Vessel Handling & Maneuvering
Master propeller walk, pivot point, spring lines, docking, MOB recovery, and stopping distance. This guide covers every maneuvering concept tested on the USCG OUPV exam.
Topics Covered
1. Propeller Walk (Prop Walk)
Also called the paddle-wheel effect. The single most important maneuvering characteristic of any single-screw vessel.
The Core Rule — Memorize This
Forward gear, right-handed prop: stern walks to starboard, bow swings left. Vessel tends to turn to port.
Reverse gear, right-handed prop: stern walks hard to port. This is the dominant effect when backing. Always expect the stern to kick to port on a standard single-screw.
Why it happens:
The lower blade of the propeller moves through denser, slower water than the upper blade. This creates an asymmetric thrust — more on the bottom than the top — that pushes the stern sideways. The effect is strongest at low RPM and diminishes as forward speed increases because rudder authority increases with water flow.
Prop Walk by Configuration
| Configuration | Stern Effect | Bow Effect |
|---|---|---|
| Right-handed single screw — forward | Stern walks to starboard | Bow swings to port |
| Right-handed single screw — reverse | Stern walks to port (strong) | Bow swings to starboard |
| Left-handed single screw — forward | Stern walks to port | Bow swings to starboard |
| Left-handed single screw — reverse | Stern walks to starboard | Bow swings to port |
| Twin screw — counter-rotating (standard) | Prop walk cancels out | No net lateral force |
Twin-Screw Advantage
Twin-screw vessels with counter-rotating propellers eliminate prop walk by design — one walks port, the other walks starboard, and the effects cancel. The real power of twin screws is differential throttle: ahead on one engine and astern on the other spins the vessel nearly in place. This is called a 'kick turn' and is the primary way twin-screw vessels maneuver in tight quarters without thruster assistance.
Backing and filling (single-screw): Alternating between short bursts of forward (turning bow with rudder) and short bursts of reverse (using prop walk) to rotate the vessel in a tight space. The technique exploits prop walk deliberately rather than fighting it.
2. Pivot Point
The pivot point is the fulcrum around which the vessel turns. Its location changes with vessel movement — and understanding it prevents collisions in tight quarters.
| Condition | Pivot Point Location |
|---|---|
| At rest (stopped) | Near amidships — approximately 50% from bow |
| Moving ahead (slow) | About 1/3 ship length from bow |
| Moving ahead (full speed) | About 1/4 to 1/3 from bow |
| Moving astern | About 1/4 ship length from stern |
| Turning with tug assist | Varies — near tug attachment point |
Practical Implication — Bow vs Stern Swing
When moving ahead with the pivot point 1/3 from the bow, the stern sweeps a much larger arc than the bow. In a marina with 10 feet of clearance astern, this matters. A vessel swinging its bow 15 degrees to port may be sweeping its stern 20+ feet to starboard. Always watch the stern when maneuvering in restricted waters.
Pivot Point Shifts With Tugs
When a tug is made fast to the bow of a large vessel and pulling, the tug becomes an external force that effectively shifts the pivot point toward the tug attachment. The stern then swings freely on a longer radius. When a tug is pushing amidships on the beam, the pivot point shifts toward the push point and both bow and stern swing in opposite directions around it.
Exam Question Pattern:
The USCG exam frequently asks where the pivot point moves when a vessel moves ahead vs astern. The answer: forward (1/3 from bow) when making headway; aft (1/4 from stern) when backing. Questions may also ask whether the bow or stern sweeps the larger arc — the stern sweeps larger when making headway because it is farther from the (forward) pivot point.
3. Single-Screw Maneuvering
Single-screw vessels require skill and planning. Every maneuver must account for prop walk, pivot point, and hull momentum simultaneously.
Docking Port-Side-To (Right-Handed Prop)
Port-side-to is the preferred side for right-handed single-screw vessels because backing to stop drives the stern into the dock rather than away from it.
- 1.Approach at 30–45 degrees to the dock, bow aimed at a point slightly ahead of the berth.
- 2.Reduce speed to bare steerage as you close the dock.
- 3.When the bow is within a few feet of the dock, shift to reverse with helm amidships.
