2026-05-07 · Product Knowledge

Position Measurement for Marine Steering Gear and Hatch Cover Cylinders

Position measurement on ships concentrates on three classes of mechanism: steering-gear cylinders (stroke feedback converted to rudder angle, closed-loop control and returned to the bridge indicator), hatch-cover / ramp / bow-and-stern-door cylinders (open/close in-position and safety interlock), and controllable-pitch propeller and fin-stabiliser mechanisms (angle or stroke feedback). The common environment of all three is salt-spray corrosion, continuous roll and vibration, high humidity and condensation, and long cable runs; protection and weather resistance outweigh accuracy at selection. Absolute-position output of a magnetostrictive displacement sensor guarantees that rudder angle and hatch-cover state can be read immediately after power loss or a system restart, with no homing.

Steering-gear cylinders: reliability of rudder-angle feedback first

Rudder-angle feedback is the closed-loop input of the steering system and also drives the bridge rudder-angle indicator. The core requirement here is not micrometre-level accuracy — rudder-angle control is usually in degrees — but no long-term drift, no loss of position on power-down, and diagnosable faults. Traditional schemes often use a linkage plus a rotary potentiometer or resolver; the mechanical linkage develops play under roll and corrosion, and error grows with time. Measuring cylinder stroke directly shortens the measuring chain; because steering gear is a high-pressure hydraulic system, in-cylinder types must check pressure rating (by series: Series 16/16R is 350 bar working / 530 bar peak, Series 17/17EX is 350/600 bar, Series 19 in-cylinder is 300/600 bar) and the minimum piston-rod bore (generally ≥12.7 mm). Related products include Series 16 cylinder-integrated; general hydraulic closed-loop points are in Why Choose Magnetostrictive Sensing for Hydraulic Cylinder Position Control.

Hatch covers and ramps: in-position criterion and safety interlock

Hatch covers, ramps and bow/stern doors are typical opening-and-closing mechanisms; the role of position feedback is to give a continuous opening, not merely the two states of a limit switch. Continuous opening can be used for deceleration control (slowing near close to reduce shock), anomaly detection (a lengthening move time at the same opening indicating mechanism degradation) and a safety interlock (confirming fully closed under way). These measuring points have a longer stroke and are exposed on deck; external mounting needs a guard and a high-protection model. Deck areas with frequent wash-down should use IP69K; what the classes actually mean is in IP65/67/68/69K Is Not a Numbers Game. Series 13 mobile hydraulics is an option (25 g vibration / 100 g shock).

Marine measuring-point selection comparison

Mechanism	Feedback use	Recommended form	Protection suggestion	Interface suggestion
Steering-gear cylinder	Rudder-angle closed loop and indication	In-cylinder	IP67 and above	4-20 mA or CANopen
Hatch-cover / ramp cylinder	Opening, in-position interlock	In-cylinder or guarded external	IP67/IP69K	4-20 mA
Bow/stern-door / ramp lock cylinder	Lock in-position confirmation	Short-stroke in-cylinder	IP67 and above	Discrete + analog
Fin stabiliser / CPP	Angle conversion	In-cylinder	IP67 and above	Fieldbus preferred

Three endurances: salt spray, vibration and electromagnetics

Salt-spray corrosion mainly attacks connectors and cable jackets: choose high-protection connectors and seal them, keep cable runs off sections that pond water, and point connectors downward with a drip loop. Continuous roll and main-engine vibration slowly loosen fasteners; mounting brackets must be locked, and magnet-to-rod coaxiality degrades more easily under vibration. Installation practice is in Installing Magnetostrictive Displacement Sensors in Practice. The electromagnetic environment in the engine room from drives, generators and radar is complex; shield and earthing practice for the signal loop is in EMC: Why Strong Magnetic Fields Disturb Measurement.

Differences from land-based hydraulic scenes

The largest difference between marine and land-based heavy hydraulics is maintenance window and redundancy thinking: a critical sensor cannot be replaced under way, so steering-gear and similar critical loops usually require dual-channel or spare feedback; design principles are in What Is Redundant Output? The Story Behind Dual-Channel Safety Design. Control logic of opening-and-closing mechanisms is close to lifts and gates — see Elevator Traction and Hydraulic Lift Cylinder Monitoring and Water Gates and Hoists: Maintenance-Free Outdoor Long-Stroke Measurement.

Practical tips for engineers

For in-cylinder mounting, piston-rod bore lower limit is ≥12.7 mm (Ø10 rod). Series 17 also has a Ø13 mm through-hole + M18×1.5 on the cylinder cap; Series 16 uses Ø18G7. Do not mix pressure ratings: Series 16/16R is 350 bar working / 530 bar peak, Series 17/17EX is 350/600 bar, Series 19 in-cylinder is 300/600 bar.
The sensor rod should be protected against wear inside the cylinder.
Series 19 in-cylinder types are rated 300 bar with a 600 bar peak; use these figures for selection and pressure testing.

Frequently Asked Questions

Q: How is rudder-angle position measured?

It is converted from steering-gear cylinder stroke or tiller angle. Magnetostrictive sensing reads absolute position directly, so rudder angle is not lost on power-down, which benefits navigation safety.

Q: How is a marine salt-spray environment protected against?

Choose IP67 or above, salt-spray-resistant materials and coatings, and point connectors downward; wet zones can use Series 13 IP69K.

Q: Do critical mechanisms need redundancy?

Safety-related mechanisms such as steering gear should use dual-channel redundancy, so that the other channel can still be read if one fails; see Series 16R redundant in-cylinder.