In mast furling consists of a roller furler unit fitted inside a mast section that has a slot in the aft end for the mainsail to roll in and out of. This mast section is larger than normally required and may require fewer spreaders due to the extra stiffness. The mainsail because it furls like a jib cannot support battens, hence the mainsail needs to be cut with leach hollow like a jib/genoa. Recently vertical battens have helped increase mainsail roach.
A list of production yachts at the Annapolis Boat Show using In mast furling include; Jeaneau, Hunter, caliber, Gozzard, Fingulf, Oyster, Hylas, Halberg Rassey, Bavaria, Island Packet, Catalina 6, Dufour, Beneteau, cruisers, Passport, Robi, Impression, & Wauquiez,
The Sparcraft in mast furler is one example of in mast furlers
In Mast furler pros & cons
In mast furling although a very convenient furling system it does has its pitfalls.
| In Mast Furling Pros | Cons |
| Cheap | Weight up high |
| Simple to use | Reduced sail area |
| No boom cover | Poor light air performance |
| Furl to any sail size | If the main furler jams you may not unable to drop main |
In Mast Furling
Increasing sail Area
One complaint about mast furlers is the reduced sail area from the leech hollow. there are a couple of ways of increasing sail area.
The air batten From Halsey is an inflatable batten which is inflated when the sail is set, giving you much more sail area. More
Another idea from Halsey is the vertical batten.
In Mast Furling
Modifying an existing mast
Bamar
There are some behind the mast options that you can retrofit your existing mast if you wish to convert to main sail reefing. Bamar external mast furling unit to add to existing mast section.