Extensive testing
As well as benefiting from the knowledge gained from building hundreds of ASD Tugs, the Damen ASD Tug 3212 design has undergone rigorous testing over the last few years, both at Damen’s own Research & Development Department and at the renowned Dutch maritime institution, the Maritime Research Institute Netherlands (MARIN).
The ASD Tug 3212 has a completely revised hull form when compared to previous vessels as a result of these tests. The vessel has a higher bow with a more flared shape and a revolutionary new hull form with a more pronounced “V shape” in the forward section, more slender lines in the bow, and bilge keels.
A relatively low wheelhouse guarantees low acceleration for improved crew comfort and increased stability. The shape of the hull guarantees optimal manoeuvrability. The design has also been based on measurements taken on more than 350 ASD Tugs already in operation. Damen uses Dieudonné tests to take measurements on all of its ASD tugs.
Damen actively participated in the Joint Industry Project SAFETUG, which examined tug escorting in exposed sea conditions in detail. The project discovered that high peak loads in the towline are a limiting factor in operations. Staying connected to the assisted ship is vital for the tug operation and very high peak loads can lead to the towline breaking. SAFETUG II was successfully completed in 2011 and many of its findings have been incorporated into the new design.
Safetug
With the knowledge gained from SAFETUG II and the challenge to prove the pioneering new ASD Tug 3212 hull shape, the new design underwent rigorous model tests in the towing tank at MARIN, including escorting and seakeeping assessments in waves. An experienced Smit tug captain carried out the tests, where a model of the ASD Tug 3212 was actively controlled in 3m waves with a towing wire attached. The Render / Recovery winch was also used to ensure power in the towing line was as stable as possible. This gave a thorough analysis of the dynamic loads on the towline and these tests exactly mirrored real conditions.
Damen’s in-house developed simulation program Tugsim
To predict the escort capabilities of ASD tugs, Damen Research has developed the computer program ‘TugSim’ in cooperation with Delft University of Technology and MARIN.
Naturally crew comfort and safety are always foremost in Damen’s mind and the ASD Tug 3212 has improved workability, largely due to the new hull. The dimensions of the unique shape of the skeg and bilge keels were designed by Damen Research together with MARIN, using TugSim calculations.
The TugSim program makes it possible to calculate escort forces on the towing line and the performance of the tug. TugSim can also be used as a design tool, allowing Damen to optimise the design of the ASD Tug 3212 at an early stage.
TugSim applies fundamental hydrodynamic theory concerning hull shape, skeg, bilge keels and thruster forces. In combination with information on the propulsion installation and the location of the towing point, this quasistatic approach gives the maximum breaking and steering force in each direction. A capability plot can then be made for every escorting speed.
Escort tests at a speed of 10 knots in waves up to 3m were carried out during the model tests. Dynamic forces of 2.5 x the tractive force occurred in the towing lines. The maximum loads on the fairlead and the bitt can increase up to a maximum of 200 tonnes during escorting and the line can turn at a maximum angle of 120 degrees.
Dieudonné trials
Manoeuvrability of the ASD Tug 3212 is of the utmost importance and to this end much effort was spent on optimising the hull, skeg and bilge keels during development.
To assess the manoeuvrability of the ship, Dieudonné trials were conducted at MARIN whereby the continuous rate of turn at a certain thruster angle setting was recorded while the vessel was in deep, open water.
Repeating this for a wide range of thruster angles determined the inherent dynamic stability of the tug sailing ahead and astern.
Damen Research then used this data to validate its predictions and model tests and for making further improvements where needed.
DUTCH MARITIME KNOWLEDGE
All Damen vessels benefit from knowledge gathered during ongoing research programmes within the Group. Damen works alongside world-renowned research institutes such as Delft University of Technology, Maritime Research Institute Netherlands (MARIN) and the Netherlands Organization of Applied Scientific Research (TNO), as well as other reputable universities and leading maritime companies.