Section 23A. A town bordering on tidewater may, at an annual town meeting, vote to instruct its selectmen to petition in writing the county commissioners of the county in which said town is situated, in this and the two following sections called the commissioners, to establish, lay out and maintain, on behalf of the county, a shore reservation bordering on tidewater in such town, and thereupon said selectmen shall so petition. This section and sections twenty-three B and twenty-three C shall not apply to cities.