Massey's patent frictionless sounder, c.1836. Used to determine the depth of water below a ship.

This sounding machine is a modification of the one patented by Edward Massey in 1836.

The rigid guard ring protected the rotator from damage, especially if the sounder struck against the ship's hull while being hauled inboard. During the hauling-in operation the vanes are prevented from rotating by a stop attached to a metal plate which is forced down by the water pressure.

The sounder was used with a deep-sea lead of 56lbs weigh, being connected to it by 3 feet of sounding line. In earlier sounders the rotator was separated from the counting mechanism by a short length of line.