Sentence:  The 12-<WSD>metre</WSD> yachts ... can be sailed efficiently with four paid hands. 
Meaning of the word marked with <WSD> tags:  The basic unit of length in the International System of Units (SI: Système International d'Unités), equal to the distance travelled by light in a vacuum in 1/299 792 458 seconds. The metre is equal to (127) (approximately 39.37) imperial inches.