Marine Wiki Forum

SETTING THE STAGE

Most of us have heard of the Thekkady boat tragedy and the investigation that happened after that. We also knew where the issue was and we all had opinions on what needed to be done to avoid that. Mine is here: http://blog.navgathi.info/2009/10/thekkady-boat-tragedy-will-we-learn.html.

Kerala govt. formed a committee to look in to drafting the rules (to their credit, this committee was working on it six months before the accident). However, a sense of urgency was created by this accident. I was also fortunate to play a part in the committee by offering our expertise in the matter. In a few meetings and discussions, it was evident that this committee also did not appreciate the importance of having stability criteria.

If must be clear from the above blog that, the rules are inadequate here. There are no stability criteria for the Inland vessels except the freeboard requirement. The IRS is also bereft of any stability criteria for Inland rules and they conveniently puts it on the respective administration to frame that - knowing the situation in India, and considering that they are an international organization, surely they could have set a benchmark of minimum criteria.

The proposal was to add two criteria: Initial GM and passenger heeling.

QUOTE:
RULE . 25. Stability
(i) An inclining experiment shall be carried out to determine the elements of stability. Unless particulars of the position to transverse metacentre at various drafts are available the experiment shall be carried out with the vessel loaded with weights to represent the fully laden condition.
(ii) Calculation showing the transverse metacentric height and the angle of heel which would occur with two-third of the passengers distributed on one side of the vessel and one-third on the other side requires approval of the surveying authority. Each passenger shall be represented by a weight of 65kgs.
(iii) In decked vessels the passengers shall be taken as congregated at 0.27 sq. metres each on the uppermost deck or decks to which they have access and the centre of gravity of the passenger at 0.75 m above the deck.
(iv) In open vessels the center of gravity of passengers shall be taken at 0.3 m above the seat.
(v) In no case shall the surveyor certify a vessel for any number of passengers unless he is satisfied that the vessel has sufficient stability and freeboard to carry that number safely.
(vi) Stability of Hovercrafts shall be specially considered.
(vii) Initial GM must be at least 0.15 m.
UNQUOTE

In the latest draft that came out in Jan 18th, I am yet to get hold of that copy (some reluctance to part with it from Chief Engineer), the last line for Initial GM is removed. In the last meeting, I personally, after discussing with experts in the field suggest to remove this, however to add a line stating that, " The stability of the vessel to be ascertained as per the stability criteria which would be prepared by the Technical committee at a later date." The aim here was to rope in more people (from Class, Owners, Operators, Designers, Shipyards, etc.) to arrive at the criteria. However, they conveniently removed the Initial GM and do not speak anything about any criteria.


FRAMING THE DISCUSSION

Inland Rules criteria is always a mixed bag. Many people feel that for Inland vessels Initial GM criteria is more than enough. We all know that a ship with high GM can, while inclined, rapidly loose the stability is the GZ curve dips down (because of hull shape). This mens that the dynamic stability criteria are important. The seagoing criteria of Max GZ, Area under the curve are very stringent if applied to inland vessels where there are hardly such waves. So, a necessity to have a less stringent criteria than sea going, but better that just resorting to Initial GM criterial. Seek opinion in this matter from all experts.

Ref: Sea going conditions
3.1.2 Recommended general criteria
3.1.2.1. The area under the righting lever curve (GZ curve) should not be less than 0.055 metre-radians up to θ = 30° angle of heel and not less than 0.09 metre-radians up to θ = 40° or the angle of downflooding θf see footnote if this angle is less than 40°. Additionally, the area under the righting lever curve (GZ curve) between the angles of heel of 30° and 40° or between 30° and θf, if this angle is less than 40°, should not be less than 0.03 metre-radians.
3.1.2.2. The righting lever GZ should be at least 0.20 m at an angle of heel equal to or greater than 30°.
3.1.2.3. The maximum righting arm should occur at an angle of heel preferably exceeding 30° but not less than 25°.
3.1.2.4. The initial metacentric height GMo should not be less than 0.15 m.
3.1.2.5. In addition for passenger ships, the angle of heel on account of crowding of passengers to one side as defined in paragraphs 3.5.2.6 to 3.5.2.9 should not exceed 10°.
3.1.2.6. In addition for passenger ships, the angle of heel on account of turning should not exceed 10° when calculated using the following formula:
MR = 0.196 x V^2 x Δ x (KG - d/2) / L
where, MR = heeling moment in kNm, V = service speed in m/s, L = length of ship at waterline in m, Δ = displacement in tonnes,
d = mean draught in m, KG = height of centre of gravity above baseline in m

3.2 Severe wind and rolling criterion (weather criterion)

I understand the need of Dynamic Stability Assessment in case of small crafts even if they are not operating in sea because of the rolling and capsizing under winds. Two years back, I was a member of a team analysing the Stability of sail boats. This was the case of relaunching a sail boat in scotland which capsized earlier bacause of the loss of inherent stability. That time we considered the compliance with ISO 12217 rules. A brief description of these rules is as under:

This part of ISO 12217 specifies methods for evaluating the stability and buoyancy of intact (i.e. undamaged) boats. The flotation characteristics of craft vulnerable to swamping are also encompassed.

The evaluation of stability and buoyancy properties using this part of ISO 12217 will enable the boat to be assigned to a design category (C or D) appropriate to its design and maximum load.

This part of ISO 12217 is applicable to boats of hull length less than 6 m, whether propelled by human or mechanical power, except habitable sailing multihulls. Boats of hull length less than 6 m, which are fitted with a full deck and quick-draining cockpit(s) complying with ISO 11812, may alternatively be assessed using ISO 12217-1 or ISO 12217-2 (for non-sailing and sailing boats respectively), in which case higher design categories may be assigned.

This part of ISO 12217 excludes: it does not include or evaluate the effects on stability of towing, fishing, dredging or lifting operations, which should be separately considered if appropriate.

ISO 12217 has following parts for different kind of small crafts:

ISO 12217 - 1: Non Sail boats of hull more than 6 m in length
ISO 12217 - 2: Sail boats of hull more than 6 m in length
ISO 12217 - 3: Boats of hull less than 6 m in length

In our case we can refer to ISO 12217 - 2 for Inland Small crafts of non sail boat type. This rule considers Crew loading moment and max heel angle caused by them, downflooding angle and height, resistance to beam waves and winds, Static heel due to wind and Floatation tests. We can even measure the stability of Jal Kanyanka boat against these rules and make out the conclusions.