Revision and assessment
0 of 3 hands-on
01 Introduction
This lesson brings the course together. Use the table and cards to check what you remember, try the review questions, and then take the final exam when you feel ready.
Objectives
- Recall the main ideas about tides, currents, waves, layers and visibility
- Apply them to short dive-planning scenarios
- Prepare for the final exam
02 Watch
Course review
4 min · Video in production
- 1
A single dive plan assembled step by step: forecast, tide, current, entry, layers, visibility and exit.
- 2
A short recap of each lesson with one picture and one sentence.
- 3
A diver checking conditions on the day and deciding to go or to call the dive.
- 4
A preview of the exam format and pass mark.
03 Learn
The course at a glance
| Topic | Key idea | Habit |
|---|---|---|
| The ocean as a system | Wind, the Moon and Sun, and density differences move the sea | Think about what is driving the conditions today |
| Tides | Two highs a day, about 50 minutes later each day. Springs are largest, neaps smallest | Check the tide table and the stream, not just the height |
| Currents | One knot is about 30 m a minute. You cannot out-swim a strong current | Plan, carry a surface marker buoy, and never fight a current |
| Waves and surge | Swell comes from distant storms and becomes surge in the shallows | Watch the waves before a shore entry and time it in a lull |
| Temperature | Layers form, and water takes heat about 25 times faster than air | Choose your suit for the water, and end the dive if you shiver |
| Visibility | Particles scatter and absorb light | Stay close, use a line, and look after the silt |
| Weather | Wind follows pressure. Wind against tide makes a rough sea | Check the forecast, ask locally, and be ready to cancel |
A dive plan in six questions
- 1.What is the weather and sea state doing, and what is forecast?
- 2.Where are we in the tide, and what will the current do?
- 3.How will we enter and leave, given the waves?
- 4.How cold will it be, and are we dressed for it?
- 5.What will the visibility be, and how will we stay together?
- 6.What would make us call the dive, and what is the plan if we are separated or swept away?
Quick numbers
- Time between high tides: about 12 hours 25 minutes. Tides are about 50 minutes later each day.
- One knot is about 0.5 metres per second, or about 30 metres per minute.
- Deep water wavelength is about 1.56 times the period squared, in metres.
- Salt water is about 2.5% denser than fresh water.
- Water removes heat about 25 times faster than air.
- Sound travels about 1 km in 3 seconds, which helps estimate the distance of a storm.
Take a guess first
A tide table shows high water at 08:00 today. Estimate the time of the first high water tomorrow morning.
04 Explore
Try it yourself
Test yourself: flip each card to check the answer.
Flip each card to check your answer.
Tap a card to flip it.
05 Apply
Scenario
You are planning a boat dive. The forecast shows a force 5 wind rising later, the tide is at springs with a strong stream at mid-tide, and the site had heavy rain two days ago. You have 20 dives of experience.
What is the sensible way to approach the plan?
06 Check
07 Summary
Key points
- Wind, tide, current, waves, layers and visibility all affect a dive.
- Use six questions to plan: weather, tide and current, entry and exit, temperature, visibility, and when to call the dive.
- Know the quick numbers: 50 minutes, 30 m per minute, 25 times, 2.5%.
- When you are ready, take the final exam.
Before you apply this in the water
- Have I been trained by a qualified instructor for this?
- Am I medically fit to dive?
- Do I have a buddy and a plan?
- Am I diving within my training and limits?
Answer every question in the Check section to mark this lesson complete.