What traffic management service is operated by the U.S. Coast Guard in certain designated water areas to prevent ship collisions, groundings and environmental harm?

Vessel Traffic Service (VTS).

US Coast Guard provides the VTS service. The Vessel Traffic Service (VTS) actively monitors and communicates instructions to ships passing through congested or smaller waterways. The service consists of surveilled and non-surveilled monitoring.

For concise yet comprehensive description, please see US Coast Guard VTS services for vessels

US Coast Guard VTS Info

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What is a bridge-to-bridge station?

A VHF radio station located on a ship’s navigational bridge or main control station that is used only for navigational communications.

Bridge = navigational bridge or control station.

Code of Federal Regulations, Title 47 Chapter I Subchapter D Part 80 Subpart A General § 80.5 Definitions:

47 CFR 80.5 “Bridge to bridge station” A radio station located on a ship's navigational bridge or main control station operating on a specified frequency which is used only for navigational communications, in the 156-162 MHz band.

Bridge to bridge implies two bridges communicating with each other regarding navigations.

When a ship uses port operations service, the messages can be only of navigational communications, using frequencies in the 156-162 MHz band.

YouTube Video: The Sailing Vagabond Epicurean has a good overall video worth watching called VHF - An interview with the US Coast Guard and some basic procedures

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When may a bridge-to-bridge transmission be more than 1 watt?

When broadcasting a distress message and rounding a bend in a river or traveling in a blind spot.

To promote safety, FCC permits exceeding the normal power limit when it will prevent unsafe condition that could result in the loss of life and/or damage to property.

Radio wave propagation is affected by atmospheric, topographic, and other conditions. Increasing the radiation power may help reaching other entities.

Code of Federal Regulations, Title 47 Chapter I Subchapter D Part 80 Subpart H - Frequencies

47 CFR 80.373(f) Footnotes to Frequencies in the 156-162 MHz Band:

4 Use of 156.875 MHz is limited to communications with pilots regarding the movement and docking of ships. Normal output power must not exceed 1 watt.

5 156.375 MHz and 156.650 MHz are available primarily for intership navigation communications. These frequencies are available between coast and ship on a secondary basis when used on or in the vicinity of locks or drawbridges. Normal output power must not exceed 1 watt. Maximum output power must not exceed 10 watts for coast stations or 25 watts for ship stations.

18 156.575 MHz is available for port operations communications use only within the U.S. Coast Guard designated VTS radio protection area of Seattle (Puget Sound) described in § 80.383. Normal output power must not exceed 1 watt. Maximum output power must not exceed 10 watts.

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When is it legal to transmit high power on Channel 13?

All of these.

• Failure of vessel being called to respond.
• In a blind situation such as rounding a bend in a river.
• During an emergency.

To promote safety, FCC permits exceeding the normal power limit when it will prevent unsafe condition that could result in the loss of life and/or damage to property.

Code of Federal Regulations, Title 47 Chapter I Subchapter D Part 80 Subpart H - Frequencies

47 CFR 80.373(f)

Channel 13
Ship transmit 156.650 MHz
Coast Station 156.650 MHz

Footnote to Frequencies in the 156-162 MHz Band:

5 156.375 MHz and 156.650 MHz are available primarily for intership navigational communications. These frequencies are available between coast and ship on a secondary basis when used on or in the vicinity of locks or drawbridges.

Normal output power must not exceed 1 watt. Maximum output power must not exceed 10 watts for coast stations or 25 watts for ship stations.

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A ship station using VHF bridge-to-bridge Channel 13:

May be identified by the name of the ship in lieu of call sign.

Code of Federal Regulations, Title 47 Chapter I Subchapter D Part 80 Subpart C - Operating Requirements and Procedures

§ 80.102 Radiotelephone station identification.

47 CFR 80.102(c) Ship stations transmitting on any authorized VHF bridge-to-bridge channel may be identified by the name of the ship in lieu of the call sign.

The traditional parlance when identifying is the Vessel Name; and has been for thousands of years.
Radios have callsigns. Ship with a radio has both a Vessel Name and a Callsign.

For more info, please see US Coast Guard article on U.S. VHF Channel Information

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The primary purpose of bridge-to-bridge communications is:

Navigational communications.

From FCC article on Ship Radio Stations

"NAVIGATIONAL - (Also known as the bridge-to-bridge channel.) This channel is available to all ships.
Messages must be about ship navigation, for example, passing or meeting other ships.
You must keep your messages short.
Your power output must not be more than one watt.
This is also the main working channel at most locks and drawbridges."

For more details, please see:

47 CFR 80.371(c) Working frequencies in the marine VHF 156-162 MHz ban

47 CFR 80.373(f) Frequencies in the 156-162 MHz Band

Bridge-to-bridge communications occur between the navigational bridges of two vessels. Thus, these communications are almost always related to navigation or safety.

All the other options imply intraship communications and would therefore not constitute bridge-to-bridge communications.

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