How did you get on?
Let’s deal with the nature of seabed first.
Green cS.G.bkSh - Course sand, gravel and broken shells
Blue M.fS.bkSh - Mud, fine sand and broken shells.
If you are unsure what things mean, there is a publication called Chart 5011
I know it says chart, but it really is a book that gives you the meaning of every symbol and abbreviation on an admiralty chart.
Now let’s look at the tides question.
July 08 add 1 hr for summer time
LW 0846 1.6m
HW 1339 8.6m
Range 7m
| Using the % rule 1st hr 10% 0.7 2nd hr 15% 1.05 3rd hr 25 1.75 HW 8.6m 0946 8.6m - 0.7m = 7.9m 1046 7.9m - 1.05m = 6.85 1146 6.85m - 1.75m = 5.1m |
Using the rule of 12 th’s 1st hr 1/12 0.58m 2nd hr 2/12 1.17 3rd hr 3/12 1.75 |
The question asks for the depth of water at HW HW-3 and LW at the 2 wreck sites
The black circle wreck at
HW will be 3.2m + 8.6m = 11.8m
HW - 3 will be 3.2 + 5.1 (8.6 - 0.58 - 1.17 - 1.75) = 8.3m
LW 3.2m + 1.6 = 4.8m
In this instance, if you used the rule of 12th’s you will have the same answer
The red circle wreck is on the 20m contour line
HW will be 20 + 8.6 = 28.6m
HW - 3 will be 20 + 5.1m (8.6 - 0.58 - 1.17 - 1.75 = 5.1m) = 25.1m
LW will be 20 + 1.6 = 21.6m
In this instance, if you used the rule of 12th’s you will have the same answer
Reward yourself with tea and cake if you managed to find the correct answers.