A propeller wrap is probably one of the big worries of the novice (and not-so-novice) sailor. What is more frustrating is that sometimes collecting a line is not always avoidable.
If you sail in coastal waters for long enough, especially at night, it’s highly likely that you will collect a line or net or some other debris around your prop, rudder or keel. In part this is due to the location of fishing tackle which is too regularly laid on the approach to harbours, or along charted contour lines, meaning that even the most wary yachtsman is likely to collect an unlit buoy at some point if regularly approaching smaller harbours at night.
If you are motoring, collecting a line is pretty bad news. The most important thing, if you notice the line, is to select neutral and try to avoid it (of course). If your prop collects it, don’t keep on motoring! If you do this the line will almost certainly keep winding around the prop until one of three things happens;
The line wedges hard and stalls the engine (that requires a lot of seizing!) or
the line wedges hard and pops the prop off the prop shaft or damages the gearbox / drive shaft - goodbye propeller and, potentially, lots of money! or
the line seizes into the stern gland, damaging it and either causing a leak or causing damage sufficient to warrant a lift and repair.
Some yachtsmen fit propeller protectors to their prop shafts, just forward of the propeller. This is a pretty good insurance policy, but it isn’t completely foolproof. Sometimes, waiting until morning and calling out a diver might be the best answer.
If sailing, collecting a line is frustrating but it’s not necessarily the end of the World. If you have a folding prop, you’re unlikely to get a prop wrap if the prop isn’t turning. That’s why starting an engine to get away from a line caught on your bottom is a very bad idea!
You might try sailing off, by tacking or, in the right conditions, backing the mainsail and trying to sail off astern. If all else fails, the only ‘self-rescue’ remedy left might be to cut the line using a sharp knife taped securely to a boathook. You might consider entering the water but clearly the conditions must be right and a proper risk assessment is essential. Carrying a phone, VHF, sharp serrated sailing knife, diving mask, snorkel and wetsuit are good calls! But mitigate risks. For example, can you get back in? How cold is the water? How strong is the current? What if you lose contact with the boat? Who comes to get you if the boat is stuck fast?!
In the Mediterranean, a prop wrap in harbour is most likely caused by a misplaced dock line, mooring line or untended dinghy painter or ‘slime line’ running across your bottom.
Always be careful when pulling up mooring lines that you don’t accidentally pull the dock line taught under your midships and allow a turning propeller to grab it. If towing a dinghy allocate one crew to tending it and the painter and if possible make the painter line out of floating polypropylene rope.
If you do snag a line and a dive is required in harbour this can be an unpleasant and potentially dangerous activity. Other water users need to know you are down there and, frankly, the water in most marinas is not exactly bathing ready!