Beyond the boat they could plainly see the waters breaking over the Ledge; the sun lit up the white foam that leaped and flew over the black rocks just showing their teeth above the water as the tide went down.
Here is a problem—you may find plenty like it in every book of algebra. Given a boat drifting upon a ledge of rocks with the current and the tide; given a boat sailing in pursuit with a fair wind aft; given also the velocity of the current and the speed of the boat and the distance of the first boat from the rocks: at what distance must the second boat commence the race in order to catch up the first before it drives upon the rocks?
This second boat, paying close attention to the problem, came up hand over hand, rapidly overtaking the first boat, where the two men not only understood at last the danger they were in, but also that an attempt was being made to save them. In fact, one of them, who had some tincture or flavour of the mathematics left in him from his school days, remembered the problems of this class, and would have given a great deal to have been back again in school working out one of them.
Presently the boats were so near that Peter hailed, 'Boat ahoy! Back her! Back her! or you'll be upon the rocks. Back her all you know!'
'We've broken our oars,' they shouted.
'Keep her off!' Peter bawled again.
Even with a plank taken from the bottom of the boat a practised boatman would have been able to keep her off long enough to clear the rocks; but these two young men were not used to the ways of the sea.
'Put up your hellum,' said Peter, quietly.
'What are you going to do?' The girl obeyed first, as one must do at sea, and asked the question afterwards.
'There's only one chance. We must cut across her bows. Two lubbers! They ought not to be trusted with a boat. There's plenty of room.' He looked at the Ledge ahead and at his own sail. 'Now—steady.' He tightened the rope, the boat changed her course. Then Peter stood up and called again, his hand to his mouth, 'Back her! Back her! Back her all you know!' He sat down and said quietly, 'Now, then—luff it is—luff—all you can.'