The board shall annually fix the rate of tolls or wharfage for the use of the wharf or chute, to produce an income of not less than fifteen nor more than twenty-five per cent per annum on the fair cash value of the wharf or chute, and on the cost of its repair and maintenance, exclusive of the amount paid for the license required by this chapter. The value, and the cost of repair and maintenance shall be fixed by the board when fixing the rates of tolls or wharfage, by hearing evidence and examining the assessment rolls of the county. When fixed, the rates shall be furnished the owner, and a printed or written copy conspicuously posted on the wharf or chute.