Whither Towage: John Clandillon-Baker

February 24th, 2013 by JCB
Posted in Articles, Features, History, Technical and Training | 2 Comments »

The Paddle Tug

JMW Turner: The Fighting Temeraire being towed to Rotherhithe for scrapping in 1838. 

These first tugs were steam powered paddle tugs which, rather than being used to manoeuvre vessels alongside berths or into locks (which was still mainly undertaken using winches, capstans and manpower) were generally used to tow vessels up and down rivers and estuaries which considerably reduced the delays resulting from having to wait for favourable tides and winds. We are fortunate to have a record of this era in the form of the painting of the warship Fighting Temeraire ( apparently referred to as the Saucy Temeraire by her crew!) by JMW Turner which depicts the towage of the vessel from Sheerness to Rotherhithe for scrapping in 1838. Widely regarded as Turner’s greatest work it was voted Britain’s favourite painting in a BBC Radio 4 poll in 2005.

The wonderful resource of the Internet reveals that the tug was the wooden hulled Monarch which was built by Edward Robson of South Shields in 1833. At just under 20m long she was fitted with a 20HP single cylinder steam engine! The Monarch was acquired by John  Watkins & William Ogilby in 1834 and served the port of London until she was scrapped in 1876. Unfortunately, I haven’t been able to find the name of the pilot!

Despite the advent of screw propulsion in the 1840’s the world of towage was very conservative and paddle tugs were still being commissioned as the tug type of preference late as 1899. This was despite the evidence from what must be the most famous “tug of war” in maritime history between the screw propelled HMS Rattler and the paddle wheel driven HMS Alecto in 1843 which proved conclusively that screw propulsion was more efficient with the Rattler pulling the Alecto astern at 2kts!

HMS Rattler & HMS Alecto:                                               Lithograph, Science Museum

Even in the 20th Century some paddle tugs were still being constructed and the last one to be built for civilian use was the  John H Amos which was launched in 1931.

This tug was in daily service on the Tees  until 1967. She has survived (just!) and is currently undergoing restoration by the Medway Maritime Trust.

www.medwaymaritimetrust.org.uk/johnhamos/pages/history.html

The Soviet Union continued to build paddle tugs up until the mid 1980’s and some of these are still in use, their shallow draught enabling them to work in shallow rivers where conventional tugs are unable to operate.

Single Screw Tugs

The single screw tug eventually replaced the paddle tug as the preferred towage vessel type around 1900 and this design remained the tug of choice right up until the 1960’s . Their versatility for harbour, barge and deep sea towage work means that many of these tugs are still earning their keep around the World. Here again though, Britain lagged behind the rest of the World because despite the Diesel engine being widely installed in European  tugs from the 1930’s onwards the UK tug owners continued to commission steam powered tugs right up until the 1950’s !

Another continental invention that enhanced propeller efficiency, especially for tugs and small craft, was the Kort Nozzle. Originally invented by the Italian aeronautic engineer Luigi Stipa to enhance aircraft performance in 1931, it was Ludwig Kort who adapted the design for marine use and who produced the first “Kort Nozzle” in 1934. It appears that Stipa never received any credit for the maritime application and unfortunately his aeroplane prototypes were never successful although the principles were later used in both turboprop and turbofan engines.

A typical single screw tug was the Sun XXV11 operated by London’s Alexandra Towage Company.

Here, your crusty old editor has a personal nostalgic moment since during the early part of my career with the PLA the majority of the tugs were conventional single screw. Checking on the history of  a couple of these, the 1965 built Sun XXV1 and the 1968 built Sun XXV11, owned by the Alexandra Towage Company were typical of the tugs operated by towage companies around the UK. Both these tugs served in London until 1997. They were modified in the 1980’s and fitted with Kort Nozzles and these modifications resulted in an increase in bollard pull from around 25 tonnes to 35 tonnes from the same hull, thus proving the efficiency gains achievable by the fitting of Kort Nozzles on tugs. The latest  information that I can find is that both these tugs are still working as port tugs in Trinidad under the names of Saga Moon and Saga Sun.

Voith Schneider Propulsion (VSP)

The Voith Schneider propulsion system is based on an invention by Ernst Schneider, an Austrian who designed it for use as a hydro-electric turbine. Although it proved to be no improvement on existing turbines for hydro-electric generation, a  chance meeting with the Voith company  led to it being developed as a propulsion system where its enhanced manoeuvrability potential was realised and then proven by trials on Lake Constance.

The manner in which the system works is too complex to detail in this article but  basically vertical blades mounted on a rotating plate are angled to generate thrust which can be directed in any direction. For those interested, information and animations can be viewed on the Voith website (www.voith.com)  In  1929 a German minesweeper became the first ever vessel to be fitted with VSP and this was followed in 1931 by the first commercial vessel called the Kempten, an excursion vessel, owned by the German  State Railway Company.

The advantages of VSP came to the attention of the Southern Railway Company who had Britain’s first VSP vessel, the MV Lymington constructed by William Denny and Bros in Dumbarton in 1938.

