Capsize again

[Red Lead Ted]

Howard, My friend, Sorry Red Lead Ted, I don’t really understand your last comment. I’ve been under about a dozen ships in drydock and they were all flat bottomed or very nearly so. Every tanker, container ship and ferry that I ever sailed on would have stood upright if grounded on a flat surface.
Nearly every would have stood upright, Would this Merchant ship have stood upright without support along with thousands like her {I don't think so } Terry.

[Ivan Cloherty]

Think there may be a bit of confusion arising out of the flat bottom discussion. Since the late 1920's cargo ships started getting bigger and therefore deeper draughted, in fact too deep draughted to enter some ports; to overcome this problem ships started to have broader beams and their hull shapes were altered when the keel plates and the garboard strakes and 'B' strakes (and later 'C' and 'D' strakes) took on a flat profile, rather than the old sailing ship hull configuration with large bilge keels which had been carried over into steel constructed vessels. Therefore ships bottoms became flatter and bilge keel profiles were reduced, these bilge keels apart from being useful for shoring up in drydock, were useful in reducing roll, but their main function was to increase strength along the turn of the bilge and usually ran two thirds of the vessel's length until they reached the sheer at bow and stern both of which controlled the vessel's co-efficient of fineness. Depending upon the scantlings of the vessel together with her light displacement decide whether or not she could safely sit aground, both in ballast and loaded condition. It was usual for vessels above 2500/3000 tons to have a clause in their Charter Parties that the vessel should only be berthed where she could be safely afloat at all conditions of tide and cargo loaded. Large vessels sitting aground will introduce hogging or sagging effects into their structure by their own weight, thus weakening the structure and introduce false draught readings.

Ships below this 2500/3000 grt usually had heavier scantlings than their bigger siblings, as these vessels had a flat keel, and usually only strakes 'A' and 'B' flat with the bilge started to be rounded at strake 'C' this, together with deeper bilge keels gave them the ability to 'safely sit aground' on a suitable berth. With the bilge starting to turn at strake 'C' gave them the ability not to provide a large flat mud suction area, making it easier for them to refloat on a flood tide.

The problem with auto carriers is that they have the reverse characteristics of the tramp/cargo vessels as we knew them, in-as-much that they have a greater surface above the waterline than below it and much more susceptible to wind sheer and navigation turning moments causing a list not experience on normal cargo ships. These vessels carry about 7000 vehicles, and each has a certain amount of delivery fuel in their tanks, once a list has started this fuel will flow to the low side and will have a stability moments affect on the vessel.

[happy daze john in oz]

There was a car carrier similar to this one that turned turtle off the California coast about ten years ago.
It was righted with most f the vehicles still in place.
Saw a video of it at the time and was amazed at how it was done.

[Red Lead Ted]

Think there may be a bit of confusion arising out of the flat bottom discussion. Since the late 1920's cargo ships started getting bigger and therefore deeper draughted, in fact too deep draughted to enter some ports; to overcome this problem ships started to have broader beams and their hull shapes were altered when the keel plates and the garboard strakes and 'B' strakes (and later 'C' and 'D' strakes) took on a flat profile, rather than the old sailing ship hull configuration with large bilge keels which had been carried over into steel constructed vessels. Therefore ships bottoms became flatter and bilge keel profiles were reduced, these bilge keels apart from being useful for shoring up in drydock, were useful in reducing roll, but their main function was to increase strength along the turn of the bilge and usually ran two thirds of the vessel's length until they reached the sheer at bow and stern both of which controlled the vessel's co-efficient of fineness. Depending upon the scantlings of the vessel together with her light displacement decide whether or not she could safely sit aground, both in ballast and loaded condition. It was usual for vessels above 2500/3000 tons to have a clause in their Charter Parties that the vessel should only be berthed where she could be safely afloat at all conditions of tide and cargo loaded. Large vessels sitting aground will introduce hogging or sagging effects into their structure by their own weight, thus weakening the structure and introduce false draught readings.

