13. Dry Docking

Question 1

List the Frequency of Dry Docking Surveys:

Answer 1

3 Years max between dockings

1. Inital Survey docking( New build)
2. Intermediate Survey (2.5 year)
3. Renewa/Special survey (5 Year)

If ship has run aground, Loadline Certificate becomes invalid, must advise Ships company, Flag state and Port state.

Question 2

What types of Methods of Docking:

Answer 2

1. Synchro Lift
2. Floating Dock
3. Travel Lift (Cradle Lift)
4. Careening (low tide on bracing)
5. Beaching
6. Graving Dock (like a lock)
7. Wet Dock (trimming or listing the vessel in emergency)
8. Heaving down (Sail boats)
9. Slipway

Question 3

List Preparations for Dry docking:

Answer 3

1. Review docking plan and provide to dock master ahead of time:
   
   • Where to place blocks, lifting strops or shores(stop you from capsizing)
   • Tank locations/Drain plugs
   • Fire main connection, Such as your international shore connection
   • Appendages - Props/Rudder/Stabilizers/
   • 2x safe access and emergency escape.
   • Stiffening arrangments.
   • All through hole openings.
   • Power connections
   • Water connections
   • Sewage connections
   • Air draft
2. Lighten ship as much as possible:
   
   • Empty tanks or have them pressed
   • Lower G as much as possible, to create large GM.
3. ​ ​Trim vessel slightly by the stern
4. Note location of all movable weights and tank soundings(make sure not leaking) and contents(to replace before refloat)
5. Work Plan agreed with Shipyard
6. Ensure Security plans in place
7. All unessecary personnel off during docking process.

Question 4

Key Safety during Docking:

Answer 4

• Trimmed by the stern
• Keel to touch down blocks back aft initially. (strongest part of the vessel)
• Do not let whole keel touch at the same time.

Question 5

Define “Critical point or time” in dry docking?

Answer 5

It is when the keel first touches down on the blocks aft and the ship experiences an upthrust (P).

Question 6

Define “Critical Period” in dry docking?

Answer 6

Is the time from when the whole keel is set on blocks and shores are in place and bouyancy is removed.

Question 7

Define “Critical Instant” in dry docking?

Answer 7

Is the time just before the whole keel fully sets on the blocks.

Question 8

Define “Critical Moment” in dry docking?

Answer 8

Is a trimming moment caused by the upthrust force (known as “P”) until vessel settles on blocks.

Question 9

What is “P” Force?

Answer 9

Is the “upthrust” created when the aft part of the keel takes the first block.

Results in a loss of GM and transverse stability.

Sometimes described as a loss of bouyancy leading to a lowering of M, thus a loss of GM

or

also sometimes described as a virtual rise of G leading to a loss of GM.

Question 10

Explain the loss of transverse stability during dry docking?

Answer 10

Ships will all experience a loss of transverse stability during the dry docking process. this is due to a combination of things, resulting in an upthrust force known as “P”, this may lead to a list or rolling over in the dock.

2 accepted methods fo explaining”

1. a loss of Buoyancy, thus a reduction in KB and BM, lowers M thus reducing GM and even mking it negative as the water evenutally is non exsistent.
2. a virtual rise of G created with the “P” again reducing GM or making it negative.