Revised by BoatUS editors in April 2012
To call snatch blocks "useful" is an understatement. They are very practical and versatile pieces of sailing hardware. Their principal attribute is that they can be opened for a line to be inserted, rather than having to be threaded as conventional blocks need to be. Most snatch blocks feature snap shackles, which add to their convenience by allowing them to be placed anywhere along a line. However, despite their obvious plus-points, it would be a mistake to assume that they are perfect for all jobs. This is a consequence of their compromised design. As a result, for example, they are unsuitable for permanent applications such as jib fairleads, sheeting blocks, or turning blocks for genoas-the load would be too high. Where snatch blocks excel is when adjustments or changes need to be made to the gear permanently in place, or as an extra control device. Some of the uses for these blocks:
As a backup genoa lead block. The system involves the use of a second sheet led through the snatch block, releasing the pressure on the actual sheet and allowing the repositioning of the genoa fairlead. Attaching a trunnion snatch block to the toe rail with a short line can provide an effective and easy barber haul system. This has the double benefit of allowing the crew to "open the slot" by adjusting the jib leads outwards and forwards in heavy winds, as well as reducing twist while reaching.
The unpredictable nature of spinnaker handling provides a good application for these blocks, as an auxiliary spinnaker lead. For convenience, spinnaker leads are normally positioned at the point of a boat's maximum beam. It is hard for these to be adjusted. The spinnaker blocks are normally as far aft as possible, but this can lead to the spinnaker moving up and down, or the sheets fouling the boom. Using a snatch block allows the crew to bring the sheet down onto the rail in a different position, eliminating these problems.
The ultimate number of uses that these blocks can be put to is hard to guess. We've seen them used as temporary halyard blocks, as part of the tackle to recover a man overboard, as a bow roller, and even as a temporary repair device on a trapeze system. One problem they may have is their need for full articulation to avoid breakage. Like any gear, use them safely and wisely and don’t use them for purposes unintended by the manufacturer. Read the manufacturer’s warnings and instructions.