Looks like cured barrel wood, say from a barrel cover or base. Reason I say this while digging up the coast in your area, friends called me in when they found two large wood barrels buried side by side. Although partially disintegrated, it was obvious these were buried in an upright position. The remaining base looked similar to what you have in appearance. No evidence was found nearby to indicate their purpose. However, the area and the original property owners was known as a fishing community. I suspect the barrels served as a temporary bait wells. Notably, the entire property was loaded with nineteenth century artifacts--including net weights. HOWEVER, your piece is shaped at the tip and makes me think it served as a small rudder to a skiff or sailboat similar in size. Only other alternative is an end to an oar, however, its width and lack of shape across the width tends to rule out that possibility. That is my synoposis.
