Boomless mainsail

[Chiara’s slave]

Also on a few dinghies e.g. Tasar.
A spanner controls the rotation of the mast.
Not really much like a boom, in the sense that a boom is there to 'boom out the sail' i.e. hold its corner away from the mast.

Being bolted to, rather than pivoted on, the mast. It's a rotating mast feature. My DF800 had one.

 

[oldbloke]

That was the J classes in the 20s I thought. That is the 1920s, just in case.

"Park Avenue" boom, seen on Enterprise which was the American J in 1930

 

[Chiara’s slave]

"Park Avenue" boom, seen on Enterprise which was the American J in 1930

Thanks, yes. I knew the name, slightly out on the year. The era of Lipton and Vanderbilt.