Fitted with twin Voith units this vessel served on the Lymington – Yarmouth service between the Isle of Wight and the mainland between 1938 and 1972. In 1974 she was purchased by the Scottish Western Ferries company and renamed Sound of Sanda serving on the Hunter’s Quay to McInroy’s Point run until 1989 when she was switched to ferrying cement lorries to the Faslaine naval base until 1992. Since then, despite attempts to restore and preserve her, she was stripped of her engines and abandoned as a hulk on mooring buoy.

Despite the evident advantages for manoeuvrability, tug companies were slow to adopt the Voith propulsion system with, so far as I can ascertain, the first Voith tug being the Stier constructed for German owners in 1955. The UK was then quick to realise the advantages of the VSP with several companies commissioning them in the 1960’s. One of the major advantages of this type of tug is that with the drive units being placed forward, the risks of “girting” and capsize were dramatically reduced. Voith tugs are also referred to as “tractor tugs”

In the 1980’s the twin Voith configuration enabled more power to be delivered and thus facilitated their use on larger tugs and they rapidly started to replace the traditional screw tug as the tug of choice for ship handling and they also serve well as sea towage tugs.

In London I was  still a junior pilot when the first Voith tug (Waterloo) arrived to join the Alexandra fleet in 1992, closely followed by the Sun Anglia in 1993.

The Sun Anglia (now Svitzer Anglia) in Gravesend Reach in 2010. Note that the tug is steaming stern first. This is the normal steaming mode for the Voith tugs in the river since the wash is less than that generated when steaming ahead.               Photo: David Berg

For us pilots, the capability to put a tug on a single line on a centre lead aft and move it from one quarter to the other in a few seconds made for safer and  easier ship handling so we were all delighted when  more Voith tugs appeared and by 1995 we were normally allocated at least one Voith tug for manoeuvring. By 2000 all the Thames tugs were Voith tugs but currently, the new tugs being introduced by Svitzer towage (who currently manage the main Thames tug fleet) as the older Voith tugs are replaced  are Azimuth drive tugs. The Svitzer Anglia only left London last October and is currently for sale, laid-up on the Tees.

Azimuthing Stern Drive (ASD)

Also known as Z-pellor tugs and sometimes “reverse tractor”, this type of tug is currently a very popular model due to its efficiency and economy when compared to the Voith. Although the azimuthing drive was developed by the Schottel company in the 1950’s it was the British company JP Knight who were the first company to introduce an ASD tug in Europe in 1981 with the Japanese built tug Kinross which is still in service at Invergordon.

With twin drive units that can be rotated through 360 degrees ASD tugs are very manoeuvrable and, at first glance, seem to represent a return to the traditional tug format. However, the difference is that on this type of tug the towing winch is fitted forward rather than aft. The advantages of this arrangement are twofold. Firstly they protect against girting and capsize and secondly they can rapidly change from pulling to pushing mode when made fast alongside on the hull making them ideal for handling tankers and bulk carriers. When made fast on the stern they, along with Voith tugs, perform very well as escort tugs. The big drawback with this type is in their restrictions for use as a bow tug made fast on a centre lead forward. There have been several incidents involving the loss of control of an ASD tug whilst operating in the “bow to bow” mode and pilots operating with ASD tugs should all read the MAIB report into the Thorngarth – Stolt Aspiration incident. The problem for an ASD tug operating in this mode is that if the tug is allowed to drift more than a few degrees of the ship’s heading alignment when the ship is moving at speed through the water it can become impossible for the tug Master to recover the alignment and the tug will be swept around under the flair of the bow. There is a very dramatic photograph of this happening to the tug “Fairplay 21” on the Internet. Having stated that, there are some ASD tugs with skegs which provide enhanced directional stability when running astern which enables them to operate at higher speeds but generally the maximum recommended speed for these tugs to operate in the bow to bow mode is 4 – 5 kts and some tug companies won’t permit their ASD tugs to operate in this mode at all. The consequence of these restrictions is that this can make their use with container ships largely impractical when made fast anywhere other than on a centre lead aft. The reason for this is that container ships are designed to go fast between ports and the large engine and propeller configuration can result in “dead slow ahead” speeds as high as 11 knots. Also the hull design has a large flare on the bow and also a cut away on the stern which results in a very small section of parallel body for a tug to push up on thus making it very inefficient   to use tugs in the “push-pull” mode on these ships. This is especially the case for the forward tug which frequently has to move so far aft to be in a position to operate that it’s frequently aft of the pivot point! The other problem with these containerships is that they often have no towing bollards fitted on the main deck aft of the fo’c’sle!

Azimuth Tractor Drive (ATD) Tugs

Also referred to as Azimuth Tractor or Azimuth Forward Drive tugs, this design is basically a twin Voith tractor tug fitted with twin azimuthing drives instead of the Voith Schneider units. We have two ATD tugs in London and the tug Skippers’ like working with them and confirm that they handle very much the same as a Voith. The increased efficiency is revealed in the bollard pull which is 60 tonnes for these tugs compared with 52 for the similarly sized Voith tugs in use. I also understand that the running and maintenance costs are cheaper than for a VSP tug.

