NavList:

Tony, you asked: "Is it an abmormal refraction"?

Yes, that's very likely. Sights taken near shore (or from a coastal point) in Spring often show a repeatable offset like this. Some things you could try:

• compare morning sights with afternoon sights (especially if there's a dependable change in the wind direction from onshore to offshore during the day).
• change your height of eye. Is there a platform you could stand on? The effect of different temperature layers in the lowest level of the atmosphere can change dramatically when shift from 2 meters height of eye to 5 or 10 meters.
• double-check your height of eye, and remember that you need your height above the wave tops (of the waves out at the visible horizon, so if it's calm in close to shore but very choppy a few miles offshore, your estimate of dip might be too large).

Frank Reed