Boatswain rhymes with:
moscowane, baudoin, chapdelaine, chilblain, cyclohexane, duplechain, finucane, hexane, ibogaine, lamountain, madelaine, moscowane, octane, ptomaine, ramtane, tremayne
Boatswain sounds like:
baptism, bateson, batson, battison, beatson, beautician, biddison, bodkin, bophuthatswana, botkin, botswana, buddhism, budson, budzyn, butson, butzen, butzin