Single-Screw Maneuvering, Prop Walk, and the Regulatory Framework for Vessel Handling

TL;DR — The master or licensed mate must direct vessel movement at all times, accounting for the vessel's handling characteristics; pre-departure equipment tests (steering, propulsion, communications) must be completed within 12 hours of getting underway, and an emergency steering drill must be logged within 48 hours of entering U.S. waters.

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What the Rule Says

Who Controls the Vessel

Under 46 CFR §185.304, the movement of a vessel must be under the direction and control of the master or a licensed mate at all times. The master is specifically required to keep the safety of passengers and crew foremost in mind and to direct the vessel so as to prevent a casualty. 33 CFR §164.11 reinforces this by requiring the wheelhouse to be constantly manned by persons who both direct and control the movement of the vessel and fix the vessel's position, and that each such person is competent to perform that duty.

Factors the Conning Officer Must Know

Both 33 CFR §164.11 and 46 CFR §185.304 enumerate the factors the person directing movement must actively consider. These include:

• Current velocity and direction for the area to be transited 33 CFR §164.11
• Predicted set and drift 33 CFR §164.11
• Tidal state 33 CFR §164.11
• Prevailing visibility and weather conditions 33 CFR §164.11
• Density of marine traffic 33 CFR §164.11
• Damage that might be caused by the vessel's wake 33 CFR §164.11
• The vessel's handling characteristics 46 CFR §185.304
• Magnetic variation, deviation, and gyrocompass errors 33 CFR §164.11
• The tendency of the vessel to squat and suffer impaired maneuverability when underkeel clearance is small 33 CFR §164.11

The vessel's handling characteristics are explicitly listed as a factor requiring special attention 46 CFR §185.304. This is the regulatory hook for understanding how a single-screw vessel behaves differently from a twin-screw vessel — the conning officer must know the vessel's peculiarities before getting underway.

Maneuvering Information Required on the Bridge

33 CFR §164.35 requires that specific maneuvering information be prominently displayed on a fact sheet in the wheelhouse. This includes:

• A turning circle diagram to port and starboard showing time, distance, advance, and transfer required to alter course 90 degrees with maximum rudder angle and constant power settings 33 CFR §164.35
• Time and distance to stop the vessel from full and half speeds (or full and slow speeds), maintaining approximately the initial heading with minimum rudder application 33 CFR §164.35
• For a vessel with a fixed propeller, a table of shaft revolutions per minute for a representative range of speeds 33 CFR §164.35
• For a vessel with a controllable pitch propeller, a table of control settings for a representative range of speeds 33 CFR §164.35

Critically, the maneuvering data on that fact sheet is valid only under the following baseline conditions: calm weather (wind 10 knots or less, calm sea), no current, deep water (water depth at least twice the vessel's draft), and clean hull 33 CFR §164.35. The fact sheet must carry a warning statement that vessel response may differ if any of those conditions — or intermediate drafts or unusual trim — are varied 33 CFR §164.35.

If a pilot not a member of the crew is employed, that pilot must be informed of the vessel's draft, maneuvering characteristics, and peculiarities, as well as any abnormal circumstances that may affect safe navigation 33 CFR §164.11.

Pre-Departure Equipment Tests

No person may cause a vessel to get underway on the navigable waters of the United States unless, within the preceding 12 hours, the following have been tested 33 CFR §164.25:

1. Primary and secondary steering gear — including visual inspection of the gear and connecting linkage, operation of each remote steering gear control system, each bridge steering position, the main steering gear from the alternative power supply if installed, each rudder angle indicator against actual rudder position, each remote steering gear control system power failure alarm, each remote steering gear power unit failure alarm, and full rudder movement 33 CFR §164.25 2. All internal vessel control communications and vessel control alarms 33 CFR §164.25 3. Standby or emergency generator, for as long as necessary to show proper functioning including steady-state temperature and pressure readings 33 CFR §164.25 4. Storage batteries for emergency lighting and power systems in vessel control and propulsion machinery spaces 33 CFR §164.25 5. Main propulsion machinery, ahead and astern 33 CFR §164.25

Additionally, an emergency steering drill must have been conducted and logged within 48 hours prior to entry into U.S. waters, unless the drill is conducted and logged on a regular basis at least once every three months 33 CFR §164.25. That drill must include at minimum: operation of the main steering gear from within the steering gear compartment, operation of communications between the navigating bridge and the steering compartment, and operation of the alternative power supply for the steering gear if so equipped 33 CFR §164.25.

Propulsion Engine Control Requirements

A vessel must have two independent means of controlling each propulsion engine, providing control of engine speed, direction of shaft rotation, and engine shutdown 46 CFR §184.620. One of those means may be the ability to readily disconnect the remote engine control linkage to permit local operation 46 CFR §184.620. A propulsion engine control system must be designed so that a loss of power to the control system does not result in an increase in shaft speed or propeller pitch 46 CFR §184.620.

