They were usually spritsail rigged on two masts. Topsails were added by 1460, then a spritsail under a bowsprit. The loose footed spritsail was suited to river work. The yachts varied from 25-ton cutters to 18-foot spritsail lake boats. The dandy rig had spritsail on the main and a lugsail on the mizzen. The precursor to the square spritsail barge was the London lighter or dumb-barge. The spritsail rig was normally used without a boom. The stays for the jib sails made the spritsail top both irrelevant and inconvenient. She is a "mulie", with a spritsail rigged mainmast, a topmast and a gaff-rigged mizzen. The spritsail is another rig with a four-sided fore-aft sail. The boat already featured a spritsail, adding to the mobility of the harbour vessel. A spritsail has four corners&colon; the throat, peak, clew, and tack. Mulies were rigged spritsail on the main and gaff rigged on the mizzen.