IDC Underwater Navigation & Dive Planning 1 — Questions and Answers
Question 1: What are the two primary methods of underwater navigation taught in PADI training?
- GPS and electronic chart navigation only
- Natural navigation (using environmental features) and compass navigation (using a magnetic compass) (Correct answer)
- Following a guideline or dive flag
- Surface support radio communication only
Correct answer: Natural navigation (using environmental features) and compass navigation (using a magnetic compass)
PADI teaches two primary navigation methods: natural navigation using underwater landmarks, current direction, and bottom contour; and compass navigation using a magnetic compass.
PADI's Navigation Specialty teaches two complementary navigation methods: Natural navigation uses underwater environmental cues — sun angle and light patterns, bottom topography, current direction, depth contours, and distinctive landmarks. Compass navigation uses a magnetic compass mounted on the wrist or integrated into a dive computer. Divers learn to take a heading before diving, follow that heading, and use reciprocal headings to return to the starting point. Both methods are complementary.
Question 2: How do you calculate the reciprocal heading on a compass when navigating in a straight line?
- Multiply the original heading by 2
- Add 180 degrees if the heading is below 180, or subtract 180 degrees if it is 180 or above (Correct answer)
- Divide the original heading by 2
- Use the original heading plus 90 degrees
Correct answer: Add 180 degrees if the heading is below 180, or subtract 180 degrees if it is 180 or above
The reciprocal (return) heading is found by adding 180 degrees if the original heading is less than 180 degrees, or subtracting 180 degrees if it is 180 degrees or greater.
A reciprocal heading is the direct opposite direction on a compass. To calculate it: if your outbound heading is less than 180 degrees, add 180 degrees (e.g., heading 045 becomes reciprocal 225). If your outbound heading is 180 degrees or greater, subtract 180 degrees (e.g., heading 270 becomes reciprocal 090). This allows divers to navigate out in one direction and return on a direct opposite course.
Question 3: What is a 'natural navigation check-in point' and how should divers use it?
- A location marked with a buoy line for navigation practice only
- A distinctive underwater landmark that divers identify to confirm their position during a dive (Correct answer)
- A feature only used by dive guides — not relevant for recreational divers
- A surface landmark used before descending
Correct answer: A distinctive underwater landmark that divers identify to confirm their position during a dive
Natural check-in points are distinctive underwater landmarks (rock formations, coral heads, anchors) that divers identify during the dive to confirm their position and progress.
Natural check-in points are distinctive features of the underwater environment that divers use to track their position during a navigation dive. Examples include: a distinctive coral formation, a large rock, an anchor, a depth change, a sand channel, or a color change in the substrate. Before the dive, divers should mentally note key landmarks as they pass them. If a diver returns to a check-in point from the expected direction and finds it at the expected depth, they can be confident their navigation is accurate.
Question 4: What key elements should a dive plan include?
- A marketing document for the dive shop
- Maximum depth, dive duration, air turnaround pressure, buddy assignments, entry/exit procedures, signals, and emergency contacts (Correct answer)
- A sketch of the dive site made after the dive
- Only the no-decompression limit calculation
Correct answer: Maximum depth, dive duration, air turnaround pressure, buddy assignments, entry/exit procedures, signals, and emergency contacts
A dive plan is a comprehensive pre-dive planning document covering all safety-critical parameters: depth, time, air management, buddy system, site-specific procedures, and emergency response.
A complete dive plan includes: (1) maximum planned depth and bottom time, (2) no-decompression limit check, (3) air turnaround pressure, (4) buddy assignments and communication signals, (5) entry and exit procedures specific to the site, (6) emergency procedures including EAP contacts and nearest hyperbaric facility, (7) equipment check requirements, and (8) contingency plans for common problems. The dive plan is reviewed during the briefing so all participants understand and agree.
Question 5: What does the 'rule of thirds' refer to in dive air management?
- Spending one-third of the dive at maximum depth
- Using one-third of the air supply for the outbound journey, one-third for the return, and keeping one-third in reserve (Correct answer)
- A navigation technique dividing the dive site into three zones
- The maximum visibility range before a buddy is considered lost
Correct answer: Using one-third of the air supply for the outbound journey, one-third for the return, and keeping one-third in reserve
The rule of thirds is an air management principle: use one-third going in, one-third for the return, and keep one-third as an emergency reserve.
The rule of thirds originated in cave diving, where running out of air has fatal consequences. The principle is: use the first third of your air supply on the outbound portion of the dive, use the second third for the return, and keep the final third as an emergency reserve. This means if you have a 200-bar tank, you turn around at approximately 133 bar and surface with roughly 67 bar remaining. PADI instructors in overhead environments teach it as mandatory, and many recommend it for all open water diving.
Question 6: What factors should a PADI Instructor consider when selecting an appropriate dive site for student training?
- Only depth and visibility — other factors are secondary
- Conditions (current, visibility, temperature), entry/exit safety, presence of hazards, depth appropriate for training level, and proximity to emergency services (Correct answer)
- Distance from the dive shop and parking availability
- Only the preferences of the majority of students in the class
Correct answer: Conditions (current, visibility, temperature), entry/exit safety, presence of hazards, depth appropriate for training level, and proximity to emergency services
Site selection for student training requires evaluating multiple safety and pedagogical factors: environmental conditions, physical hazards, appropriate depth, emergency access, and alignment with the students' training level.
Key factors include: water conditions (current strength, visibility, wave action), entry and exit (safe, accessible, low-stress for student skill level), depth (appropriate for the skills to be practiced), bottom composition (sandy bottoms are safer for learning), potential hazards (boat traffic, marine life hazards, overhead obstacles), emergency access (proximity to road access, phone signal, nearest hyperbaric facility), and the students' certification level and experience.
IDC Underwater Navigation & Dive Planning 1
What are the two primary methods of underwater navigation taught in PADI training?