The following discourse is actually about steering systems for your catamaran so you hopefully won’t need to travel in the economy classes.
This old print of a Fijian charter boat illustrates the ubiquitous vessel steering problem; how to see where you are going at the front end while steering from the ass end, (note this ship is moving away from us despite the pointy bits).
The two lads manning the 20’steering oar can’t see around the deckhouse, so a lad in the bows is calling directions which are being relayed back through the fellow on the coachroof. A third lad at the steering station appears to be disputing whether to push or pull on the oar. I can’t readily explain the point of sail or the tell-tales, but everyone looks quite jolly in any case and satisfied with the performance, two lads apparently fishing more coconut wine from the port hold.
To alleviate the typical steering /communication problems, there has always been some considerable incentive to engineer remote steering arrangements whereby the guy at the helm can actually see where he is going. (The recent regression in this matter exhibited by some modern catamaran designs might possibly be attributed to some genetically transmitted ancestral nostalgia.)
The practice of using a tiller to steer with didn’t disappear with the 16th century as suggested by the diagram above, though the whipstaff has become a relative rarity, at least in its boating connotation.
If your vessel is really too small for one anyway, you can just do away with the deckhouse. You can then sit with a tiller in hand, see where you are going, and take what’s coming to you, (wind, spray, sleet etc.) It’s perhaps not as robust as it looks; despite the apparent simplicity there is a lot of stuff here to consider. Each hinged joint in the tiller and rudder assembly is subject to potentially very high twist loading, you have to concede the space for the sweep of both tillers and the exposed tie bar, plus there is no apparent provision here for the times you may want to let go for a few minutes. (The apparent disagreement between the rudder angles is a little hard to explain.)
Also in the above catamaran example, there is little apparent improvement in the above helmsman’s seating comfort over the yacht practice of 1500 years ago;
The protection and comfort of the helmsman make a major contribution to the safety of the vessel, another motivation for remote steering systems.
Ropes, Cables and Chains
Moving ahead to the 17th century plus, we see the advent of rope and pulley systems and the birth of a new nautical decor theme, the ships wheel.
The helm of the rope system will look something like this, at least in principle…
or this. The common sailboat pedestals now use chains and cables rather than ropes and pulleys, but they are still a hybrid of figure ‘H’ in the ‘Progress’ diagram above.
Figure ‘F’ illustrated in the diagram would have a lot of slop in it as it doesn’t take into account the arc of the tiller; when the ropes are snug amidships, they will slack off as the tiller traverses. As will this more modern experiment…
You wouldn’t think of driving your car away from the curb without 100% steering confidence but boaters seem to be less fussy. The bronze rudder, rudder port and tiller are up for the job, the tiller extension and cup hooks for the turning blocks are not. There are no rudder stops. Even a small boat can run over someone in the water, to say nothing of the embarrassment of pranging the dock. Hopefully this installation was revisited before the sea trials.
To keep the ropes, cables or chains tight throughout the arc of tiller travel, you have to use a quadrant rather than a straight tiller to keep the geometry consistent. These come in a variety of forms;
This otherwise Herculean installation does not appear to have a top bearing for the very long rudder stock. As a result, the steering load and cable tension are imposed as bend stress in the stock and exaggerated side loading in the rudder port bearing. Again no stops are in evidence. The installation looks much more robust than it actually is; despite the use of a nice vintage sprocket quadrant.
The cable quadrant in this case is actually a complete ‘wheel’, the cables wrapping around aft. This stock has a top bearing. The two stubby things with rubber hose over them are the stops provided by the quadrant manufacturer. It was left up to the builder to give them something to bear against, nothing is in evidence however. Notice the weight of the rudder assembly is borne by the aluminum quadrant bearing on the bronze stuffing box which in turn is held up by the hose, all in a nice mildew farm/corrosion encouraging environment. Steering gear never seems to get much respect, as long it sort of works, though its integrity is of prime concern to a cruising vessel owner.
Cable systems provide lots of concerns regarding installation, wear and maintenance. Note the example in the upper left uses conduits to guide the cables rather than sheaves, permitting some artistic routing. The owner of the hand with the cloth running along the cable is searching for ‘meat hooks’, broken cable strands that indicate imminent cable failure. Have some Band-Aids handy. It is interesting to note that the cable securing methods and general hardware quality commonly used for yacht steering gear would never be acceptable for even the vessel’s least critical standing or running rigging. Maybe that’s because you can’t usually see the steering gear.