Ships below this 2500/3000 grt usually had heavier scantlings than their bigger siblings, as these vessels had a flat keel, and usually only strakes 'A' and 'B' flat with the bilge started to be rounded at strake 'C' this, together with deeper bilge keels gave them the ability to 'safely sit aground' on a suitable berth. With the bilge starting to turn at strake 'C' gave them the ability not to provide a large flat mud suction area, making it easier for them to refloat on a flood tide.

The problem with auto carriers is that they have the reverse characteristics of the tramp/cargo vessels as we knew them, in-as-much that they have a greater surface above the waterline than below it and much more susceptible to wind sheer and navigation turning moments causing a list not experience on normal cargo ships. These vessels carry about 7000 vehicles, and each has a certain amount of delivery fuel in their tanks, once a list has started this fuel will flow to the low side and will have a stability moments affect on the vessel.

Ivan, You have explained that to the letter, But lets not forget there are still 1.000s of conventional cargo ships still afloat and working and still need the stability as I have shown in my last pic,
And after reading this without taking a lot of precaution as in ships ballast etc... even these big bulk carriers and Tankers still need stability { Paramount }

A complete guide of bringing a ship to dry dock
Written by Capt Rajeev Jassal on April 10, 2016

If you have the experience of dry docking of a ship, you would agree that dry docking is a great experience.
I personally love to be on a ship due for dry dock. After all, you get to see things which you don’t see during routine operation of the ship.
I was lucky enough to get a chance to be in dry dock in each rank I have served on. I was even lucky to experience the double-hull conversion of a tanker during dry dock.
But if you have not been to a dry dock, there would be one thing that might come to your mind on hearing the word Dry Dock. And that is dry dock calculation that we read in ship stability, probably during our Mate’s exams.
That’s purely theory part. And I believe theory without practical experience is just a theory.
So here I am going to write about the practical aspect of taking a ship to dry dock.
But before I proceed, in layman’s terms I will summarize what we had read about dry docking in ship stability.
We read and understood these things
The time from “when Stern touches the blocks” to when “full ship is on the blocks” is the critical period.
During the critical period, the vessel’s GM reduces. This is because vessel’s ‘Gravitational center G moves upwards when Stern touches the blocks.
It is required and a good practice to have the least trim while docking so that the critical time is minimal.
Preparing for Dry Dock
Well, I am not going to the company specific parts of dry docking, like preparing repair specifications.
I will specifically be talking about taking the ship into the dock and making it sit on the blocks.
And then, of course, bringing the ship out of dry dock.
Days before the planned dry dock, Dock master will make the first contact with the ship. He can do so either directly or through the company representative such as superintendent.
The dock master has a huge responsibility of calculating the stresses on the dock as well as the ship’s structure. Any miscalculation can lead to serious accidents resulting in huge damages. These damages can be to the ship as well as dock itself.
The dock master is trained for block arrangement and stability during dry docking. For all these calculations, dock master needs certain information from the ship. Among other things, he will ask for
a copy of Vessel’s Docking plan
Arrival Stability conditionPre-docking condition
Pre-docking condition

Some of the content of his email might look something like this

From the docking plan, dock master wants to know
1) Hull structure so that he can arrange the blocks to support the ship’s hull.
2) locations of transducers for log and echo sounders so that these do not come beneath the blocks.

3) Location of sea chests and drain plugs for the same reason.
Based on the docking plan provided by the ship, dock master prepares his own docking plan for the ship. Below are some of the sections of actual docking plan prepared by dock master for s ship arriving for dry dock.

As you can see, dock master has planned which blocks he needs to remove and where he needs to put blocks. He also has specifically marked the location of echo sounder and speed log.
Have a look at the more closer view below, which is again from same docking plan prepared by dock master.

I think the above image make it more clear about what dock master is trying to achieve from the docking plan. If you want to see the stern view too. Here is it.

