ASA 105: Skill 16, Plotting

 

16:

Chart a course of at least 20 miles and three course changes using the above skills.



Training for a coastal distance race of 75 nm and three major legs.  Tide tables, current charts, weather, and a detailed preplan including chartwork, food and rest are all as important as sail training.  
Cruising yachts make the same preparations as racers.


Demonstration route from Dutch Harbor to Cleveland Ledge Channel entrance 

The sample plotting scenario is to sail from Dutch Harbor on Conanicut Island, RI to the entrance to the Cape Cod Canal which is Cleveland Ledge Channel.  The part of the trip through the Canal to a marina at the East end is omitted as it is off the chart.  The demonstration looks at the trip as a unit composed of many smaller parts.

A.  Overview:
  • Start on Friday July 1, 2022 and end before sunset on the same day.
  • Sunrise and sunset from Eldridge 2022 page 226
  • Narraganset Bay currents from Eldridge 2022 pages 87 and 90
  • Current elsewhere from Eldridge 2022 page 69 and current charts pages 72 -83
  • Assume an average speed of 6 knots
  • Assume sailing on a reach or run without tacking or gybing
  • Current in Canal turns fair at 1824 hrs see Eldridge 2022 page 49
  • Total distance is 39.7 nm or about 7 hours plus another 2 hours in the Canal
  • Courses are given in True for simplicity
B.  Leg 1:  West Passage, Dutch Harbor to Beavertail Pt
  • Dutch Harbor departure at 1000 hrs RB Qk Fl R Gong
  • Sunrise is 0511 hrs
  • Course 178 deg T
  • Distance is 3.2 nm or 30 min
  • Destination is Beaver Tail Point RB Bell
  • Current is Slack High at 1011, very weak and fair for the 30 minute leg
C.  Leg 2:  Across Newport Harbor, Beavertail Pt to Brenton Pt
  • Arrive/depart 1030 hrs
  • Course 105 deg T to Brenton Point R "2" Fl R 4 sec Whistle 
  • Distance is 2.9 nm or 30 min
  • ETA 1100 hrs
  • Ebb current is very light on port beam, no correction required
  • Caution, do not mistake R "4" Gong  off Brenton Pt. (unlighted) for the next mark!
D.  Leg 3: Along the Rhode Island shore to Buzzards Bay Entrance
  • Arrive/depart 1100 hrs
  • Course 087 deg T for "3" Fl G 4 sec Gong off Gooseberry Point
  • Distance 15.8 nm or 2h 36m
  • ETA is 1336 hrs
  • Current ebb starts at Pollock Rip at 1212, Eldridge 2022 page 69
  • From 1100 to 1212 the current is weak if not slack
  • From 1212 to ETA 1336 current is foul at 1/2 knot
  • buoys near track allow for speed and leeway checks
  • Adjust speed to 6 knts first hour and 5.5 knts second hour, 5.75 kts
  • Adjusted ETA is 1344 as time on leg is increased by 8 min
E.  Leg 4:  Entering Buzzards Bay headed towards Cleveland Ledge Channel and the Canal
  • Arrive/depart 1344 hrs
  • Course 058deg T for "1" Fl G 4 sec at the entrance to New Bedford Harbor Channel
  • Distance 9 nm or 1 hr 30 min
  • ETA is 1506
  • Current is weak to 1/2 knot against.  See Eldridge 2022 pages 80 and 81
  • A foul current of .5 knots for 1.5 hrs slows the yacht by 0.75 nm at 6 knots or 7 minutes
  • Weak currents are best observed by looking at water flow around buoys
  • Adjust ETA to add 7 minutes:  New ETA 1513
F.  Leg 5:  Buzzards Bay to Cleveland Ledge Channel
  • Arrive/depart 1513 hrs
  • Course 050 deg T to R "12" Qk Fl R one half nautical mile South of Cleveland Ledge Light
  • Distance is 8.8 nm or 1 hr 28 min
  • ETA is 1641
  • Current is weak, see Eldridge 2022 pages 82 and 83
  • The Canal channels are about 13 nm total.  The current in the canal will be fair building to 4 knots.  The transit is expected to take just over an hour for arrival around sunset.
G.  Final thoughts
  • Leave an hour earlier
  • If delayed anchor in Pocasset Harbor and transit the Canal with the morning flood beginning at 0645 on July 2nd.







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