MMario, Let a Certificated Able Seaman explain, It is (or was) spelled holly stones but pronounced Holy stones, but not because of "Holy as in saintly" but as in "Holy as in full of holes", they were bade from machine-cut blocks of Pumice like abraisive-like material and were used (certainly when I served in the mid-60s) as a means of removings damaged and dead wood and foot marks from sun-bleached wooden decks. A Holly stone looked like a large squeezey Mop you know the kind, with a large square of sponge at the bottom with a handle that folds it to squeeze out the water, except ,of course, the stone did not bend.It was propelled in front of you like a broom and weighed several pounds and used dry for coarse work and wet for fine."The Prayer book" was a small version for doing akward corners. It was frequently in use on wooden decked Passenger ships and cruise liners. Needless to say this was a very tedious job and was given as "day work" to Deckies on long trips along with in-board ship painting and maintenance. Only worn and used-up Holy stones (because along with the weight they became saturated with water and any junk metal was used as a sinker for a corpse. The Ships Carpenter, usually the best at canvas sewing, did the job and it was a point of honour that the "Tarpaulin jacket" fitted like a second skin. The final stitch, by tradition, goes through the canvas and the nose of the corpse and a large loop of the tarred sail twine left sticking up so that the captain can check there actually is a corpse inside. The stitcher-up is paid a special fee for this.