Every day pilots handle ships with the aid of tugs and whilst the vast majority of the manoeuvres pass off safely’ such operations  are inherently  dangerous and tragically when tug operations do go wrong they almost inevitably end up with a loss of life to the tug crew. It is therefore essential that all pilots are fully aware of the dangers posed to the tug, particularly when picking up the tow line from a forward centre lead.

   In this feature,which is edited from an article included in the Summer issue  of International Tug and OSV magazine, Capt Henk Hensen FNI FITA considers tug operations near a ship’s bow – the risks, the tragedies, what we can learn and what we should be doing now to prevent further catastrophes and with respect to this pilots play an essential role.

The article is reproduced here with the kind permission of both the author and the IT&OSV magazine.  JCB

Tug operations near the bow of a ship having headway are very risky. The higher the ship’s speed, the larger the risks. This is nothing new. On 6th September 1954, the tug Fairplay 1, came under the bow of the cruise ship Italia and was run down whilst attempting to make fast at the bow of the ship which still had considerable  headway. There were two casualties so this accident highlighted the risks to persons on the tug This disaster and similar accidents prompted the German Ministry of Transport and Traffic to commission a study into how these accidents can happen, and in particular to find out how they can be avoided.

However, despite the study being carried out and the lessons learnt from it,tragically such accidents still occurred. These led to more studies, but the tragedies continue to occur. How is that possible? Do we accept that in this sophisticated world, with all the knowledge we have, people on board a tug may lose their lives during tug operations in or near a port? We should not!

Therefore, with the victims firmly in mind, this article will focus on these accidents, and try to suggest ways in which they may be avoided. First, let us take a look at the studies carried out.

1964 

The periodical Hansa published an article by Capt W Mockel following tank tests which had been carried out with a model of a tanker using tug models of different types and propulsion systems, The first model tests simulated tugs that had already come alongside the ship’s bow, and tried to come free again. Then they studied tugs approaching the bow from aft in order make a tow-line connection. The tests were carried out at speeds of 6 knots and below, with separation distances between tug and ship of only a few metres. The results were very interesting. Among the findings were the following:

A conventional tug without a bow thruster cannot turn away from the fore body of the ship once the tug is alongside in contact with the tow. Tugs with a very powerful bow thruster can get clear under certain favourable conditions, but the only tug which could get clear virtually under any condition was the Water Tractor tug equipped with Voith Schneider propulsion under the fore body.

When a tug is overtaking a ship at close range, the forces and turning moments working on the tug change very quickly when it is passing the forward shoulder. The most dangerous position is when the tug is passing the forward part of the bow, where the out-turning moment working on the tug quickly changes to an in-turning moment. If, at that position, the tug is steering towards the ship, then it becomes difficult for the tug to avoid a collision.

The higher the speed of the tug, compared to the speed of the vessel, the higher the turning moments are. The turning moments increase with the square of the speed.

Subsequent accidents have continued to highlight the inherent dangers of passing a towline near the bow of a ship at speed is very dangerous for all types of tug and further studies have confirmed the effects and conclude that when tugs come alongside the bow, the only safe escape manoeuvre for the tug is ‘full astern’.

“Correct and safe procedures should be followed by all parties when making a towline connection forward with a ship making way”.                   

Photo: Alfred Memelink. www.memelink.co.nz

1976 

Dr Dand, in the UK, undertook model tests with two types of ships and two single screw tug models at speeds of approximately 6 knots. Among the conclusions were:

Near the fore body of a ship is a hazardous region for the tug as it may ‘drive’ itself under the ship’s bow if the application of correcting rudder and reduction of power are not rapid enough.

Interaction forces vary, approximately as the square of the speed, and reduce with distance off. Their  severity may be most easily reduced by a reduction in ship’s speed.

2011

On 1st August 2003, a further tragic accident happened with the ASD tug Burcht near the Antwerp locks. The tug tried to make fast at the bow of a container ship, came under the bow and capsized. One person drowned.

Model tests were carried out at Flanders Hydraulics Research in Antwerp. A model of a 65-tonne bollard pull ASD tug was used together with the model of a 229m long container ship and various ship speeds, different separation distances between ship and tug, and differing tug drift angles were investigated.

Some of the conclusions from these tests were:

An ASD tug sailing in close proximity to the bow of a large container vessel will experience strong interaction forces.

