A superyacht or megayacht is a large and luxurious pleasure vessel. There are no official or agreed upon definitions for such yachts, but these terms are regularly used to describe professionally crewed motor or sailing yachts, ranging from to more than in length, and sometimes include yachts as small as . Superyachts are often available for charter with a staff that caters to guests at a high standard of comfort. They may be designed to emphasize comfort, speed, or expedition capability. Depending on the season, superyachts may be most frequently found in the Mediterranean or the Caribbean. Many are available for charter at prices that exceed 100,000 per week. Larger examples may have more than one swimming pool; they may carry a variety of water toys, other boats, and some a helicopter. Yacht#History At the beginning of the 20th century, when wealthy individuals constructed large private yachts for personal pleasure, some manufacturers, such as Cox & King and Charles L. Seabury and Company, were noted for their large steam yachts. The first half of the 20th century saw the first large motor yachts, including Charles Henry Fletcher's Jemima F. III (1908) at , Savarona (1931) at , and Christina O (1947 conversion) at . The "Large Commercial Yacht Code (LY2)" of Great Britain and its dominions defines a "large yacht" as one that is or more at the waterline and is in commercial use for sport or pleasure, while not carrying cargo or more than 12 passengers, and carrying a professional crew. The code regulates the equipping of such vessels, both at sea and in port—including such matters as crew duty times and the presence of a helicopter on board. The code has different levels of standard for vessels above and below 500 gross tons. Other countries have standards similar to LY2. Whereas yachts of 24 metres and below may be constructed of fiberglass, larger yachts are more likely to be constructed of steel, aluminum or composite fiber-reinforced plastic. Such yachts may be considered "superyachts" and are more commonly at or more in length.