And this is no theory. This is an actual docking plan prepared by dock master for a ship arriving at dry dock.
I know I am kind repeating myself but I can’t say it enough. That is because I get excited to see real thing than just theory.
Stability condition and weight distribution
Apart from docking plan, dock master would ask arrival weight distribution of the ship.
There can be up to 4 stages for which stability calculations are required. These stages are

Arrival Dry docking port
Pre-docking condition
Ship sitting on the blocks but dock not yet empty (also called wet condition by dock master)
Ship on the blocks and dock empty (called Dry condition by docking master
Let’s discuss each of this condition
Arrival Dry docking port
On arrival dry docking port, you need to have least possible ballast. By least possible I mean, propeller should be immersed. And also you should be complying with all stability requirements.
Pre-docking stability condition
So we know that we cannot arrive with zero ballast as our propeller need to be immersed and the ship needs to be stable.
But what is the logic behind having other three conditions? Why can’t we just remove all the ballast and go inside the dock?
Let’s understand the logic behind these conditions
Docking with zero ballast is the ideal condition. But most of the times this would not be possible. That is because docking master would limit you for the maximum trim that you can have. In zero ballast condition, your trim may be more than 2 meters.
Dock master would want you to reduce the trim to around 0.5 meters. This depends on the dock on how much trim you can have before docking.

We have already discussed the reason for the need of least trim while docking. This is to have the least critical period. More trim we have more will be the time required to bring the vessel from stern on the block to full ship on the block. And this is the critical period with least GM value. We do not want to have the ship in the critical period for longer time.
Most of the ships will have considerable stern trim in light weight condition. So most ships will need to have some ballast forward in Pre-docking condition.
The amount of ballast would depend on how much trim dock master has advised you to have.
Stability condition while ship on blocks but dock not empty
When the ship is on the blocks, you have already passed the critical period. Dock master will tell you to start deballasting. The only concern dock master will have is the ship should not refloat.
The ship can refloat if dock deballasting cannot compensate for the decrease in the draft because of deballasting.
The condition is monitored by the dock master and he would tell you on how much ballast you can remove in this condition.
But the question is why the dock master need the vessel to remove the ballast concurrently when he empties the dock?
This is because dock water does not want to have more weight on the blocks. When the ship is sitting on the blocks but has water inside the dock, there is a certain amount of buoyancy ship has. This buoyancy acts like upthrust which reduces the effective weight acting on the blocks.
This condition will be discussed by the dock master and he will advise when and how much ballast you can remove.
As I said earlier, dock master bases his calculations on not to allow the ship to refloat. Regards Terry.

[Ivan Cloherty]

Well this is second time, as first effort disappeared into the ether. Drydocking system well known to me, as a supt have dry docked scores of ships in UK/Continent and India, Dry Dock-Dock Masters are not always competent, whilst in Bombay (Mumbai) had a vessel in D-Dock (1970's) with bottom plates off when Dock Master decided to flood the dock, luckily no dock employees were drowned, though many got a soaking and a rapid transit up the dock. Managed to get the flow stopped before any damage to the vessel as plates off under the engine-room. Despite intensive investigations no one was to blame as no one knew who gave the order, as usual on the Indian sub continent the buck never stops anywhere, as it is always someone else's fault, but of course everyone wants a bonus when things need to be done.

I know that supts are not flavour of any month with seafarers, but it is the supt who carries the can if things go wrong, not the dock master

[Des Taff Jenkins]

Took the Sydney Ferry South Steyne twice into dry dock in Sydney. We had to get a diver down to make sure that the keel was lined with the slots in the centre row of blocks, a few ships before us they had started letting the water out and where putting up the shoring timbers when she tilted over, they where lucky she stopped with a tilt on her.
Cheers Des.
This shot in dry dock me on the very left of picture

Dry Dock Steyne.jpg

[Red Lead Ted]

Ivan, Talking of Stabilizing the flat bottom in dry dock its a good job you never tried to dry dock my missis with a rear like hers now that would have taken all your skills Terry. p.s. I hope she never looks in on this site

[Captain Kong]

Terry I have just copied it and posted it on Face book so all her mates can see it.
DO NOT GO HOME TONIGHT.....DANGER.!

[Red Lead Ted]

Terry I have just copied it and posted it on Face book so all her mates can see it.
DO NOT GO HOME TONIGHT.....DANGER.!

Bri, I thought we where mates

[Captain Kong]

Chuckle.