I can understand the attempt to deter the rebel regatta action, but can't find any relevance of section 21:
Extracts from Medway Ports River Byelaws 1991
21. The Master of a power driven vessel underway shall either be on the
bridge or control position of the vessel himself or ensure that there is
on the bridge or control position a member of the crew who is capable
of taking command of the vessel and, when a pilot is on board, is
capable of understanding the pilot’s directions.
Maybe they are confused with section 21 of the Town Police Clauses Act, 1847 - which covers obstruction and road closures for processions.
A sea-borne attack on Kingnorth power station looks to have been sunk by a river byelaw.
Protestors had planned to sail and paddle a number of homemade rafts along the River Medway on Saturday in a bid to stop coal-carrying ships from reaching the plant's jetty.
But the Harbour Master at Medway Ports Authority has today issued a special direction refusing to give anti-coal campaigners permission for any public procession or regatta to take place.
Kent police chiefs confirmed the direction gives officers the power to arrest any activists who ignore the order.
Harbour Master Captain Stephen M Gobbi said: “Medway Ports has empowered the police to represent us in the enforcement of Section 21 of the Medway Ports Byelaws.
“This is because of our concerns for the safety of all river users, particularly the raft regatta participants.”
Assistant Chief Constable Gary Beautridge said: “We share the ports authority’s concerns for the safety of those who had planned to join in this activity.
“The regatta would put lives at risk - those of participants and also those of members of the emergency services who would be called upon should anything untoward happen.”
Officers are set to distribute 1,000 leaflets to protestors giving them information about the legal powers under which the regatta has been stopped.
Posters are also being displayed at the entrance of each site.
ACC Beautridge added: “We want people at the climate camp to be aware that the event is not safe and cannot happen.”
The planned sea-borne strike – dubbed the Great Rebel Raft Regatta – was part of a three-prong attack planned by the Camp for Climate Action.
A Camp spokesman said: “We will be launching an armada of rafts of every shape and size into the River Medway.
“From pirate ships to Viking boats, a multitude of different themed rafts, made out of recycled materials, are already under construction.”
On land, an ‘orange pod’ is set to head straight for the plant’s main entrance in a colourful, musical demonstration and the ‘green guerrillas’ will approach through the surrounding fields and wood, looking for weak points in the perimeter fence.
Police move to ban rebel raft regatta
Kent Police plan to distribute leaflets to Climate Campers warning them against taking part in Saturday's rebel raft regatta.
The leaflets will say the protest, part of a three pronged effort to invade Kingsnorth Power Station, cannot go ahead because of safety concerns.
A river byelaw has been enacted in a bid to stop the proposed cross-river flotilla.
The Harbour Master at Medway Ports Authority has issued a Special Direction refusing to give permission under river byelaws for any public procession orregatta to take place. Climate campers say they intend to ignore it.
The Harbour Master has authorised the police to act on his behalf and enforce the Special Direction for 'the safety of all river users.'
Captain Stephen M Gobbi, the ports authority’s Harbour Master, explained the decision:
"Medway Ports has empowered the police to represent us in the enforcement of Section 21 of the Medway Ports Byelaws.
"This is because of our concerns for the safety of all river users, particularly the raft regatta participants."
Asst Chief Constable Gary Beautridge said: "We share the ports authority’s concerns for the safety of those who had planned to join in this activity.
"The regatta would put lives at risk - those of participants and also those of members of the emergency services who would be called upon should anything untoward happen."
Officers are to distribute 1,000 leaflets to protestors giving them information about the legal powers under which the regatta has been stopped.
Posters are also being displayed at the entrance of the site.
Details are also being given to the climate camp community residents’ liaison team as part of continuing discussions.
ACC Beautridge, continued: "We want people at the climate camp to be aware that the event is not safe and cannot happen.
Officers have the power to arrest anyone who ignores the Special Direction from the Ports Authority.
Climate camper Kevin Smith said: "Our legal teams are researching it at the moment but it doesn't really alter our plans.
"People have always made it very clear that they are willing to break the law if that is what it takes to highlight the madness of going down the route of building more coal fired power stations.
