STCW Advanced Fire Fighting (AFF)

Correct: Under 33 CFR Part 104, vessel personnel are required to control access to the ship and supervise the delivery of ship’s stores and maintenance equipment. Verifying credentials against a pre-approved list and inspecting incoming containers ensures that only authorized individuals enter and that no prohibited items are introduced into restricted areas during the high-activity maintenance period.

Incorrect: The strategy of granting contractors master-key access is a major security breach that compromises the integrity of restricted areas. Relying solely on the port facility for screening is insufficient because the vessel’s security personnel maintain an independent responsibility to protect the ship’s perimeter. Opting to suspend internal patrols creates a dangerous surveillance gap in a critical area, increasing the risk of sabotage or unauthorized modifications to ship systems.

Takeaway: Vessel security during maintenance requires rigorous identity verification and physical inspection of all contractor equipment at the point of entry.

Correct: Under maritime security regulations and the Ship Security Plan, security integrity must be maintained at all times, including during emergencies or drills. Emergency situations often create vulnerabilities where crew members are distracted, making it essential to ensure that access control and gangway monitoring are either continued or specifically accounted for through compensatory measures to prevent unauthorized boarding.

Incorrect: The strategy of deactivating access controls creates an unacceptable security risk by allowing unrestricted movement to sensitive areas without oversight. Relying solely on shore-side facility teams is inappropriate because the vessel maintains independent responsibility for its own security under federal maritime law. Opting to delay the recording of drill data fails to meet the regulatory requirement for timely and accurate documentation of all security-related training and exercises.

Takeaway: Security measures must remain operational or be compensated for during emergency drills to prevent exploitation of crew distraction.

Correct: Under the Maritime Transportation Security Act and 33 CFR Part 104, personnel with designated security duties are responsible for controlling access to the vessel. This requires verifying the identity of all persons seeking to board and ensuring their visit is authorized by the Ship Security Plan. Proper identification, such as a TWIC or other government-issued ID, must be checked against a manifest or expected visitor list to prevent unauthorized access.

Incorrect: The strategy of leaving the gangway unattended to notify an officer creates a significant security breach by leaving the primary access point vulnerable. Choosing to allow boarding based solely on appearance or equipment like safety vests is a failure of security protocol, as unauthorized individuals can easily use disguises. Opting to search only those without specific credentials like a TWIC is insufficient, as the Ship Security Plan may require various levels of screening for all individuals regardless of their documentation status.

Takeaway: VPDSD must strictly enforce access control by verifying the identity and legitimate purpose of every individual attempting to board the vessel.

Correct: In accordance with 33 CFR Part 104 and the Maritime Transportation Security Act (MTSA) framework, effective risk mitigation involves physical security measures such as controlling access points and maintaining active surveillance. Raising ladders and maintaining a continuous watch directly addresses the identified vulnerability of unauthorized boarding by creating physical barriers and ensuring early detection.

Incorrect: Relying solely on deactivating AIS is an incomplete strategy that may violate safety regulations and does not prevent visual detection by local threats. The strategy of conducting drills every six hours is likely to cause extreme crew fatigue, which significantly degrades overall security awareness and response capabilities. Opting to remove deck personnel from security duties ignores the necessity of ‘boots on the ground’ for visual lookouts and physical security checks in vulnerable areas of the ship.

Takeaway: Risk mitigation requires combining physical access controls with active surveillance to address specific vessel vulnerabilities identified in the Ship Security Plan.

Correct: Under 33 CFR Part 104, the Vessel Security Plan (VSP) dictates the specific intervals for testing and calibration of security equipment. These records must be kept for a minimum of two years to ensure the vessel remains in compliance with U.S. Coast Guard requirements.

Incorrect: The strategy of testing only during MARSEC level changes ignores the requirement for routine maintenance to ensure equipment readiness at all times. Focusing only on electronic sensors fails to account for the broad definition of security equipment, which includes physical access controls. Choosing to follow manufacturer guidelines over the VSP is incorrect because the VSP is the legally binding document approved by the Coast Guard for that specific vessel.

Takeaway: Security equipment maintenance must follow the Vessel Security Plan’s schedule, with all records kept for two years.

