I know that ships have to constantly deal with growth on the bottom of their hulls like barnacles and algae. Most ships are drydocked and then cleaned and repainted with a bottom paint that can repel growth, but only for a year or two. Even a small amount of growth can cause a huge amount of drag underwater.
If aircraft carriers are constantly moving about the world, how do they clean their hulls? I can only think of three options and none seems viable:
Drydocking- must be impractical because of their schedule and immense size.
Scuba divers- must also be impractical because of the immense size.
Do nothing- Since they have almost unlimited power, they might not worry about fuel consumption as much as a diesel ship.
I did read an article about an underwater robot being invented that could clean ship hulls in port but I can’t find any info through a search.
Carriers DO spend substantial time in port receiving maintenance. Last time I checked around 3 or 4 of our 11 carriers were actually in port. Presumably barnacle trimming is on the list of maintenance items. This being said, I got no evidence saying we don’t strip barnacles while our floating Mayberries are on tour…
I don’t think the size is that big a deal. I saw a show where Royal Caribbean drydocked one of their cruise ships, the Sovereign of the Seas, to clean the bottom. It seem pretty routine. It’s 880’ with a 106’ beam. For comparison, the USS George Washington is 1,094’, so just a bit bigger.
Modern anti-fouling paint is so good that this is less of a problem than it used to be. Modern paints are “self polishing” which is to say that they gradually wear away, constantly exposing fresh anti-fouling over a full period between dockings (typically five years).
I know I sound like a stuck record, but as I say in (on average) about a thread a month, the public perception is that aircraft carriers and cruise liners are the biggest ships, because they are high profile, but commercial shipping people think of them as medium to large at most.
I should think that carriers just dry dock when they need to. If the USS George Washington is typical, they are bit shorter than a VLCC (Very Large Crude Carrier) and much shorter than an ULCC (Ultra Large Crude Carrier).
There’s no problem with finding dry docks that will fit such ships.
As for scheduling, most of the time (thank goodness) most military assets are just hanging around waiting for the call. They’d have no problem fitting in a docking.
A specific ship i.e. aircraft carrier or crude oil tanker, was built in a dry dock.
So then there is at least one, maybe more, dry docks able to provide for defouling!
It’s been a while since I walked under a Carrier. The point about the paint and frequency of time in the docks is very true. This isn’t that huge of a problem.
The drydock has IIRC 300 to 400 blocks the ship sits on. They are about six feet a side and the tops are made to match the contour of the hull. When they float the ship in, there is a +/- 1 foot fore and aft and abeam to set the ship down when they pump the water out.
The next two times it’s drydocked they use a different pattern on the supports so every bit of the hull gets painted every couple of cycles.
Oh, and dry docking takes like… all day. Dry docking is a time-consuming, intense, expensive and exacting practice. Avoiding dry dock thru use of specialized paints and coatings is (and did I hear eletrically treated hulls???) is a big bonus.
I served on the USS Ranger CV-61 in the late 80’s.
A large part of reducing barnacles was a cathodic protection system.
From what I recalled we ran a low frequency, low voltage DC charge to the hull and at the expense of Zinc and Platinum anodes we limited both Barnacle growth and oxidation.
There was also degaussing equipment to reduce our magnetic signature but I cannot remember the exact issue with this.
In addition the antifouling paint was helpful and divers did do hull checks when we were in port. I think the divers mainly were inspecting and replacing anodes however.
They’re not? How do they build them, then? Modularly? In the water or something? I don’t want to hijack the thread, but I always just assumed ships were built in drydock.
Carrier and Battleships are built in drydocks in the US. I can’t speak for other nations, but as a Navy Veteran, this is just how it is done in the US.
Cite?
How would they paint the finished hull if it’s in the water?
I suppose they could assemble enough of the hull (painted) on land and then finish the upper half with the hull in the water, but why? If they have to build a large enough structure to support enough of the hull to start the project why would they not just finish it in dry dock?
If you can reasonably call a flat area of land a dry dock, then I suppose yes, but I thought the term referred to a dock that could be closed and drained after the ship enters.
It would seem that a dry dock is a place that already built ships can go where the water is pumped out to create a dry dock. Ships can also be built here.
What Mangetout is thinking of is something different, not sure what they’re called.
No; a dry dock is a berth that ships can sail in or out of, that can be closed off and drained or pumped dry; as the above article implies; building in dry dock is one way to do it (and may be the method of choice today), but building on land and slipway launching was common in the past; the Titanic was launched that way.
NB: I’m not asserting that there is any vessel in existence that is too big for any drydock, only countering the assumption that all ships are built that way.