Chains and sprockets aren’t too bad for it, but cable and sheave arrangements have considerable frictional losses, especially with tight cables. Flexible conduit cables rely on the integrity of the plastic liners to minimise friction, demanding the fewest possible wide radius bends.
The above diagrams are of monohull installations, designed to turn one rudder. The simplest way to control a second remote rudder is by means of a tie bar between a tiller arm on the controlled rudder stock and a tiller arm on the ‘slave’ rudder stock. In practice this can be rather tough to accommodate in a catamaran. The ideal placement of the rudders fore and aft should dictate the position of the stocks and tiller arms. Practical limits on the vertical positioning will be dictated by the shape of the hull and bridge deck stern sections. Expedient arrangements to fit a tie bar internally can compromise both the steering system and the shape of the vessel, so the
tie bar may sometimes be found outside, exiting one hull and entering the other. This arrangement inevitably results in the exposure of the rest of the steering gear and the aft compartment to the full effects of the environment as the hull openings can never be made watertight.
Tie bars and end fittings can be easily acquired in marine grade materials and configurations but this may not always be done.
The assembly on the top is an automotive adaptation with a tapered pin mount, (potentially very hard to deal with without a cutting torch if the taper releases before the nut comes off, or the builder has neglected to correctly taper the hole in the tiller arm in the first place). The industrial style on the bottom may be acquired in stainless steel and permits the use of a through bolt attachment (nice to have).
This one is a lightweight hardened anodized aluminum joint with a replaceable Delrin ball mount that insulates the components against galvanic corrosion. Though possibly an aircraft technology derivative, it seems to be ideal for our kind of marine application.
The tiller arms and quadrants need to be of sound construction with solid connection to their rudder stocks. There are lots of manufactured castings in aluminum that do the job well with minimal weight but they are not always used.
In the above example, the anorexic rudder stock has been reduced still more dramatically by grinding a square end on it. The stock’s diameter and its other structural properties should rightly be subject to calculations that take into account the speed of the vessel, size of the rudder, rudder balance, bearing spacing and presence or not of a heel support bearing (open rudder or skeg arrangement). This installation doesn’t look to me like it would measure up? Even if the top of the stock doesn’t twist off, the tiller arrangement puts all of the steering force into one of the bolts. Peculiarly the imaginative stainless steel welded fabrication would cost more than a real marine cast tiller arm, bit of a mystery here on several counts. It is usually easier and cheaper to just do it right in the first place.
Hollow stocks have the advantage over solid ones by saving weight. The extra material entailed by increasing the diameter is more than offset by the removal of the core material which has a minimal contribution to the torsional strength.
This example of a custom tiller arm rightly relies on clamping pressure to make its connection with the stock. Locating keys or pins are always secondary to the transmission of the load and if these do come into play, the proper clamping force has failed. It looks like this cat’s steering system design occurred rather late in the design process. Though the stock, bearing and custom tiller arm look rather elegant, the motivator appears to be a push-pull cable system; incongruous and not so nice.
This is the same vessel’s push-pull cable anchor which is expected to take the full steering load, it certainly doesn’t look like any kind of a match for the stock and tiller capabilities.
In any case, the push-pull steering hardware is derived from the outboard motor and stern drive market which has different requirements for integrity than what we expect for an offshore cruising boat.
The only incentive in trying to adapt it to a cruising catamaran would be initial cost constraints. It’s hard to see how that can be justified.
This is reportedly an installation in a 49’ cat. There must have been no residual cash left over by the time someone remembered its steering system. Do any of the cable components look like a sea going propositions? I guess the little pin sticking up is a rudder stop.
Nutty Steering Gear prize goes to this cat with two helms connected via push-pull cable systems to track and car arrangement connected to rudder quadrants via cables and pulleys. Wow, avoided installing a tie rod though…
Perhaps you are wondering why I keep mentioning rudder stops?
Peculiarly, the greatest loads on the rudder, stock and steering gear are experienced when going astern.
