Question 1

A hand-bearing compass reads 045°. Variation is 2°W, deviation on this bearing is 3°E. What is the true bearing?

Accepted Answer

Apply TVMDC (True-Variation-Magnetic-Deviation-Compass) formula. Compass 045° → apply deviation: 045 + 3 (East deviation, add) = 048°M → apply variation: 048 - 2 (West variation, subtract) = 046°T. True bearing = 046°T. Mnemonic: "CADETS" (Compass, Add East = True to Magnetic, Subtract East = Magnetic to True) — or memorise: error East, compass least; error West, compass best COMPASS ERROR CALCULATION: the TVMDC formula is the standard method. Working from Compass to True: Compass + Deviation (E positive, W negative) = Magnetic. Magnetic + Variation (E positive, W negative) = True. Here: 045 + 3 = 048°M; 048 - 2 = 046°T. Error East (deviation) = compass reads LESS than magnetic — "compass least, error East." Hand-bearing compasses do have deviation (from nearby metal), but it is typically smaller and less well-characterised than the steering compass. For exam purposes, apply as given.

Question 2

The standard port (Portsmouth HW) is 1800 hrs, height 4.8m. The secondary port time difference is -0020 and height difference is -0.4m. What is the HW time and height at the secondary port?

Accepted Answer

HW time: 1800 - 0020 = 1740 hrs. HW height: 4.8 - 0.4 = 4.4m. Note: differences are applied directly when given as simple offsets. When height ratios are given (not simple differences) use: (secondary HW - secondary LW) / (standard HW - standard LW) × tidal range Secondary port calculation: apply the time difference algebraically (negative = subtract; positive = add). Height differences work the same way. This example is the simple case where differences are given as absolute values. The more complex case (in reed's and almanac) uses ratio calculations interpolating between MHWS/MHWN differences. Always read the secondary port data carefully — some almanacs give "differences" that require interpolation between spring and neap values based on the standard port's predicted height. This is a core Coastal Skipper exam topic.

Question 3

A skipper is relying entirely on a chartplotter with AIS for passage navigation. What are the key limitations that require maintaining traditional skills?

Accepted Answer

Chartplotter limitations: 1) Chart data may be out of date (new wrecks, changed cardinal marks, silting); 2) GPS antenna failure = no position; 3) Power failure = no display; 4) Small-vessel AIS (Class B) is not fitted to all vessels — canoes, kayaks, small fishing boats, naval vessels are all invisible; 5) Chartplotters can show the vessel in a precise but wrong position (datum error, signal multipath). Maintain paper chart, compass, and watch-keeping skills ELECTRONIC NAVIGATION DEPENDENCE: the RYA and MCA explicitly teach that electronic navigation must be backed up by traditional skills. The most dangerous failure mode is overconfidence — the GPS shows a precise position, but the precision may be wrong (multipath, datum error, chart error). AIS Class B is not compulsory for vessels under 300gt recreational — the majority of vessels the Coastal Skipper will encounter (ferries, fishing vessels, RIBs) may have no AIS. A vessel 200m off track in a channel with GPS can be in danger. Paper chart and compass DR must remain a practised skill.