical requirements due to practical considerations (i.e.,
forward masthead light height, vertical separation and position in
relation to the sidelights).
- There does not appear to be any compelling safety advantage for a tug
and barge pushing combination to exhibit one set of lights over the
- Exhibiting lights of a single power-driven vessel, with its two mast head
lights, might be considered more readily identifiable to some, or that it
provides a greater indication of the vessel's aspect.
- However, being able to differentiate between a tug pushing a barge from a
single vessel provides useful additional information to other vessels in the
- To persons familiar with the Collision Regulations, both light arrangements
facilitate vessel detection and collision avoidance.
- The term "rigidly connected" in the Collision
Regulations means that the connection results in
there being no relative motion between the pushing
vessel and the vessel being pushed ahead.
Advantages of New Interpretation
- Consistent with the U.S. interpretation.
- Consistent with common industry practice where ATBs are not considered
- Easier to implement without creating additional regulatory exemptions from the
- Clearer interpretation resulting in greater consistency.
- Ensures correct positioning of lights, in accordance with positioning and
technical requirements of Annex 1, Collision Regulations.
- No relative movement or misalignment of navigation lights during the voyage.
- Tug/Barge arrangements that have such a connection will almost certainly have
similar operating characteristics of a power-driven vessel in all circumstances.
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