As long as you are going forward, the flow over a rudder with a stock positioned well toward its leading edge tries to push the rudder to the amidships position where it may trail with no significant load. This makes for a kind of ‘fail safe’ condition. When going astern however, the flow tries to twist the rudder around backward and the force may easily exceed the normal forces necessary to steer the vessel. Strong rudder stops placed to limit the swing to about 35⁰ are necessary to prevent the reverse flow from damaging the rudders and steering gear by forcing them beyond their physical limits. Even if the steering gear was free to swing 360⁰, surprisingly strong and rapid rudder pressure when going astern can easily overwhelm the helmsman and even cause injury, to say nothing of the loss of vessel control. Rudder stops designed to take the load will at least limit the forces to be dealt with.
In the absence of rudder stops a cable/chain steering system may reach its mechanical limits by crunching a chain-to-cable splice into a helm sprocket for example. This kind of repetitive mishap will soon do damage to the components.
Hydraulic Steering Systems
Hydraulic systems have offered a ‘new’ alternative for connections between the helm and the rudder. This is a sheet stolen from Kobelt Manufacturing that explains the principles;
You may easily add additional helm pumps for multiple steering stations and an autopilot pump to the circuit. They are very versatile.
Hydraulic steering systems can easily have great power and integrity and readily scale up for large size installations,
but in the pleasure boat scale of things, the components and piping deal with very low flow rates and high sensitivity. This means that the quality of the components must be very good despite the small size and cost limitations of a competitive market.
This example is in a 49’ aluminum vessel installation using stainless fittings and hose connections. The bypass valve permits emergency steering by tiller. The cast bronze ram construction is certainly not the weakest link, but it is bolted to aluminum with no insulators apparent. Mixing copper based alloys with aluminum is not at all good for galvanic corrosion and should be kept in mind when selecting fittings and installation methods.
This is a 53’ cat installation using industrial plated steel hose connection fittings and an aluminum bodied ram. The ball end fitting looks particularly unhappy, the hoses and fittings are past their best before date. (Sometimes a picture itself seems to smell of mildew and bad bilge water.) Industrial hydraulic hoses commonly have fine braided steel reinforcement under the rubber cover to hold the required pressure. Exposure at the end fittings or perforations of the cover can rust away that reinforcement wire, something else to watch for in the marine environment.
For a sailboat, hydraulic steering has one drawback that needs to be recognized. With the exception of a few oddballs;
all of the current boat helm pumps are rotary in design and displace a determined volume of fluid per turn either direction, which is a critical match to the ram used in order to establish the desired mechanical advantage (turns lock to lock).
This particular model has adjustable displacement for more or less turns/mechanical advantage.
There is always some leakage by the pumping elements. This leakage is very low by industrial standards but so is the flow in the boat system and inevitably there can be no such thing as a ‘master spoke’ in the helm wheel. The wheel will gradually creep under load as you are steering against some rudder pressure. This means you need to rely on a rudder angle indicator rather than a master spoke to tell you the rudder position. The small rod in the rust installation shown above will be there to operate an electronic sender unit for an indicator or autopilot feedback.
In a catamaran installation it is possible to connect a separate ram to each tiller and eliminate the tie bar, which may solve an awkward installation situation. This requires that the two rams be connected in series, the oil from one discharging into the other, rather than parallel, both receiving fluid directly from the helm pump. This arrangement compels the two rams to move synchronously, keeping the two rudder angles in agreement. The minor leakage past the ram seals will gradually allow the alignment to wander a little so a valve is provided to make corrections every so often.
The bane of all hydraulic steering systems is the entrainment of air pockets in places where you would expect fluid. The air is compressible whereas the fluid is not. This makes for spongy response and skips or outright ineffectual pump action. To get the air out of the system it is necessary to vent it out at a few spots where it would otherwise be trapped. Rather than circulate, steering fluid just moves back and forth so ‘bleed’ fittings are usually required at the ram ends. Series ram arrangements as shown in the above diagram may be particularly tricky to fill and bleed.
Long tube runs with small internal diameter and restrictive fittings add up to a lot of frictional losses in hydraulic systems, especially when quick response is called for and flow rates peak. The drag may be quite noticeable when spinning the wheel over.
