Dropping a big mainsail on a breezy day is one of the moments that separates a relaxed crew from a stressed one. Without something to catch it, the sail spills over the deck, into the cockpit and sometimes over the side, while someone balances on the coachroof trying to gather armfuls of cloth. Lazy jacks and stack packs exist to stop that from happening.

Quick answer: lazy jacks are a set of lines running from the mast to the boom that guide the mainsail down onto the boom as you lower it. A stack pack (also called a lazy bag or sail pack) is a zip-up sail cover permanently attached to the boom and held up by lazy jacks, so the sail drops straight into its bag. Lazy jacks alone are cheaper and simpler; a stack pack adds a built-in cover and tidier stowage, at the cost of a little extra windage, weight and maintenance. Most cruising sailors with a slab-reefed main end up with one or the other.

Controlling the Mainsail When You Drop It

A traditional mainsail with full battens can be heavy and stiff. When the halyard is released, it falls in folds that want to slide off whichever side of the boom is downhill. On a small boat that is a nuisance; on a 40-footer with a large main it can be dangerous, because the crew has to work on deck to tame it, often in the same conditions that made them want to drop or reef the sail in the first place.

A good mainsail handling system should do three things: keep the sail on the boom when it comes down, make reefing tidier, and make covering the sail quick enough that you actually do it every time. It is worth noting that boats with in-mast or in-boom furling usually do not need either system; if you are still deciding on the mainsail itself, see our comparison of in-mast furling vs a traditional mainsail.

What Are Lazy Jacks?

Lazy jacks are light lines that form a cradle on each side of the mainsail. A typical setup has a topping line on each side running from a block or eye partway up the mast, splitting into two or three legs that attach to the boom at points along its length. Together, the legs form a funnel that catches the sail as it drops and guides it onto the boom in rough folds.

Retractable lazy jacks

The most useful refinement is making the lazy jacks retractable. The upper ends run down to the deck or cockpit, so you can slacken them and pull the legs forward to the mast while sailing. That keeps the lines away from the sail (reducing chafe and batten snags) and away from the leech, then you tension them again before you lower the sail. Some sailors retract them only when hoisting; others leave them slack whenever the sail is up.

Pros and cons of lazy jacks

• Pros: inexpensive, light, simple to install and adjust, very little windage, and easy to repair or replace with ordinary line.
• Cons: the sail still needs to be tied down with sail ties and covered separately; battens can snag on the lines when hoisting; lines can chafe the sail if left tight while sailing.

What Is a Stack Pack (Lazy Bag)?

A stack pack is a sail cover built as a long, open-topped bag that is fastened along the boom, often via a bolt rope in a slot or a set of fastenings under the foot. Its sides are held up by lazy jacks attached to the top edge of the bag. When you drop the main, it falls into the bag, and you close it with a zip running along the top. When you hoist, you unzip the bag and the sail rises out of it.

The bag usually has stiffening battens in its sides so it stands up, plus a front section that wraps around the mast and a shaped end at the clew. Names vary by sailmaker: stack pack, lazy bag, sail pack and mack pack all describe broadly similar products.

Pros and cons of a stack pack

• Pros: the sail is covered and protected from UV within seconds of dropping it; no separate sail cover to fit or store; tidy appearance; the bag helps contain the sail when reefing.
• Cons: more windage and some weight on the boom; the bag itself is exposed to sun and wears over time; the zip needs care; the cloth can catch rainwater or debris if not closed properly; may cover reefing hooks or block access to the boom.

Lazy Jacks vs Stack Pack: Side by Side

Factor	Lazy jacks only	Stack pack
Catches the sail when lowered	Yes	Yes
Sail cover	Separate cover needed	Built in
Time to stow and cover	Longer: ties plus cover	Short: zip it closed
Windage and weight	Minimal	Some extra
Cost	Low	Higher
Batten snags when hoisting	Possible	Possible
Maintenance	Replace lines occasionally	Zip, stitching and cloth exposed to UV
Best for	Smaller boats, racing, owners who flake neatly	Cruisers, short-handed crews, larger mains

For a cruising boat with a big fully battened main, the stack pack usually wins on everyday convenience. For a smaller boat, a club racer or an owner who likes a neatly flaked sail under a fitted cover, plain lazy jacks are often enough.

Avoiding Batten Snags When Hoisting

The main complaint about both systems is that battens catch on the lazy jack lines as the sail goes up. A few habits nearly eliminate it:

• Hoist head to wind. With the boat pointed into the wind and the mainsheet eased, the sail rises straight up instead of being blown against the lines.
• Slacken or retract the lazy jacks before hoisting if your system allows it.
• Watch the leech as the sail rises. If a batten catches, stop, lower a little, and let it clear rather than winching harder.
• Position the legs carefully. The attachment points on the boom and the height of the upper blocks can be adjusted so the legs sit clear of the batten ends.
• Re-tension before dropping. Lazy jacks only work if they are snug when the sail comes down.

If you sail alone, these steps matter even more, because you cannot leave the helm to free a snag. Our guide on how to sail single-handed covers setting up a boat so one person can manage sail handling, and good self-steering helps too (see windvane vs autopilot).

Alternatives: Dutchman and Traditional Covers

Dutchman system

A Dutchman uses a few vertical monofilament lines that pass through small guides sewn into the mainsail, running from a topping lift down to the boom. As the sail drops, it is guided down the lines and flakes neatly back and forth onto the boom. It keeps the sail tidy without the windage of a bag, but it needs a sail that has been fitted with the guides, and the lines need to be set up and tensioned correctly.

Traditional sail cover

A fitted boom cover with no lazy jacks is the simplest and lightest option. It works well on smaller boats where flaking the main by hand is easy, or where the crew prefers a clean rig. The downside is that you need hands on deck to control the sail as it comes down and time to fit the cover afterward.

Installation and Care Tips

• Get the geometry right. The upper blocks are usually placed somewhere around a third to two-thirds of the way up the mast, depending on the boat and sail. Too low and the lines don’t contain the upper sail; too high and they interfere with the leech and battens. Follow the sailmaker’s or kit’s guidance for your rig.
• Use good line and fittings. UV-resistant line and smooth blocks or fairleads reduce chafe. Check where the lines rub on the sail and spreaders.
• Let a sailmaker fit a stack pack. The bag needs to be cut for your boom length, mast position, reef points and lazy jack layout.
• Care for the zip. Rinse salt from zips and clean them periodically; a seized zip is the most common stack pack failure.
• Check UV damage. Inspect the bag and its stitching each season and re-stitch or re-cover as needed. Our guide to repairing sails covers the basics.
• Keep reefing accessible. Make sure reefing lines and tack hooks still work with the bag closed partway or open.

For more on the lines and hardware involved, see what is sailboat rigging?, and for the wider picture of how a cruising boat is equipped, cruising sailboats: parts and features.

Lazy Jacks vs Stack Pack: Summary

Lazy jacks guide the mainsail onto the boom as it comes down; a stack pack adds a built-in cover held up by those same lazy jacks. Choose plain lazy jacks if you want a light, low-cost and low-windage system and don’t mind tying and covering the sail. Choose a stack pack if you sail a cruising boat with a larger main and want the sail stowed and protected in seconds. Either way, hoist head to wind, keep the lines adjusted, and look after the hardware, and dropping the main will be one of the easier jobs on board.