Hydraulic Steering

By Tom Burden, Last updated 6/25/2019

Hynautic Three Line Helm Pump

The H-21 helm is a heavy-duty three-line helm used in Hynautic big boat systems.

Hydraulic steering makes handling high-torque engines and high-speed boats easy and safe. Feedback is eliminated and holding a steady course is simplified because no steering effort is required until you actually want to turn the engine or rudder. We offer hydraulic steering systems packages. Most packages include a hydraulic steering helm, a hydraulic steering cylinder and hydraulic steering fluid. Some kits also include hydraulic steering hoses and hose fittings. We stock components to fit virtually any pleasure or commercial boat’s hydraulic steering needs.

Types of Hydraulic Steering Systems

Two-line manual systems: In these systems the helm pump moves the hydraulic cylinder directly. In use, a clockwise turn of the steering wheel will send fluid from the helm unit into the starboard hydraulic line. This fluid will be pumped into the cylinder and either extend or retract the cylinder rod. Incoming fluid pushes a piston which is pinned to an external rod. As the piston is moved the rod is either extended or retracted, and the boat turns. Outgoing fluid from the other end of the cylinder is returned to the helm via the port side line.

Three-line manual systems Hynautic: Three-line systems are pressurized and contain a separate reservoir and pressure-relief valve. Common on work and pleasure vessels up to 70 feet. Helms are simpler since they do not contain the reservoir or relief valve. The fluid fill is at a remote reservoir, instead of the helm. They use soft refrigeration type copper tubing, instead of nylon hose.

Power assist: For outboards 150hp and above and for twin and triple engine applications, bass boats, pontoon boats, power catamarans and inboard cruisers without engine-driven power assist. Uses an electronically-controlled on-demand hydraulic pump to give your boat the same easy steering you are accustomed to in your car.

Power steering: Larger boats require a bigger system that can handle higher loads typically experienced at the rudder(s). Power steering systems include two distinct operating circuits:

Electrically controlled pump

SeaStar Power Assist is an upgrade for existing hydraulic steering that taps into the hydraulic lines. This electrically-controlled pump boosts the pressure to make steering easier and more responsive.

  • A “manually-operated” hydraulic system of a standard SeaStar helm pump and hydraulic cylinder (fitted with an integral servo cylinder and power steering valve), and
  • A “power” steering system of either an engine-driven pump (conventional) or an electrically-operated power assist pump.

The manual circuit provides the control portion of the steering system, and the power circuit provides the power to turn the rudders. See the diagram of the new Optimus 360 system, which is NMEA 2000 compatible and uses a joystick control.

Parts of a Hydraulic System

There are two basic hydraulic steering parts: the helm and the cylinder. More complicated systems may have fluid reservoirs, specialized valves, relief valves and autopilot pumps

The helm consists of a hydraulic pump and a system of valves, which pumps fluid into the hydraulic lines. The pump is activated by turning the steering wheel, which causes a swashplate to press on a series of small piston pumps. The use of small pistons and ball bearings makes the pump action very smooth—nothing like a normal piston pump. The internal valve assembly acts as a check valve, preventing the outgoing fluid from returning, while effectively eliminating kickback to the wheel. In systems like the popular SeaStar and SeaStar PRO, the helm serves several functions, incorporating a hydraulic fluid reservoir and a relief valve as well. Some systems have a helm, reservoir and relief valve as separate components.

In use, a clockwise turn of the steering wheel will send fluid from the Helm Unit into the starboard hydraulic line. This fluid will be pumped into the cylinder and either extend or retract the cylinder rod. Incoming fluid pushes a piston which is pinned to an external rod. As the piston is moved the rod is either extended or retracted, and the boat turns. Outgoing fluid from the other end of the cylinder is returned to the helm via the port side line.

Helm pump

SeaStar PRO 2.0 helm HH5770 includes unique check valves to counteract torque from large outboards (similar in function to No FeedBack mechanical steering).