Correct: Under 33 CFR Part 104 and standard maritime security protocols, detection equipment is used to identify prohibited items. If an X-ray scan is inconclusive due to the density of the object or suspicious components like wiring, the item must not be allowed on board. The Vessel Personnel with Designated Security Duties (VPDSD) must maintain the security perimeter and escalate the matter to the Ship Security Officer (SSO) for a thorough physical search or further assessment before the item can be cleared.

Incorrect: The strategy of allowing the delivery driver to manipulate the contents could lead to the accidental or intentional triggering of a device if the item is hazardous. Relying solely on adjusting machine settings is insufficient when the initial scan indicates a potential threat that the technology cannot resolve. Choosing to move an unvetted, suspicious item onto the vessel for later inspection violates the core principle of preventing security threats from crossing the ship’s boundary while in port.

Takeaway: Inconclusive electronic screening results must lead to immediate denial of boarding and escalation to the Ship Security Officer for physical verification.

Correct: Under 33 CFR Part 104 and the ISPS Code framework, vessel personnel must control access and monitor the handling of ship’s stores and waste. This involves verifying the identity of any person seeking to board and ensuring that waste containers are not used to smuggle weapons, incendiaries, or unauthorized persons onto or off the vessel.

Incorrect: Focusing primarily on environmental logbooks addresses pollution prevention rather than the immediate security threat of unauthorized access. Relying on the Port Facility Security Officer to manage ship-side security duties ignores the vessel’s independent responsibility to maintain its own security perimeter. Opting to prioritize the weight of bins for billing purposes is an administrative function that does not mitigate the risk of smuggling or security breaches.

Takeaway: VPDSD must treat waste removal as a potential security vulnerability by verifying personnel identities and inspecting all containers for unauthorized items.

Correct: According to 33 CFR Part 104 and the ISPS Code, personnel with designated security duties must follow the communication protocols established in the Ship Security Plan. Immediate notification of the Officer of the Watch (OOW) ensures that the vessel’s command can assess the threat and escalate the security response if necessary. Maintaining continuous observation provides the bridge team with the real-time data needed to make informed tactical decisions regarding the vessel’s safety.

Incorrect: The strategy of waiting for a specific distance threshold before reporting fails to provide the bridge team with sufficient early warning to prepare a response. Opting to activate the Ship Security Alert System (SSAS) is inappropriate in this scenario because the SSAS is strictly reserved for situations where the security of the ship is under immediate and grave peril, not for initial investigations of suspicious craft. Choosing to deploy deterrents independently without authorization from the Master or Ship Security Officer violates the established chain of command and could lead to an unnecessary escalation of force.

Takeaway: VPDSD must prioritize immediate reporting through the internal chain of command to ensure a coordinated response to potential security threats.

Correct: Under 33 CFR 104.275 and the ISPS Code, vessel personnel must control the delivery of ship’s stores to prevent tampering and the introduction of unauthorized substances. This process requires a multi-layered approach including document verification against the manifest, physical inspection of the external packaging for anomalies, and positive identification of the personnel making the delivery.

Incorrect: Relying solely on a pre-approved vendor list is insufficient because it fails to account for the possibility of the delivery being intercepted or compromised during transit. The strategy of requiring the SSO to personally open every single box is an impractical use of senior officer resources and exceeds standard regulatory requirements for routine deliveries. Focusing only on a pallet count from a distance is a major security lapse as it does not allow for the detection of hidden prohibited items or signs of package tampering.

Takeaway: Vessel security during provisioning requires verifying documentation, inspecting for tampering, and confirming the identity of all delivery personnel involved in the process.

Correct: Under 33 CFR Part 104 and the Maritime Transportation Security Act (MTSA) framework, the vessel must control access at all times. The VPDSD is responsible for executing the Ship Security Plan (SSP), which requires positive identification of all individuals seeking to board. In U.S. jurisdictions, this specifically involves checking for a valid Transportation Worker Identification Credential (TWIC) or other approved government identification against the authorized crew manifest to prevent unauthorized access.

Incorrect: Relying solely on company uniforms or equipment is an insufficient security measure as these items can be easily forged or stolen by unauthorized actors. The strategy of delegating security responsibilities to third-party contractors like transport drivers is a violation of the SSP, as security duties must be performed by trained vessel or facility personnel. Focusing only on unrecognized individuals creates a significant vulnerability, as it bypasses formal verification protocols and relies on subjective memory rather than objective documentation.

