Steering Gear and Auxiliary Machinery: What Must Work, and From Where

What the rule requires

The two rudder clocks

Each self-propelled vessel must be provided with a main steering gear and an auxiliary steering gear, arranged so that the failure of one will not render the other inoperative and so that transfer from main to auxiliary can be effected quickly 46 CFR §58.25-5.

The main gear and rudder stock must be of adequate strength for and capable of steering the vessel at maximum ahead service speed, and capable of moving the rudder from 35° on either side to 35° on the other at deepest load line draft and maximum ahead service speed — with the 28-second limit attached to the 35°-to-30° sweep under those same conditions 46 CFR §58.25-10. The gear must also be designed so it will not be damaged when operating at maximum astern speed, though that need not be proved by trials at maximum astern speed and maximum rudder angle.

The auxiliary gear must be of adequate strength, capable of steering at navigable speed, capable of being brought speedily into action in an emergency, and capable of the 15°-to-15° swing in not more than 60 seconds at deepest load line draft and one-half maximum ahead service speed or 7 knots, whichever is greater.

Maximum ahead service speed is the greatest speed the vessel is designed to maintain in service at sea at the deepest load line draft — not a trial speed and not a bell setting .

When the gear must be power operated

Two different rudder stock diameters govern, and they are easy to swap under time pressure. Main steering gear must be power operated when necessary to meet the 28-second requirement, or when the rudder stock diameter is over 12 centimetres (4.7 inches) in way of the tiller, excluding strengthening for navigation in ice. Auxiliary steering gear must be power operated when necessary to meet its 60-second requirement, or when the stock diameter is over 23 centimetres (9 inches) in way of the tiller .

When no auxiliary gear need be fitted

Double-ended ferryboat with independent main steering gear fitted at each end — no auxiliary means of steering required.
Main gear with two or more identical power units, and one of four conditions met: on a passenger vessel, the gear meets the 28-second performance with any one power unit not operating; on a cargo vessel, it meets that performance with all power units operating; for an installation completed after June 9, 1995 (or on or after September 1, 1984 on an international voyage), a single failure in the hydraulic piping or in one power unit can be isolated so steering is maintained or speedily regained in less than ten minutes; or, for a pre-September 1, 1986 international installation not meeting that isolation standard, the gear has a proved record of reliability and is in good repair.

Vessels of 70,000 gross tons or over do not get a choice: the main steering gear must have two or more identical power units. And no thruster counts toward required steering capability except on a vessel with an integrated system of propulsion and steering .

Small passenger vessels are governed separately. Under subchapter T the auxiliary means of steering must meet the same 15°/15°/60-second standard, must be of adequate strength, and must be controlled from a location that permits safe manoeuvring without exposing the operator to personnel hazards in normal or heavy weather. A suitable hand tiller may be accepted where the cognizant OCMI is satisfied, and no auxiliary is required where the main gear and its controls are duplicated, where multiple screws with independent pilothouse control can steer the vessel, where no regular rudder is fitted and steering is by changing the setting of the propelling unit, or where a rudder and hand tiller are the main steering gear 46 CFR §182.620.

Your vessel's maximum ahead service speed is 12 knots. At what speed is the auxiliary steering gear demonstrated, and how long may the 15°-to-15° swing take?

At 7 knots, in not more than 60 seconds. One-half of 12 knots is 6 knots, which is below the 7-knot floor, so the greater figure — 7 knots — governs . The 60 seconds does not change with speed.

Where the controls live

Every power-driven steering-gear system must have at least one steering-gear control system, and the main gear must be operable from the pilothouse with full followup control of the rudder; supplementary control not giving full followup may also be provided there 46 CFR §58.25-70. Full followup control is closed-loop control relating helm position to a specific rudder angle, stopping the rudder automatically when the selected angle is reached .

The pilothouse transfer switch is a favourite question. One operation of its lever must automatically supply power to a complete system and its associated power unit or units; it is operated by one lever, arranged so not more than one control system and its power units can be energized from the pilothouse at any one time, so the lever passes through "off" during transfer, and so the switches for each control system are in separate enclosures or separated by fire-resistant barriers .

Four things must be in the steering-gear compartment: a switch that disconnects each control system from its power source and from the gear it serves, each motor controller, a means of starting and stopping each motor, and — on a vessel of 500 gross tons or above — controls by which each main and auxiliary gear's power units are operable locally, which must not be rendered inoperable by failure of the controls in the pilothouse.

Automatic pilots and ancillary steering gear must allow immediate resumption of manual operation of the required pilothouse control system, and a switch must be provided at the primary steering position in the pilothouse to completely disconnect the automatic equipment from the steering-gear controls. No single failure in that automatic equipment may affect the proper operation and independence of the main or auxiliary gear, the required controls, the rudder-angle indicators, or the steering-failure alarm 46 CFR §58.25-80.

