Assignment 5 Section B (15 points) updated 4 PM 11/13/06


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Deadline: Tuesday, November 14, 2006 11 PM

In this exercise, you learn how to plan a SCUBA diving trip at a location where there are strong tidal currents. This can be a dangerous activity, because the strong currents may sweep you away from your partners and drag you into great depths. This is what happened to the diver whose 1995 accident is presented in Lecture 18.

The destination is near Turn Rock Light off the shores of the town of Friday Harbor in San Juan Channel (see aerial photos). To dive safely at this location, a diver must choose a time when currents are at or near zero. The diver will probably stay under water for as long as an hour, being sure to surface before strong currents begin to flow.

We will look at the dive plans of two divers for June 11, 2006. Steve Zissoux is a beginning diver who barely passed Ocean 101. Steve Zissoux knows that you need to pay attention to the tides when you go diving. He calculates the times of high and low tides, figuring that those are the times when slack water occurs. He also knows that the nearest location to the planned dive site for which tidal heights can be calculated is Friday Harbor, and that the reference station for tidal heights in this region is Port Townsend.

   

3 - 16. (3.5 pts., 0.25 pts. each) Using the tidal height tables provided, enter the necessary reference and difference values and calculate the missing times and values for tidal heights in Table 1 below. Use the values supplied as a guideline to help you. Be sure to account for Pacific Daylight Time by adding 1 hour to the values in the official tide tables. Enter these values in WebQ according to the numbering in the table cells.

TABLE 1
Date
 Tidal Stage
 Port Townsend Tidal Time (PST/PDT)
 Port Townsend Tidal Height Friday Harbor Time Difference
 Friday Harbor Height Ratio
 Friday Harbor Time Prediction
 Friday Harbor Height Prediction
6/11/06
 LHW
 0222
 8.1
 +0:33
 *0.91
 0255
 7.37

LLW
 1025
 -2.8
 +0:51
 *0.92
 1116
 -2.58

3.
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 5.
 6.
 7.
 8.
 9.

10.
 11.
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 13.
 14.
 15.
 16.

17. (0.5 pts.) Steve Zissoux wants to dive when there is at least some daylight. What are the names and times of the two tidal stages that he would choose for diving on this date?

   
     

Jack Cousteau is an experienced diver who aced Ocean 101. He knows that in some narrow channels where the currents are very strong, the times of slack water sometimes do not closely match the times of high and low water. He calculates the times of the tidal currents. He knows that the nearest location to the planned dive site for which tidal currents can be calculated is 1.9 miles NW of Turn Rock Light, and that the reference station for currents in this region is San Juan Channel.

18 – 39 (5.5 pts., 0.25 pts. each) Using the tidal current tables provided, enter the necessary reference and difference values and calculate the missing times and speeds of tidal currents in Table 2 below. Use the values supplied as a guideline to help you. Be sure to account for Pacific Daylight Time by adding 1 hour to the values in the official current tables. Enter these values in WebQ according to the numbering in the table cells.

TABLE 2


San Juan Channel Currents
 Turn Rock Light Differences
 Turn Rock Light Currents
Date
 Current Stage
 Time
 Speed (kt)
 Time
 Speed Ratio
 Time
 Speed (kt)
6/11/06
 Flood
 0151
 1.0
 +1:22
 *0.4
 0313
 0.4

Slack<ebb
 0345
 0
 +0:20
 -
 0405
 0

Ebb
 0758
 -3.6
 -0:01
 *0.5
 0757
 -1.8

Slack<flood
 1120
 0
 +1:19
 -
 1239
 0

18.
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 22.
 23.
 24.

25.
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27.
28.

29.
 30.
 31.
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36.
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38.
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40. (0.5 pts.) Jack Cousteau also wants to dive when there is at least some daylight. What are the names and times of the two tidal stages that he would choose for diving on this date?

41. (1 pt.) If they both survived, Steve and Jack would get together at the end of the day to discuss their diving experiences. For each of the two possible dive opportunity on this date, compare the relative safety of Steve’s and Jack’s choices of dive time, and describe the reason for any difference.

42. (0.5 pts.) What other conditions not accounted for in tide tables might create hazardous current conditions?

43. (1 pt.) Why do most areas of the oceans have two high and two low tides per day?

44. (0.5 pt.) Why are the highs and lows in a given day unequal in most areas of the ocean?

45. (0.5 pts.) Was this location experiencing spring or neap tides on June 11, 2006? How can you tell?

46. (0.5 pts.) What arrangements of the Earth, moon and sun in space cause the spring and neap tides?

47. (1 pt.) Why is the length of the tidal day 24 hours and 50 minutes instead of 24 hours?