The performance and the ergonomic aspects of various PPU solutions

The choice of the right PPU depends on several factors. This approach of comparing PPU types was presented and discussed for the first time at the 2018 IMPA conference in Dakar, in occasion of a presentation held by Cadden on PPU technology. Its content was well perceived. The delegation of international pilots as well as all main PPU vendors attending agreed that this is a good summary of the main types of solutions available nowadays. The interesting thing about this table is that the key performance metrics have been mapped to give a general idea of what to expect from a type of PPU. Ergonomics is also taken into account, as well as the weight and dimension, finally the pricing. Five main types of PPU hardware are considered:

1. A PPU made of two wireless beacons with RTK type of precision
2. A PPU made of two beacons connected via one cable with RTK type of precision
3. A PPU made of two wireless beacons with SBAS type of precision
4. A pilot plug receiving navigation data from the AIS and having its own embedded gyro
5. A pilot plug receiving navigation data from the AIS without any other type of aiding sensor neither embedded nor connected

Let´s take a look at these one-by-one:

Two wireless beacons with RTK type of precision

• RTK precision means that a GNSS receiver delivers a precision of position of 1cm horizontally and 2cm vertically. This is most accurate precision one can have therefore POS (1cm) and SOG (1cm/sec) rank TOP.
• Since the beacons are not connected by cable, they can be placed far apart from each other and deliver an excellent performance in terms of Heading (see formula) and ROT. Heading and rotation is calculated using GNSS sensors, implementing a so called GPS compass.
• The separate beacons need individual means of power supply, they must have ways to communicate amongst each other and require connecting with a RTK base station based on land. This pose some constraints in terms of volume and weight. This type of PPU is not yet so light and small to be carried inside a pocket, therefore the ergonomics is not the best possible, however, the absence of cables make it simple to use and less prone to points of failure.
• On the other hand, the fact that the two beacons are isolated, means that the cost of the technology behind a multi-constellation RTK GNSS L1/L2 receiver is double making a PPU of this type cost as much as a nice German car.

Two beacons connected by cable with RTK type of precision

• RTK precision is TOP, like in the previous case, so no changes here.
• Since the beacons are connected by cable, they cannot be placed far apart from each other and deliver a good performance in terms of Heading but not the best one can have (see formula).
• The two beacons can be powered by a single battery. They communicate amongst each other via the cable connector which links the two GNSS antennas to the same receiver. This poses less constraints in terms of volume and weight but still makes this type of PPU not so light and small to be carried inside a pocket, therefore the ergonomics is not good at all, especially since cables make it cumbersome to use and set up but also prone to failure.
• The fact that the two beacons not isolated, means that the cost of the technology behind the RTK GNSS receiver is nearly half of the one behind a wireless system which needs two separate receivers, making a PPU of this type cost circa 40% less of an equivalent one wireless. The price is therefore comparable to a modern city car.

Two wireless beacons with SBAS type of precision

• RTK precision means that a GNSS receiver delivers a precision of position of 50-70 cm horizontally and circa 1-2m vertically. This is OK but still not the most accurate precision one can have therefore POS (50cm) and SOG (10cm/sec) rank OK.
• Since the beacons are not connected by cable, they can be placed far apart from each other and deliver an excellent performance in terms of Heading (see formula) and ROT. Please note that a Moving Base Line (MBL) can be implemented with a so called relativeRTK precision despite the level absolute precision of position delivered by SBAS technology.
• The separate beacons need individual means of power supply, they must have ways to communicate amongst each other. This pose some constraints in terms of volume and weight. This type of PPU is still not as light and as small to be carried inside a pocket, therefore the ergonomics is not the best possible, however, the absence of cables make it simple to use and less prone to points of failure.
• On the other hand, the fact that the two beacons are isolated, means that the cost of the technology behind the GNSS receivers, (which is less than RTK receivers) is still quite high since one needs to have two L1 SBAS GNSS receivers still making a PPU of this type cost as much as a city car.

An AIS pilot plug with gyro

• Using AIS data is a good idea butGNSS positioning is not precise (2.5m-4.0m CEP-Horizontal). Furthermore, SOG is only accurate when navigating offshore, not fit for navigation at slow speed or inside harbours. The AIS provides a low update rate which is not constant. Pilots use pilot plugs mainly for situational awareness. Another benefit is to have the choice of being independent from the ECDIS. Clearly, this solution is not fit for navigation.
• This type of solution must be complemented with other sensors, one of the typical solution is to embed a good gyro inside the pilot plug. This gives ROT which is good enough in some types of non-extreme situations. The heading information provided is not the best one can get but it is still OK. Fusing the data from the AIS with the embedded gyro is the key element which provides the right HDG during the interval between each AIS feeds. However, when the intervals are too long even a good gyro might lose a few degrees per minute.
• The great thing about this equipment is that it is light and small. The ergonomics is high, except that in some cases, the pilot plug on the ship is not wired correctly and this makes it a solution which comes with some risks, therefore it still does rank 5 stars in terms of ergonomics, but it is not the ideal solution.
• The price is mainly driven by the quality of the gyroscope embedded and is equivalent to a moto scooter.

An AIS pilot plug with no aiding

• Same as above, this solution is not fit for navigation but for situational awareness and to be independent from the ECDIS.
• This equipment is light and small. The ergonomics is high, same as above.
• The price of the hardware is mainly driven by the quality of the wireless features (Wi-Fi, or Bluetooth) and some software which helps the configuration. We can safely say that e pilot plug costs as much as a bicycle.

