Hydraulic steering offers rugged dependablity

Although not seen often in cruising boats under 50 feet, hydraulic steering has its place in vessels of every size, with a few caveats. The principles by which it works are quite simple and easy to understand. The helm is attached to a hydraulic pump, which usually incorporates a set of checking valves and a spool. When the wheel is turned, the pump sends fluid down one of two hydraulic lines to a hydraulic cylinder-piston arrangement. The addition of fluid to the balanced cylinder increases the volume to one chamber, causing the piston to extend, which acts upon a tiller attached to the rudderstock, causing the boat to turn. When the wheel is turned in the opposite direction, fluid is sent down the other hydraulic line, to the corresponding chamber, causing the piston to retract, drawing the tiller arm in the opposite direction. There are other configurations that utilize sets of unbalanced cylinders acting on a single tiller arm; however, the principles remain the same, as do the results: the wheel is turned and the rudder moves.

Advantages and disadvantages

There are more than a few reasons to choose hydraulic steering over conventional cable with sheave or mechanical gear systems. Hydraulics have a proven record of accomplishment in extremely harsh environments. Today, everything from nuclear submarines to mud-encrusted earth-moving equipment bristles with hydraulic pumps, cylinders and hoses. So there’s no doubt the system is tough and reliable, provided it’s properly engineered, installed and maintained. For the cruising vessel, hydraulic steering provides several advantages. There are no cables or sheaves to chafe, wear or break, and hydraulic lines do not require clear, straight runs. In fact, one of the major advantages of hydraulic steering is the ease of installation. A hose can be installed where a moving cable cannot. Additionally, hydraulic systems offer the benefit of including a second steering station, in the cabin for instance. Hydraulics also lend themselves very well to interfacing with autopilots, requiring only a very durable and reliable hydraulic pump without the need for an additional tiller arm. Remember, however, anything plumbed into a hydraulic steering line, such as an autopilot pump, must utilize a set of service ball valves, which are rated for the full working pressure of the system.

There are also a few disadvantages of hydraulic steering for offshore vessels. Primarily and undeniably, hydraulics are not easily repaired and once the beaten path has been left behind, service personnel who are experienced in their repair are not easily found. Jury-rigging hydraulic systems is also difficult at best, while cable and sheave systems can often be repaired temporarily with little more than a length of wire. Finally, it may be argued that hydraulic systems don’t often require repair, but when they do they almost always require the use of very specialized parts in order to effect that repair. The message is carry spares if you have hydraulic steering.

Maintenance and longevity

As far as hydraulic steering is concerned, especially for vessels voyaging offshore, maintenance and longevity are closely related. A well-maintained hydraulic steering system is usually quite reliable, provided it is properly designed, engineered and installed. The primary maintenance item involves the condition of the fluid. Unlike lubricating oils used in internal combustion engines, hydraulic steering fluid is not subject to combustion byproducts. As a result, if the system remains closed and clean, the fluid should not require replacement for years. However, if the system should become contaminated with dirt, water or debris from failed components such as hose or copper tube lining, failures usually follow close behind. The best defense in this case is to use only the fluid specified by the steering system manufacturer. This is usually high quality hydraulic oil, which is available in many parts of the world. In an emergency, some systems specify automatic transmission fluid, but this is only for an emergency. If fluid of the wrong viscosity is used, the result is usually no more than cavitation and poor performance.

If the wrong type of oil is used, such as engine oil or brake fluid, the results could be far worse - along the lines of total system failure. Never use brake fluid or motor oil in a hydraulic steering system. Other maintenance items include a close inspection of seals and the polished surface of the piston, on which the seals ride. The slightest scratch or score in this surface could lead to a leak. If a seal is leaking due to a damaged piston, replacement of the seal will only stem the leak temporarily. The irregular piston surface will quickly damage a new seal as well.