Internal Communications

A vessel equipped with pilothouse control must have a fixed means of two-way communications from the operating station to the location where propulsion machinery is controlled 46 CFR §184.602. A vessel equipped with an auxiliary means of steering must have a fixed means of two-way communications from the operating station to where that auxiliary steering is controlled 46 CFR §184.602. Where locations are sufficiently close together, direct voice communications satisfactory to the cognizant OCMI may substitute for a fixed system 46 CFR §184.602.

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Why It Matters on the Exam

Exam questions on this topic test three things simultaneously: regulatory compliance timelines, the content of required bridge documents, and the factors a master must account for when handling a vessel with specific propulsion characteristics.

The 12-hour rule for pre-departure tests under 33 CFR §164.25 is a frequent distractor. Candidates confuse it with the 48-hour emergency steering drill requirement. Know both numbers cold and know what each covers.

The maneuvering fact sheet required by 33 CFR §164.35 is tested directly. Candidates must know what information must appear on it (turning circles, stopping distances, RPM tables for fixed-pitch propellers, pitch tables for CPP vessels) and under what baseline conditions the data is valid. A question may ask what the fact sheet must state at the bottom — it must carry the warning that vessel response may differ if the listed baseline conditions are varied 33 CFR §164.35.

The vessel's handling characteristics are a required consideration under 46 CFR §185.304. The exam may present a scenario where a master fails to account for a known vessel peculiarity and ask which regulation was violated.

Squat is specifically called out in 33 CFR §164.11 as a factor affecting speed selection — the tendency of a vessel underway to squat and suffer impaired maneuverability when underkeel clearance is small. This is directly relevant to single-screw vessels operating in shallow or restricted waters.

Buoys alone may not be used to fix position 33 CFR §164.11. However, if no other aids are available, buoys alone may be used to establish an estimated position — not a fix. That distinction is tested.

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Common Pitfalls

Confusing the 12-hour and 48-hour requirements. The pre-departure equipment test window is 12 hours 33 CFR §164.25. The emergency steering drill must be within 48 hours of entry, or conducted at least once every three months on a regular logged basis 33 CFR §164.25. These are separate requirements with separate timelines.

Assuming the maneuvering fact sheet data applies in all conditions. The data is valid only under the four baseline conditions (calm weather, no current, deep water, clean hull) 33 CFR §164.35. Intermediate drafts or unusual trim also invalidate the data. A vessel in ballast, in a current, or in shallow water will not perform as the fact sheet shows.

Forgetting that rudder orders and engine orders must be executed as given. 33 CFR §164.11 requires that rudder orders are executed as given and that engine speed and direction orders are executed as given. This is not discretionary.

Overlooking the pilot briefing requirement. When a compulsory or voluntary pilot not a member of the crew is employed, the master must ensure the pilot is informed of draft, maneuvering characteristics, peculiarities, and any abnormal circumstances 33 CFR §164.11. Failure to do so is a regulatory violation, not merely a courtesy lapse.

Treating the Great Lakes exception as universal. Several requirements under 33 CFR §164.11 and 33 CFR §164.35 are excepted for vessels operating on the Great Lakes and their connecting and tributary waters. These include the continuous depth recording device, the RPM indicator, the CPP pitch indicator, and the lateral thrust indicator 33 CFR §164.35. Do not apply Great Lakes exceptions to coastal or inland waters outside that system.

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Quick Check

How many hours before getting underway must the pre-departure equipment tests be completed?

No more than 12 hours before entering or getting underway on the navigable waters of the United States. 33 CFR §164.25

What is the required frequency for emergency steering drills if not conducted within 48 hours of entry?

The drill must be conducted and logged on a regular basis at least once every three months. 33 CFR §164.25

Under what four baseline conditions is the maneuvering information on the wheelhouse fact sheet valid?

Calm weather (wind 10 knots or less, calm sea); no current; deep water (water depth twice the vessel's draft or greater); and clean hull. 33 CFR §164.35

May buoys alone be used to fix a vessel's position? What may they be used for?

No. Buoys alone may not be used to fix a vessel's position. However, if no other aids are available, buoys alone may be used to establish an estimated position. 33 CFR §164.11

What must a master inform a non-crew pilot of before the pilot takes the conn?

The master must ensure the pilot is informed of the vessel's draft, maneuvering characteristics, and peculiarities, and of any abnormal circumstances on the vessel that may affect its safe navigation. 33 CFR §164.11

What does 33 CFR §164.11 require regarding the vessel's tendency to squat?

The person directing movement must set the vessel's speed with consideration for the tendency of the vessel underway to squat and suffer impairment of maneuverability when there is small underkeel clearance. 33 CFR §164.11

What must a propulsion engine control system be designed to prevent in the event of a loss of power to the control system?

A loss of power to the control system must not result in an increase in shaft speed or propeller pitch. 46 CFR §184.620