Single-Line Reefing: Is It Right For Your Sailboat?

In a Nutshell

Single-line reefing makes shortening your mainsail simple, using one control line to handle both the front and back of the sail at the same time. While it’s a brilliant setup for solo or short-handed sailors on smaller boats, allowing you to stay safe in the cockpit, it can be a real pain on larger vessels. On boats over 35 feet, the system can get bogged down with too much friction, and you lose the fine control over sail shape. For serious offshore sailors, a traditional two-line slab reefing system often feels more reliable and gives you the control you need when the weather really gets nasty.

What is Single-Line Reefing?
Getting to Grips with the System
Single-Line vs. Two-Line Slab Reefing: The Verdict
Is Single-Line Reefing Suitable for Larger Boats?
Optimising Your Single-Line Reefing System
Internal vs. External Systems: Which is Better?
Maintenance, Safety & Emergency Procedures
The Role of Other Rigging Components
Summing Up
Frequently Asked Questions

What is Single-Line Reefing?

Single-line reefing is one of those clever solutions designed to make life on the water a little bit easier. Think of it as a simplified version of standard slab reefing. Instead of faffing about with two separate lines—one for the luff and one for the leech—you have just one continuous line. This single line is rigged from the cockpit, through the boom, and up to the sail’s reefing points.

When you pull on the line, it works like a charm, cinching down both the tack and the clew of the sail at the same time. After that, you just need to re-tension the mainsail halyard to secure the new tack. It’s a beautifully simple process that lets you shorten sail without ever having to leave the relative safety of the cockpit, which is a massive plus when the sea is lumpy.

However it does have its limitations, which we'll come to shortly...

Getting to Grips with the System

The great thing about single-line reefing is that it’s almost a one-step operation. The reefing line is rigged so that a single pull handles both ends of the sail at once.

Here's the simple rundown:

Prep the Sail: Ease your vang (kicking strap) and mainsheet to take the pressure off the sail. Point the boat into the wind to get the mainsail to luff.

Support the Boom: Give the topping lift a good yank to hold the boom up as the sail comes down.

Lower the Sail: Ease the mainsail halyard until the reefing cringle is at the boom.

Pull the Reef: From the cockpit, pull in the single reefing line. You'll see it simultaneously tighten up both the luff and the leech.

Secure It: Re-tension the halyard to secure the new tack, then ease the topping lift back to its normal position.

Final Trim: Trim your mainsheet and vang to get the sail set properly for the new wind conditions.

jiffy reefing, tying back the reefing lines to keep the foot of the sail taut.

Whatever form of jiffy reefing you go for, the reefed sail should be as flat as possible if a baggy sail is to be avoided, and it won't be if the bottom section isn't pulled tight along the boom.

This is achieved by making sure that the windward and leeward parts of the reefing line are angled back towards the end of the boom as shown here, inducing a horizontal component of force along the bottom part of the reefed sail as the reef is pulled in.

I use a short light line (the blue one) to prevent the reefing lines from creeping forward, which they otherwise would.

Single-Line vs. Two-Line Slab Reefing: The Verdict

Choosing between a single-line and a traditional two-line slab reefing system often comes down to a trade-off between convenience and control. Each system has its own strengths and weaknesses, so let’s break them down.

Single-Line Reefing

Pros	Cons
Simplicity & Safety: One line, one motion—it's that easy. You can do the whole thing from the safety of the cockpit, which is great for solo sailing.	Too Much Friction: All those turns the line makes through the boom create a ton of friction. It can be a real struggle to pull in the reef, especially on larger boats.
Reduced Deck Action: No need for a trip to the mast, which is perfect when the sea is a bit rough and you're flying short-handed.	Limited Control: You can't adjust the luff and leech independently, which means you can’t get that perfect sail shape every time.
Neater Rigging: A simpler setup with fewer lines to clutter up the cockpit.	Hard to Release: The same mechanical advantage that helps you pull the reef in works against you when you're trying to let it out.
Ideal for Small Boats: On smaller vessels (think 25-35 feet), the loads are manageable, and it works a treat.	Line Chafe: High loads and multiple turns mean the line is more prone to chafe and wear.

A single line rigged thus will pull a slab in

Standard Slab Reefing (Two-Line System)

Pros	Cons
More Control: Separate lines for the luff & leech let you fine-tune the sail shape. You can get a flat, efficient sail that really performs.	A Bit More Work: It's a two-step process that can be more complex to manage, especially if you're new to it.
Less Friction: The lines have a more direct path, resulting in far less friction & making the process of both reefing & shaking out the reef much easier.	More Movement: You often have to go forward to the mast to set the tack, which is less ideal in rough seas.
Rock Solid Reliability: A very robust system for heavy weather sailing. You can count on it when you need it most.	More Hardware: All those extra lines & blocks can make the deck & cockpit a bit more cluttered.
For Any Size Boat: This system works on everything from small dinghies to big cruising yachts & can accommodate a third deep reef for storms.

Two lines, one for the luff and one for the leech

Is Single-Line Reefing Suitable for Larger Boats?

As a cruiser with plenty of sea-miles under his keel, I’ve seen this play out first-hand. While single-line reefing is a nifty solution for smaller boats, its practicality on a bigger vessel—say, over 40 feet—just doesn't hold up. Here’s the long and short of it.

The biggest issue on a large boat is the sheer amount of load on the sail. The forces involved when you’re reefing a big mainsail in 25 knots of wind are immense. That single line, with all its friction points and turns, can become a real beast to pull by hand. I’ve seen sailors struggle to even get it done with a powerful winch.

