The crews of privately-owned yachts were technically part of the merchant service, but I have included them in a separate section for convenience.
Vessels classed as yachts and registered with British yacht clubs have varied a lot over the years. In the 19th and early 20th centuries they were sailing vessels owned only by the wealthy for the purpose of holidaying or for racing. By the end of the 19th century, more and more were acquiring a small engine and during the First World War many of these motor yachts were requisitioned as coastal patrol vessels looking for U-boats, German agents, and survivors from ships sunk by enemy action.
Shown in the slide show below are the assembled crew of the motor yacht Oimara in about 1900; the two-masted schooner Cambria in 1870; His Majesty’s Yacht Britannia (a cutter) off Portsmouth in about 1925; and some of the crew of Garland in the bows while moored at sea in 1885.
There are various ways to trace a named yacht. There were voluntary indexes published annually such as Lloyd’s Register of Yachts (from 1878), which often describe ownership, dimensions etc. Copies are sometimes available online, or you can contact a maritime archive or library in the UK. A more reliable source is the Mercantile Navy List, which contains less information than Lloyd’s Register, but is comprehensive since all vessels over a quarter of a ton had to be registered from 1855. You can access many copies of the List online from here.
There was often a distinctive appearance for yachting crews. From about the 1870s onwards, they typically wore a jersey with the name of the yacht woven into a box or cartouche on their chests. Often the thread used was white so it stands out well, but if red was used it may be difficult to see in a black and white photo. The cartouche had various shapes and styles, as the slides below demonstrate. Sometimes the yacht name is prefixed by ‘SY’ (sailing or steam yacht), ‘SV’ (sailing vessel), or ‘MY’ (motor yacht). Crewmen also tended to wear a sailor’s cap with the yacht’s name woven into a ribbon or tally tied around it.
These images also illustrate that the cartouche often incorporated the abbreviations of the owner’s sailing club as well. You can usually decode these initials, by typing them into Google, but be careful because many clubs used the same initials. RTYC, for example, could be the Royal Thames Yacht Club (London), Royal Temple Yacht Club (Kent), or Royal Torbay Yacht Club (Devon).
The careers of crewmen from the past can be pursued by finding a crew list for the yacht concerned, or otherwise using a similar strategy to that adopted for tracing merchant navy ancestors. Note that yachtsmen often joined the Royal Naval Reserve in wartime, and also were frequent volunteers for the lifeboat service. You can see four yachtsmen in the picture of the Poole lifeboat crew shown below (c.1900).
Finally, members or officers of certain yacht clubs might adopt a gold cap badge bearing the club’s emblem. Below are photos of the Marquis of Downshire (c. 1865), and Edward VII when Prince of Wales (dated 1884). Both men wear the cap badge of prestigious club the Royal Yacht Squadron (Cowes, Isle of Wight). The Marquis was simply a member, whereas the Prince was this yacht club’s most senior officer: the commodore.