A ferry glide is crossing a tidal stream or current in a straight line over the ground by pointing the bow partly into the stream, so that the boat crabs across instead of being carried downstream. Use a transit to check you are holding the line.
When you cross a stream, the water carries you sideways while you move across it. If you point straight at your destination, you are swept downstream and end up curving in, or missing it altogether. A ferry glide is the technique of aiming upstream of the destination by enough to cancel out the stream, so that your track over the ground is a straight line. The name comes from the old cable and river ferries that crossed this way.
How to do it:
- Pick a transit: two fixed objects that line up along the track you want, such as a beacon in front of a building, or two marks on the far shore. If they stay lined up, you are on your track.
- Point the bow upstream of your destination. As a starting point, the stronger the stream compared with your boat speed, the bigger the angle needed.
- Watch the transit. If the two objects come out of line, the stream has moved you off your track. Steer towards the nearer object until they line up again, then hold a slightly different angle: more into the stream if you were set downstream, less if you were drifting upstream.
- Keep adjusting. The stream is often stronger in the middle of a channel and weaker near the edges, so the angle needed changes as you cross.
The same idea works for coming alongside a pontoon or picking up a mooring in a stream: approach into the stream, using it as a brake, and let it help you slide sideways onto the target.
Common mistakes:
- steering at the destination and only noticing the set when it is too late to make it up;
- going slowly, which gives the stream longer to act and needs a bigger angle;
- forgetting that leeway from the wind adds to the stream's effect.
Safety note: if there is a hazard downstream, such as moored boats, a bridge pier or a moored ship, give yourself extra margin. A boat set onto a moored vessel or a pier by a strong stream can be pinned against it.
More in the book: Chapter 14, Buoys, charts and tides