So what is halyard wrap and why should it matter to you? Halyard wrap occurs when your jib halyard gets "sucked in" to your roller furling foil as you furl your sail. This doesn't sound all that bad, and often times it doesn't do any harm, but there is a real possibility of doing serious damage to your headfoil, forestay, or even bringing your mast down. The reason for having a swivel at the top of your roller furler is to let the halyard remain stationary while your foil and sail spin beneath it. If the halyard spins with the foil, bad things happen! If you're ever furling your sail and notice more resistance than usual, look up and make sure you're halyard isn't moving with the foil. You should never use a winch to tension your furling line unless you are absolutely certain you're not wrapping your jib halyard in the furler.
The most common cause of halyard wrap is improper halyard tension (not tight enough), closely followed by improper halyard lead angle. The idea behind adding halyard tension before furling the sail is that you're taking any unnecessary slack our of the line. If the halyard is slack, it's more likely to be able to flop arond and snag the foil. With a tight halyard, it's likely to stay in a straight line and not get snagged on anything. Proper tension becomes even more important the lower the hoist on your jib is. If there is a long distance between the furler swivel and the mast, that leaves even more room for the halyard to get wrapped in the foil. More on that in a moment.
Proper halyard lead angle will help keep the jib halyard as far away from the foil as possible. General guidelines recommend an angle of at least 7 degrees. Often times to acheive the proper angle, a halyard restrainer is installed on the mast a few inches below where the halyard exits the mast. The halyard runs through the restrainer before continuing on to the top furling swivel. This deflects the halyard below the furler and away from danger. At the same time, you don't want to mount the restrainer too low on the mast, and create an unfair lead to the sail. Some deflection is fine, but if your halyard is making a 90 degree bend through the restrainer, you'll want to rethink your arrangement.
Related to halyard tension and lead angle, reducing the distance between the top swivel of the furler and the mast will help prevent wrapping. Often the sail won't allow you to hoist the swivel all the way to the mast. If you don't address it, this can leave too much jib halyard running down the foil before it hits the swivel. A cheap and easy fix for this is to add a strop between the sail and the swivel. The strop is usually made from wire, and is there to let the swivel hoist closer to the mast. If you have different size headsails that you hoist on your furler, different length strops for each sail will keep the swivel hoist at the same height for each sail.
If you've experienced halyard wrap in the past, make sure you closely inspect all furling components. Check the foil for any damage and determine if that section needs to be replaced. Closely check your forestay or headstay wire to make sure it hasn't been twisted and that all the wire strands are aligned properly. And make sure your jib halyard isn't partially cut through or chafed. With all your gear properly installed and inspected regularly, you'll be able to spend more time on the water and less time at the shop.