Inside an electro-hydraulic gear

The gear transmits power from the steering engine to the rudder stock. A common arrangement is a ram unit mounted athwartship — a single ram worked by opposed cylinders, connected by links to the tillers of twin rudders — served by a power unit containing two independent pumping systems, one on service and one on standby. Each pumping system has a variable-delivery axial-piston main pump and a vane-type auxiliary pump driven by a single electric motor through a flexible coupling; the auxiliary pump supplies control oil and supercharge flow. The on-service main pump runs constantly, but its tilt box sits at zero stroke and moves no oil in the main system until steering is called for NAVEDTRA 14104 Ch. 10 — Electrohydraulic Steering.

Two transfer valves are linked to one hand lever, usually between the trick wheels, with positions P (port pump on the ram), N (neutral, neither pump connected) and S (starboard pump on the ram). Because both valves move together, one pump lines up to the ram while the other is isolated, and both can never be lined up at once. The lever is normally connected to the motor switches, so selecting a pump and starting its drive motor is one operation.

Follow-up comes from a rack on the rudder yoke driving pinions and follow-up shafts back into the differential control box. As the ordered angle is approached the box realigns the tilt box, and at the ordered angle the tilt box is at zero stroke — ordered signal and actual signal agree. Trick wheels give local hydraulic control if the remote steering system fails; a hand pump and its service lines give local manual operation of the ram if both hydraulic pump units fail.

The bridge reports no rudder response to the helm. The pumps are running normally and hydraulic pressure is good. What is your first steering alternative, and what is left if both pump units are then lost?

Take local hydraulic control at the trick wheel — that is what it is provided for when the remote steering system fails. If both hydraulic pump units fail, local manual operation of the ram is by the hand pump and its associated service lines . Watch checks that catch this developing are oil level and pressure, absence of leaks, rudder response to helm orders, and correct functioning of rudder-angle indicators and alarms; low oil level, an overheating pump, or sluggish or hunting rudder response are reported and corrected at once NAVEDTRA 14104 §10-2.

Remote stopping, ventilation, and fluid power scope

At each inspection for certification and periodic inspection, remote control for the means of stopping machinery driving forced and induced draft fans, fuel oil transfer pumps, fuel oil unit pumps, and fans in the ventilation systems serving machinery and cargo spaces must be tested 46 CFR §61.20-3. Learn that list as a list; distractors are built by substituting a pump that is not on it.

Machinery space ventilation is judged against a worst case, not normal operation: each machinery space must be ventilated so that with machinery or boilers at full power in all weather including heavy weather, an adequate supply of air is maintained for operation of the machinery and for the safety, efficiency and comfort of the crew 46 CFR §58.01-45.

The fluid power subpart reaches further than the steering gear. Its detailed requirements apply to main and auxiliary steering apparatus including bow thruster systems, cargo hatch operating systems, watertight door operating systems, automatic propulsion boiler control, starting systems for internal combustion engines used for main propulsion or auxiliary power or as prime mover for required emergency apparatus, centralized control systems, lifeboat handling equipment, controllable pitch propeller systems, all systems containing a pneumatic or hydropneumatic accumulator, and all pneumatic power and control systems with a maximum allowable working pressure over 150 psig 46 CFR §58.30-1. A system counts as fail-safe only if a component failure results in a slow and controlled release of the loading so as not to endanger personnel.

Two smaller values worth knowing because they are easy to ask: heating boilers must be tested or examined every three years 46 CFR §182.310, and automation of vital systems under part 62 excludes steering systems, which are referred back to subpart 58.25 and to subpart 111.93 46 CFR §62.01-5.

Telling it apart

Seven defined terms cover the chain from helm to rudder stock. The criterion is which link of the chain the term names 46 CFR §58.25-5.

Steering gear — the whole machinery: power actuating systems, control systems and ancillary equipment necessary for moving the rudder to steer the vessel. The broadest of the seven.
Main steering gear — the machinery, including power actuating systems, and the means of applying torque to the rudder stock, such as a tiller or quadrant, necessary for moving the rudder in normal service.
Auxiliary steering gear — the equipment, other than any part of the main steering gear, necessary to steer in case of failure of the main gear. It expressly does not include a tiller, quadrant or other component serving the same purpose, so a shared quadrant is not the auxiliary gear.
Control system — the equipment transmitting orders for rudder movement from the pilothouse to the steering-gear power units: transmitters, receivers, feedback devices, hydraulic servo-control pumps with their motors and controllers, differential units and hunting gear, the gearing, piping, shafting, cables and circuitry, and the means of bringing power units into operation.
Power actuating system — the hydraulic equipment applying torque to the rudder stock: rudder actuators, steering-gear power units, and the pipes, valves, fittings, linkages and cables transmitting power from the units to the actuators.
Steering-gear power unit — for electro-hydraulic gear, an electric motor, connected pump and associated electrical equipment such as motor controller, disconnect switch and feeder circuit; for hydraulic gear, the pump and its prime mover.
Ancillary steering gear — steering equipment other than the required control systems and power actuating systems that either is not required at all, such as an automatic pilot or non-followup control from the pilothouse, or performs a specific required function such as automatic detection and isolation of a defective section of a tanker's hydraulic steering gear.

