Port-Revel_Marine-marchande

More practical exercises...

Manœuvres using anchors

Day three focuses on manœuvres using anchors: dropping anchor, of course, but also docking or undocking while dredging an anchor dropped at the right moment, and an emergency stop in a channel using the anchors.

As ships increase in size, they are becoming systematically assisted by tugs, so captains and pilots of large vessels do not necessarily carry out manœuvres in confined waters or berthings with anchors very often. And yet, in the event of serious damage, even a 300 000 t ship can be slowed down by dredging her anchors⁽¹⁾. But this is obviously a very tricky manœuvre that takes practice ... which is where Port Revel comes in.

Trajectory map of a turn using two anchors

Berthing with anchors
(photo. Port Revel)

(1) In this case of "emergency anchoring" the chain length must be perfectly gauged (not too long), so that the anchors that have been dropped to dredge do not dig in. Otherwise they are sure to break...

Confined waters and bank effects

The last day is devoted to tests of meeting and overtaking in the Suez Canal, both under normal conditions and with various types of failure.
Remark: ships do not meet or overtake each other in the real Suez Canal, but the one at Port Revel is the ideal place for this type of shiphandling exercise.

Before boarding, the students receive a brief reminder of the hydrodynamic phenomena at play in narrow, shallow waters (ratio of depth to draught less than 1.5). In general, a moving ship disturbs the mass of water around her (over a distance approx. twice her length and one and a half times her draught), causing overpressure fore and aft and negative pressure in the middle, thus lowering the water level. The ship is thus sucked down and changes trim. If the under-keel clearance decreases, the effect is increased. This effect is called "squat". This phenomenon is generally proportional to the ship’s length and the square of her speed (charts give squat as a function of various parameters specific to the boat and the waterway). The proximity of the banks amplifies these effects even further.

The GRENOBLE and the BEN FRANKLIN meeting in the Suez Canal

On the same morning we had naturally noticed the effects – particularly pronounced in confined and shallow waters – of the ship being pushed towards the bank (!) by the bow wave of the oncoming ship and, on the contrary, being drawn in by her propeller. Therefore, when two ships meet "in parallel", their captains must not hesitate to "aim for" the approaching ship’s bow wave (which pushes the two ships apart), and then move well away from each other as they actually meet abeam in order to counteract the effects of being pulled in by their propellers.

Overtaking


Fortunately this overtaking exercise was completed perfectly, because the instructor was waiting... boat hook in hand!

It is important to remember that the water displaced by the approaching boat will tend to push the boat being overtaken towards the bank, and that the effect is reversed after overtaking.

The two "refresher" students also had an opportunity to practise drifting and manœuvres in waves, or mooring at a SPM/FPSO with waves or current.
SPM : Single Point Mooring (oil tanker terminal mooring)
FPSO : Floating Production, Storage and Offloading system (vessel anchored or dynamically positioned for crude oil production and storage)


Wave generator	Drifting in the waves and corresponding trajectory map

Ship movements in waves depend on the wave direction, amplitude and frequency as well as on the ship’s length, block coefficient and speed and the water depth in relation to her draught. All these parameters can be tested using the Port Revel wave generator. Tests backed up with trajectory tracking can be used to measure the drifting of a ship caught in waves in a black-out, for example: her underwater resistance makes her turn in one direction or the other..

Scale models and simulators: two complementary tools

Students who have been lucky enough to try out both of these tools are unanimous in saying that they complement, rather than compete with, each other. On the lake, the ships sail in their real environment (albeit in fresh water), with real gusts and whirlwinds. The crew really feel the ship rolling and see the deck dashed by waves! Or even feel the anxiety of navigating in fog. And the sensations are all there if ships collide or run aground.

On the other hand, simulators reproduce more accurately a real bridge with all the instruments and controls (of course, the model ships also have the main controls) and can also simulate in detail the surroundings of an approach to a port. However, the mathematical models on the simulators do not fully reproduce secondary hydrodynamic phenomena such as the propeller pitch effect or altering course when full astern.

All the manœuvres can be completed on the Port Revel model ships thanks to their 360° vision, which is not the case with some simulators.

" We reckon that the Port Revel course becomes particularly beneficial after four years of pilotage. At that point, pilots are familiar with all the phenomena related to ships. The courses at Port Revel go into extreme subtleties and we can achieve things that are out of reach with a real ship, because of the risk of damaging her," says a manager of the shiphandling simulator at the Havre-Fécamp pilot training station.

To conclude...

Is a sailor not proud when he completes a fine manoeuvre safely, even - and especially - in difficult conditions? A course at Port Revel is the perfect opportunity for him to further improve his understanding of how ships behave (their possibilities as well as their limits) and become more aware of his own abilities.

Regular high-level training for captains (IMO A 960 recommends every 5 years) enhances the image of the shipping company. This type of course enables captains and pilots to analyse manœuvres and discuss them in detail ... in circumstances other than an accident investigation! But navigation at Port Revel is far from being child’s play, and many students confess to feeling a little more stressed when piloting a scale model than when on a simulator…

To close, greetings to the week’s students, thanks again to our instructors and all the Port Revel staff and, lastly, for students making a 8 000 or 10 000 km round trip to take the course, a few ideas for places to visit in this region lying between Lyons and Grenoble.

The LABRADOR, one of the first model ships at Port Revel (1969),
an ice-breaker … which avoided ending up on the scrapheap


Mooring the BERLIN and fitting a check stopper and a sensor to measure the breaking load (right: the mooring did indeed break after the NORMANDIE overtook)


As she overtook the moored BERLIN, the NORMANDIE moved her far enough to break the check stoppers.