>Thank you for an informative post.
>
>How about hull design?
>Are there breakthoughs in hull design for cargo ships which make some
>shipbuikders more advance then the other?
You're welcome.
First, the world's biggest ship
http://en.wikipedia.org/wiki/Knock_Nevis The largest
supertanker—indeed the world's largest ship ever —was the Jahre Viking
or Seawise Giant (now the permanently moored storage tanker Knock
Nevis), weighing in at 564,763 DWT. She was built with 70s
technology. Her size proved to be unfortunate in service and is now
used as a floating tank. 500,000 DWT looks like the likely upper
limit for VLCCs. VLCCs can unload only in deep water platforms that
allow these giants to pivot freely with the tides.
VLCSs (containerships) have to dock to unload their cargo.
Dredging of East Waterway of the Duwamish River
http://www.portseattle.org/business/seaport/expansion.shtml
The Port and the U.S. Army Corps of Engineers are conducting a joint
dredging project for the first 3,000 feet (914 meters) of the East
Waterway of the Duwamish River. The project, estimated at $7.5 million
(the Port's share is $4 million), will help make several more of the
Port's container berths deep enough to accommodate the next generation
of container ships, some of which can carry 6,000 TEUs (20-foot
equivalent unit containers). This will help create additional jobs on
the waterfront and throughout the region. Under terms of the
agreement, the channel between Terminals 46, 37, 39 and 25 to the east
and 18 to the west will be dredged to a depth of 51 feet (16 meters)
in those areas where it does not already reach that depth.
The dredged depth is 51 feet. Facilities in USA pretty much determine
world standards for shipping. They're the biggest customer.
The deepest seaway on a shipping route is
http://en.wikipedia.org/wiki/Malaccamax
Malaccamax is a naval architecture term for the largest ships capable
of fitting through the Straits of Malacca. The restriction is caused
by the shallow point on the Strait, where minimum depth is 25 m, 5m
deeper than the Sunda Strait's 20m maximum depth. A post malaccamax
ship would need to circumnavigate Australia, use the Lombok Strait, or
use the proposed yet-unbuilt Kra Canal.
Bulk carriers and supertankers have been built to this size, and the
term is chosen for very large crude carriers (VLCC).[1] Not
constructed yet but envisioned, a Malaccamax container ship would be
470 m long and 60 m wide, with 20 m of draft with a 300,000 DWT for
18,000 TEUs.[2] The ports growth requirements could be leading to the
creation of new terminals dedicated to those ships.[3]
This above paragraph gives the dimensions for such a Malaccamax
container ship. So that's about the maximum size they will get,
300,000 DWT as compared to 500,000 DWT in a VLCC.
The Malacca Straits' 20 metres draft is 65 feet. Seattle docks is 51
feet. You need at least 5 feet clearance, more likely 10 feet to be
on the safe side. To have a 300,000 DWT hull resting on the dock bed
during low tide stresses the hull enough to ruin the hull permanently.
So you have to design a 300,000 DWT ship that draws only 40 feet of
water. It has to cruise at 27.5 knots. For a given displacement you
can calculate the engine horsepower needed. A VLCS hull is pretty
simple. A bow with a bulb and a stern carrying a single screw and
single rudder. In between is a parallel section box. If all cargo
ships look pretty much the same except for size it is because there
are engineering rules of thumb such as an ideal ratio between length
and breath and cross section. Punch in all the numbers and you have a
ship's hull. Easy. What goes on deck is just cargo handling and cargo
stowage. Since this is larger than any existing VLCS it will have to
undergoe tank tests to confirm the design dimensions. Also twin screws
and twin rudders may be a better design solution. I don't know about
VLCSs but all VLCCs have to have a double hull to contain the oil
cargo in the event of a hull breach.
More interesting tidbits.
An aspirated low speed diesel, aspiration means that the exhaust is
recirculated in the engine to draw the last bit of energy out of the
air fuel mixture. I can't recall the exact technique but I suspect it
will be the revival of the triple expansion steam engine principle.
Go to
http://en.wikipedia.org/wiki/Triple_expansion_steam_engine for
[An animation of a simplified triple-expansion engine.
High-pressure steam (red) enters from the boiler and passes through
the engine, exhausting as low-pressure steam (blue) to the condenser.]
In an aspirated low speed diesel it is likely the exhaust of the first
cylinder with a bit of fresh fuel and air is fed into the second
cylinder then into the third cylinder before finally exhausting the
gasses.
Another interesting tidbit is (heck, I should have just gone straight
to this link.)
http://en.wikipedia.org/wiki/Emma_M%%C3%%A6rsk
Interesting facts.
1. Draft is 50 feet. It won't be using Seattle.
2. Engine recycles exhaust.
3. Silicone based paint.
4. Needs only 13 crew.
5. Its only 157,000 DWT
Search YouTube to see how big this monster is.
Engine and the environment
The Emma Mærsk is powered by a Wärtsilä-Sulzer 14RTFLEX96-C engine,
currently the world's largest single diesel unit, weighing 2,300 tons
and capable of 109,000 horsepower (82 MW). The ship has several
features to protect the environment. This includes recycling the
exhaust, mixed with fresh air, back into the engine for reuse. This
not only increases efficiency by as much as 12%% but also reduces
engine emissions.[3] Instead of biocides, used by much of the industry
to keep barnacles off of the hull, a special silicone-based paint is
used.[3] This increases the ship's efficiency by reducing drag while
also protecting the ocean from biocides that may leak. The silicone
paint covering the part of the hull below the waterline is credited
for lowering the water drag enough to save 1200 tons of fuel per year.
Specifications
Dimensions
length overall (LOA) = 397 m /1302' 6"
beam = 56 m / 183' 8"
hull depth = 30 m / 98' 4" (deck edge to keel)
draft = 15.5 m / 50' 10"
Tonnage
gross = 170,974 bt
net = 55,396 nt
deadweight (DWT) = 156,907 DWT
Power
80 MW (109,000 hp) Wärtsilä 14RT-Flex96c plus 30 MW (40,000 hp) from
five Caterpillar 8M32
Speed
more than 25.5 knots/ 47 km/h.
Crew
The ship has accommodation for 30 people, though the normal crew is
only 13.
