Mahomet had made his preparations for the siege with so much skill that his preliminary works advanced with unexpected rapidity.  The numerical superiority of his army, and the precautions he had adopted for strengthening his lines, rendered the sorties of the garrison useless.  The ultimate success of the defence depended on the arrival of assistance from abroad; but the numbers of the Ottoman fleet seemed to render even this hope almost desperate.  An incident occurred that showed the immense advantage conferred by skill, when united with courage, over an apparently irresistible superiority of force in naval warfare.  Four large ships, laden with grain and stores, one of which bore the Greek and the other the Genoese flag, had remained for some time wind-bound at Chios, and were anxiously expected at Constantinople.  At daybreak these ships were perceived by the Turkish watchmen steering for Constantinople, with a strong breeze in their favor.  The war-galleys of the Sultan immediately got under way to capture them.  The Sultan himself rode down to the point of Tophane to witness a triumph which he considered certain and which he thought would reduce his enemy to despair.  The Greeks crowded the walls of the city, offering up prayers for their friends and trembling for their safety in the desperate struggle that awaited them.  The Christians had several advantages which their nautical experience enabled them to turn to good account.  The good size of their ships, the strength of their construction, their weight, and their high bulwarks were all powerful means of defence when aided by a stiff breeze blowing directly in the teeth of their opponents.  The Turks were compelled to row their galleys against this wind and the heavy sea it raised.  In vain they attacked the Christians with reckless valor, fighting under the eye of their fiery sovereign.  The skill of their enemy rendered all their attacks abortive.  In vain one squadron attempted to impede the progress of the Christians, while another endeavored to run alongside and carry them by boarding.  Every Turkish galley that opposed their progress was crushed under the weight of their heavy hulls, while those that endeavored to board had their oars shivered in the shock, and drifted helpless far astern.  The few that succeeded for a moment in retaining their place alongside were either sunk by immense angular blocks of stone that were dropped on their frail timbers, or were filled with flames and smoke by the Greek fire that was poured upon them.  The rapidity with which the best galleys were sunk or disabled appalled the bravest; and at last the Turks shrank from close combat on an element where they saw that valor without experience was of no avail.  The Christian ships, in the mean time, held steadily on their course, under all the canvas their masts could carry, until they rounded the point of St. Demetrius and entered the port, where the chain was joyfully lowered to admit them.