BML Revision: Tides & Currents (Section 1, part 2)

Revision card 2 of 16 — Boatmaster's Licence, Tier 1 Level 2 Underpinning Knowledge, MSN 1853 Annex 10. This whole section is new for Level 2 — Tier 1 Level 1 (Annex 9) doesn't test tidal work at all, since Categories A, B and non-linked C don't require it.

What You Need to Know

• Read and apply tide tables and tidal stream atlases
• Know what causes spring and neap tides
• Define: height of tide, Mean High Water Springs, Mean Low Water Springs, range of tide, chart datum, height of charted objects, drying heights, spring and neap ranges
• Use tidal diamonds when working from charts
• Find the height and time of high and low water using tide tables
• Calculate the height of tide at a given time, using tide tables and tidal curves
• Calculate the time the tide will reach a given height, using tide tables and tidal curves
• Correct soundings to chart datum

Quick Self-Check

• Can you define chart datum without checking a book?
• Work out the height of tide at a stated time using a tidal curve — could you do it under exam pressure?
• Why does a sounding need correcting to chart datum before you trust it?

Related Reading

• Key Bora — grounded on a passage plan built on inaccurate depth data, with no abort action taken despite warning signs. A direct lesson in not trusting uncorrected soundings