- 4.Reverse gear stops forward motion and the prop walk kicks the stern to port — toward the dock.
- 5.Get the bow line ashore first, then stern line, then adjust with springs.
Docking Starboard-Side-To (Right-Handed Prop — the Hard Side)
When backing, prop walk drives the stern to port — away from a starboard dock. Additional technique is required.
- 1.Approach at a shallower angle (15–20 degrees) to give more time to work the helm.
- 2.Use a forward quarter spring line early — loop it around a dock cleat and work against it.
- 3.With the spring holding the stern, use short forward bursts with helm turned toward the dock to walk the stern in.
- 4.Alternatively: approach the dock and deploy a fender, then put the helm hard to starboard and use a short burst astern — the rudder deflects propeller wash onto the hull and pushes the stern to starboard despite prop walk.
Turning in Tight Spaces — Backing and Filling
When there is not enough room to make a full ahead turn, backing and filling uses prop walk to rotate the vessel without moving far.
- 1.Put the helm hard over to the desired turn direction (say, port).
- 2.Short burst ahead — bow swings to port, stern swings to starboard.
- 3.Shift to reverse (helm can remain or go amidships) — prop walk kicks stern to port while vessel moves astern.
- 4.Repeat until vessel has rotated to desired heading.
- 5.Net rotation is always to port for a right-handed prop — the vessel 'walks' the stern to port on every astern burst.
Undocking Against Wind or Current
When wind or current pins you to the dock, spring lines are the solution. Use the forward quarter spring: put the engine ahead with the helm away from the dock. The spring holds the stern while the bow is driven away. Once the bow is clear, slip the spring and back out. This technique works even when wind is pressing hard on the beam — it converts engine thrust into rotational force rather than fighting the wind directly.
4. Bow and Stern Thrusters
Thrusters provide lateral thrust at the bow or stern independently of the main engine. They transform maneuvering in tight quarters but have important limitations.
When Thrusters Help
- Docking with no wind or light wind in any direction
- Holding position while crew handles lines
- Slow-speed precision maneuvering in marina alleys
- Compensating for prop walk when docking starboard-side-to
- Repositioning alongside a dock without using engine
Thruster Limitations
- Wind over ~15 knots: thruster thrust is overwhelmed by windage on topsides and superstructure
- Current over ~1.5 knots: thruster becomes ineffective at countering cross-current set
- Speed over 3–4 knots: water flow past the thruster tunnel causes cavitation and loss of effectiveness
- Duty cycle: electric thrusters have duty cycle limits (typically 30 seconds on, 2–3 minutes off) before overheating
- Shallow water: thruster wash reflects off bottom and reduces effectiveness
Thruster Physics — What the Exam Tests
A bow thruster pushes the bow laterally but the stern stays (approximately) in place — or rather, the stern acts as a pivot. Similarly, a stern thruster moves the stern while the bow pivots. Having both bow and stern thrusters allows a vessel to move sideways (translate) without rotating, which is the equivalent of a tug alongside.
The exam may test the direction of thruster effect: if you push the bow to port with a bow thruster, the bow moves to port and — because the vessel is pivoting around a point aft of the bow — the stern swings slightly to starboard. This is different from a rudder turn, which swings the stern first and the bow follows.
Current effect on thrusters: A strong current running from bow to stern will carry the thruster wash aft before it can act on the hull. The effective thrust is reduced and may be deflected. Always account for current direction when relying on thrusters.
5. Docking Techniques
Every docking situation is different, but the same principles apply: plan the approach, use wind and current to your advantage, and always have a contingency.
Alongside (standard port-side-to)
Approach: Approach at 30–45 degrees to the dock, bow in first
1. Slow to bare steerage. 2. When bow is close, put helm toward dock and use short burst astern to stop forward motion and swing stern in. 3. Secure bow line first, then stern, then springs.
Alongside (single-screw, starboard-side-to)
Approach: More difficult due to prop walk in reverse
1. Approach at shallower angle (15–20 degrees). 2. Use forward spring early. 3. Back down slowly — stern will walk to port (away from dock). 4. Use short bursts of forward with helm toward dock to counter.