For instance, I know a few skippers who've had internal single-line reefing systems on their boats, and they've run into all sorts of trouble. The line jams, or the friction is so high they simply can't get it to run. This is the last thing you want to deal with when a squall is on its way. That’s why so many offshore sailors swear by a two-line system led back to the cockpit. It might be a two-step process, but you have the reliable control you need when it truly counts.

Optimising Your Single-Line Reefing System

If you’ve got a single-line reefing system and want to get the best out of it, there are a few things you can do to make it run more smoothly.

Upgrade your hardware: Swapping out standard blocks for low-friction ball-bearing blocks can make a huge difference. They’re built to handle heavy loads with minimal resistance. Similarly, consider using low-friction rings at the reefing cringles to reduce wear and tear.

Pick the right line: The type of rope matters. High-modulus, low-stretch lines like Dyneema are perfect for reefing. They have a brilliant strength-to-diameter ratio, so you can use a thinner line that runs more easily, and they won't stretch under load.

Proper lead angles: Make sure your lines have the straightest path possible, avoiding sharp turns. A quick check to ensure the line isn't twisting inside the boom will save you a world of trouble later on.

Proper tensioning: Once the reef is set and the halyard is pulled taut to secure the new tack, make sure the reefing line itself is snug on the leech side. This proper tensioning is what helps set a flatter, more efficient sail shape.

Internal vs. External Systems: Which is Better?

Most single-line reefing systems are either installed inside or outside the boom. On smaller boats, you can often retro-fit a system with external blocks and lines. While this might look a bit messier with loose lines on the boom, it has a major upside: if something breaks or a line jams, you can get to it easily and sort things out on the spot.

By contrast, many larger boats use internal systems for a cleaner, more aesthetic look. While tidy, internal systems on larger boats can be a proper nightmare to fix if something goes wrong. A line jam inside the boom often means you have to unstep the boom and take it apart. It’s a risk most serious cruisers just aren’t willing to take.

Maintenance, Safety & Emergency Procedures

Regular maintenance is the best way to ensure your reefing system is ready when you need it. It’s far better to catch a problem at the dock than in the middle of a gale.

Annual Inspection: At the start of each season, give your reefing lines a good look over. Pay close attention to any signs of chafe, especially where the line runs through blocks or at the cringles. Make sure all your blocks are running smoothly and that there’s no damage to the sheaves inside the boom.

System Cleaning: If your system is internal, dirt, salt, and sand can build up inside the boom, acting like a brake on the lines. Flushing it out with fresh water can prevent jams.

Emergency Plan: A single-line reefing system is convenient, but it can be more prone to failure than a two-line setup. If the single reefing line were to break or jam completely, you'd be in a tough spot. So, a wise sailor always carries a set of sail ties and knows how to manually tie off the reefing points. For the worst conditions, having a trysail ready to hoist is the safest backup if the mainsail becomes too much to handle.

The Role of Other Rigging Components

Your reefing system is part of a team, and it won't work correctly without the help of the rest of your rig.

Topping Lift: This is your boom's support. Always take up on the topping lift before easing the halyard. This prevents the boom from crashing down and putting extra strain on the reefing line or, worse, on a person.

Vang (Kicking Strap): The vang pulls the boom down. You must ease it completely before you start the reefing process to take all the tension off the sail and allow the boom to lift freely.

Sail Ties: After a reef is set, sail ties are used to secure the loose sail cloth. This stops it from flogging in the wind, which can cause damage to the sail and drive you mad with the noise. For a more comprehensive understanding of all mainsail reefing techniques, from single-line to traditional systems, be sure to check out our ultimate guide on Reefing a Sail: The Ultimate Guide to Control & Safety at Sea.

Summing Up

While the convenience of a single-line reefing system is brilliant, its suitability really comes down to the kind of sailing you do and the size of your boat. For the weekend sailor or those sailing short-handed on a smaller vessel, the benefits of cockpit-controlled reefing usually win out. However, for the serious offshore sailor, the lack of independent control, the high friction on larger rigs, and the risk of failure when you need it most often make traditional two-line reefing the better bet. Ultimately, the best system is the one you trust to get you through any conditions quickly and safely.

Article written by Dick McClary, RYA Yachtmaster & Yachting Journalists Association (YJA) member.

Frequently Asked Questions

Can I convert my standard two-line slab reefing system to single-line reefing?

Yes, you can. It typically involves installing new blocks and re-routing the lines through the boom to create the continuous single-line system.

What is a "third reef" and is it possible with single-line reefing?

A third reef is a very deep reefing point, used in extreme storm conditions. Single-line systems often can’t accommodate a third reef due to boom space and complexity, so a separate, traditional two-line setup is usually used for that purpose.

Does single-line reefing work with in-mast furling?

No, they're two completely different systems. In-mast furling is a way of stowing the sail inside the mast, while single-line reefing is for shortening a conventional mainsail with battens.

How do I reduce friction in my single-line reefing system?

To reduce friction, make sure you’re using high-quality, low-friction blocks. Also, check and lubricate these components regularly. Consider using a thinner, high-strength line like Dyneema, which has lower friction.

Is an internal single-line system better than an external one?

An internal system looks much cleaner and protects the lines from UV and chafe. However, it can be more expensive to install and is much more difficult to repair if a line jams or a component breaks inside the boom. External systems are generally easier to troubleshoot and maintain.