Takeaway: Vessel personnel must verify the identity of all on-signing crew against authorized lists using valid credentials to ensure maritime security compliance.

Correct: Under 33 CFR 104.265, when the MARSEC Level is raised to Level 2, the vessel is required to implement additional protective measures identified in the Ship Security Plan. This specifically includes increasing the frequency and detail of screenings for persons, personal effects, and vehicles to provide a higher level of deterrence and detection during periods of heightened risk.

Incorrect: The strategy of suspending all shore leave and prohibiting visitors is typically a measure reserved for MARSEC Level 3 or specific extreme threats rather than a standard requirement for Level 2. Opting to transfer all screening duties to the port facility is incorrect because the vessel maintains its own regulatory responsibility to secure its perimeter regardless of the facility’s actions. Simply increasing the number of personnel at the gangway without actually intensifying the screening process fails to meet the legal requirement for enhanced security measures during an elevated threat level.

Takeaway: MARSEC Level 2 requires vessel personnel to implement intensified screening and search procedures for all individuals and items boarding the ship.

Correct: Under 33 CFR Part 104 and the ISPS Code, vessel personnel with designated security duties must immediately report all security threats or incidents to the Ship Security Officer. This ensures the vessel’s security organization can coordinate a response according to the Ship Security Plan and notify the Master or Company Security Officer as required.

Incorrect: Choosing to confront the individual directly can lead to unnecessary physical altercations and may compromise the safety of the crew member. The strategy of monitoring the individual without reporting allows a potential threat to progress further into sensitive areas of the vessel. Relying on finding a land-based guard in person results in a critical delay in communication and leaves the immediate area unmonitored. Focusing only on personal verification of credentials ignores the established internal communication chain required by federal maritime security regulations.

Takeaway: VPDSD must prioritize immediate communication of security threats to the Ship Security Officer through established internal channels.

Correct: Under 33 CFR Part 104, vessel personnel with designated security duties must follow the Ship Security Plan (SSP) to prevent the carriage of prohibited weapons, incendiaries, or explosives. Combining physical screening with behavioral observation is a standard security practice to identify both physical threats and potential human intent, ensuring that the security of the vessel is not compromised by overlooked items or suspicious behavior.

Incorrect: Relying on verbal confirmations from known crew members creates a vulnerability that can be exploited by coerced or radicalized insiders. Focusing exclusively on electronic devices fails to address a wide range of other prohibited items such as knives, firearms, or liquid explosives. Choosing to suspend searches due to weather conditions compromises the security perimeter and violates the mandatory screening requirements established in the vessel’s security framework regardless of the credentials presented.

Takeaway: Security inspections must be consistently applied to all individuals and items as specified in the Ship Security Plan to maintain a secure perimeter.

Correct: Under 33 CFR Part 104 and the ISPS Code, bulk carriers with low freeboard are particularly vulnerable to boarding via the sides or the anchor chain. A proper risk assessment must identify these physical vulnerabilities to implement effective deck lighting and watchkeeping as required by the Ship Security Plan.

Incorrect: Relying solely on electronic sensors like radar is insufficient because small wooden craft often have poor radar cross-sections and may not use AIS. The strategy of assuming shoreside patrols are enough fails to account for the ship’s responsibility for its own outboard security under the Ship Security Plan. Focusing only on the main gangway ignores the reality that unauthorized boarders frequently use climbing hooks or the anchor chain to bypass formal entry points.

Takeaway: Effective risk assessment for bulk carriers must prioritize physical vulnerabilities created by low freeboard and accessible mooring equipment or hawse pipes.

Correct: According to 33 CFR Part 104 and the Maritime Transportation Security Act (MTSA) framework, a Declaration of Security (DoS) is the primary tool used to coordinate security concerns between a vessel and a facility. When there is a mismatch in security levels, the DoS identifies specific responsibilities for each party to ensure all security gaps are addressed during the interface.

Incorrect: The strategy of automatically raising the vessel’s security level without SSO or Company Security Officer authorization ignores the established chain of command and regulatory protocols for level changes. Relying solely on the facility’s security team is a failure of the vessel’s independent responsibility to maintain its own security integrity as outlined in the Ship Security Plan. Opting to report the facility to the National Response Center is inappropriate because differing security levels are a recognized operational reality that should be managed through coordination rather than incident reporting.