Choosing a Helm

Selection of the proper components is relatively easy, since the number of components is limited. Select the SeaStar 1.7 helm for boats to 40', outboard engines with up to V-6 engines, and speeds to 50mph. For boats with larger outboards to 300hp and speeds over 60mph, select the SeaStar PRO. It operates at pressures up to 1,500psi, and offers the best steering control and reduced wheel walk and chatter. Its increased 2.0cu.in. displacement provides faster steering responsewith slightly higher helm effort. The SeaStar regular helm is available in 2.0 and 2.4cu.in. displacements for boats with larger cylinders or special needs.

Bezel/back plate kits allow for reduced helm protrusion from the dash, and allow retrofitting of SeaStar front mount helms to boats in which mechanical steering or older SeaStar systems were previously installed.

Tilt steering is available as an option for BayStar, SeaStar and SeaStar PRO, but not available for Capilano or Hynautic systems. Replace the standard helm with a tilt model.

Hydraulic Cylinders

The cylinder: Consisting of a ram, bored cylinder and attaching hardware, the cylinder is moved by fluid pumped from the helm when the wheel is turned.

The current generation of outboard-mounted cylinders makes installation easy since they use the tilt tube of the engine for support and act directly on the engine’s steering attachment point. In other words, the cylinder acts between two points on the outboard, and exerts no force on the boat’s hull or deck.

Outboard hydraulic cylinder

Front-mount pivoting outboard cylinder HC5345 is the most popular model for SeaStar and SeaStar PRO systems.

This type of cylinder is what is known as a balanced cylinder, meaning that port and starboard deflections take the same amount of hydraulic fluid. This, in turn, makes it ideal for autopilots, since they act symmetrically port and starboard. Note that some older BayStar steering kits (HK4200 and HK4230) use an unbalanced cylinder, and cannot be used with autopilots.

There are a wide variety of inboard and sterndrive cylinders available to fit practically any boat, but selecting the right ones can be tricky. SeaStar Solutions (formerly Teleflex) offers extensive technical help at their web site, www.seastarsolutions.com, which will guide you step-by-step through the selection process. Of course please contact us if you need more information.

Several helm displacements and cylinder choices are available (except for SeaStar PRO) for a choice in the number of lock-to-lock steering wheel turns, so you can tailor the system to fit your boat’s handling characteristics and your individual driving style.

Steering Hose: A special hydraulic hose that carries the fluid from the helm to the cylinder and back. Outboard steering hoses are pre-manufactured to specific lengths. Modification after manufacture is not recommended and could result in steering failure. (Tubing is used in some I/O and inboard hydraulic systems.)

Tie Bar Kits: Hardware to allow steering connection of two or three engines in unison. Some systems use a mechanical tie bar, some a drag link fitted to fixed-mount cylinders, and some connect the engines or rudders using a liquid (hydraulic) tie bar.

Autopilot: Installation requires a pump that is teed into the hydraulic system. Some systems require that you add a third hydraulic line (called the compensating line). The SeaStar Add-A-Station Autopilot Fitting Kit (HF5501 for outboards or HF5502 for stern drives or inboards) contains hardware for this. Some autopilot installations also require a rudder position sensor.

BayStar and SeaStar Outboard Systems

BayStar™ Outboard

  • Single-engine boats up to max. 150hp including runabouts and inflatables. Standard engine tilt tubes. Balanced cylinder.
  • Compact helm with 5" footprint, needs 3" dash hole. 4.5 turns lock-to-lock
  • Optional 5-position tilt helm, BayStar PLUS helm for quicker response

Not recommended for use with high performance, 150HP engines (such as Mercury Optimax 150HP engines) or single engine, high-speed boats (such as bass boats). Not for smaller HP outboard engines that use wing nut type transom mount clamping screws.

SeaStar Outboard (Front Mount)

  • General purpose system. Typical applications include center console fishing boats and cruisers.
  • Single and multiple engine capability. Independent engine tilt for twin engine installations. Total power to 700hp.
  • Five turns lock-to-lock steering response.

