If this is rule 35 (h), there is no mention of “optionalâ€
Deck
Rules of the Road: BOTH INTERNATIONAL & INLAND A 200-meter vessel is aground in restricted visibili...
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ElJefe; Review the last line of 34(h)..."A vessel aground shall give the bell signal... A vessel aground may in addition sound an appropriate whistle signal." Appropriate signal options are found in Pub 102, international Code of signals. There are several pages of signals concerning vessels at anchor.