Takeaway: A Declaration of Security (DoS) must be used to coordinate responsibilities when security levels differ between a vessel and a facility.

Correct: Under 33 CFR Part 104, internal audits must confirm that the Ship Security Plan is being implemented effectively. Maintaining detailed records of drills and exercises, including the resolution of any deficiencies found, is a mandatory regulatory requirement that demonstrates a functional and improving security system.

Incorrect: The strategy of leaving the Ship Security Plan in an unsecured location violates requirements for protecting Sensitive Security Information (SSI). Focusing only on physical access points is insufficient because a comprehensive audit must also evaluate communications, security equipment maintenance, and procedural compliance. Opting to delegate the entire audit to junior personnel without qualified oversight or independence undermines the validity of the review and fails to meet the standard for a professional security assessment.

Takeaway: Comprehensive documentation of security drills and corrective actions is essential for demonstrating regulatory compliance during maritime security audits.

Correct: Under 33 CFR Part 104 and the ISPS Code, security duties must be integrated into emergency response procedures. The Ship Security Plan (SSP) contains specific provisions for maintaining security during emergencies. This ensures that the distraction caused by a fire or medical crisis is not used by adversaries as an opportunity to gain unauthorized access or commit acts of sabotage.

Incorrect: The strategy of deactivating all access controls and leaving restricted areas open creates significant vulnerabilities that could be exploited by external threats during a crisis. Opting to cease all security monitoring entirely ignores the requirement that security must be maintained even during safety incidents. Relying on a remote Company Security Officer for tactical instructions during a fast-moving onboard fire is impractical and contradicts the established emergency procedures managed by the Ship Security Officer and the Master.

Takeaway: Vessel personnel must balance emergency safety responses with security protocols to prevent security breaches during periods of operational distraction or crisis.

Correct: According to 33 CFR Part 104 and the Ship Security Plan, vessel personnel must control access to the ship and monitor restricted areas. This involves verifying the identity of all persons seeking to board, checking baggage or equipment for dangerous substances, and ensuring that visitors only access areas necessary for their specific tasks.

Incorrect: Granting unrestricted movement between work areas and common spaces like the galley undermines the principle of access control and increases the risk of unauthorized entry into sensitive zones. Relying solely on the port facility for security screening neglects the vessel’s regulatory obligation to maintain its own security perimeter. Delaying security rounds until after the work is finished prevents the timely detection of security breaches or the introduction of unauthorized items during the maintenance period.

Takeaway: Security personnel must maintain strict access control and monitoring of external contractors throughout the entire duration of on-board maintenance activities.

Correct: Under 33 CFR Part 104, which implements the Maritime Transportation Security Act (MTSA) requirements, all unaccompanied baggage must be screened before being taken on board a vessel. This ensures that no prohibited items, such as explosives or weapons, are introduced into the secure areas of the ship, regardless of the MARSEC level.

Incorrect: Focusing only on manifest verification and visual inspection is insufficient because it does not detect concealed threats inside the baggage. The strategy of accepting baggage based on the reputation of a transport company is inadequate as it bypasses the vessel’s mandatory security screening protocols required by the Ship Security Plan. Opting for a time-delayed loading process is not a recognized substitute for active screening and fails to meet the regulatory standards for preventing the introduction of dangerous substances.

Takeaway: United States maritime regulations require that all unaccompanied baggage undergo thorough screening before being loaded onto a vessel at any MARSEC level.

Correct: In accordance with United States maritime security regulations and the Ship Security Plan, personnel must ensure that all deliveries are expected and verified. This involves checking the delivery manifest against the ship’s records and verifying the government-issued identification or TWIC of the personnel involved to prevent unauthorized access or the introduction of prohibited items.

Incorrect: The strategy of loading stores immediately without verification creates a significant security vulnerability by allowing potentially unauthorized items or persons on board. Relying on chemical swab tests for fuel hoses is not a standard first-step security requirement and does not address the primary concern of unauthorized access. Opting to contact the Coast Guard for a routine delivery escort is unnecessary for standard operations and does not fulfill the specific duties assigned to vessel personnel under the Ship Security Plan.

Takeaway: Vessel personnel must verify delivery documentation and personnel identification before allowing any provisions or bunkers to be transferred to the ship.

