The tidal Thames is a fantastic place to cruise -- seeing London from the river in your own boat is a most satisfying experience. The Tideway can, and should, be used by all types and sizes of boat, but owners must be aware of the challenges and hazards they may face. The tide can run very fast, and there is still a considerable amount of commercial traffic, mostly now in the form of trip-boats, some of which travel at high speeds.
Tides and other vessels, as much as the wind, can combine to create an unpleasantly lumpy surface. As a result, piers and pontoons are often lively. Despite the best efforts of the PLA to clean up the river, you still need to keep a very sharp lookout for flotsam and jetsam, especially on spring tides.
It is the normal practice to keep clear of all commercial traffic, as many of these types of craft have difficulty in manoeuvering and stopping. Barges towed by tugs are particularly difficult to manoeuver through bridges, and many of the bigger trip boats can only alter course slowly. A careful lookout should be maintained astern as well as ahead, and appropriate avoiding action should always be taken in plenty of time.
Remember that large vessels under way are frequently confined to the deep water part of the channel. They cannot take quick avoiding action, and in narrow channels may not be able to take any avoiding action at all. If you find yourself in close proximity to a large vessel, a strong sense of self preservation is recommended. Get clear as quickly as possible.
Any boat approaching a bridge or bend in the river when going against the tide should give way to a boat approaching with the tide. Oarsmen never give way to anyone - it's just one of those things!
If you overtake another boat, you should keep well clear of the slower boat. If you are being overtaken, officially you should maintain your speed - you may decide to slow down to let the other boat past, but don't speed up. Sound signals should be made in good time as appropriate.
When it becomes necessary to cross the river, this should be done as swiftly as possible, with a good lookout for other traffic. Any attempt to cross ahead of oncoming traffic could prove very hazardous. A vessel crossing the river has no right of way over other traffic.
Keep to the right
When proceeding up or down the river, all power driven vessels should, while it is safe and practicable, keep to the starboard (right hand) side of mid-channel.
Above Wandsworth there is a speed limit of 8 knots (9 mph) through the water. Below Wandsworth there is no specific limit, but speed should be adjusted to ensure that there is no damage caused by excessive wake. For most pleasure craft this is not likely to be a major problem, but bear in mind that there is a fine of up to £1000 available!
Unobstructed arches for navigation are denoted by two orange/red lights placed horizontally at the head of the open span. Other spans may also be clear for small craft, but if in doubt it's probably best to stick to the marked spans.
A triangle of red disks or three red lights hanging apex downwards from the arch of a bridge indicates that the arch is closed to navigation. If the span of a bridge is restricted in headroom, due to maintenance or repair work, a bale of straw will be hanging from the scaffolding. Honestly, they really do use bales of straw - they have to, it's the law. At night the bale of straw will be replaced by a white light.