You are to sail from Elizabethport, N.J., on 17 November 1983 with a maximum draft of 27 feet. You will pass over an obstruction in the channel near Sandy Hook that has a charted depth of 25.5 feet. The steaming time from Elizabethport to the obstruction is 1h 50m. What is the earliest time (ZD +5) you can sail on 17 November and pass over the obstruction with 2 feet of clearance?
• Under-keel clearance (UKC) and how to combine ship draft, desired clearance, and charted depth to find the minimum height of tide needed • How to use a tide table and corresponding height-of-tide graph or table for Sandy Hook on 17 November to find the times when the tidal height is sufficient • How to adjust for steaming time (1h 50m) so the ship arrives over the obstruction at the right stage of the tide
• First, calculate the total water depth you need over the obstruction, then figure out how much tide above chart datum you must have to safely pass • Look at the tide table for Sandy Hook on 17 November: which high or low water has a height that will give you your required tide height at some time? Use the tidal curve or interpolation to find the first time the tide reaches that height • Once you know the earliest safe time over the obstruction, work backward by 1h 50m to get the earliest sailing time from Elizabethport (ZD +5)
• Be sure you correctly compute the required tide height: Ship’s draft + required clearance − charted depth • Verify you are using the correct day (17 November) and correct location (Sandy Hook) in the tide tables and any tidal curves • Double-check that you subtract the steaming time (1h 50m) from the time of sufficient depth, and that your final answer matches one of the given ZD +5 options
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