Had a strange issue. On motor and was accelerating and helm started to shudder violently. Went back to neutral. Tried to motor forward slow and felt like wet blanket on prop. Waited a bit and gently backed up and things "got better". But since then, noticing at about 4.5 to 6.5 knots, still some noticeable helm vibration. Above that and below it feels fine. Backing up feels fine full range of speeds. Inspected cutlass bearing, mount, shaft, prop, and engine alignment. All look aligned and tight and unblemished. Vibration doesn't translate to the engine as viewed at the transmission, or into the hull, just helm. Think alignment is OK. Also don't feel it under sail I don't think but need to check again. Maybe the rudder bearing or sleeve is loose or damaged now(?). No place to pull this out to check it all here. 2 or 3 days sail to houston where I can haul her out. Maybe put in the emergency tiller and see how much play there is by holding the wheel still and trying to move her?