A sudden jar that shook the Olivette from stem to stern promptly dislocated the trend of the two Scoutmasters\' surmises. For thirty seconds or more the motors laboured heavily, until Warkworth, who was taking his trick in the engine-room, declutched and cut off the ignition.

The Sea Scouts on deck gave inquiring glances at Mr. Armitage; but, true to his principles of letting the lads act on their own initiative, he gave no solution for the cause of the mishap or any suggestion as to what ought to be done.

Presently Woodleigh grasped the reason for his Scoutmaster\'s silence. It was "up to" the Patrol Leader to act.

"Motor all right, Warkworth?" he inquired.

"Yes," was the reply. "I switched off because I fancy something\'s fouled the propeller. Send somebody down, and we\'ll try to turn the shaft round by hand."

Desmond volunteered to assist Warkworth. The removable floor-boards over the shaft were taken up, and both lads, by means of pipe wrenches, tried their hardest to turn the massive metal rod, which in ordinary circumstances could be moved with very little effort.

"Prop\'s foul of something," announced Warkworth.

Woodleigh and most of the Sea Scouts on deck were aft. By this time the Olivette had lost way and was rounding-to broadside on to the now slight breeze. Lying at full length, and leaning over the short counter, the Patrol Leader could discern the three-bladed propeller, its boss a couple of feet beneath the surface.

"There\'s rope wound round it," he declared, "about half a dozen turns. Get a boat-hook, somebody; I think I can get it off."

Hayes brought the desired article. With a couple of fellows holding on to his legs the Patrol Leader tried for a full five minutes, until, red in the face and cramped in body and limbs, he desisted from his unsuccessful attempt.

"The stuff\'s as hard as a chunk of iron," he announced. "I\'ll get Warkworth to start up again and put the gear into the reverse. That might throw the rope clear. Stand by with that dinghy\'s painter: we don\'t want that fouled as well."

The motor being warm it did not take long to restart even on paraffin. Then Warkworth let in the clutch in the reverse, and, although the engine did not labour quite so much, the desired result was not attained. An examination of the propeller, after the motor had been running for a couple of minutes, revealed the disconcerting fact that the rope was still wound tightly round the boss. In the ahead position the undue strain on the shaft almost pulled the engine up dead.

"I suppose the only thing to be done is to set a square-sail and make either for Torquay or Brixham," remarked Woodleigh. "We\'re bound to get a tow in, and at low tide we can cut the rope away."

"Then we won\'t make Plymouth to-day," added Flemming.

"Let me have a cut at it, Woodleigh," said Jock Findlay quietly.

"How?" asked the Patrol Leader.

"By diving for it," replied Jock.

Findlay was the champion diver of the 9th Southend Troop of Sea Scouts. Only a few weeks previously he had carried off first prize in a plate-diving co............