5

In the same Hornblower story that inspired this question, Hornblower tricks the French captain by acting as if to tack, but stopping and swinging back. When the French try to do the same they are unable to do so.

'He's coming about, sir!' reported Prowse. 'He's casting off the braces!'

He must make quite sure.

'Mainsail haul!'

This was the danger point.

'He's past the wind's eye, sir. His foretops'ls coming round.'

'Ava-a-ast!'

...

'She's in irons, sir. She's all a-back.'

That was the very thing Hornblower had hoped for. He had believed it likely that he would be able to effect his escape to leeward, perhaps after an exchange of broadsides; this present situation had appeared possible but too good to materialise. The Loire was hanging helpless in the wind. Her captain had noted Hotspur's manoeuvre just too late. Instead of going round on the other tack, getting his ship under command, and then tacking once more in pursuit, he had tried to follow Hotspur's example and revert to his previous course. But with an unskilled crew and without a carefully prepared plan the improvisation had failed disastrously. While Hornblower watched he saw Loire yaw off the wind and then swing back again, refusing obstinately, like a frightened horse, to do the sensible thing.

Source Emphasis mine.

This brings up my question, is there a point when tacking after which you can't turn change back right away to your original course but need to fully swing onto the new tack for a while before tacking back?

6

Yes there is, but the situation being described is probably not exactly that.

If we consider a standard sailboat with a headsail and mainsail, as the boat turns into the wind the wind pressure on the headsail tries to push the front of the boat away from the wind. As the prow turns across the wind, i.e. through the point where the boat points direct upwind, the jib changes side and the wind on the headsail is now pressuring the boat to complete the turn. This is the change of sides meant by "the foretops'l has crossed over'. Turning back is now more difficult, if not impossible. A simple sailboat gets around this effect (which undesirably slows the turn) by releasing the headsail during the tack and resecuring it on the other side. A larger ship with more sails probably cannot do this with all their sails.

However there is a much more important effect at play here. As a ship turns through the wind the sails no longer are propelling the ship forward. The ship relies on momentum it already has in order to complete the turn. If the turn is not completed, or it attempts to turn back without sufficient forward speed, the ship can find itself facing upwind with no forward speed. Because it is facing upwind the sails do not drive it forward, and because it has no forward speed the rudder is not effective and it cannot turn away from the wind. The ship stops and becomes virtually impossible to maneuver. This is what is meant by "in irons". It was likely this effect that stopped the Loire - it wasn't that they were past an absolute point of no return, but that the Loire, "with an unskilled crew and without a carefully prepared plan", was too slow in reversing the turn, and lost too much speed, leaving them without the forward momentum required to finish off the reverse turn.

A ship in irons can take a long time to get out, and makes no progress while it does so. The chasing ship no longer has any chance of catching the Hotspur.

  • 1
    The scenario described frequently befalls upon the head of catamaran sailors when a turn is done sloppily. – whatsisname Mar 5 '18 at 4:56

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