It’s amazing to think that just 45 years ago there were still shipping companies resisting putting radars on ships and even when I went to sea in 1969 it was still a temperamental instrument whose electronics filled a whole mast house on deck. The display was restricted to the unstabilised ship’s head up mode making plotting targets or land features a convoluted process, especially if the ship was yawing in a seaway. In the 1970’s, gyro input into radars became commonplace and this resulted in the “North Up” gyro stabilised mode which matched the chart presentation, made position plotting easy and thus became the preferred display mode for most navigators, your editor included. 

With the advent of ECDIS and integrated displays some navigators, particularly on cruise ships, consider that it’s time to return to using the Ship’s head up mode to enhance the situational awareness by having displays matching the view through the bridge window.

Gladstone (Australia) pilot, Paul Chapman, has not only embraced this concept but also taken the it one stage further by developing techniques using the advanced facilities offered by modern radars with respect to making critical turns using the unstabilised head up display to advantage. Paul has kindly granted me permission to use extracts from his research papers which have also been featured in SeaWays magazine.  JCB

HEAD UP PILOTAGE

Captain Paul Chapman FNI

Information presented by a North Up display requires mental rotation to re-align the information to the observer’s operating orientation, Head Up. This mental rotation is a skill refined in experienced navigators but in times of high workloads, this re-alignment may cause confusion, especially on southerly courses. There is very compelling research suggesting that Head Up is the better orientation in pilotage waters by delivering improved situation awareness, faster decision making and less errors thus making for safer piloting.

North Up Display

The user friendliness of different chart  presentations has been researched by Dr. Thomas Porathe, an assistant professor in information design who has identified that for track keeping in confined waters, Head Up is a better chart orientation than North Up

The best display though, is a three dimensional egocentric Head Up display

North Up Display

The user friendliness of different chart  presentations has been researched by Dr. Thomas Porathe, an assistant professor in information design who has identified that for track keeping in confined waters, Head Up is a better chart orientation than North Up

The best display though, is a three dimensional egocentric Head Up display

A Three Dimensional display

The ease of reading and following a planned track on a three dimensional ego-centric Head Up display is supported by the simplicity of vehicle navigation displays.

 

CONCENTRIC INDEXING:

 A STRAIGHTFORWARD APPROACH TO CONTROLLED TURNS

The characteristics of head up orientation during a turn may be used for planning, executing and monitoring turns. This particularly applies to radars that allow the Variable Range Marker (VRM) ring to be offset. Many radars have this ability coupled with an unstabilised display and the presentation of target wakes or trails.

Notable features of the head up orientation during a turn are:

A target at the turn centre will remain stationary.

All other fixed targets will follow a circular path around the turn centre.

The amount of movement of a target is proportional to its distance from the  turn centre.

The procedure for performing a planned turn with a radar in the Head Up orientation involves three steps:

Planning the turn from a chart

Setting up the radar

Executing the turn.

Planning from the chart

A conspicuous radar target is selected as the reference point. Ideally the reference point will be abeam when the vessel completes the turn and steadies on the next track.

The desired turn centre is identified, either by bisecting the initial track and next track and selecting an appropriate radius or drawing lines parallel to the initial and next track at a distance of a desired radius.

The distance of the reference point from the turn centre is measured.

Setting up the radar

The head up orientation is selected with a range scale suitable for monitoring the turn.  The target trails feature should be selected if available.

 

The VRM centre is offset abeam of the bow at the turn radius distance and the VRM range is set to the distance between the turn centre and the reference point

Executing and monitoring the turn

When the selected reference point is about a ship’s length or less from touching the VRM, the turn is started. In a manner similar to parallel indexing to follow a straight track, the apparent path of the reference point can be kept on the circular path of the offset range ring by adjusting the vessel’s rate of turn.

The correct rate of turn will keep the reference point (In this case the island ahead of the vessel) on the range ring as per the following images.

 

If the rate of turn is too low, the reference point will move below the VRM In such a case the rate of turn must be increased to bring the reference point “back on track”

Conversely if the rate of turn is too fast the reference point will move outside the range ring and reducing the rate of turn will correct this.

 

All radars offer head up orientation but have different features. Some models don’t have trails available on head up mode, others curiously have stabilised trails on the head up mode.

With radars that do not have the option to offset the VRM, the EBL can be offset with the range marker set at the reference point distance. This ranged EBL can be used to monitor the reference point path against the planned turn by rotating the EBL.

Conclusion

This method of conducting controlled turns is straightforward and easy to use. The planning is simple and results in turns being defined by their radius and a reference point’s distance from the turn centre. These two values allow for a quick and simple radar set up to provide continuous monitoring from a single source. Further, as the turn is referenced from the ship, the effects of set and drift will be detected and be compensated for by rate of turn adjustments.

Similar to the role of parallel indexing in passage planning, the safe navigation of vessels in confined waters would be enhanced if this technique was widely understood and radar designs allowed for its simple application.

Paul’s full paper is available on-line at:

www.niqld.net/ni_presentations_planned_turns.html

Also available from Nautical Institute publications is Paul’s monograph:

Monitoring turns Using Radar