PPU are becoming increasingly important

When it comes to rules on navigation safety there is no official obligation for pilots to use a PPU. The IMO (International Maritime Organization) sole hint to its usage can be interpreted in the Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs)both in Rule 5 (Look-out):

“Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and or the risk of collision.”

And in Rule 7 (Risk of collision):

“(a) Every vessel shall use all available means appropriate  to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist.”

The term “by all available means appropriate” is where we can assume that a PPU is a good candidate to minimize risk.

These rules, last edited more than 10 years ago, clearly focus on making sure that conventional equipment is properly working such as radar technology.

“(b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observations of detected objects.

(c) Assumptions shall not be made on the basis of scanty information, especially scanty radar information.”

As we witness a huge increase both in the size of the modern vessels and in their traffic in busy harbors and seaways. Pilots tend to minimize some risk factors by means of more modern tools providing insightful situation awareness information to make a full appraisal of the risk of collision. Proper look-out is definitely better off with additional modern navigation aid tools such as a PPU.

In this article, we will discuss 7 most important situations when a PPU is useful.

Limited Visibility

A PPU is a great piloting aid system in conditions of limited visibility. Traditional look out can be hard due to the huge size of modern vessels, furthermore, in circumstances when large structures block the sight (i.e. a high stack of containers) the job of the pilot can become quite stressful. The problem becomes more noticeable at night or when extreme meteorological conditions such as thick fog or heavy rain, reduce visibility. In extreme conditions, a PPU sensor can also be considered as an excellent navigation tool.

Up-to-date Charts

Bathymetry and cartography does change. As the size and the weight of modern vessels goes increasingly up, the need for accurate and up-to-date charts becomes a key factor. There can be situations when notably, the ECDIS or the printed charts cannot be trusted completely. Pilots can bring accurate charts provided to them by specialized local authorities, but they need to plot onto them, their vessel in real time. The most common method is to plug their tablet to the AIS plug, making this the most basic form of Portable Pilot Unit, in this way they can at least be detached by ECDIS. In situation when extreme accuracy is necessary, other types of navigation sensors can also be brought onboard, but, in any case, the main objective of using their own chart is achieved, and this is very important.

Precise SOG, POS, HDG and ROT

For most of the reasons discussed in this article, pilots are in demand of berthing aid tools that provide accurate vessel location and speed in real-time. Accurate heading information can be determined in several ways. The ROT is equally important. For a deeper analysis on this topic, it is strongly advised that you read the articles on how to determine vessel ROT and accurate heading as well as the article on vessel position and speed accuracy.

The main characteristics of a PPU is to deliver accurate navigation information to provide pilots with sufficient aid to do their job better, safer and with less stress. There are several ways to provide the accuracy required. For more information on these differences, please see the article: the choice of a PPU depends on several factors.

Navigating very heavy/large vessels

When the weight of a vessel is so big that she makes very little headway, the forces which must be applied are massive. This has an impact both on the fuel consumption but also on the attention which goes to applying thrust in a way that is optimal. Generally, this type of operations take a long time and are performed very slowly to reduce risks but also to control the huge amount of power applied. If a very heavy ship accelerates more than expected the predicted position must be calculated sufficiently ahead of time to control her motion. Detecting with accuracy these types of acceleration requires sensors which evaluate the situation very often, and amongst all, with extreme accuracy (1cm/sec), in this case a PPU is the answer.

When it comes to long and large vessels, brings yet another difficulty, to control the drift both on the stern and on the bow and to evaluate the ROT with extreme accuracy. Imagine a vessel which boasts a length of 350m whose ROT is not accurately monitored. It is unthinkable. The water space needed for maneuvering must be enormous, and unfortunately, in some cases, a pilot must assist the commander in tight water spaces.

In tight water spaces

Even in cases when ships are not over 300m in length, it is not uncommon to have vessels with beams over 30m. The size of vessels in the last decade has rocketed up. On the other hand, harbors, canals, rivers, locks have not been able to grow adequately. Despite intensive dredging, building new and larger harbors, today, it is not uncommon that a huge ship must enter a water space with a margin of a few meters. And if this was not a problem big enough, the traffic has also gone up, so the space available needs to be shared. The need to control is never been so crucial as never. This is also why the usage PPU has taken off in the last few years.

For real-time dynamic under keel clearance

So far in this article, we have not touched upon another huge issue, probably the biggest of all: UKC. Depth limits are above all a commercial handicap for shipping companies. On the section of the Elbe river before Hamburg, vessels with a combined beam of more than 90 meters cannot meet in the navigation channel.  Access to some ports is limited in small time windows and is dictated by the tide. In some cases, commanders must take the risk to navigate in circumstances where the UCK is at the limit. To achieve this, they must have and excellent control of the position of the ship, the bathymetry must be accurate, the meteocean information must be in real time, the areas with restricted access must be clearly marked. A PPU plugs itself in this scientific environment as a technological tool which acts as a precision sensor of position both on the horizontal plane but also on the vertical axis. Some have inertial sensors which measure the heave of the ship, and the pitch, which in some cases helps detecting the SQUAT effect.

For training and in case of emergency

Some software allows saving and replaying manoeuvres. This is an excellent way to train less experienced pilots. At the same time, more experienced pilots, can learn new ways, once they have been recorded by others.

In the unfortunate event when a complicated situation starts developing, pilots can ask for support to other peers who are more experienced with the problem. Some navigation software, which works in combination with PPU sensors, have a solution for broadcasting  in real time on the internet, what is seen on the screen of  the pilots on board. Any pilots, even off duty, can be alerted. They can connect to the server using their smartphone and they can see what is going on, in this way they can make a quick precise assessment of the situation and provide support remotely.