"Look at the distance he's dived." "He has to thank the tide for part of this, though," said Freckleton, looking at his watch.

"Why, it's--" An exclamation from Cresswell stopped him.

Dick had reappeared, but he was twenty yards at least astern of the boat, and drifting back every moment.
At first he did not seem to be aware of it; but, treading water, waved one hand exultantly to celebrate his long dive.
But when he began to swim, leisurely at first, but harder presently, he suddenly realised his position, and saw that instead of making way back to the boat, he was losing distance at every stroke.
Some of my readers may have been in a similar position, and know the horror of helplessness which, for a moment, comes over the swimmer at such a time.

Dick was not given to panic, still less fear, but, for all that, the minute which ensued was one of the most terrible in his life.
At certain times of the tide, the current between the Sprit Rock and the long Fiddle-Sandbank rushed like a mill-race.

The boys knew this; they had been reminded of it at starting.