Mediterranean Moor
Approach: Back stern-to into a slip or against a quay
1. Drop anchor at 2–3 times the slip depth ahead of the berth. 2. Back slowly toward the quay while paying out anchor rode. 3. Secure stern lines to bollards ashore. 4. Tension anchor rode to hold bow off.
Anchor Moor (single anchor, bow-to current)
Approach: Anchor ahead, drop back, secure stern to dock or mooring
1. Pass the berth, drop anchor well ahead. 2. Back slowly to berth while paying out rode. 3. Secure stern lines. 4. Take up on anchor rode until vessel is in position.
General Docking Rules
- Always approach into the wind or current (whichever is stronger) — it gives you directional control and braking
- Never approach faster than you are willing to hit the dock
- Have fenders deployed before you begin the approach — not while you are maneuvering
- Brief the crew on which line goes first, where to make it fast, and the abort signal
- If the approach goes wrong, abort early — clearing out and starting over is always better than forcing a bad approach
- On the Mediterranean Moor, ensure the anchor is deployed in a straight line ahead of the intended berth — an offset anchor will cause the vessel to cant across neighboring boats when tension is applied
6. Spring Lines
Spring lines are the most powerful and most underused tool in the mariner's toolkit. Understanding how to use engines against springs is essential for single-screw maneuvering.
| Spring Line | Primary Use |
|---|---|
| After bow spring (leads aft from bow) | Back engine against spring to swing stern away from dock |
| Forward quarter spring (leads forward from stern) | Ahead engine against spring to swing bow away from dock |
| Forward bow spring (leads forward from bow) | Hold vessel from moving forward; control alongside berthing |
| After quarter spring (leads aft from stern) | Hold vessel from moving astern |
Forward Quarter Spring — Departure Technique
This is the standard single-screw departure. Take a line from the stern quarter, lead it forward, and make it fast to a dock cleat ahead of the vessel. Put the engine ahead (low power) with the helm turned away from the dock. The engine drives the bow away from the dock while the spring holds the stern. When the bow is well clear, slip the spring and back out. The right-handed prop walking stern to port on reversal helps swing the stern away from the dock as you back out.
After Bow Spring — Stern Out Technique
From the bow, lead a line aft to a dock cleat aft of the vessel. Put the engine astern (low power) with the helm turned toward the dock. The engine drives the stern away from the dock while the bow spring holds the bow against the dock. When the stern is well clear, slip the spring and power ahead. This is especially useful when the bow is hemmed in by a neighboring boat and you need to get the stern out first.
Spring Line Nomenclature — Exam Terminology
Spring line names describe where the line leads, not where it is attached. An 'after spring' leads aft. A 'forward spring' leads forward. Combined with bow/stern attachment point:
Forward bow spring
Attached at bow, leads forward along dock — prevents vessel from moving forward
After bow spring
Attached at bow, leads aft along dock — prevents vessel from moving aft; used to work stern out
Forward quarter spring
Attached at stern quarter, leads forward — the standard departure spring
After quarter spring
Attached at stern quarter, leads aft — prevents vessel from moving forward; used at fuel docks with current
7. Wind and Current Effects
Wind and current are external forces the mariner cannot control — but their effects are predictable and can be planned for.
| Condition | Effect on Vessel |
|---|---|
| Beam wind, no current | Leeway — vessel slides downwind of intended track |
| Following current | Vessel speed over ground increases; steering response feels sluggish relative to ground |
| Head current | Reduced speed over ground; vessel maneuvers more crisply relative to water |
| Cross-current during docking | Sets vessel onto or off the dock depending on direction |
| Strong beam current at anchor | Vessel lies beam to anchor rode; heavy snatch loading; possible dragging |
Leeway
Leeway is the sideways drift of a vessel caused by wind pressure on the hull, superstructure, and rigging. It is measured as the angle between the vessel's heading and its actual track over the ground. A vessel making 10 degrees of leeway is pointing 10 degrees upwind of its actual course made good.
High-windage vessels (sailboats, power yachts with tall superstructures) make more leeway than low-profile vessels. Leeway is most pronounced at slow speeds because there is less hydrodynamic grip on the keel or hull.
