UPDATE: There over a dozen articles on project Orion at this site. A couple go over how to minimize fallout and EMP and another looks at bomb selection and other big rocket designs.
"This is Rocket Science" has some nice photos.
A more extreme design called for a ship with a pusher plate with a diameter of 400 meters. This ship would have been launched from a site at Jackass Flats on the nuclear testing range in Nevada. The initial explosions would have been made with conventional explosives, to avoid extreme pressures, temperatures and fallout, with the ship sitting on 76 meters high towers. The mass of the ship would have been in the order of millions of tons.
400 meters in diameter means that the area (footprint) is about 30 football fields. 4 football fields long by 8 football fields wide. The height of the super-orion is about the height of skyscraper like Taipei 101 or Petronas Towers. The base of the Great Pyramid forms a nearly perfect square with about 230 m (756 feet) on a side. When newly completed, the Great Pyramid rose 146.7 m (481.4 ft)—nearly 50 stories high. Super-Orion would have had the volume of about 10 Great Pyramids.
The million ton or multi-million ton super-Orions would carry several times the cargo of the largest cargo ships and super-tankers
500,000 ton super oil tanker.
Large loaded aircraft carriers top out at about 100,000 tons
Seldan Ball has an great collection of links and pictures on project Orion
These are comparisons of different sized Project Orion designs. Over the two photos going from the 10-M (10 man) design up to 40,000 ton and then up to super-Orion size.
Rhys Taylor has excellent photos from his videos
The BBC had a piece that showed some of the external pulse propulsion tests and the history of the project. As Arthur Clark says, "Chemicals are feeble compared to atomic bombs...project Orion is only way we are getting large payloads around the solar system even now".
This site has covered project Orion and nuclear pulse propulsion several times.
Major ship size groups include:
* Handy and Handymax: Traditionally the workhorses of the dry bulk market, the Handy and more recent Handymax types remain popular ships with less than 60,000 dwt. The Handymax sector operates in a large number of geographically dispersed global trades, mainly carrying grains and minor bulks including steel products, forest products and fertilizers. The vessels are well suited for small ports with length and draft restrictions and also lacking transshipment infrastructure. This category is also used to define small-sized oil tankers.
* Panamax: Represents the largest acceptable size to transit the Panama Canal, which can be applied to both freighters and tankers; lengths are restricted to a maximum of 275 meters, and widths to slightly more than 32 meter. The average size of such a ship is about 65,000 dwt. They mainly carry coal, grain and, to a lesser extent, minor bulks, including steel products, forest products and fertilizers.
* Capesize: Refers to a rather ill-defined standard which have the common characteristic of being incapable of using the Panama or Suez canals, not necessarily because of their tonnage, but because of their size. These ships serve deepwater terminals handling raw materials, such as iron ore and coal. As a result, "Capesize" vessels transit via Cape Horn (South America) or the Cape of Good Hope (South Africa). Their size ranges between 80,000 and 175,000 dwt. Due to their size there are only a comparatively small number of ports around the world with the infrastructure to accommodate such vessel size.
* Aframax: A tanker of standard size between 75,000 and 115,000 dwt. The largest tanker size in the AFRA (Average Freight Rate Assessment) tanker rate system.
* Suezmax: This standard, which represents the limitations of the Suez Canal, has evolved. Before 1967, the Suez Canal could only accommodate tanker ships with a maximum of 80,000 dwt. The canal was closed between 1967 and 1975 because of the Israel - Arab conflict. Once it reopened in 1975, the Suezmax capacity went to 150,000 dwt. An enlargement to enable the canal to accommodate 200,000 dwt tankers is being considered.
* VLCC: Very Large Crude Carriers, 150,000 to 320,00 dwt in size. They offer a good flexibility for using terminals since many can accommodate their draft. They are used in ports that have depth limitations, mainly around the Mediterranean, West Africa and the North Sea. They can be ballasted through the Suez Canal.
* ULCC: Ultra Large Crude Carriers, 300,000 to 550,000 dwt in size. Used for carrying crude oil on long haul routes from the Persian Gulf to Europe, America and East Asia, via the Cape of Good Hope or the Strait of Malacca. The enormous size of these vessels require custom built terminals.