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Chartwork and Tides

Chartwork and Tides. We will cover. Tidal Ranges, Times and Currents The Chart Distance Buoys and the Buoyage System Where to Snorkel. Tidal Range. Tidal Times. Referenced to the standard ports UT(GMT) & (B.S.T.) Heights above Chart Datum. Tidal Times. Wicklow on July 3 rd

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Chartwork and Tides

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  1. Chartwork and Tides

  2. We will cover • Tidal Ranges, Times and Currents • The Chart • Distance • Buoys and the Buoyage System • Where to Snorkel

  3. Tidal Range

  4. Tidal Times • Referenced to the standard ports • UT(GMT) & (B.S.T.) • Heights above Chart Datum

  5. Tidal Times • Wicklow on July 3rd • High water at: 10:35 + 1h – 41min 10:54, 3.91m • Low water at: 22:59 + 1h – 41min 23:18, 0.91m

  6. Tidal Ranges, Rule of Twelfths

  7. Example: Wicklow on July 3rd. at 1354 ? H.W. at Wicklow 1054, 3 hours after H.W. Range: 3.91 - 0.91 = 3.00 Meters. 1/12th.: 3.00/12 = 0.25 Meters. 3 Hrs. after H.W. the Height of Tide is: 1/12th. + 2/12th.+ 3/12th. = 6/12th. Height is: 6 X 0.25 = 1.5 Meters. Height above Chart Datum = 1.5 + 0.91 = 2.41m

  8. Tidal Currents • Tidal Arrows • Tidal diamonds

  9. The Chart • British Admiralty Charts, normally Mercator projections • High quality tough paper • Rolled up or folded along its normal folds • Use a soft 2B pencil & soft eraser • Admiralty publication: • ‘Home Waters Catalogue, Admiralty Charts and other Hydrographic Publications’

  10. Chart Information • Title and Number • Scale • Soundings • Chart Corrections REPUBLIC OF IRELAND - EAST COAST ARKLOW to the SKERRIES ISLAND DEPTHS in METERS SCALE 1:100,000 at Lat 53°30’

  11. Symbols and Abbreviations (Admiralty Chart 5011) • Compass Rose • True North • Magnetic North • Variation

  12. Distance

  13. Distance • On the Latitude scale • 1° = 60 Minutes • 1 Minute = 1 Nautical Mile = 6076 Feet = 1852 Metres = 10 Cables (1 Cable is 200 Yards)

  14. Finding co-ordinates • Dublin Lat. 5320’46”N Long. 612’30”W • Galway Lat. 5316’19”N Long. 92’56”W

  15. Time Time = Distance/Speed or Speed = Distance/Time or Distance = Speed x Time Snorkel speed is 2 Knots, how long for 4 miles ? Time = Distance / Speed Time = 4 / 2 = 2 Hour

  16. Buoys and the Buoyage System • I.A.L.A Buoyage System • The direction of buoyage

  17. Buoys • 5 main types • Lateral marks, or channel markers (red and green) • Cardinal marks • Safe water marks • Isolated danger marks • Special marks • Not advisable to snorkel across marked channels

  18. Where to Snorkel • Shelter • Shallow water • Bottom type – sd, r, sh... etc • Current • Overfalls and Tide-rips

  19. Summary • Tidal Ranges, Times and Currents • The Chart • Distance • Buoys and the Buoyage System • Where to Snorkel

  20. Questions?

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