Ferry Angle
The ferry angle is the heading offset required to maintain a straight track across a current. A vessel crossing a river with a 2-knot current while making 8 knots through the water must angle upstream. The ferry angle is calculated using the ratio of current speed to vessel speed: sin(ferry angle) = current speed divided by vessel speed.
Cross-track error occurs when the ferry angle is insufficient — the vessel drifts downstream of the intended track. GPS chartplotters display cross-track error (XTE) directly.
Wind Effects During Maneuvering
Bow-heavy vs stern-heavy windage: Vessels with tall bows or raised foredecks will weathercock with the bow downwind — the bow blows away. Vessels with large cockpit enclosures or tall superstructures aft will weathercock with the bow into the wind. Knowing which way your vessel naturally lies to wind tells you how it will behave during a slow-speed maneuver.
Wind against prop walk: If a 20-knot beam wind is pushing the stern the same direction prop walk is pushing it, the effect is additive and much stronger than expected. If wind and prop walk oppose each other, they partially cancel. Always analyze wind direction relative to desired stern movement before maneuvering.
Docking downwind: Approaching a dock with the wind at your back means the wind is pushing you onto the dock. Reduce throttle early and use reverse to stop. The wind will close the gap for you — your task is to slow the approach so it is controlled. This sounds easy but is commonly bungled by leaving the throttle in forward too long.
8. Turning Characteristics
Advance, transfer, and tactical diameter are the three measured parameters of a vessel's turning circle. These appear directly on the USCG exam.
Advance
Distance traveled in original direction from helm-over to 90 degrees of turn completed
Transfer
Perpendicular distance vessel moves sideways during a 90-degree turn
Tactical Diameter
Perpendicular distance between original course and vessel position after 180-degree turn
Turning Circle Diameter
Diameter of the circle the vessel scribes at full rudder
Kick
Sideways movement of the stern in the opposite direction when helm is first applied
Turning Rate
Degrees per minute the vessel turns; increases with rudder angle and speed
Turning Circle Summary
A vessel's turning circle is measured by putting the helm hard over at a given speed and recording where the vessel travels. The key points to remember for the exam:
- Tactical diameter is always less than the turning circle diameter — the vessel spirals inward
- Advance is always greater than transfer for the same 90-degree turn
- Higher speed = larger turning circle (less effective rudder relative to momentum)
- More rudder angle = smaller turning circle but more drag and speed loss
- The kick (initial stern swing opposite to the turn) can cause momentary risk if close to an obstruction on the stern side
9. Stopping Distance and Crash Stop
Momentum kills. A vessel at 12 knots does not stop in 20 feet. Knowing stopping distance is fundamental to safe speed under Rule 6.
| Speed | Approx Stopping Distance |
|---|---|
| 6 knots | Approximately 1–2 boat lengths (small vessel) |
| 8 knots | Approximately 3–5 boat lengths |
| 12 knots | Approximately 6–10 boat lengths |
| 20 knots | Approximately 15–25 boat lengths |
| Crash stop from 12 knots | 3–5 boat lengths with immediate full reverse |
Why Stopping Distance Scales with Speed Squared
Kinetic energy equals one-half times mass times velocity squared. Double the speed and you quadruple the energy that must be dissipated to stop. This is why stopping distance at 12 knots is not merely twice that at 6 knots — it may be four times as long or more. The USCG exam may test this relationship directly.
Crash Stop — Full Astern Emergency
A crash stop is achieved by shifting immediately to full astern from any forward speed. The limitations:
- Propeller cavitation occurs in the transition — prop loses efficiency momentarily
- Prop walk will swing the stern during crash stop — bow swings toward one side
- Rudder becomes ineffective as forward speed drops — vessel is not steerable during the stop
- Transmissions and stern gear stress: always follow manufacturer guidelines for crash stops
Safe Speed — Rule 6 Factors
ColRegs Rule 6 requires every vessel to proceed at a safe speed so it can take proper and effective action to avoid collision and stop within a distance appropriate to the prevailing circumstances. The exam tests which factors are listed in Rule 6:
10. Anchoring Under Power
Anchoring is one of the most frequently tested practical skills on the USCG exam. Know the scope formula cold.
