I own a Beneteau First 260 Spirit, my problem is at speeds between 5 and 5.5 knots a humming / vibration is coming from one of the twin rudders / hull. I have changed the fitting which holds the rudder housing to the hull from a long bar to a nut and bolt and all other fittings are tight. Has anyone any ideas on what action I can take to rectify this annoyance and also how I can check that both rudders are angled correctly. Howard Kent