The spares locker for the offshore cruising vessel equipped with hydraulic steering should be well stocked. You must include spare seals for the piston(s), both ends if equipped with balanced units, spare hydraulic line fittings, be it copper or nylon tubing or Aeroquip-style hose. If your system utilizes the latter of the three, be sure that you have spare end fittings and the installation mandrel as well. Of course, the spares kit should include generous lengths of compatible hose or tubing. Take note, even systems that are installed using all copper plumbing must use lengths of flexible hose to connect the rigid copper to the moving hydraulic cylinder. If you want to have the last word in spares for your hydraulic steering system, carry a spare helm pump, too. This is usually the most costly part of the system; however, it’s also the most difficult to repair for a non-hydraulic technician. Finally, many hydraulic cylinders require the use of a special spanner wrench for disassembly, evidenced by odd notches or holes in the cylinder’s end cap. If this is the case, one of these tools will be required for disassembly. The alternative is to use locking or slip-joint pliers, which can distort the cap, making leak-free reassembly impossible.


If you intend to install hydraulic steering where none existed before, do your homework. Familiarize yourself with all of the specifications offered by the manufacturer. For offshore vessels, my rule of thumb is to determine the helm pump and piston sizes the manufacturer calls for, then go up one size.

The most common failure area for retrofit hydraulic steering systems is the piston attachment. The loads imparted on this component, repetitive and momentary, are tremendous. As a result, the interface between the piston and the hull should be overbuilt, preferably attached to hull stringers. This attachment point calls for grinding and heavily tabbed-in (with roving and mat) wood blocks for GRP vessels, through bolted attachments for timber and substantially welded gusset installations for metal. Make no mistake, this is the area I have seen fail most often on retrofit hydraulic steering systems. In addition, the piston should not double as a rudder stop. Conventional, heavy rudder stops must still be used, as with any cable over sheave system. The rudder must stop before it reaches the maximum extension or retraction of the piston(s). Massive is the only word an observer should use to describe these components.

If you are doing the retrofit yourself, follow the manufacturer’s installation instructions to the letter. Avoid air trapping high spots in hydraulic lines and remember to install a bypass valve or quick release pin on the hydraulic cylinder so you will be able to use an emergency tiller if the system should fail. If you fail to include this component, the rudder may lock if the system malfunctions.

Autopilot-equipped, hydraulically steered vessels offer one additional advantage: redundancy. I was transporting a 50-foot ketch once when the helm stopped answering. I turned the wheel and it spun freely with no effect on the rudder, the key had sheared. While I took the binnacle apart, another crewmember was able to continue to sail and steer the boat with the autopilot’s power steering mode. Of course, this will only work if the hydraulic portion of the system remains functional, and in this case it did.

The heavy weather equation

Hydraulic steering systems are standard equipment for many offshore-bound vessels, from U.S. Navy destroyers to single-handed circumnavigators. Since many larger vessels are, by virtue of their size, offshore bound, they also experience more than their share of heavy weather. For properly engineered and installed hydraulic systems this presents little if any difficulty. I’ve sailed several thousand miles aboard American Promise, the 60-foot Ted Hood sloop used by Dodge Morgan for a record-setting 150 day solo-circumnavigation in 1985/1986. She’s now operated by the U.S. Naval Academy as a sail and navigation training vessel. Her steering system is completely hydraulic - original equipment. Although it suffered a few teething problems (due to some design miscalculations) when new, Morgan went on to sail around the world, much of his course through the Southern Ocean, with nary a problem. With basic routine maintenance, this same hydraulic steering system, 16 years and many thousands of sea miles later, continues to serve the Navy reliably during regular offshore passages. Failure is rare for systems that are properly matched to the vessel’s size, weight and operating conditions (vessels bound for heavy weather should have hydraulic systems that are at least one size larger than the manufacturer’s minimum recommendations). Failure is due generally to neglect and inattentiveness on the crew’s part. Hoses may chafe and seals may wear; however, these problems are often noticeable if routine inspections are carried out.

If the unthinkable occurs and your hydraulic system packs up entirely, you must have a workable manual steering system plan in place. Even the most thoroughly planned, engineered and installed systems may suffer from an unforeseeable material defect. For this reason, it is necessary to practice installing and steering with an emergency manual tiller. In the years I’ve worked in boat yards, I have seen many nicely-made manual tillers that don’t actually fit their matching rudder stocks. Ensure that yours does, and that it will work for hundreds of heavy weather sea miles.

Steve C. D’Antonio is boatyard manager at Zimmerman Marine in Cardinal, Va., and recently competed in the Marion to Bermuda Race aboard American Promise.

By Ocean Navigator