Correct: Direct bridge-to-bridge communication on VHF Channel 16 or 13 is the standard procedure under United States Coast Guard and FCC guidelines to coordinate safe passage. This allows the operators to exchange real-time information regarding the length of diver umbilicals or the presence of sub-surface equipment that may not be visible or reflected in electronic charts.

Incorrect: The strategy of using Digital Selective Calling for an urgency announcement is inappropriate for a standard approach and should be reserved for genuine safety concerns where life or property is in immediate jeopardy. Relying solely on Automatic Identification System data is insufficient because AIS does not provide the actual radius of the diving operation or the current status of divers in the water. Choosing to use high-frequency radiotelephony for local coordination is technically incorrect as HF is intended for long-range communication and would not facilitate immediate bridge-to-bridge safety coordination.

Takeaway: Direct VHF bridge-to-bridge communication is essential for coordinating safe passage when encountering vessels engaged in underwater diving operations.

Correct: Sea Area A4 is specifically defined as the area outside the coverage of geostationary satellites, typically located above 70 degrees North or below 70 degrees South latitude. In these polar regions, vessels cannot rely on Inmarsat and must utilize High Frequency (HF) radio or non-geostationary satellite systems like Iridium for distress and safety communications.

Incorrect: The strategy of identifying this as Sea Area A3 is incorrect because A3 is strictly limited to the coverage area of geostationary satellites, excluding A1 and A2. Focusing only on Sea Area A2 is a mistake as that area is defined by the range of Medium Frequency (MF) coastal stations, not polar regions. Opting for Sea Area A1 is technically inaccurate because A1 is restricted to the short-range coverage of Very High Frequency (VHF) coastal stations, usually within 20 to 30 nautical miles.

Takeaway: Sea Area A4 covers polar regions where geostationary satellite signals are unavailable, necessitating HF or polar-orbiting satellite equipment.

Correct: Under FCC and ITU regulations adopted by the United States, the Urgency signal PAN-PAN is used when a station has a very urgent message to transmit concerning the safety of a mobile station or a person. The correct GMDSS procedure requires an initial DSC announcement with ‘Urgency’ priority to alert watch-keeping receivers, followed by the voice transmission on the frequency specified in the DSC alert.

Incorrect: The strategy of using a Distress alert for a non-life-threatening steering failure is incorrect because Mayday signals are strictly reserved for situations involving grave and imminent danger. Focusing only on a Safety announcement is insufficient as Securite signals are intended for navigational or meteorological warnings rather than urgent vessel conditions. Choosing to bypass the DSC alert phase entirely is a procedural error that ignores the automated alerting requirements of the GMDSS framework, which ensures that other vessels’ equipment is triggered to monitor the priority message.

Takeaway: Urgency communications must be initiated with a DSC Urgency call followed by a voice message using the PAN-PAN signal.

Correct: FCC and USCG regulations require monthly self-tests using the designated test switch to ensure operational readiness without triggering a false distress alert. The HRU is a critical component of a Category I EPIRB that ensures the device floats free; it must be replaced by the expiration date indicated by the manufacturer to remain compliant with SOLAS and USCG safety standards.

Incorrect: Choosing to activate the EPIRB in the ON position even briefly is a violation of radio regulations and can cause unnecessary SAR resource deployment. The strategy of extending the life of an HRU through manual marking or visual inspection is unsafe because the internal release mechanism is subject to age-related failure that cannot be seen. Relying on water-submersion tests is improper as it risks accidental distress alerts and does not follow the manufacturer’s approved testing protocol. Opting to delay the replacement of life-saving equipment until a future survey date when the expiration occurs sooner compromises vessel safety and regulatory compliance.

Takeaway: Monthly EPIRB checks must use the self-test function, and hydrostatic release units must be replaced prior to their expiration date.

Correct: VHF Channel 06 (156.3 MHz) is internationally recognized and mandated by the ITU and USCG for on-scene search and rescue coordination. It is specifically designated for communication between ship stations and aircraft stations for safety purposes during SAR operations.

Incorrect: Relying on Channel 70 is ineffective because it is dedicated exclusively to Digital Selective Calling (DSC) data and cannot facilitate the necessary voice coordination. Choosing Channel 13 is incorrect as this frequency is primarily used for bridge-to-bridge navigational safety between vessels and is not the standard for aircraft-to-ship SAR operations. Opting for 2182 kHz is inappropriate for survival craft handhelds which operate in the VHF band and are not compatible with this medium frequency.

