Swell Idea

Fast thinking by the master of a Mitsui OSK Lines car carrier has helped the ship escape from pirates close to Tanzania.  Pirates fired rocket propelled grenades at the 5,232-vehicle “Felicity Ace” (built 2005).

Taking advantage of the increasing choppy seas at the start of the monsoon season the captain turned his ship into the swell, making it impossible for the skiff to keep pace with the ship.

There has been a seeming hesitancy amongst masters to use the biggest, most effective weapon they have….the ship to best effect.

Speaking on the subject in the upcoming Nautical Institute guide to Anti-piracy, Steven Jones states the importance of manoeuvring and using vessels as a defensive tool. He believes it is vital that Masters and officers understand the positive use that can be made of interaction between attacked vessel and pirate skiff.

Where circumstances allow Jones believes, “Masters should consider “riding off” attackers craft by using heavy wheel movements as they approach. The effect of the bow wave and wash may deter attackers and make it difficult for them to attach poles, ladders or grappling irons to the ship.

Increased speed and evasive manoeuvring have prevented attacks. Though according to the characteristics of the individual vessel these may be more or less successful than others, the implications of such evasive actions for a tug and tow at 8kts are obviously not the same case as a container ship at 24kts.

Avoid making a lee for the pirate skiff. If possible try and get the wind and sea well forward of the beam on the weather side, also try and keep the pirates on the weather side if possible.”

Alterations of course can be an important part of the evasive manoeuvres, but the implications of any alterations on the speed should be remembered. Turning can slow the vessel down, and may make it easier for the pirates to get closer to the vessel.

It is also important to consider the hydrostatic effect and the role that interaction can play in ensuring pirate skiffs are unable to come alongside. These hydrostatic elements move around a “pivot point”. When making headway, as we would want to do if under attack, the forces experienced at a steady forward speed ensure the pivot point lies approximately 1 quarter of the ships length from forward.

When a ship is making headway a positive pressure area builds up forward of the pivot point, while aft of the pivot point the flow of water down the ships side creates a low pressure area.

The positive pressure wave extends out from the ship, and can act as a barrier to small craft trying to move closer to the vessel. However, further astern the low-pressure region acts as a “suction” zone and affords some scope for small hostile craft to get close enough to attempt a boarding.

The higher the speed of the vessel the greater the pressure exerted and the greater the effect on the pirates trying so hard to board the vessel.

While the armed vs unarmed debate rages on, it is important that we do not forget to make best use of the resources already availiable in the battle against pirates.

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