Current

What happens

The wind pushes on the topsides; the current acts on the underwater hull and carries the boat in its own direction. It is described by where it is going: a current setting north carries the boat northwards.

So there are two speeds:

• speed through the water, the boat’s speed relative to the water, as measured by the log;
• speed over the ground, the boat’s speed relative to the seabed (and the quay), which you get by adding the current to the speed through the water.

The rudder and keel only feel the first. The pontoon, your neighbours and your bow only know the second.

What it changes when manoeuvring

• Into the current, water flows over the rudder and keel while the boat barely moves relative to the quay: for the same speed over the ground, you have more control. You can even hold the boat in place, or slide her sideways, with speed through the water but none over the ground.
• With the current behind you, it is the other way round: to keep steerage you need speed through the water, and the current adds to it. The minimum speed over the ground to stay in control becomes much higher, and the margin for error very small.
• With the boat stopped, the current has its full effect, because you can no longer steer. With no way on, wind or current turns the boat beam-on. Way itself depends on the current: see Carrying way.
• In the berth, the current also pushes the boat sideways or swings the bow off, just like the wind; springs hold her.

How to use it

• Bow to the stronger element. Manoeuvring in wind or current is simpler with the bow pointing towards whichever is stronger. In a tidal harbour, the first rule is to keep the bow to the tide.
• Work out whether wind or tide is winning. Pointing the bow into the tide to see what happens is not the best test. Better to lie across the tide with just enough speed to steer: the effect of the current shows straight away.
• If in doubt, the tide wins. Helmsmen feel the wind and often underestimate the tide; if in doubt, assume it is the stronger.
• Set your speed over the ground. The trick is to control the throttle to keep speed through the water, but not over the ground; a transit ashore (two marks one behind the other) lets you check it.
• Brake gently astern if the wind is pushing you too fast against the tide, without big bursts astern that break the flow over the keel and rudder.
• Wait. Tidal streams change strength and direction quickly. An almost impossible berth can become easy at the turn of the tide: sometimes it is better to tie up elsewhere for a few hours.

Pitfalls

• A down-tide berth. Only take one on if the tide is very weak and you have experience of similar situations: with the tide behind you, it is hard to abort halfway through.
• The tide pushes too soon. As you enter a berth, make sure it doesn’t push the boat in too early, putting your stern onto the neighbour.
• The current is not the same everywhere. Near the banks it weakens and can form back eddies, especially in bends and near obstacles. At the pontoon, the current in the berth isn’t necessarily the one in the channel: go and look from the end of the pontoon before you leave.
• Counting on the tide, then losing it. If it is the tide that has to bring you onto the pontoon, do the manoeuvre before slack water, while it is still running.