Let us use the Catalina 22 National Sailing Association requirement for boom heightFor pre ‘85 boats that have the longer mast, about twenty-five feet, this is three feet six inches from the mast step to the top edge of the boom for pre ‘85 boats. For post ‘85 boats with the shorter mast, about twenty-four feet nine inches, this is three feet three inches from the mast step to the top edge of the boom for post ‘85 boats.As you indicate you have a ‘87 boat, I will assume three feet three inches for your measurement. However, if at this position the luff of the main completely fills the space from the tack to the mast truck and the luff is not tight at full hoist, then use the three feet six inch measurement.Either of these measurements is ideal for the boom vang and mainsheet. In both cases, one achieves an effective angle that lets both the vang and mainsheet function properly.Note one measures from the mast step to the top edge of the boom. The National Association permits up to one inch of materiel positioned between the mast step and the deck. The rational here I believe permits strengthening of the deck below the mast step, necessary as there are many variances in how Catalina built these boats.