RYA Day Skipper Theory common mistakes
RYA Day Skipper Theory · Understand the traps and how to avoid them.
Reading the tidal curve at the wrong reference port, or applying the secondary port differences to the standard port's high water time rather than to the standard port times that bracket the secondary port's HW/LW, so the height or time is out by up to an hour or more.
Candidates memorise the procedure as a formula and skip the step of checking which standard port times actually bracket the secondary port's own HW or LW, especially when the standard and secondary port HW times fall on opposite sides of a spring/neap boundary or on different days.
What to do instead
Always write out the four-step sequence explicitly: (1) note secondary port HW/LW times from the almanac, (2) find the standard port HW/LW times immediately before and after, (3) apply the time and height differences to those bracketing times, (4) interpolate on the curve between the corrected times. Practise with at least five secondary ports where the standard port HW is earlier than the secondary port HW and five where it is later.
Plotting a position fix and then reading the latitude/longitude off the nearest graticule line instead of interpolating between the minutes of arc on the chart's border, giving a position that is wrong by a mile or more.
The chart border is crowded with minutes and seconds, and candidates under time pressure read across to the wrong tick or forget that one minute of latitude equals one nautical mile and must be subdivided by eye or with dividers.
What to do instead
Use dividers to transfer the distance from the nearest whole minute of latitude to the position, then read the seconds off the border scale; do the same for longitude along the top or bottom edge. Check by measuring the distance between your plotted fix and a known charted feature and confirming it matches your expected range/bearing.
Applying variation and deviation in the wrong order or with the wrong sign when converting between true, magnetic and compass bearings, so a course steered is offset by the sum rather than the difference of the two errors.
The mnemonic 'variation east, magnetic least' is remembered but not understood, and candidates confuse whether deviation is added to or subtracted from magnetic to get compass, particularly when variation and deviation have opposite signs.
What to do instead
Write the conversion ladder True–Variation–Magnetic–Deviation–Compass and always work in one direction, adding easterly and subtracting westerly at each step, then reverse the signs coming back. Do a sanity check: if variation is 4°W and deviation is 3°E, the net correction from true to compass should be 1°W, not 7°.
Calculating a course to steer or an estimated position using speed through the water and ignoring the tidal stream, or adding the stream as a single vector instead of resolving it as a set and drift over the passage duration.
Candidates treat the tidal stream as a small correction and apply it as a bearing offset rather than as a distance vector over the whole passage, and they forget that set and drift change with the tidal cycle on longer legs.
What to do instead
Draw a proper vector triangle: water track and speed through the water from the origin, tidal set and drift from the end of that vector, and the ground track from origin to destination. For passages over two hours, split into hourly (or half-hourly near HW/LW) steps and re-plot the tidal vector for each.
Planning a passage that crosses a charted headland or shoal at the planned course without checking the charted depths, drying heights and under-keel clearance along the whole track, not just at waypoints.
Candidates check depth at the waypoint positions only, and forget that the ground track between waypoints may pass over a drying bank or a rock awash at chart datum, or that charted depths must be corrected for height of tide and for the vessel's draught.
What to do instead
Lay off the track, then run a 'corridor' check: scan the chart for the whole width of the vessel's safe water either side of the track, convert charted depths to actual depths using the tide height at the time of passing, and confirm at least the planned under-keel clearance (typically 10% of draught or a set minimum) at every point, including at low water if the passage spans it.
In a collision situation, identifying the give-way vessel but then taking action that is either too late, too small, or in the wrong direction (for example altering course to port across the other vessel's bow in a head-on encounter).
Candidates learn the rule numbers but not the practical geometry of a close-quarters situation, and under exam pressure they default to 'turn away' without checking which side the other vessel is on or whether the alteration will be obvious.
What to do instead
For each rule, memorise the required action and the geometry: head-on both alter to starboard; crossing give way to the vessel on your starboard side and pass astern of it; overtaking keeps clear. Practise sketching the encounter and stating the alteration in degrees and the expected result (passing astern, opening bearing).
Confusing the lights, shapes and sound signals for vessels of different status (under way, at anchor, aground, not under command, restricted in ability to manoeuvre, fishing, sailing) and giving the wrong day shape or light configuration.
The lists are long and similar, and candidates learn them as isolated facts rather than grouping by 'which lights are in a vertical line' and 'which shapes are balls, cones or cylinders', so recall collapses under exam conditions.
What to do instead
Build a one-page matrix: rows for vessel status, columns for lights (masthead, sidelights, sternlight, all-round red/white/green), shapes and sound signals. Learn the anchor ball, the two-cone fishing shape, the cylinder for constrained by draught and the three all-round reds for not under command as anchor points, then derive the rest.
Failing to allow for the height of tide when calculating a bridge or overhead clearance, or using the charted clearance without checking whether it is quoted above chart datum or above high water.
Charted bridge clearances are usually given above MHWS or chart datum depending on the chart, and candidates apply the tide height without checking which datum the figure uses, or forget that air draught must be compared to clearance at the time of passing.
What to do instead
State the datum of the clearance figure before calculating, then compute the actual clearance at the planned time as charted clearance plus or minus the height of tide relative to that datum. Compare with the vessel's air draught plus a safety margin, and check the clearance at the most adverse tide on the passage, not just at the planned arrival.
Writing a passage plan that lists waypoints and courses but omits the pilotage plan for the harbour approach: no transit bearings, no clearing bearings, no contingency anchorages, no abort points.
Candidates treat passage planning as an offshore exercise and underestimate the pilotage element, or they produce a plan that cannot be executed in poor visibility or at night because it relies on visual identification of unlit marks.
What to do instead
For every harbour entry, write a pilotage plan with at least three elements: leading lines or transits with the bearing and the 'not to port/starboard of' limits, clearing bearings off identifiable charted features, and a stated abort point with a contingency anchorage and the depth there. Check that each element works in reduced visibility or darkness using lit marks or sound signals.
Recording the log, position and course steered inconsistently, or failing to note the time of each fix, so the dead reckoning cannot be reconstructed and the tidal stream cannot be deduced from the difference between DR and fix.
Candidates see the log as paperwork rather than as the working record from which the estimated position and the tidal set and drift are derived, and they round times loosely or forget to record the log reading at each fix.
What to do instead
Adopt a fixed log format: time, log reading, course steered, speed, position fix, and remarks. At each fix, compare the DR position (from the previous fix advanced by course and distance through the water) with the fix, and measure the offset as set and drift over that interval. Record every fix to the minute.