Scope Formula — Memorize This
Scope = Rode Length ÷ (Water Depth + Bow Height)
Minimum 5:1 for calm conditions with all chain. Standard 7:1 for rope/chain rode. 10:1+ in heavy weather.
Example 1
15 ft depth + 4 ft bow = 19 ft total. At 7:1 scope: 133 ft of rode.
Example 2
30 ft depth + 5 ft bow = 35 ft. At 7:1 scope: 245 ft of rode.
Tidal Adjustment
Add maximum tidal range to depth before calculating scope.
Pre-approach
- Select anchorage: check chart for depth, holding ground, swinging room
- Calculate scope needed: (depth + bow height) times scope ratio
- Prepare anchor: flake rode on deck, attach to windlass, open chock
- Identify hazards: other vessels, shoals, mooring balls, cables
Approach
- Approach from downwind/down-current into wind or current
- Slow to bare steerage as you reach the drop point
- Mark your drop point relative to landmarks or GPS
- Stop the vessel — do not drop while still moving ahead
Setting the anchor
- Lower anchor to bottom — do not throw it
- Allow vessel to drift back (or use reverse) while paying out rode
- When full scope is deployed, snub the rode briefly
- Apply astern power to set the anchor — feel for drag vs hold
- Confirm holding: take bearings on fixed objects ashore
Riding at anchor
- Display anchor ball (day) or white all-round anchor light (night)
- Record GPS position and set anchor drag alarm
- Calculate swinging circle: scope radius plus vessel length
- Check for nearby vessels within your swinging circle
Holding Ground Types
Sand: Excellent holding; most anchors perform well
Mud: Good holding with enough scope; plow and Danforth-style anchors excel
Clay: Good holding but anchor may be difficult to break out
Rock: Poor holding; anchor may not set; fouling risk
Weed / Grass: Poor holding; anchor slides on top of vegetation
Swinging Room Calculation
Swinging room = length of rode deployed + length of vessel. All vessels at anchor swing around their anchor in a circle of this radius. If two vessels are anchored near each other with different amounts of rode out, they may collide as wind shifts — each vessel traces a different-sized circle around its own anchor.
Also account for: tidal variation changing scope; other vessels with different windage that swing at different rates; and the direction of dominant current vs wind.
11. Man Overboard Recovery
MOB is a life-safety emergency. The exam tests your knowledge of the three primary recovery patterns — know when to use each.
Immediate Actions — All Methods
Quick Stop
Use when: MOB seen; calm to moderate conditions; motor vessel
- 1.Immediately hard over toward MOB side
- 2.Maintain full turn — nearly a circle
- 3.Reduce speed on final approach
- 4.Approach from downwind/down-current
- 5.Stop with victim at swim platform or boarding ladder
Williamson Turn
Use when: MOB not seen; poor visibility; restricted water
- 1.Hard over to MOB side (or either side if unknown)
- 2.At 60 degrees off original heading, shift to full opposite rudder
- 3.Continue turn until on reciprocal heading (180 degrees)
- 4.Advance on reciprocal track until victim found
Racetrack (Anderson Turn)
Use when: MOB seen and remaining in sight; offshore powerboat
- 1.Hard over to MOB side immediately
- 2.Complete a 270-degree turn (three-quarter circle)
- 3.Vessel ends up on a reciprocal course offset to windward of MOB
- 4.Approach from upwind/up-current
Final Approach to MOB
The final approach to a person in the water should always be made from downwind and/or down-current, approaching into the wind or current. This means:
- The wind helps you slow and stop near the victim
- The vessel does not drift onto the victim while stopped
- The vessel's lee side (downwind side) is calmer and lower in the water for retrieval
- Stop the engine when the victim is within 10–15 feet to prevent propeller strike
- In heavy seas, approach bow-into-waves to maintain control even if this means approaching from upwind
12. Restricted Visibility Maneuvering
Rule 19 governs restricted visibility — fog, rain, snow, haze. The rules change significantly from clear-weather rules.
