Mainsail Slab Reefing

Harken slab reefing

Mainsail Slab reefing is the most traditional & simplest form of reefing. You only need some grommets in the sail and some blocks and reefing lines to make this system work.

A list of production yachts at the Annapolis Boat Show using Slab reefing include; Impression, Dufour , Southerly, Outbound, Fingulf, Valiant, Delphia, Grand Solie, X41, Wauquiez, J Boats, Shannon, Catamarans, marla, Geronimo, Fountain Pajot, Alerion, Etap, Sabre, Hanse, Tartan, Caliber, Sunsail, Moorings, Hunter, Morris, Crealock,

How slab reefing works

Harken slab reefing
Harken page slab reefing layout and equipment


The slab reefing system is the cheapest simplest and easiest to add to your main. This Harken diagram details the blocks and lines you need to assemble a slab reefing system

Video tips on slab reefing


Single Line reefing makes slab reefing simple. Instead of a reef line for the tack and the clew, there is one line for both. The process of reefing involves easing the main halyard to the desired point and then taking up on the single reef line. The line starts by pulling the tack of the main down tightening the luff and then the load automatically pulls the leech tight.

Slab Reefing    
Pros Cons  
Traditional Physical effort
Cheap May involve getting out of cockpit
Simple High reach for boom cover
Easy modification Loose sail material after reef


Dutchman system

Dutchman system
Dutchman system

When you use a slab reefing system you will find as the sail is lowered it flaps around a lot. There is nothing to hold it in place. This may not be a problem and once you have secured the reef, there are grommets in the sail to tie the loose sail down.

However there are two systems you can add to control the sail; the Dutchman System and the Lazy Jack System.

The Dutchman system helps the mainsail fold itself while lowering. The Dutchman lines are led from side to side through the sail. Its almost automatic flaking.

Imagine a window blind that has a central line that goes through each slat. this is how to look at the Dutchman System. While reefing the Dutchman works the same way flaking the sail until you get to the reef point.

To use a Dutchman System you will need sail slides on your mainsail. It will not work on a bolt rope mainsail.

To learn more about the Dutchman System click here

Lazy Jacks

Harken Lazy Jacks

Along with the Dutchman System, lazy jacks are another way of capturing the mainsail while its drops or is reefed.

Lazy Jacks work by having lines either side of the mainsail. Hence the main sail is always captured between the lines so when you lower the sail it so captured and will no fall on the deck.

This diagram from Harken shows how the system works

This link will take you to more information on Lazy jacks

Mainsail Slab reefing

Main sail slide system and Boom w Lazy Jacks

Gull Wing Boom

Hall Gull Boom
Hall Gull Boom

There is a mainsail on that boom even though you would think it was a bare boom until you see the head at the front end. It is not a furling boom, the main sail is simply flaked, with the help of lazy jacks. Typically you would see a lot of sail sitting on top of the boom plus a stack of battcars at the luff.

The combination of Halls gull wing composite boom and Harkens Switch T track which reduces the height of the mainsail cars, makes for a very clean look on the Shipman 65.

Harken Switch Track

Harken Switch track
Harken Switch track


Harken Switch Track mainsail batten car track which lowers the stack height of batten cars

The Switch T Track looks like a railway switching system. The battcars alternately fall down the portside then the starboard side helping the sail flake itself and lower stack height.

In the picture of the forward end of the boom you can see the Switch T Track just above the mainsail cover. You can see lazy jacks pulled forward in the picture above. Lazy jacks work well with Antal’s low friction rings

Other mainsail Luff batten car systems

A car system that will help the mainsail raising and lowering is Ronstan’s balls slide cars this car has ball bearings yet will fit in a bolt rope track.

Yet another is Tides Strong track


Doyle Stack pack