Working a question

A 1,600 gross ton freight vessel, maximum ahead service speed 14 knots, rudder stock 6 inches in diameter in way of the tiller, electro-hydraulic gear with two identical pump units and no separate auxiliary gear fitted. The marine inspector asks you to demonstrate compliance.

Identify which gear is in question. Two identical power units serving one gear is a main-steering-gear arrangement, so the main gear standard applies, and the question of whether an auxiliary is required is answered by the exemption for identical power units 46 CFR §58.25-10.
Decide whether power operation is mandatory. Stock diameter 6 inches is over 4.7 inches, so the main gear must be operated by power regardless of what the timing trial shows.
Apply the main gear clock. 35° on either side to 30° on the other, not more than 28 seconds, at deepest load line draft and 14 knots. Not hard-over to hard-over, and not at half speed.
Test the exemption on the right side. This is a cargo vessel, so the applicable condition is that the gear meets that 28-second performance with all power units operating. Applied to a passenger vessel the condition would be tougher — the performance must be met with any one power unit not operating.
Check the single-failure condition for the installation date. For an installation completed after June 9, 1995, a single failure in the piping or in one power unit must be capable of isolation so that steering capability is maintained or speedily regained in less than ten minutes. Where isolation valves join the piping by a flange, that joint is itself a single-failure point.
Verify the local controls. 1,600 gross tons is above the 500-gross-ton threshold, so the power units must be operable by controls in the steering-gear compartment that survive failure of the pilothouse controls; the motor controller and the means of starting and stopping each motor must be in that compartment as well 46 CFR §58.25-70.

Where candidates lose the point

Attaching the 28 seconds to hard-over to hard-over. The 35°-to-35° swing is required, but the 28-second limit is written on the 35°-to-30° sweep. An option reading "35° to 35° in 28 seconds" is a distractor built on exactly this slip.
Halving the service speed and stopping there. On a vessel making 12 knots or less, half speed falls below the 7-knot floor, and the auxiliary gear is demonstrated at 7 knots. Candidates who compute 6 knots have done the arithmetic and missed the rule.
Swapping 4.7 inches and 9 inches. Both numbers sit in the same section. The smaller diameter belongs to the main gear, the larger to the auxiliary — the more capable gear carries the tighter trigger.
Counting the bow thruster as steering capability. It is plausible on deck and wrong on paper: no thruster counts toward required steering capability except on a vessel with an integrated system of propulsion and steering 46 CFR §58.25-5. Note that thruster fluid power systems are inside the fluid power subpart, which is a different question 46 CFR §58.30-1.
Putting the autopilot disconnect in the steering-gear room. The switch that completely disconnects the automatic equipment from the steering-gear controls is at the primary steering position in the pilothouse 46 CFR §58.25-80. The switch in the steering-gear compartment is the one that disconnects a control system from its power source and from the gear it serves.
Lining up both pumps to the ram to get more force. The linked transfer valves exist to prevent that; the arrangement puts one pump on the ram with the other isolated, and the hand lever's N position connects neither NAVEDTRA 14104 Ch. 10 — Electrohydraulic Steering.

Check yourself

You are asked at what draft and speed the main steering gear timing trial is run. What do you answer?

At the vessel's deepest load line draft, running at maximum ahead service speed — the greatest speed the vessel is designed to maintain in service at sea at that draft 46 CFR §58.25-10, 46 CFR §58.25-5.

A double-ended ferryboat has independent main steering gear at each end. What auxiliary steering requirement applies?

None. No auxiliary means of steering is required on a double-ended ferryboat with independent main steering gear fitted at each end .

The pilothouse transfer switch is being examined. Name two arrangements the inspector is verifying beyond the fact that it works.

That not more than one control system and its associated power units can be energized from the pilothouse at any one time, and that the lever passes through "off" during transfer from one control system to another. The switch must also be operated by one lever, with the switches for each control system in separate enclosures or separated by fire-resistant barriers 46 CFR §58.25-70.

Which remote stopping controls must be tested at each inspection for certification and periodic inspection?

Those for machinery driving forced and induced draft fans, fuel oil transfer pumps, fuel oil unit pumps, and fans in the ventilation systems serving machinery and cargo spaces 46 CFR §61.20-3.

A hydraulically operated cargo hatch system is claimed to be exempt from the detailed fluid power requirements as fail-safe. What must be shown?

That an alternate mechanical means of operation is fitted and that the Commandant has approved the system as hydraulically or pneumatically fail-safe, meaning a component failure results in a slow and controlled release of the loading so as not to endanger personnel 46 CFR §58.30-1.

On an oceangoing vessel with power-operated steering gear, what arrangement is required for shifting from one steering gear to another?

Arrangements for steadying the rudder, both in an emergency and during the shift. On hydraulic gear, a suitable arrangement of stop valves in the main piping is acceptable .

You find the machinery space ventilation adequate at normal sea load but marginal with the boiler at full output in a gale. Is that acceptable?

No. The space must be ventilated so that with machinery or boilers operating at full power in all weather including heavy weather, an adequate supply of air is maintained for the operation of the machinery and for the safety, efficiency and comfort of the crew 46 CFR §58.01-45.