Rule 19 Requirements
- Safe speed: reduce to allow stopping in available distance
- Engines ready: must be able to maneuver immediately
- Radar plot: if radar-equipped, use it and plot contacts
- Sound signals: sound required signals every 2 minutes
- No overtaking rules: Rule 13 (overtaking) and Rule 15 (crossing) do not apply in restricted visibility
- Fog signal forward: if you hear a fog signal forward of the beam, stop or slow to minimum — do not increase speed
Sound Signals in Restricted Visibility (Rule 35)
Radar Use in Restricted Visibility
Having radar does not change the obligation to proceed at safe speed — it merely changes the factors used to determine what safe speed is (Rule 6 lists radar capability as a factor). Radar-equipped vessels must use radar properly, which means:
- Plot contacts: determine course, speed, and closest point of approach (CPA) for each target
- Do not assume: a single radar observation is not a plot — take multiple ranges and bearings
- Small vessels: many small boats and debris have poor radar cross-sections — radar is not all-seeing
- AIS supplement: AIS-equipped targets show course, speed, and MMSI — correlate with radar
- Action timing: if evasive action is required, take it early — radar range gives advance warning but the fog signal is the legal trigger under Rule 19(d)
13. USCG Exam Tips — Vessel Handling
The exam tests conceptual knowledge, not hands-on skill. Know the vocabulary, the formulas, and the patterns.
What the Exam Tests Most
- Direction of prop walk in forward and reverse (right-handed vs left-handed)
- Location of pivot point when making headway vs backing
- Scope calculation given depth and bow height
- MOB recovery method selection (Quick Stop vs Williamson)
- Advance vs transfer vs tactical diameter definitions
- Which spring line to use for a given departure scenario
- Sound signals in restricted visibility
- Effect of current on docking approach angle
Common Mistakes on the Exam
- Confusing forward spring with after spring — read the question carefully for which direction the line leads
- Forgetting to add bow height to water depth in scope calculations
- Selecting Williamson Turn for a visible MOB in calm conditions (Quick Stop is faster)
- Believing tactical diameter equals turning circle diameter
- Applying overtaking/crossing rules in restricted visibility — Rule 19 supersedes them
- Stating that prop walk direction is the same in forward and reverse — it reverses
- Forgetting that pivot point shifts forward when underway ahead — not aft
Key Formulas and Numbers to Memorize
Scope calculation
Scope = Rode ÷ (Depth + Bow Height)
Anchoring
7:1 scope — standard rope/chain
Maneuvering
Pivot point 1/3 from bow underway
Maneuvering
Pivot point 1/4 from stern when backing
Prop walk
Right-handed prop: stern to port in reverse
MOB
Williamson Turn: hard over, shift at 60 degrees, reciprocal at 180
Turning
Advance greater than transfer (90-degree turn)
Turning
Tactical diameter less than turning circle diameter
Stopping
KE = ½mv² — double speed, quadruple stopping distance
14. Practice Problems with Solutions
Work through these before your exam. Expand each answer only after writing your own answer.
Problem 1 — Scope Calculation: You anchor in 18 feet of water. Your bow chock is 4 feet above the waterline. What length of rope/chain rode must you deploy for a 7:1 scope?
Solution:
Total depth = water depth + bow height = 18 + 4 = 22 feet.
Rode needed = 22 feet times 7 = 154 feet.
Note: If there is a 3-foot tidal rise expected, add it: (18 + 3 + 4) times 7 = 175 feet. Always account for the maximum depth during your stay at anchor, not just the depth when you drop.
Problem 2 — Prop Walk: Your right-handed single-screw vessel is backing into a slip. Which direction will the stern walk, and how should you plan for it?
Solution:
In reverse, a right-handed propeller walks the stern to port.
Planning: If your slip is oriented so port-kick helps you (e.g., backing into a slip with the port side toward the dock), angle your approach to allow the stern to naturally kick toward the dock. If the kick works against you (backing in with starboard toward the dock), you must counter the kick with short forward bursts and opposite rudder, or use a bow thruster if available.
Problem 3 — Pivot Point: A vessel moving ahead at 6 knots puts the helm hard to starboard. The bow swings to starboard. Relative to vessel length, which end sweeps the larger arc?
Solution:
The stern sweeps the larger arc.
When making headway, the pivot point is approximately 1/3 of the vessel's length from the bow. The bow, being close to the pivot point, swings a relatively short arc. The stern, being roughly 2/3 of the vessel length from the pivot point, swings a much larger arc. This is why collisions often occur stern-to-stern in narrow channels when vessels turn.