A tug master should be aware of these interaction phenomena since the forces are of sufficient magnitude to give rise to tug handling difficulties. The tug will experience either a repulsive or attractive interaction sway force, or a bow-in or bow-out interaction yaw moment. A combination of these forces will necessitate a steering force to enable station keeping.

2012 

On 11th November 2010, during stormy weather, the tug Fairplay 22, while trying to make a towline connection at the bow of the ferry Stena Britannica, came under the bow and capsized with two fatalities – the Captain and the engineer.

The Fairplay 22 being recovered after the capsize, a tragic reminder of the inherent dangers of bow tug operations.

The calculations were carried out at various speeds and using various distances between ship and tug. The key findings were:

The turning moment is at one location outward, but at a more forward-lying position, when the forward  perpendiculars of ship and tug are level, there is a strong inward turning moment working on the tug. This inward turning moment is significant in relation to the manoeuvring possibilities of the ASD tug.

If the tug is then steering with a drift angle of almost 10 degrees towards the ship, the hydrodynamic forces and turning moment working on the tug increase significantly, so consequently there is an increased risk that the tug cannot get away from the ship.

Suction forces and turning moments increase with ship’s speed and decreasing distance between ship and tug. The recommended speed through the water should not be higher than 6 knots.

General conclusions

All the investigations carried out during the past 40 years have reached similar conclusions:

There are strong interaction forces, including turning moments, around the bow of a ship making way. These interaction forces and turning moments can fluctuate and rapidly change direction.

The forces and turning moments vary by ship type, so there is some difference in the outcome of the studies.

The interaction forces and turning moments working on the tug increase with ship’s speed and with decreasing distance between tug and ship.

In shallow and narrow waters, the interaction forces increase as well.

The interaction forces can be so strong that the tug’s manoeuvring capabilities are not large enough to manoeuvre the tug away from the ship’s hull. If a tug comes alongside the ship’s bow, it may not be able to get free again.

The only safe escape manoeuvre for the tug is always full astern.

Tugs with the propulsion forward, such as Voith tugs and Azimuth Tractor Tugs ATT)* can better compensate for the interaction forces, because when setting the propulsion units away from the bow the tug will move away.

Conventional tugs, or ASD tugs operating as a conventional tug, when steering away from the bow, will experience a force towards the ship and the tug’s stern will move quickly inwards. This is a consequence of the aft lying rudder(s) and propulsion. It should be noted that most of the studies focus on tugs which are approaching the bow from aft, which is not always the case.

Recommendations

• Be aware of the interaction forces. The problem is, of course, that these interaction forces change with ship type, draft, trim, speed, underkeel clearance, width of fairway and drift angle. Although tug masters have a lot of experience and know there is a lot of difference between, for instance, a loaded bulk carrier and a container vessel, it is difficult for them to assess where the safety limits lie.

• A safe speed of not more than 6 knots is recommended. That is a speed also recommended by the International Harbour Masters Association and the European Harbour Masters Committee. A speed of 6 knots is indeed, in general, a safe speed for bow tugs. Problems can arise with ships having a very high dead slow ahead speed in combination with steering problems when the engine is stopped.

• Correct and safe procedures should be followed by all parties when making a towline connection forward with a ship making way.

• Tractor tugs, and tugs with propulsion units forward, are much safer to operate as bow tugs. They can better compensate for the interactions forces.

Various questions can be asked when reading reports, but in the cases of the Barta, which came under the bow of the Magdalena in 1988 and Fairplay 22, both reports give a good impression of what happened, and the following factors played a role:

• The ships’ speeds and the consequent interaction effects between tug and ship.

• Visibility from the tug wheelhouse. The findings of the investigation of the Fairplay 22 accident also show that the drift angle may have played a role, along with the visibility from the wheelhouse and wind influence. It is not clear to what extent each of them contributed to the outcome.

• Wind.

• The procedures used for passing a towline forward.

• Openings not closed and limited stability (Fairplay 22).

• Type of tug, operating mode and suitability played a role.

A few remarks occur to the author at this point

The ferry sailed with a drift angle up to 10 degrees. There were wind gusts up to 50 knots. A tug positioning itself to take the heaving line will normally sail on the lee side close to the ship and parallel to it. It is therefore always important that the pilot or ferry master tells the tug the drift angle he is steering, so the tug master can take that into account.