Every extra fitting is a potential leak point. The piping is unsecured and subject to mechanical damage. Regardless of what a manufacturer may advise, in practice copper tubing will immediately turn green and fuzzy in a salt environment and have a very short lifespan. The brass fittings are apparently screwed into the aluminum valve blocks, electrolysis will shortly turn the aluminum to white powder. With the widespread availability of direct drive electric motor/pump equipment, many having integrated valve bodies, why would you use such a hokey belt driven arrangement? (It does look pretty when new.) There are several manufacturers of complete engineered systems with competitive pricing.
If a hydraulic steering system is well engineered and installed, free of air entrainment and leaks, it will work indefinitely and it offers a good deal of versatility and scant wear of the components.
For cruising boats an autopilot has become an essential option. The autopilot cares not for your wheel and is best installed as close to the business end of the steering gear as practical. This may allow it to remain effective even if there is some disability in the mechanical connections to the wheel, thereby making it a possible emergency steering option.
These after the fact arrangements or under-pedestal chain and sprocket drive motors rely on the cable and pulley system to transmit the steering effort. The ‘dumb’ autopilot can apply taxing forces to the steering gear that you would not sensibly do if you had the wheel yourself, you may soon discover the weakest link. (Do you think this guy’s wheel nut is actually only on by one thread?)
Autopilot motors are often installed as a structural afterthought though their power capacity generally exceeds that of a manual helmsman. The anchoring and connections need to be at least as strong as any other component of the steering gear. This example uses a chain and sprocket on a common shaft with the manual helm. The motor power is transmitted through the chains, turnbuckles, cables, sheaves and quadrant entirely in common with the manual steering gear.
Autopilot actuators are commonly available for direct attachment to a tiller arm. I think that is a better option if you can swing it. In this way, the power transmission doesn’t rely on the integrity of all the helm related hardware.
This example is a self-contained hydraulic unit with integrated ram, pump and motor. It looks like the mount bracket is pretty solid and the installation is neat and serviceable. The tiller and rod ball end look to have suffered some corrosion.
This example of a hydraulic autopilot actuator and its pump has an electronic rudder position feedback unit apparently attached with hose clamps. You have to imagine that you may be reliant on this kind of stuff in the middle of the ocean, in bad seas, at night, and select your gear accordingly. It doesn’t have to be large, clumsy or heavy to work well.
Hydraulic rams will have some resistance even with the valves set to bypass fluid directly from one end to the other. This means that some manual steering resistance or damping will be felt. To alleviate the general tendency of hydraulic steering systems to drag, very thin hydraulic fluids in common with aircraft control systems are generally used rather than the heavier industrial oils.
I like to see engineering ‘elegance’ in the steering equipment and its installation, (minimal exposed junk and connections). If you are going to use electrical power anyway, the hydraulic actuator seems like a roundabout way of doing things. Developments with straight electric linear actuators with increased power and clutch features makes the look pretty attractive.
These are two examples of electric direct drive actuators. The one on the top is rotary in nature and requires a drag link to connect it to a tiller arm, the black thing being an electronic follow up unit. The one on the bottom is configured to drive a tiller arm directly.
This is another electric linear actuator (above) that comes with a neat video of the guts in motion –http://www.youtube.com/watch?v=mYN3IQdaV_Q&feature=player_embedded
Shaft and Gear Steering System
By now you are wondering what happened to the direct geared steering system illustrated in figure ‘G’ of the Progress diagram way back at the beginning. I thought it should be a case of the best saved for the last.
Up until about the middle of the 20th century, geared systems were the norm, even for small boats, but the systems fell out of general use as they were heavy and had practical installation limitations. Developments in CAD CAM manufacturing efficiencies and the realization that both cable and hydraulic systems were perhaps rather precious for certain applications rejuvenated the idea that you could configure a shaft and gear system that would be affordable and of acceptable weight and versatility. Though not apparently cost competitive at initial purchase, vessels with expectations beyond the boat show dock may consider such a system, comprised of standardised components.
Specific to the sailing catamaran installation problems, the geographical separation of the rudder and helm positions may be more expediently dealt with than by cable and pulley and the positive direct drive has none of the losses associated with hydraulics. The maintenance may be confined to periodic inspections of the sealed grease filled gear boxes and fittings. No chains, cables, hoses, tubes or associated fittings required.