Z-Tech

As can be seen from above this is a variation on the Azimuth Tractor design with twin azimuthing units located forward but in a less vulnerable position being protected by the skeg and presumably this makes them a shallower draught than the ATD tug. I don’t have much operational information on this class of tug but from the promotional data they are basically and ASD tug with the wheelhouse moved aft and reversed, the advantage of this being that they can work closer under the flare of a ship’s bow than an ASD. I have no information as to whether they experience similar problems to the ASD when working as a bow tug at speed but the large skeg would seemingly offer good directional stability. I am not aware of any Z-Techs working in the UK.

Rotor©Tug

The Rotor©Tug is a very interesting tug developed by the Dutch company Kotug which incorporates 3 azimuthing drive units, two forward and one aft. I must admit that I only learned that such a tug design existed a couple of years ago but have discovered that the design dates back to 1999 when a Kotug engineer came up with the concept in response to a tender for tugs from Milford Haven. Although Kotug didn’t win the Milford Haven contract they decided to develop the  concept and there are now many Rotor©Tugs operating in Holland and Germany. The exclusivity of the design and commissioning now lies with Robert Allan Ltd and Rotor©Tug is a trade mark of the Dutch KST company.

The initial reaction of most companies is why on earth do we need three drive units? The answer is not just that they are obviously extremely manoeuvrable but also flexible as result of the three engine configuration. The ability to operate on one, two or three engines not only  makes them extremely safe in the case of an engine failure but also offers considerable fuel savings. Harbour tugs are fitted with very powerful and fuel hungry engines but this power is only used for a small percentage of the time when involved in manoeuvring ships. For the majority of the time, harbour tugs’ engines are idling on stand-by so being able to run on one engine when not actually engaged in towing is a major economy, an important factor given the increasing cost of bunkers.

6 kts sideways! A rotor©Tug on trials

EDDY Tug

One design of tug that is brand new is the EDDY tug. EDDY stands for Efficient Double-ended Dynamic’ tugs and features two azimuthing drives, one at each end of the tug. Baldo Dielen Associates Ltd (BDA Ltd) created the design and SMIT has participated in the development and model testing program. Although no EDDY tugs have yet been commissioned the designers claim that the design will offer superior safety, performance and economy. There is a portfolio of several different sizes but it’s probable that the standard model will be a general purpose tug 30m long and around 60 Tonne BP. Being double ended it is anticipated that the handling will be entirely intuitive and independent from the direction the tug master is facing. Each end classifies as bow and tank trials indicate that the tug performs well in either direction in all conditions. A central skeg is designed to provide good directional stability and a substantial increase in line force when operating in the indirect towing mode. The proposed towing arrangement is a double-drum towing winch with two towing fairleads, one for close quarters ship handling and one for (indirect) escort towing. The single deck level accommodation is designed to offer better clearance when working under the flare of large ships. Running “light”, an economical, low wake, 12 knot speed is designed to be achieved using a single drive unit. It can generate push and pull forces in any direction, with minimum delay.  When assisting under speed, high dynamic forces of up to twice the tug’s bollard pull can be generated both by the stern and the bow tug since they are designed to be as effective at the bow as at the stern which is aimed to address the need by tug operators to standardise their fleets without the need to choose between ‘ASD’ or ‘tractor’ type tugs.

The above information has been provided by BDA Ltd who inform me that they are optimistic that a firm order will be placed for the first EDDY tug soon.                                       

RAVE tug

You wait a whole career for a tandem propulsion tug to be designed and then two turn up together! Like the EDDY concept, the RAVE (Robert Allen Voith Escort) has a drive unit fitted at each end of the tug but in this design the units are Voith propulsion rather than azimuthing drives. It is interesting to see a new design using Voith units but in recent years a fundamental re-engineering of the units has resulted in an increase in efficiency and the advantages of more precise control of thrust and faster redirection of thrust make it competitive for certain applications. The RAVE is a big tug of around 37m and, as its name suggests it’s designed for escort work. Again I am not aware of any RAVE’s having yet been commissioned but the concept is gaining a lot of interest.  JCB

Updated information 

Since writing this article, Robert Allan has provided me with the following clarification: “The RAVE is a concept of the Voith Sneider Propulsion drive configuration, and not a specific design, and the fore & aft configuration can be (and has been) applied to almost any size of tug.  It just happened that the first concept developed was for a large escort tug.  More recently designs have been developed for a 29 metre harbour tug version, which has attracted some very serious interest from European tug Owners.”

A novel form of tug!

This quarter’s feature on tugs was collated from various sources and I hope that it has helped to update readers on the various types of tug, their advantages and limitations. Henk Henson provided me with many useful contacts but a particularly valuable resource was a presentation on tugs by the well known tug expert and author, Jack Gaston, who kindly gave me permission to plagiarise his work and to use the above picture . Jack is a skilled model maker and he explained that his daughter presented him with the, originally static, duck display model as a challenge to transform it into a remote controlled model, which, as you can see, was achieved without problem much to the delight of Jack’s grandsons and, no doubt, all the onlookers at the local pond!

Firefighting tugs save the day!