Sail Slug Lubricants

What to Do If Raising the Mainsail Becomes Difficult

Sail Slug Lubricants
Photo © Tom Lochhaas.

On many sailboats, sail slugs attached to the luff of the mainsail fit into a groove in the mast and slide up and down within the groove when the sail is hoisted or lowered. As with most other equipment and gear on a boat, the slugs and sail groove often need maintenance or repair.

The Problem

If it’s difficult to hoist or lower your mainsail, you have a problem as well as a potential safety concern. If the sail does not rise easily up the mast but requires heavy winching, this is stressing the halyard and likely causing friction wear of some parts of the system. If the sail does not come down easily by its own weight, then you are at risk for a problem if you need to drop the sail quickly in an emergency or have to struggle with it when reefing.

Common causes of difficult sail hoisting and lowering include:

  • The sail slugs are worn or dirty
  • The sail groove is worn or dirty
  • The system is poorly designed

Your best solution depends on the cause of your particular difficulty.

Diagnose the Problem

Has the sail always been difficult to raise and lower, or has it become gradually worse? If it’s always been a problem, it may still be an issue of worn or dirty sail slugs that can be corrected with lubrication—or you may need to upgrade your system. It’s always worth trying a lubricant before spending potentially big money on a new system.

Full-batten mainsails are more likely to bind and jam in the sail groove because of uneven forces on the slugs from the weight and twisting forces from the battens as the sail is moved up or down. On larger sailboats especially, a track-and-car system such as the one made by Harken may be the only solution. This is rather expensive equipment, however, so it’s worth trying simpler solutions first.

If the problem has occurred gradually, first inspect the sail slugs for wear to determine if they should be replaced. Some types have metal parts covered with nylon, and if the nylon wears down and the metal of the slug rubs against the metal of the mast groove, the friction increases greatly. If you do need to replace sail slugs, be sure to use the same size and type as the originals.

Look straight up the mast for any damage to the groove. Usually damage is obvious and causes difficulty raising or lowering the main only intermittently as each sail slug moves through the damaged area. If you suspect mast damage, this is a problem for a professional.

But if your inspection reveals nothing unusual, you may only need to clean and lubricate the slugs and groove.


Various lubricants are sold for use with sail slugs. Chandleries often carry a spray lubricant that dries nongreasy and does not attract dirt. The Sailkote brand shown in the photo works well.

When using any lubricant, it’s a good idea first to clean the mast groove. You can do this with a piece of cloth shaped to fit in the groove, hoisted with the halyard, with a light line attached to bring the cloth back down. First run a dry cloth up and down the mast groove until you see no more dirt on the cloth. Then saturate the cloth with the lubricant and take it up and down again. Then spray each of the sail slugs with lubricant, and raise the sail.

You should feel a big difference in how easily the sail rises. If not, you likely have a problem with worn sail slugs.

One problem with silicon and other lubricants is that you need to use them periodically, perhaps frequently. They’re time consuming and can become expensive.

An old sailor’s trick often works just as well or better: lubricate the sail slugs and groove with everyday liquid dish soap. Not only is this much less expensive, but you also don’t have to clean the track first because the lubricant also cleans, and there’s no buildup. Every time it rains, the groove and slugs are cleaned by the water and soap residue.

True, you may need to use your soap lubricant more frequently, but with a good method of application, it shouldn’t take more than a few seconds each time. Shown in the photo is a large syringe (needle removed) sold by hardware stores for injecting wallpaper repair glue. It works very well to squirt the dish soap in the groove above the sail slugs as they are hoisted up.