Takeaway: VHF Channel 06 is the primary frequency for on-scene search and rescue coordination between ships and aircraft stations.

Correct: Under GMDSS protocols, Digital Selective Calling (DSC) is the primary method for establishing contact with a specific station. In United States waters, VHF Channel 13 is specifically designated for bridge-to-bridge safety communications. Using the survey vessel’s Maritime Mobile Service Identity (MMSI) allows for an efficient, automated alert that does not congest the international distress frequency (Channel 16) unnecessarily while ensuring the target vessel receives the notification.

Incorrect: The strategy of using continuous blind transmissions on Channel 16 is incorrect because it creates excessive interference on the international distress and calling frequency. Opting for an Urgency message via Inmarsat-C is inappropriate because the situation does not yet involve an immediate threat to the safety of a vessel or person. Focusing only on AIS text messaging is insufficient for safety coordination as it is not a substitute for the mandatory GMDSS voice communication required for real-time maneuvering agreements.

Takeaway: Initiate contact using DSC on Channel 70 and conduct bridge-to-bridge safety coordination on VHF Channel 13 in United States waters.

Correct: Standard maritime practice requires using VHF Channel 16 for initial hailing or the designated safety watch frequency specified in the Coast Pilot or local regulations. Once the FPSO acknowledges the call, both parties shift to a working channel to keep the hailing frequency clear for other traffic and potential distress calls, ensuring efficient and safe coordination within the safety zone.

Incorrect: The strategy of using HF DSC for close-range maneuvering is inappropriate because High Frequency signals are intended for long-range communication and would cause unnecessary interference across a wide geographic area. Relying solely on AIS safety-related text messages is insufficient because it lacks the immediate, interactive feedback required for safe navigation and mooring operations near offshore structures. Choosing to activate an EPIRB for routine identification is a severe violation of FCC and international regulations, as these devices are strictly reserved for situations involving grave and imminent danger.

Takeaway: Initial contact with offshore units must occur on hailing frequencies before shifting to working channels to maintain safety and frequency discipline.

Correct: Automatic Repeat Request (ARQ) is the standard point-to-point communication mode for Radiotelex (NBDP). It uses a two-way handshake where the receiving station automatically requests the retransmission of any data blocks that contain errors. This ensures that the final received text is an exact, error-free copy of the original transmission, which is critical for medical or technical data.

Incorrect: Broadcasting via Forward Error Correction (FEC) mode is less reliable for sensitive data because it sends information in a one-way stream without a feedback loop to verify reception. The strategy of using Digital Selective Calling (DSC) for the full report is incorrect as DSC is strictly for short-burst alerting and channel assignment. Choosing to dictate long reports over voice frequencies is inefficient and prone to human error compared to automated digital printing systems.

Takeaway: ARQ mode in Radiotelex provides reliable, error-corrected point-to-point data transmission for critical maritime documentation when satellite systems are unavailable.

Correct: The detection range of a SART is primarily determined by the line-of-sight horizon, making the height of the antenna the most critical factor for successful radar interrogation.

Incorrect: Relying on a low mounting position on the floor of the craft significantly reduces the radar horizon and may cause the signal to be obscured by waves. The strategy of delaying activation until a visual sighting occurs risks missing rescue vessels that are scanning the area with radar. Opting for a horizontal orientation is incorrect because SARTs must be held vertically to maintain the correct polarization and omnidirectional coverage for radar interrogation.

Correct: Under the Vessel Bridge-to-Bridge Radiotelephone Act in the United States, towing vessels of 26 feet or over must maintain a continuous listening watch on VHF Channel 13 (156.650 MHz). This frequency is specifically designated for the exchange of navigational safety information between vessels to prevent collisions in navigable waters.

Incorrect: Using the international distress and calling frequency for routine tactical maneuvers is incorrect because it congests the channel meant for emergency alerts and initial contact. Attempting to use the digital selective calling frequency for voice communications is a technical violation of FCC rules as that channel is reserved strictly for data. Focusing only on the intership safety channel for all communications ignores the legal requirement to monitor the designated bridge-to-bridge safety frequency in US waters.

Takeaway: US regulations mandate a continuous watch on VHF Channel 13 for bridge-to-bridge safety during towing operations in domestic waters.