Although mentioned in the Fairplay 22 accident report, more attention must be paid to the safest way to approach different ship types for making a towline connection forward, depending on tug type and operating mode.

It is the ship’s captain who orders the tugs  The pilot and/or captain form a team with the tug masters. This means that a pilot and/or ship’s captain should operate in such a way that the tugs are never brought into danger by the ship. In this respect, the pilot and/or ship’s captain have a certain responsibility for the safety of the tugs. However, it is only through proper training that they will be able to recognise the dangers and prevent them from happening.

It is not only conventional tugs which may come under the bow of a ship making way. It also happens with modern ASD tugs, particularly when, like Fairplay 22, they are operating as a conventional tug.

Three questions must be asked

1. Do the results of the studies find their way to the training institutes, towing companies and, most important of all, to the tug masters?

2. Can these accidents be avoided under the present method of tug operations near the bow?

3. What can be done to ensure that such accidents do not happen again?

With respect to question 1, it is the author’s opinion that, in the daily practice of tug operations, there is insufficient background knowledge about the risks related to operating with a tug close to the bow of a ship making way and what effect speed has on those risks. The situation can be improved by a better information exchange between research institutes, training institutes, towing companies and tug masters. For tug masters, the situation can be improved by implementing the lessons learnt from accidents in their training. But do tug masters in all ports of any relevance around the world have a certified training system focused on ship handling, including refresher courses?

The answer should be ‘yes’, but is mostly ‘no’. This means that many tug masters, perhaps all, miss a lot of vital information. Tug masters know of interaction effects from experience, and some simulator manufacturers are gradually paying more attention to them. However, the largest problem in daily practice is that a tug master often cannot judge when it becomes too risky for his tug and crew around the bow of a ship at speed. There is a very small margin between safe and unsafe, and the risks often are not realised or cannot be properly assessed. In addition, a tug master is often forced to come closer to a ship than he wants because of, for instance, improper heaving line usage or inexperienced crew on board the ship to be attended.

Speed is absolutely the most crucial factor. However, the possible minimum speed of a ship depends on several variables, such as the dead slow speed, the steering performance, wind and current effects. It is not always possible to sail at a minimum speed which is safe for both the ship and for the tug while trying to pass a towline near the bow.

With regard to question 2, accidents near the bow or bulb can be avoided under the present method of tug operations if a few safety measures are implemented:

• Studies should be conducted on the safest approach procedure for different ship and tug types.

• Proper and effective use of suitable heaving lines is needed. It is worth considering the use of a line-throwing gun on board the tugs. The tugs can then stay at a safer distance from the ship’s bow when a heaving line is used.

• All around visibility from the wheelhouse is an important factor.

• Optimum teamwork between the pilot and/or captain and tug master is needed, based on experience and (team) training. Simulators used for tug master training should have implemented realistic interaction effects.

Most important are:

1. A safe ship’s speed, which may depend on tug type and/or operating mode. Tug masters should not make fast if they find it too risky to pass a towline near the bow.

2. A suitable tug. If this is taken into account, then the risks for tugs and crew will  be reduced. However, the risks caused by a ship’s speed and related interaction effects will still be there and can still cause problems.

Regarding question 3 there are a number of possibilities to prevent such serious accidents in future:

The use of suitable and powerful tractor tugs – as already indicated by the research in 1964 – Rotor Tugs* or modern reverse tractor tugs.

The use of a new tug concept such as the EDDY tug* which has one thruster forward and one aft. This tug can effectively cope with interaction forces.

A change in the assisting mode of the forward tug, for example,where possible, using the tug on the shoulder where no accidents have ever been reported.

It goes without saying that all openings must always be closed during operations.

Optimum teamwork is needed to ensue safe tug operation         Photo: JCB

Conclusion

The purpose of this article is to draw the attention of all responsible professionals to these tragic tug accidents and to stimulate discussion which may lead to ideas in addition to those mentioned above. Then, finally, an awareness of the dangers of bow tug operations, and how to overcome them, may be achieved.

Unfortunately, accidents can and will happen but in this modern world it is not acceptable that crew members are killed during accidents with bow tugs, when so much research, carried out over a period of nearly fifty years, has revealed the reasons why such accidents occur.

        Henk Hensen 2012

For the feature on different tug types: Click here