Your sails are one of your biggest and most important investments on your sailboat. A good sail cover will protect your sails and help keep them in good condition for as long as possible. Mainsail covers and headsail covers protect your sails from mildew and rot, damaging UV rays, bird droppings, salt spray, and airborne particulates. Cheap sail covers are more likely to be made with lower-quality canvas, non-marine-grade grommets and fastenings, and ineffective closures — they'll wear out faster, be more prone to rips and tears, and won't protect your expensive sails as well. The best custom canvas sail cover is far less expensive than replacing your sails, so don't be cheap when shopping for sail covers.
Off-the-shelf and custom sail covers are available in the following configurations:
Canvas sail covers help protect your sails against the effects of the sun, salt spray, dirt and debris, and damage from birds.
Headsail covers (jib bags) are most often stand-alone bags that you tote topsides from below and back again. But headsail covers can be specially designed to allow you to keep the jib hanked onto the forestay, so that it's ready to hoist at any time. This will protect the jib while keeping it on deck and out of the cabin. Look for a bag that provides a secure attachment to the forestay, UV resistant marine canvas, a heavy-duty marine grade zipper closure, and a halyard clasp to lift the rear part of the bag off the deck.
Consider these points when choosing your sail cover:
A sail cover made of Sunbrella — a UV-resistant, fade resistant, and water repellant canvas — will provide the best protection for your sails.
Look for a cover with straight, even, tightly-sewed seams; sturdy marine-grade recessed zippers with a large, easy-to-use pull tab; top-quality marine stainless steel turn-button fasteners; and reinforced openings and fasteners. Ask if the thread used to sew the seams is UV resistant, and find out if the hems are reinforced.
For maximum protection, turn-button fasteners along the bottom of the cover should be spaced no further apart than every two feet.
Velcro fastening might seem like a good idea, but the hooks and loops in the Velcro collect dust and dirt; after just a couple of years, the flaps won't stay closed as tightly as they should, and your sails won't be as well protected. The advantage of Velcro closings is that the cover can be closed around the mast tightly for maximum protection. If you purchase sail covers that use Velcro closures, keep an eye on the Velcro over time, and be prepared to replace the Velcro strips as needed.
Any openings for lines, rigging, lazy jacks, or anything else should be kept as small as possible. The larger the opening, the more salt spray, dirt, rain, and damaging sun will reach your expensive sails.
The cover for your mainsail should ideally allow access to the main halyard even when the cover is on. Every sailor knows that just when you're dozing off at night is when the wind will pick up and the halyard will start slapping the mast. When you're on deck in the dark, sleepily fumbling for the halyard to tighten it down, you'll be glad you don't have to undo the sailcover just to get at the halyard.
Look for a sailcover that is easy to to put on. The easier it is to put on, the more likely you are to use it when anchoring for the night. And the more you use it, the longer your sails will last.
A sail cover with chafing protection inside the collar will help protect the cover from winches, cleats, and other fixtures on the mast.