Module 4 - Channels & Frequencies
Inter-ship and Working Channels
What you will learn
Move a ship-to-ship call from identification into a suitable inter-ship channel without turning a remembered channel list into a universal rule.
Inter-ship traffic should use an appropriate inter-ship allocation after contact. The reliable habit is to select or accept a suitable channel, not to recite one fixed list for every area and service.
If the other vessel's MMSI is known, MCA guidance gives an Individual DSC routine call that indicates the proposed inter-ship channel. After acknowledgement, the conversation starts on that channel. If the MMSI is unknown, make the brief low-power voice call on Channel 16 and move once contact is established.
A channel shown as inter-ship on one current channel plan may be restricted, unavailable or assigned differently in another jurisdiction. Check current local information and the radio's channel plan; do not assume that every numbered channel works identically everywhere.
Keep the working exchange purposeful. Identify both stations, pass the necessary information, use low power first for nearby routine traffic and end cleanly so both vessels can restore their required watch.
Make a known-MMSI routine rendezvous call
Two club yachts have exchanged MMSIs ashore and need to confirm a routine meeting point after departure.
1. Propose
Use an Individual DSC routine call and select an appropriate inter-ship channel from the current plan.
2. Confirm
Wait for the acknowledgement and check the accepted voice channel on the display.
3. Complete
Pass the short rendezvous information, close the exchange and restore the required watch.
Sense check: A known MMSI provides a selective digital route; it does not make the selected working channel suitable without checking its purpose.
Common mistake or limitation
- Keeping a routine ship-to-ship conversation on Channel 16 after contact.
- Using Channel 70 for the voice conversation because the DSC call was sent there.
- Treating a familiar inter-ship channel number as valid in every area without checking the current plan.
Recap
- Known MMSI: use an Individual DSC routine call and propose a suitable inter-ship channel.
- Unknown MMSI: call briefly on Channel 16 using low power first, then move.
- Check the current allocation and restore the watch after the exchange.
Optional quick check
Section 5 of 9
You know the other yacht's MMSI. Which routine sequence best protects Channel 16?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
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