Configuration Guide

This section provides an overview of some of the considerations to be taken into account when configuring a motion control system.

Build a system to match your needs

Ship Dynamics' product is based on standard modules arranged in three component groups.

1. Stabilising devices that generate force;
2. Hydraulic components that provide the motive power for stabiliser movement;
3. Control components that generate the command signal and manage the system.

This common technology base allows the system's capability to be built to match the clients needs, by including only as much of the complete system in their scope as required.  Usually every ship and operation is unique, and so accordingly, each stabilisation system must be unique.

For Ship Dynamics to configure a stabilisation system, generally the following series of questions require an answer.

1. Why is stabilisation being considered?
2. What control forces are required of the stabilisation system?
3. What arrangement and type of stabilisation is best?
4. How is the stabilisation system powered?
5. What level of operator control is needed?

Why is stabilisation being considered?

Stabilisation systems are fitted for a variety of reasons.  Typically they are installed to reduce the magnitude of the hull motions in waves where some scope exists to control the level of motion reduction acheived.  However, the appropriate stabilisation system is not always immediately apparent.  Ship Dynamics can help with system selection and will work with a client to acheive this, by applying a client's objectives to formulate a list of measurable criteria that define success.  For example, a clients objective to have "no person on board feel the need to hold on whilst standing", would be interpreted as a need to maintain lateral accelerations below a threshold of 0.07g, thus converting a qualitative objective to a quantitative one.

On high-speed vessels, by observing the wake on a built vessel one can normally determine whether the vessel might have been better suited with auxilary steering to supplement the steering provided by waterjet buckets.  In the case above, a zig-zagging wake might imply a lack of course keeping stability that auxilary steering could have improved. 

Alternatively, a high-speed vessel that has a staight wake, particularly in waves may demonstrate that the hull already has good course keeping stability or that it has some form of auxilary steering device.

What control forces are required of the stabilisation system?

A vessel's ability to provide satisfactory motion levels depends on a number of factors that include hull form, hull weight distribution, size & type of stabilisation system and the wave environment itself. Compliance can initially be determined through computational analysis that can assess the vessel's motion levels both with and without stabilisation. In most cases an unstabilised vessel will exhibit undesirable motion behaviour and therefore a stabilisation system would ideally provide sufficient force to keep the motion levels below required threshold limits for a given wave environment. Through computational techniques, Ship Dynamics can determine what level of force is required from a stabilisation system to maintain motion levels below these threshold limits. Alternatively, the reductions acheived by a given stabilisation system can be calculated. When required, a formal report that details the selection process can be created that outlines the assumptions, techniques and findings.

Ship Dynamics strongly recommends that a computational analysis be commissioned prior to proceeding with an equipment purchase so as to be armed with the best information.

What arrangement and type of stabilisation is best?

The ideal stabilisation device arrangement is obviously the one that provides the required level of control force with the most economical set of outcomes.  In this case, cost may not always be purely monetary value but may also include a variety of other important considerations such as

• the need for the system to fit within the hull envelope or space constraints;
• speed loss because of the system or the system performance at different speeds;
• the potential for fouling;
• draft constraints;
• weight;
• compatibility with existing appendages;
• fleet compatibility, and
• maintenance costs, flexibility and convenience.

Furthermore, the arrangement of system devices can be heavily influenced and limited by the vessel's general arrangement and in most instances, there is more than one configuration that will provide a successful result.  Therefore, the more information provided about the vessel and its operation, the better the advice Ship Dynamics is able to provide.

How is the stabilisation system powered?

All Ship Dynamics' equipment is hydraulically actuated.  Each device has a certain oil flow requirement that can be delivered from a variety of sources.  The simplest arrangement is to provide a dedicated hydraulic power source at each device.  Increased redundancy and efficiency can be achieved by grouping some or all devices on a common manifold sharing a hydraulic pump set.   In addition, stabilisation pumpsets can be shared with deck hydraulics.  This can be an ideal arrangement simply because when the vessel is in harbor or at sea, the stabilisation system and deck equpment are generally not used at the same time.

In the case where only limited electrical power is available, it may be necessary to consider driving the hydraulic pumps by a "power take off" device fitted to either the engine or the gearbox.  Alternatively, a dedicated pump drive may be installed.

What level of operator control is needed?

Ship Dynamics common network allows any device on the network to be controlled from any location on the vessel. A typical control interface is provided through a touch screen and interconnection to other ship systems is available for monitoring only.