Although very powerful, the Navy's first-rates were of limited utility at sea. For stability their lowest gundeck had to be very close to the waterline and its gunports could not be opened in anything but the calmest of seas. To do otherwise was to risk swamping the entire vessel, as occurred in 1781 when the first-rate sank at anchor at Spithead after the lower gunports were opened to air the ship. Early first-rates had little storage space to stow provisions for their large crews on long voyages, and the ships themselves routinely proved unseaworthy in winter weather; as a consequence the first-rates were restricted to summer cruising, and then only in the English Channel and nearby waters. By the mid-1700s, however, improved design had removed these limitations.