"Safety is paramount and we have spoken to the Harbour Master to get this information. Every person who steps onto a raft has to go through safety training."
"We don't know how many people will take part but there will be a mix of homemade boats and those that have been brought."
Details of regatta ban injunction
The Special Direction is issued under the powers contained in the Medway Ports Authority Act 1973.
It says: "The Harbour Master has not given permission in accordance with the Medway Ports River Byelaws 1991 to allow any public procession or regatta and invokes Section 21 of the Act in order to ensure the safety of navigation.
"You must not enter, or remain on, or in, the water within the jurisdiction of Medway Ports Authority."
The leaflets that will be distributed to people attending the climate camp have been printed on recycled paper.
Can't see how the quoted section 21 is relevant to a raft - other than vessels under 7m should not impede anything!
Seems there may be another protest going on as well?
21.—(1) A direction under this section may be given for any of the purposes set out in subsection (2) of this section by the harbour master to a vessel anywhere in the port or the Medway approach area and to a vessel prior to its entering the port from a dock.
(2) A direction under this section may be given for any of the
(a) requiring a vessel to comply with a requirement made in or under a general direction;
(b) regulating or requiring for the ease, convenience or safety of navigation the movement, mooring or unmooring of a vessel;
(c) regulating for the safety of navigation the manner in which a vessel takes in or discharges cargo, fuel, water or ship's stores.
26.—(1) The master of a vessel who fails to comply with a general or special direction shall be liable to a fine not exceeding two hundred pounds.
(2) It shall be a defence to the master of a vessel charged with an offence under subsection (1) of this section to prove that he had reasonable ground for supposing that compliance with the direction in question would be likely to imperil his vessel or any person for whom he is responsible or that in the circumstances compliance was impracticable.
27.—(1) Without prejudice to any other remedy available to the Authority, if a special direction is not complied with within a reasonable time, the harbour master may, where practicable, put persons aboard the vessel to carry out the direction or may otherwise cause the vessel to be handled in accordance with the direction.
(2) If there is no one on board a vessel to attend to a special direction, the harbour master may proceed as if the direction had been given and not complied with:
Provided that the powers of this subsection shall not be exercised—
(a) in relation to a vessel other than a lighter, unless after reasonable inquiry has been made the master cannot be found; or
(b) in relation to a lighter, unless it is obstructing the access to or exit from a dock or otherwise interfering with navigation.
(3) Expenses incurred by the Authority in the exercise of the powers conferred by subsection (1) of this section shall be recoverable by the Authority as a simple contract debt.
28. Any person who obstructs or interferes with the harbour master or with any officer or servant of the Authority in the of exercise of his powers or the performance of his duties under this Act shall be liable on summary conviction to a fine not exceeding fifty pounds.
57. Powers of harbour authorities to provide for maximum fines up to level 4 on standard scale.
— (1) Where a harbour authority is empowered to provide—
(a) in an instrument made by virtue of an enactment; or
(b) in an instrument made by virtue of an instrument made under an enactment,
that a person, as regards any summary offence (whether or not created by the instrument), shall be liable on conviction to a fine not exceeding an amount less than level 4 on the standard scale, the power shall extend by virtue of this section to making him liable to a fine not exceeding level 4.
(2) Where any enactment or instrument ( “the enabling legislation") (however expressed) provides that a person who contravenes any provision of an instrument ( “a regulatory instrument") made by a harbour authority—
(a) by virtue of the enabling legislation; or
(b) by virtue of an instrument made under the enabling legislation,
shall be guilty of a summary offence and liable on conviction to a fine not exceeding an amount less than level 4 on the standard scale, the power conferred by the enabling legislation shall by virtue of this section enable the harbour authority to provide in a regulatory instrument that a person, as regards any summary offence created by the regulatory instrument, shall be liable on summary conviction to a fine not exceeding level 4.
(these are seperate and lesser offences than breaching the 'Special Direction', assuming that has been lawfully given, and is 'reasonably' publicised, which is open to considerable debate.)