Drydocking: Its HARDER Than it Looks!

In this video, we focus on drydocking. We look at the P Force and see how it has a critical impact on ships drying out.

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[MoritzvonSchweinitz]

I think it is fascinating that, after thousands of thousands of years of sailing, high tech chemistry and sacrificial anodes, we STILL have to constantly battle the sea's corrosive powr and wildlife, and essentially scrub the same things off the hull with elbow grease as some phoenician did thousands of years ago.

[baileywright]

Fascinating! I've never really thought about the process of dry docking apart from the 'oh, she is getting repairs/refits so she won't be available for survey this season'. Kind of cool learning a bit more about the logistics of actually getting a ship into drydock :D Thanks!

[AbbyNormL]

I served on the USS Bremerton (SSN-698), a Los Angeles class fast attack submarine, during new construction an Electric Boat in Groton, CT. and at Pearl Harbor, HI. We spent the first 1-2 years going in and out of dry dock. Submarines have unique problems when entering dry dock. The worst time I had in dry dock was at Groton in the dead of winter with subzero temperatures. We would have to climb from the top of the sub into the bottom of the dry dock to ensure off-hull hose connections were not freezing once every hour.

[Gustavo.Garces]

Literally pushing 🅿️, great explanation on forces

[Sailoralso]

I have seen Great Lakes freighters, , commonly as long as any blue water boat, , clean and repair their hull by differential ballast. Not in dry dock, , but along side a pier with a suitable depth of water. Water is pumped out of the ballast tanks on one end and pumped into the ballast tanks of the other end. The bow or stern may rise completely out of the water facilitating access to the submerged hull. When perhaps the bow is repaired, cleaned, painted, , then the process is reversed, , ballast pumped into the bow, , and ballast cleared from the stern tank, , and the stern comes up out of the water for service. I have watched it being done.

[TefiTheWaterGipsy]

We've got to dry shock this singer Summer and have our hull re-blacked (2 part epoxy) new sacrificial anodes and whatever is blocking our now thrusters removed. Luckily we're not in brine or brackish water, and we're only 20m long wide beam barge. I love your videos, it makes things so clear. I know we've at least got edible growth on the hull as the water fowl like a nibble about 4am every day.

[loosegoose]

Great video! Very interesting to visualize the forces involved. In helicopters we have a similar situation called dynamic rollover where one of the skids catches on an object during picking up/setting down, becoming the point the helicopter pivots around instead of the center of gravity. Once the helicopter body passes a certain angle - no matter the control inputs - the roll is irreversible and the helicopter rolls over.

[darylovaltine]

There’s a major and obvious point missing in all this fascinating P Force talk and that’s the existence of more than a single longitudinal line of blocks along the vessel keel. No docking plan has a vessel with a single line of blocks and vessels of the size shown in the video will have 3 or 5 or even 7 lines of blocks where the hull is widest and flattest, the stern. No vessel will enter dock in perfect trim and it would be impossible for a ship to balance on a single line of blocks during docking let alone could the hull support such a point load.

[СлаваСталину-тх]

Came down to the comments expecting it to be full of innuendos, was rather susprised to see there are some communities on youtube that aren't immature.

[Sxq]

Quick question: How do you get to the parts of the hull that are covered by the support blocks?

[JH-lout]

Cool.
I worked at a small dry dock for a few years, docking vessels of up to maybe 700 tonnes.
We would do a lot of the work manually and sort of winging it, but there hasn't been a serious incident at that dock for the last 35 years.
We used to adapt the blocking to every ship, so that it would land as level as possible. At the exact time that the ship touched down, we would fix the supporting beams around the hull. These beams were just telefone poles extending from the side of the drydock and jammed against the hull with wood wedges. The crew's job was to control the mooring lines, keeping the vessel straight and centered in the dock as it settled. We often docked two, three or sometimes even four vessels at the same time. As long as they had different drafts, you could concentrate on one at the time, but those were very busy days.
If it was a more complicated docking we would open the flood gates in the dock gate to let in water at the same rate as it was pumping out, this way we could keep the water in the drydock at a specific level while working with the support beams. Not optimal, since letting in water created a lot of strong currents that wanted to push the ships out of place. Turning off the pumps was not an option, they could only be started with a filled dock.

[nicjansen]

3:39 There should be blocks placed on either side of the centre of mass, right? As shown, a single block will be unstable. With a block on either side and the ship rotating left for example, the left block will push more and the right block will push less, basically like a hull in water

[sergeysmirnov]

One thing I did not understand about this is the trim aspect. Now, please correct me if I'm wrong but at least as far as I understand it, trim is mostly done via controlling the level of water inside the ballast tanks - at least at its core, I do know that it's not quite as simple given things like the free surface effect, but, even then I'd hazard a guess that this is not as important in the conditions that would need to be present for drydocking to be safe in the first place. Tangent aside though, what I wanted to ask is why the ship's crew, after having aligned the stern on the blocks and then having maneuvred the bow into its final position not begin to fill the bow tanks to achieve a neutral trim, hence reducing the maximum P-force asserted on the vessel as the bow comes into contact with the support blocks sooner. And, related to that, as the ship is refloated, why is it a concern to keep the trim towards the stern there instead of a neutral trim given that, during refloating, there is no need to align the ship anymore.

Sorry if this question is stupid but I simply couldn't make sense of this.

[thewagon]

The best explanation of D/D stability considerations I've found...and great animations. (Liked & subscribed).

[minchmeat]

I have a book about the RMS Olympic and it contains pictures of her raised in her drydock. Those kinds of photos always amaze me

[rayoflight]

I liked (and understood) very much your explanation of how the contact of the ship's hull with the underwater block creates a rotational momentum that can capsize the ship.
Great video as per your excellent standard.
Thank you, regards...

[eamonnprunty]

You do such a great job with your explanations and videos! Keep up the great work

[Quick]

Lovely video once more, Casual Navigation never fails to let the audience down :)
Thank you for these video's, i am currently studying to become a Maritime Officer in Rotterdam and i must say you do an exceptional job at explaining everything, i will totally suggest my teachers to use your video's in lectures!
Cheers from the Netherlands Rotterdam Mainport

[Thaumazo]

ahh first year physics we meet again. Fascinating video!

[donaldpetersen]

I swear this was going to be one of those P-force memes. They scare me, or rather my inability to know what's real anymore thanks to them.