The installation of shaft and gear box systems however doesn’t lend itself as easily to ‘after the fact’ installation. The geometry of and clearance for components, gearboxes, torque tubes and drag links needs to be planned out before you get there.
At least one manufacturer offers extruded anodized aluminum componentry, allowing for some on-site assembly of items that may require adjustments to fit. This also can save a lot of weight and reduces costs considerably.
This is an anonymous (Antares??) design for a catamaran application that illustrates some of the features possible with gearbox and shaft equipment as well as some general installation considerations.
1) The tie bar function is assumed by the two drag links connecting the primary gearbox to the tillers. This permits the tie bar to be discontinuous and less demanding in regard to straight line realestate. It also permits either rudder to continue in use if its mate is damaged and disconnected.
2) The swing angles of the main gearbox arm are greater than those of the tiller arms. The resultant geometry produces more effective steering effort as the rudder angles increase, thereby proportionately reducing the load felt at the helm.
3) The transmission system is very efficient with minimal frictional and minimal lost motion.
4) The autopilot motor is directly mounted to the final motivator in the system and enjoys all the mechanical advantage of the proportional geometry.
5) All of the components including the autopilot motor and tiller arms may come from one manufacturer.
6) As long as you have ‘a plan’ the space occupied by the components is minimal.
7) The actual steering loads are taken by the primary gearbox which must be solidly mounted.
8) The rudder stops are integrated with the box itself precluding the need for separate structures by the builder.
9) Regardless of the system type, tie bars or drag links may be subject to either side loads (someone standing on them), or extraordinary buckling loads (backing down on rocks with a rudder hitting first). They are usually quite long and to help keep them straight in such circumstances, it may be expedient to have some kind of guides to limit their sideways displacement under compression.
10) By providing a bail on the emergency tiller (required by ISO standard) you can rig the old string and pulley steering if you really have to.
Steering equipment gets no attention at boat shows, it is hidden away in stuffy compartments and not glamorous. There is little incentive for a builder to do anything beyond what is barely essential, like shiny pedestals and wheels, additional expense is not in your face and readily appreciated. Autopilots are commonly installed to order after the fact by sub-contractors with no factory participation in the engineering or quality control. It remains for the boat purchaser to look at what he is getting, new or used. Regardless of the style of equipment used, the quality of the hardware and its installation will be critical to the safety of the boat sooner or later.
All of the above illustrations have been taken from actual boats, most of them built by big name builders. Unlike the purchase of a car, you can’t take the steering gear integrity for granted when considering a cruising boat, especially a catamaran with its particular steering gear design issues.
If you have read this far, you deserve some amusement. Here are some irrelevant images.
For larger vessels a mechanical assist is often useful, sometimes essential.
Otherwise you may need more guests to help steer than you really wanted to provision for.
Once the crew’s personal steering effort possibilities have been exhausted, you may need to adopt some form of power steering,
the style of which depends on the prevailing power source and the acceptable weight limits.
One of these two was a spare.
This is the installation plan for the above hardware. Either of the two steam engines could engage the geared quadrant. Notice ropes and steam capstans just aft to steer with if all else failed. Presumably the capstans also had bars so the crew could do the work the old fashioned way if necessary. The assistant deck engineer and plumber are the first to hear if the steering gear crunches just outside their cabin door, that tells you something about the prevailing confidence in mechanical systems. (Note also that the 3rd class passengers had ‘TV’(?) and a piano to distract them from the noise of the hardware just aft.)
By the way, yes this is the Titanic class vessel arrangement; evidently the ability to remotely steer in itself does not obviate the necessity to look where you are going.
We owe a debt of gratitude to those pioneers of the String and Pulley Steering System who risked their lives in flights of discovery, well before all the relevant theory was fully understood. From these early experiments a method of yacht steering would evolve that endured right through to the latter half of the 20th century and beyond. In this archival photo record, the confident participants display none of the misgivings evident in the faces of the anxious bystanders. Perhaps all the control interface issues we take for granted today were yet to be discovered, but the inspirational ‘2 in 1’ motto suggests that the dawn of the catamaran concept lay just over the horizon.