Icebreakers have been used in the marine industry to clear navigational channels which remain perpetually or seasonally covered with ice. If you have ever watched an ice breaking ship assisting a merchant vessel behind it, you'll note hat the icebreaker being used will generally have a beam higher than that of the ship being assisted by it. So what if a ship with a beam more than that of the available fleet of icebreakers needs assistance? In that case, either once icebreaker cuts a wider channel by making to and fro movements (if you are wondering that this is time consuming, you are right!) or a combination of two icebreakers is used to cut a channel of width that would allow a vessel of larger beam to pass through (again a probem of higher costs!) If you haven't seen such a operation, here is one, below.
Aker Arctic, a Finnish engineering company had solved the problem long back and based on their patented concept in 1999, recently delivered the first ship based on the concept design Aker 100 HD (where HD signifies Heavy Duty). This ship (named BALTIKA) can actually clear channels of width greater than its own width!
THE ASYMMETRICAL HULLFORM
|The direction of movement of BALTIKA in open sea conditions is just like another ship.|
|BALTIKA, like other icebreakers can cut channels of its own width.|
|That is how she can afford to cut channels of width greater than her original beam.|
- In short, the innovative design of her hull shape allows her to cut ice along two directions of motion. One, the traditional way. But when she needs to assist vessels with beam larger than her own, BALTIKA uses its flexible propulsion system to steer around and move obliquely astern. This will also give you the answer to why she has an obliquely positioned navigational bridge! The oblique end of its hull has the same contours as that needed for icebreaking action (waterlines shown in figure below).
|BALTIKA in oblique icebreaking mode. [Ref: US5996520]|
- The contour of the waterlines close to the oblique icebreaking end of the hull (marked by 14 above) show the asymmetry in the hullform which becomes even clear when compared to the contour at the sections opposite to the icebreaking end (marked by 12).
- If you have asked yourself about the resistance of the ship in this orientation, you are on the right path! Infact, the resistance in this mode is higher, but an intelligently positioned set of propulsion units overcome this effect to certain extent. Wondering why a third propeller has been used away from the keel line?
THE PROPULSION SYSTEM
I'm not going to bore you with the power and speed specifications, in this section. That you would find in every other maritime updates website. What is interesting, is the position of the propellers and their contributions to the ship's operational requirements. It is obvious that a vessel with such demands of maneuverability would definetely use azimuth propulsion units.
- In the above figure, note the three propellers (21, 22 and 23). The orientation shown in the figure corresponds to the propeller directions that are maintained during oblique icebreaking process. If you apply simple laws of vector addition, you will notice, that the net force is oriented along the direction of movement (marked A). The contribution of the third propeller (22) to this effect is significant. Infact, it has other secrets too!
- To decrease the resistance of the ship due to the interaction of the ice that has been immideately broken, the ice must be washed away from the waterline as efficiently as possible. For the propellers 21 and 22, the components of their turbulances perpendicular to the direction of motion serves this purpose.
- Not only this, the turbulence created by propellers 21 and 22 enable efficientl ice breaking by creating a turbulence under the unbroken ice and drawing water from the unbroken ice (Yes! the propellers used in BALTIKA are pulling propellers).
How is it ensured that the ice doesnot hit the propeller turntable shaft before being cut by the ship's hull? The answer lies in the figure below:
She has also been optimized for rescue and oil spill recovery operations. For the former, her forward end can be fitted with a heli-deck. For carrying out oil spill recovery (It is a process by which oceanic oill spill is sucked into the ship's tanks), she has a boom on her starboard side (can be seen in the figure above) which is deployed into the water. The oily water is sucked into the skimmer tanks which separate the oil from water. This operation is depicted in the figure below:
FEW PICTURES OF AKER 100 BALTIKA
|Flooring Construction of BALTIKA|
|BALTIKA just after its launch|
|General Arrangement of BALTIKA|
|BALTIKA during sea trials in 2014.|
Article By: Soumya Chakraborty
Author's Note: This article was written in interest of the unique hull design to meet the operational requirements of efficient ice breaking, so the ship dimensions and main particulars were not mentioned, as they can be easily found in wikipedia. In case of any doubts or queries, please comment or write to me at firstname.lastname@example.org