SeaStar Outboard (Side Mount)

  • Typical applications include center console fishing boats and cruisers
  • All engines with threaded tilt (steering) tubes. Cylinder attaches to the engine tilt tube. Single and multiple outboard engine installations. Total power to 600hp in counter rotating application. (see the SeaStar Solutions web site). Suitable for installation in shallow splashwells and on engines fitted with power steering.
  • Unbalanced cylinder with 4.8/5.7 turns lock to lock.

SeaStar Outboard (Splashwell Mount)

  • Light duty alternative to front or side mount cylinders. Transom or hull mounted cylinder typically attaches to an anchor point on or near the inside of the boat’s transom. Single and multiple engine capability. Fits engines with/without support (steering) tube.
  • Total power to 600hp in counter-rotating application. Speeds to 60mph maximum.
  • Unbalanced cylinder with 5.5/6.5 turns lock to lock

SeaStar PRO Outboard

  • High speed, single-engine outboard boats, like bass, flats, combo race/ski and other performance orientated boats capable of speeds in excess of 65mph, up to 300hp. For use with high-performance propellers and jackplates.
  • Compact helm has only a 4 7/16" footprint. Needs 3" dash hole (Tilt requires larger hole). Patented steering lock valves. 4.25 turns from lock-to-lock. Factory swaged hoses are Kevlar reinforced.
  • Optional PRO Cylinders with longer shaft bushings and larger pivot bushings for an even more solid feel

SeaStar Tournament Series

  • Extreme heavy duty cylinders and tiebars designed for high performance multiple-engine applications (also available for single engine applications)
  • Application-specific cylinders and tie bars
  • For use with SeaStar helms and hoses

SeaStar Cat/Pontoon Steering

  • For outboard-powered catamarans and pontoon boats. Dual non-power-assisted outboards up to 450hp (600 combined horsepower for counter-rotating twin engines) with standard tilt tubes. Speeds up to 75mph and dual-station helms.
  • Compact helm has only a 4 7/16" footprint. Patented steering lock valves. Independent engine tilt

Optimus 360 Joystick Control System

  • Replaces the traditional hydraulic steering system with a joystick steering/shift/throttle control system, engineered for powerboats with twin mechanically-controlled outboards. The Optimus EST system replaces the boat’s conventional outboard engine controls and cables. Optimus 360 is the culmination of the three sub systems which are interconnected and synchronized to provide intuitive joystick docking of the vessel with true fingertip control. Garmin and Raymarine each have introduced new  CANbus autopilots (the GHP 20 and Evolution EV-DBW Drive-By-Wire) that work with this system.
Dual outboard hydraulic steering schematic

Optimus 360, the new SeaStar Solutions power steering system uses “smart” hydraulic cylinders and an electronic steering wheelhub. The components communicate via CANbus. It controls twin engines independently to make docking much simpler.

SeaStar, Capilano and Hynautic Sterndrive Systems

SeaStar Stern Drive Steering

  • For non-power-assisted sterndrives and any stern drive system with an autopilot. Cylinders are specific to drive brands and models.

SeaStar/Capilano/Hynautic Heavy-Duty Sterndrive Steering

  • For sterndrive, outboard and inboard boats that require external cylinders of substantial size and strength. K-5 cylinders are nickel-plated for aesthetics and protection. System components sold separately. Required wing plates and hardware not available from SeaStar Solutions. Available Capilano 2-line and Hynautic 3-line systems.

SeaStar, Capilano and Hynautic Inboard Systems

SeaStar Inboard (2-line system)

  • Pleasure and workboat applications up to 50' with some exceptions. Most inboard-powered boats with single/twin engines. Single engine planing/displacement hulls 26' to 44'. Dual engine planing hulls 26' to 50'. Dual engine displacement hulls and sailboats from 26' to 44'.
  • Dual station steering with optional hardware

Capilano Inboard (2-line system)

  • Most inboard-powered boats with single/dual engines including planing or displacement hulls from 30' to 55'

Hynautic Inboard (3-line system)

  • Heavy-duty 3-line system for boats to 70' with a wide range of helm displacements and cylinder configurations.

SeaStar Inboard Power Steering

  • Boats up to 120'. Cylinders determined based on vessel size and hull type. Engine type determines which power steering pump is used.