Turnbuckles, or rigging screws or bottlescrews, are stainless steel devices that allows the shroud tension to be adjusted. Jointly, the assorted adjustments are often known as the 'rig' of the boat. Inside a multi-rower crew, for instance an 8, different oarsmen can make modest adjustments to their very own placement, https://forboat.eu/screws-and-fittings-for-boat/rigging-screws-for-boat/