Sheriffs and all persons employed by them or aiding in the recovery and preservation of wrecked property, are entitled to a reasonable allowance as salvage for their services, and to all expenses incurred by them in their performance, out of the property saved. The officer having the custody of the property shall detain it until the allowance is paid or tendered. But the whole salvage claimed shall not exceed one-half of the value of the property or proceeds on which it is charged, and every agreement, order, or adjustment allowing a greater salvage is void, unless ordered and allowed by the superior court of the county.