REFERENCE: THEORY AND PRACTICE OF SEAMANSHIP BY GRAHAM DANTON
I apologies for not writing for a week that is because I am little sick now and I can spare less time from my new collage course timings.
How can you possibly minimize the damage due to collision and how these action matter in a practical situation? Remember your actions can save a lot of life, including yours. Today we are going to discuss what to do if collision is imminent, means a situation where collision can not to be avoided no matter what you do. But surely you can do damage control. Here we will analyse all the situations mathematically and practically which help us make the best decision available to us. So let’s begin
UNDERSTANDING THE DYNAMICS OF COLLISION
Under this heading I will discuss the mathematical model of collision 11TH standard elementary physics nothing new. If you are not a mathematical guy you can skip this part. So that there are two type of collision.
- Elastic Collision – conservation of momentum and kinetic energy
- Non- elastic collisions – conservation of momentum only
No real life collision is elastic collision because it will have some loss of kinetic energy because of friction, sound, thermal energy etc. So basically momentum is basically conserved in any collision,
Where m1/m2 are masses of object and u1/u2 are initial velocities and v1/v2 final velocities. This simple looking equation is going to quite useful when we will discuss the ship to ship collisions. And I will refer to this equation directly in our further discussion. And damage is can be assessed by magnitude of average acceleration.
Where delta t is impact time which is generally very short. And on top of it there is modulus of final velocity minus initial velocity.
ASPECT OF COLLISION
Before we begin our little journey we should know a little about naval architecture and different plate strengths and design of ship and then we can determine best collision aspect which means if at this angle own vessel and other vessel collide the damage will be minimal. Ship designing doesn’t only comes from mathematical modeling it also comes from past experiences and approximation. Generally while designing ships they calculate the maximum bending moments and sheering force that the ship might face in his service and and plate thickness and and quality of material used is then decided accordingly. Generally speaking the most vulnerable part of ship is midship. Because it covers a maximum surface area also it is weakest link of hull. In any condition collision to midship to be avoided. It is like the heart of ship. The most strengthened part is forecastle and then stern of ship. So if collision is imminent other ship then it is advisable to follow this order.
- Forecastle to Forecastle
- Forecastle to stern
- Stern to stern
Any collision with forecastle or stern to midship will produce catastrophic results.
Sometimes a glancing collision is better than a full on collision and sometimes its not. If the object you are glancing is immovable it can scratch your ship of tanks its bad, otherwise it may be better. Grounding is always better than a collision because only one ship will be damaged.
ACTIONS TO CONTROL DAMAGE
AT ANCHOR OR MOORED
Nothing much can be done because you don’t have steering gear or engine ready for immediate maneuver. But it is advisable to take a look at some advices
- If there is sufficient current say up to 5 knots use your steering gear to change the aspect of collision or make it a glancing collision.
- If engines are available then drag the anchor or consider releasing the bitter end.
- Effective use of thruster to change aspect of collision.
- Slipping of mooring will be advantageous because when collision happens ship will move with impact causing less damage. Also, from our equation of damage it turns out to be that if we have some velocity after impact(v1) damage will be less.
- If in anchoring depths let go both anchors which will reduce the momentum of ship or we can say in our damage equations initial velocity(u1) will be less so less damage results.
- In anchoring depth let go one anchor to rapidly change the aspect of collision to make it a favorable one.
- Beaching is more desirable than a collision
- Rapid use of fender’s if available.
- Follow your company’s checklist other points which might not be in there.
- Stop the ship and try to remain in Garth until other ship can asses the damage. Because if other ship is a tanker than pulling back can cause spark and fire can lit up.
- Start pumps if flooding occurred.
- If possible list the ship on other side of damage to reduce the water pressure and delay the flooding
- Check if repair is possible.
- If the damaged compartment is not very large and can be made air tight use compressed air to fill it up and the air will push the water out of the hole.
FACTS: I am not actually very happy about this article because it don’t have many of my ideas also I didn’t have to do much research about it because it is basically the stuff of one book. But I am at T.S. Rahaman and they have a very cool library but you can’t issue books from it and that is a shame. But I found some really cool books so I will be writing more articles soon. Also please people try to celebrate a pollution free diwali its really cool.