The Roller Furling Mainsail: What You Need to Know

Not so many years ago that I would have told you that Roller Furling Mainsail Systems, be they In-Boom or In-Mast, were so performance-limiting and prone to jamming that I wouldn't be wanting either on my boat any time soon.

An in-mast mainsail furling system on fractional B&R-rigged Hunter 356

However, since those days modern in-mast and in-boom systems have seen significant advancements in design, materials, and reliability, making many of the stated drawbacks less relevant or entirely overcome.

Not only do they make reefing the mainsail a quick and easy operation, they offer several other benefits:

Convenience and Safety: Furling from the cockpit entirely eliminates the need to go on deck to reef or stow the mainsail. This is a game-changer, especially in rough weather or at night, significantly enhancing crew safety.

Infinite Reefing Points: Unlike the fixed reef points of slab reefing, roller furling allows for precise and continuous adjustment of sail area. This means you can perfectly match the sail to the prevailing wind conditions, maximizing comfort and performance.

Sail Preservation: When furled, the mainsail is neatly stowed within the mast or boom, protecting it from harmful UV rays, chafe, and environmental degradation, thereby extending its lifespan.

Ease of Single-Handing/Short-Handing: For those sailing with limited crew, these systems drastically reduce the physical effort and coordination required to manage the mainsail, making larger boats more accessible for single-handed or short-handed cruising.

In-Mast v. In-Boom Furling

Feature / System	In-Mast Furling	In-Boom Furling
Pros	Maximum safety (fully contained in mast); Minimal deck clutter; Excellent UV protection;	Better sail shape (full battens, more roach); Lower centre of gravity when reefed/stowed; Easier access to sail for repairs/maintenance if jammed;
Cons	Sail shape limitations (historically, less roach); Higher centre of gravity (sail weight aloft); Can be more challenging to clear a jam aloft;	Requires precise boom angle for furling; Boom can be larger/heavier; Sail exposed to elements in boom slot (less UV protection);
Sailing Performance	Generally flatter sail, less powerful upwind (though modern sails improve this)	Better upwind performance with full battens; minimal impact on stability
Installation	Often requires new mast; complex internal mechanisms	Requires new boom; careful alignment with mast
Maintenance	Lubrication of internal drive, inspection of slot	Lubrication of furling drum, cleaning boom slot
Suitability	Cruisers prioritizing ultimate ease and safety	Performance-minded cruisers, those wanting better sail shape

Mainsails Made for Roller Furling Gear

While traditional in-mast sails had a limited roach, modern sailmaking has overcome this. Vertically battened mainsails, particularly those made with advanced laminates or 3Di technologies from companies like North Sails or Quantum Sails, are specifically designed for furling systems.

These battens help maintain the sail's optimal shape and provide better performance, even with a reduced roach, by distributing loads more efficiently and preventing excessive stretching or bagging, common issues with older designs.

Maintenance & Troubleshooting Best Practices

Maintenance: Regular freshwater rinsing of the furling drum and internal mechanisms is essential to remove salt and dirt.

Lubricating moving parts, such as bearings and swivels, with a suitable dry lubricant (avoiding heavy grease that attracts grime) is also crucial.

The furling line itself should be inspected regularly and replaced if showing signs of wear.

Troubleshooting: Many "jams" can be prevented or quickly resolved with correct technique. For instance, ensuring consistent tension on both the furling line and the outhaul (or sheet) during furling/unfurling is key to a tight, even roll.

If a jam does occur, first try to relieve tension, then re-tension and attempt to furl/unfurl again, sometimes with a slight luff or bear-off to the correct tack. Never force the system with a winch, as this can cause significant damage.

Halyard wraps around the forestay are a common issue on headsail furlers that can also affect in-mast systems if the halyard lead isn't optimal, but often can be cleared by partially unfurling and re-furling the sail.

In many cases, if a furling system fully jams and cannot be cleared, the only option is to drop the sail by disconnecting it from the furling drum/foil and lowering it, which can be challenging offshore. Some systems have built-in emergency release mechanisms, but these should be understood and practiced.

Specific Operational Procedures

Knowing how to operate these systems correctly is paramount to avoiding problems.

in-mast roller reefing system for mainsails

In-Mast Furling: To unfurl, head slightly off the wind, release the furling line, and pull steadily on the outhaul.

To furl, head into the wind (or slightly off depending on furler type and wind direction), ensure the boom is at the correct angle (often aided by a rod kicker), maintain slight tension on the outhaul, and pull steadily on the furling line. Crucially, a tight, even roll is essential to prevent creases and jams.

In-Boom Furling: The boom angle relative to the mast is critical, typically around 87 degrees. Before hoisting, ensure the boom is at this angle (using topping lift and vang).

When hoisting, the sail is fed into the boom's slot while simultaneously managing the furling line and halyard.

To furl, ease the mainsheet, ensure the boom angle is correct, and winch in the furling line while easing the halyard.

For both, consistent tension on all lines prevents overrides and messy furling.

Cost & Value

For a 40-foot yacht, a new in-mast furling system (including mast, sail, and hardware) could range from £10,000 to £20,000 or more, depending on the complexity (manual vs. electric, carbon vs. aluminum).

In-boom systems can be similarly priced, often requiring a new boom and a specifically cut, fully battened sail.

While the initial outlay is significant, the value proposition lies in enhanced safety, reduced crew effort, and the extended lifespan of the sail due to protected storage. For many cruisers, the increased enjoyment and peace of mind outweigh the cost.

The impact on a boat's resale value is a key consideration. While opinions vary, a well-maintained, modern furling mainsail system is generally seen as a desirable feature, especially for cruising yachts, and can enhance marketability and potentially command a higher price. Many modern production cruising boats come with these systems as standard or popular options, reflecting market demand.

Prominent Manufacturers of Mainsail Furling Gear

These include:

Seldén Mast: Known for both their in-mast and in-boom solutions, often seen on production boats.

Leisure Furl (Forespar): A well-established brand for in-boom systems, recognized for reliability and ease of use, often featuring an integral sail cover.

Hall Spars: Offers high-performance carbon in-boom systems, catering to larger yachts.

Schaefer Marine: Develops innovative boom furlers designed to address common issues.

Facnor and Profurl: Offer a range of furling systems, including those that can be retrofitted* with electric drives.

*While installing an in-mast or in-boom system usually involves replacing the mast or boom (which is a significant undertaking), some systems are designed to be more easily retrofitted. For example, some in-boom systems or internal mast drives can be fitted to existing spars with modifications. The cost and complexity depend heavily on the specific boat and chosen system, often requiring professional assessment and installation.

Any Questions?

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I wrote this article using GPT-4, OpenAI’s large-scale language-generation model, as a research assistant to gather information, summarize research findings, and provide suggestions for the content and structure of the article.

Dick McClary, creator and owner of sailboat-cruising.com

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