- Source: Sealink
- Source: SEAlink
Sealink was a ferry company based in the United Kingdom from 1970 to 1984, operating services to France, Belgium, the Netherlands, Isle of Man, Channel Islands, Isle of Wight and Ireland.
Ports served by the company included: Dover, Folkestone, Newhaven, Southampton and Harwich for services to the European continent; Holyhead, Fishguard, Heysham and Stranraer for services to Ireland and the Isle of Man; Weymouth and Portsmouth for services to the Channel Islands. The Isle of Wight was also served from Portsmouth and Lymington.
Sealink also operated the Steamer passenger ferry services on Windermere in Cumbria until privatisation, when these were passed to the newly reformed Windermere Iron Steamboat Company (now Windermere Lake Cruises Ltd).
History
Sealink was originally the brand name for the ferry services of British Rail in the United Kingdom and Ireland. Services to France, Belgium and the Netherlands were run by Sealink UK as part of the Sealink consortium which also used ferries owned by French national railways (SNCF), the Belgian Maritime Transport Authority Regie voor Maritiem Transport/Regie des transports maritimes (RMT/RTM) and the Dutch Stoomvaart Maatschappij Zeeland (Zeeland Steamship Company).
Historically, the shipping services were exclusively an extension of the railways across the English Channel and the Irish Sea in order to provide through, integrated services to Europe and Ireland. As international travel became more popular in the late 1960s and before air travel became generally affordable, the responsibility for shipping services was taken away from the British Rail Regions and in 1969 centralised in a new division – British Rail Shipping and International Services Division.
With the advent of car ferry services, the old passenger-only ferries were gradually replaced by roll-on/roll-off ships, catering for motorists and rail passengers as well as road freight. However, given that there was now competition in the form of other ferry companies offering crossings to motorists, it became necessary to market the services in a normal business fashion (as opposed to the previous almost monopolistic situation). Thus, with the other partners mentioned above, the brand name Sealink was introduced for the consortium.
In November 1970, Belgium Marine joined the Sealink consortium with five car ferries and six passenger ships.
As demand for international rail travel declined and the shipping business became almost exclusively dependent on passenger and freight vehicle traffic, the ferry business was incorporated as Sealink UK Limited on 1 January 1979, a wholly owned subsidiary of the British Railways Board (BRB), but still part of the Sealink consortium. In 1979, Sealink acquired Manx Line which offered services to the Isle of Man from Heysham.
On 27 July 1984 the UK Government sold Sealink UK Limited to Sea Containers for £66m. The company was renamed Sealink British Ferries. In 1991, Sea Containers sold Sealink British Ferries to Stena Line. The sale excluded the operations of Hoverspeed, the Isle of Wight services and the share in the Isle of Man Steam Packet Company, as well as the Port of Heysham. The new owners rebranded the company as Sealink Stena Line, then again a few years later to Stena Sealink Line.
In 1996, the Sealink name disappeared when the UK services were re-branded as Stena Line. The agreement with the SNCF on the Dover to Calais route also ended at this time and the French-run Sealink services were rebranded as SeaFrance.
Livery
Prior to 1964/65 the colours were black hull, white upperworks and black-topped buff funnel.
From 1972/73 Sealink was displayed in white Rail Alphabet typeface on the side of the hull.
The livery from 1984 to 1995 was a distinctive blue-on-white. Previously, the British Rail double arrow logo had been used, with a BR corporate monastral blue hull, white upperworks and black-topped red funnel.
A reversed version of the BR symbol was used on one side of Sealink ship's funnels and flags. This was so that the 'top' arrow was always pointing towards the bow of the ship on funnels, and for flags towards the flag staff.
British Rail owned ships had red funnels with a white logo. Elsewhere in Sealink the symbol was white on blue.
Hovercraft
In the 1960s, British Rail started hovercraft services from Dover to Calais and Boulogne-sur-Mer, and also across the Solent to the Isle of Wight. Rather than use the name Sealink, the services were marketed as Seaspeed and Solent Seaspeed. Seaspeed merged with rival Hoverlloyd in 1981 to form Hoverspeed.
See also
British Railways ships
References
= Notes
== Bibliography
=External links
Media related to Sealink at Wikimedia Commons
stenaline.com
Sealink Holyhead.net a guide to the history of the sea route between Holyhead and Dún Laoghaire
SEAlink is a file transfer protocol that is backward compatible with XMODEM but features a sliding window system for improved throughput. SEAlink was written in 1986 as a part of the SEAdog FidoNet mailer written by System Enhancement Associates, creators of the famous ARC program. It was licensed with a simple "give credit" requirement, but nevertheless was not very widely used except in FidoNet mailers. SEAlink, and most other XMODEM enhancements, were quickly displaced following the introduction of ZMODEM.
Description
XMODEM breaks down the file to be sent into a numbered series of packets of 128 bytes each. Packets are sent one at a time to the receiver, who either acknowledges the proper reception by sending a ACK character or requests it to be resent by sending a NAK instead. The transfer then continues with another packet.
Although the time needed to send the ACK or NAK is almost zero, the propagation delay of the phone system itself introduces a latency. A latency of 0.1 seconds is not at all uncommon and can be much longer on overseas links. That means that the maximum transfer rate of XMODEM is a function of the phone system more than the speed of the modems themselves. At 300 bit/s this is not a serious concern, as the packet will take about 3.5 seconds to send, the 0.1 delay being insignificant. However, at 9600 bit/s the packet only takes about 0.1 seconds to send, meaning that at least half of the potential throughput is lost while the sender waits for the ACK or NAK to arrive.
SEAlink addresses this through the use of a "sliding window". In this case the sender does not wait for the ACK or NAK, and instead simply sends out its packets in a continuous stream. The receiver still has to ACK or NAK the packets, but does so by attaching a packet number to each one, allowing the sender to identify which packets worked or failed. The "window" refers to the number of packets that can be sent before an ACK or NAK is required. In the case of SEAlink, the window was six packets, allowing up to 768 bytes of data to be sent at once.
SEAlink was designed to be completely backward compatible with existing XMODEM implementations. On the receiver side, all that was required was that the receiver send back the packet number (contained in all XMODEM packets) along with the normal ACK or NAK character. On reception of the very first ACK or NAK, the SEAlink sender would "notice" the packet number and continue to use windows. If the packet number was missing, it was assumed it was sending to a non-SEAlink XMODEM, and set the window size to one.
Other features
SEAlink also included a number of features included in other XMODEM derivatives. Notable was the use of a "zero packet", which was introduced in the FidoNet-related TeLink protocol in order to send file information and support batch file transfers.
SEAlink made one minor modification to this "standard", adding a byte in position 40 of the packet to indicate whether or not to use "overdrive". When turned on, by placing any non-zero number in byte 40, the receiver no longer expected ACK messages, but only NAKs. This was intended to reduce the bandwidth required from the receiver back to the sender, which was an important consideration on many of the early high-speed modems, which featured a very slow backchannel (75 bit/s in the Telebit modems, for instance).
A later addition was "RESYNC", allowing for file transfers to be restarted from where they left off. RESYNC added another indicator in the zero packet, byte 42, to indicate that the sender supports the feature. In this case, the receiver always checks to see if an identical filename exists locally, and if so, sends a SYN character instead of the normal ACK or NAK. The SYN is followed by the packet number at which to restart.
References
SEAlink 1.20 program and source code
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