USCG Master 100 common mistakes
USCG Master 100 · Understand the traps and how to avoid them.
In crossing-situation questions, the candidate answers from a 'vessel on the right has the right of way' rule of thumb, picking the answer based on which side of the bow the other vessel appears, instead of identifying give-way and stand-on by the other vessel's aspect and relative bearing.
The driving analogy is deeply ingrained from car licensing, and the exam stem describes the other vessel's bearing and aspect in a way that invites a left/right shortcut rather than a rule lookup.
What to do instead
Redo every crossing question using the aspect test: note whether you see her green, red, or both sidelights, decide give-way or stand-on from that alone, then apply the correct action rule (give-way: take early and substantial action; stand-on: hold course and speed and sound the doubt signal if needed). Drill 20 aspect sketches before touching an answer key.
The candidate memorises manoeuvring and warning signals as bare numbers ('two short blasts = overtaking') and answers with the wrong full meaning, or fails to give the required response signal or the doubt/ danger signal when the stem describes ambiguity.
Numbers are easier to cram than full rule language, so the intent phrase ('I intend to overtake you on your starboard side') and the response signal get dropped during study and are missing on exam day.
What to do instead
Recite each signal aloud in its exact rule wording, in pairs: the signal and the required response, plus which signal is used when in doubt or when action is not understood. Say the phrase, not the number, when you self-test.
On light and shape identification, the candidate matches a memorised picture to the wrong vessel type, for example calling a towing vessel's masthead/sidelight arrangement a vessel constrained by draft, or missing that a vessel aground shows both anchor shapes/lights and the two-red 'not under command' signal.
Lights are studied as isolated diagrams and flashcards rather than as the rule text, so nothing links the number of lights, their arcs, colours and vertical spacing to the specific rule that creates them.
What to do instead
Rebuild the light and shape table directly from the rule text, column by column: arcs, colours, spacing, and shapes in daytime, per vessel type. Self-test only from the rule wording, not from pictures, and be able to state which rule number creates each configuration.
The candidate ignores the International/Inland column and applies the wrong body of rules, most visibly on narrow channels, traffic separation schemes, and the small-vessel exemptions where the two texts differ.
The stem's jurisdiction line is a single word buried in the first sentence, and candidates read the scenario before they read the governing ruleset.
What to do instead
Before reading the scenario, find and underline the jurisdiction. Keep a two-column sheet of the handful of rules that differ between International and Inland and review it the morning of the exam.
Compass conversion errors: the candidate adds where they should subtract, or plots a bearing on the chart without first converting it to true, producing a fix correctly computed from the wrong starting number.
The 'east is least, west is best' mnemonic gets applied in the wrong direction under time pressure, or the candidate skips the mnemonic entirely and works from memory.
What to do instead
Write the four-step conversion chain out on scratch paper every single time and check the arithmetic in the opposite direction back to the original value. Practice 20 conversions each way with known answers until the direction check is automatic.
Current and tide problems go wrong because the candidate confuses set with drift, or takes a height of tide or current rate straight from the reference station without applying the stated time or height correction.
Set and drift are short words that read similarly in a hurry, and the correction step feels like optional arithmetic when the table already gives a plausible number.
What to do instead
Define both terms in writing at the start of the problem (set = direction toward which it flows, drift = speed), then state the correction being applied before computing. Circle the word 'reference station' every time the stem names one.
Buoyage questions are answered with the wrong side or colour, typically stating that a red buoy marks the port side of a channel entered from seaward, or misreading a preferred-channel buoy's top band and light.
Both IALA regions are studied side by side and the correct regional convention is not fixed in memory, so the answer flips under exam pressure.
What to do instead
Lock in the marks for your region with a single memorable sentence, then add the preferred-channel convention and the light characteristic as a second layer. Draw the channel from seaward and place every mark yourself before answering.
Anchor rode is computed as depth times the scope ratio only, leaving out bow height, and the same ratio is applied regardless of whether the stem describes shelter, open water, or an overnight in a seaway.
Depth is the only number on the sounder, so it feels like the whole input; bow height and the condition-based ratio feel like embellishments.
What to do instead
Use depth plus bow height, then the ratio, and state the ratio you chose and why. Work three scenarios at different depths and conditions to see the difference in metres of chain before answering any scope question.
Stability questions are answered by intuition rather than a diagram, producing claims such as adding weight low raises the centre of gravity, or forgetting that a slack tank introduces a free surface effect that reduces effective metacentric height.
The terms are abstract and the candidate tries to reason from everyday experience with a boat rather than from the positions of G, B and M.
What to do instead
Sketch the hull and place G, B and M on the sketch for every stability question, mark the direction of every movement, and check whether each tank is slack. Only answer once the sketch agrees with the option.
Fire questions are answered with the agent the candidate associates with the fuel, for example water on a flammable-liquid or electrical fire, or a carbon dioxide extinguisher left unexploded as the first choice for a deep-seated Class A fire.
The class letters are memorised but not the agent matrix, so the answer is chosen by fuel name rather than by class and situation.
What to do instead
Build and memorise the class-by-agent grid with the reason for each exclusion (water spreads flammable liquids, conducts electricity, and does not cool a deep-seated Class A fire from the surface). Recite the grid from the class letter outward, not the fuel inward.