Problem 4 — Spring Lines: You are moored port-side-to and need to leave the dock. A 15-knot wind is blowing directly onto the dock. Which spring line technique do you use, and describe the steps?
Solution:
Use the forward quarter spring (leading forward from the stern quarter).
- 1. Cast off all lines except the forward quarter spring.
- 2. Put the engine ahead at low power, helm turned away from the dock (to starboard in this case).
- 3. The spring holds the stern from surging forward while the engine thrust pushes the bow away from the dock against the wind.
- 4. Once the bow is well clear of the dock (and clear of any vessel forward of you), slip the spring and back away.
- 5. The wind will push the bow back toward the dock as you back — be ready to turn toward open water immediately after clearing.
Problem 5 — MOB Recovery: A crewmember falls overboard at 0200 in heavy fog. You did not see them go in. Which MOB recovery method do you use and why?
Solution:
Use the Williamson Turn.
Reasoning: The Williamson Turn is designed precisely for this situation — when the MOB is not seen and the incident may have occurred some time before discovery. It returns the vessel to its exact original track line, which is where the victim is most likely to be found drifting. In fog, keeping the victim in visual sight (the advantage of Quick Stop) is impossible anyway. Steps: hard over to either side, shift to full opposite rudder at 60 degrees off original heading, complete the turn to the reciprocal course (180 degrees), advance along the reciprocal track sounding horn signals and using radar.
Problem 6 — Turning Terms: A vessel completes a full 180-degree turn at full rudder. The original course was 090 degrees. After the turn the vessel is on 270 degrees. Define the tactical diameter and explain how it differs from the vessel's turning circle diameter.
Solution:
Tactical diameter is the perpendicular distance between the original course line (090 degrees) and the vessel's position when it has turned 180 degrees (now heading 270 degrees). It is measured as the lateral offset from the original track.
Turning circle diameter is the diameter of the full circle the vessel would scribe if it continued turning at full rudder. Tactical diameter is always less than the turning circle diameter because the vessel spirals inward as it turns — it does not maintain a constant radius. The vessel's speed decays during the turn (due to drag), which causes the turning radius to tighten. The net result is that the 180-degree offset (tactical diameter) is less than the full circle diameter.
Problem 7 — Restricted Visibility: You are underway at 10 knots in fog. You hear one prolonged blast fine on your port bow. What does the signal mean, what action must you take under Rule 19, and what is the minimum action required?
Solution:
Signal meaning: One prolonged blast every 2 minutes indicates a power-driven vessel making way through the water.
Rule 19 action: You hear a fog signal from a vessel that is forward of your beam (fine on the port bow). Rule 19(d)(ii) states you must reduce your speed to the minimum at which you can be kept on course, unless you have determined there is no risk of collision. If necessary, take all way off and navigate with extreme caution until the vessel passes.
Critical point: You must NOT increase speed. You must NOT assume the other vessel will alter course. The correct immediate action is to reduce to minimum steerage speed and assess using radar. Do not alter course until you have determined the contact's bearing, course, and CPA. An alteration to starboard for a vessel forward of the beam is generally safest, but only after confirming the situation on radar.
Problem 8 — Docking Scenario: You are approaching a dock port-side-to in a 20-knot beam wind blowing off the dock. Describe your approach strategy.
Solution:
A wind blowing off the dock is working against you — it will push the vessel away from the dock during the final approach. Strategy:
- 1. Approach at a steeper angle than normal — 45 to 60 degrees — so you have positive forward progress against the wind.
- 2. Aim the bow at a point on the dock slightly forward of the intended berth.
- 3. As the bow touches or closes to within a few feet, get a bow line ashore immediately — this is your anchor point.
- 4. With the bow secured, the wind will pivot the stern downwind (away from the dock). You must counter this: use the engine in forward with helm toward the dock, or use a stern thruster, or have a crew member ashore take a stern line quickly.
- 5. Set up a forward quarter spring as the next priority — this allows you to work the engine against the spring to bring the stern in against the wind.
Alternative: If the marina allows, request a different berth on the windward side where the wind pushes you onto the dock instead of off it.
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