The pros and cons of in-mast furling

30 May 2024

In-Mast Furling – some sailors swear by it and some sailors swear at it! So, what’s the deal?

There are two common types of main sail: slab reefed and in-mast furling. A slab reefed sail is hoisted up and pulled down whereas with in-mast furling the main sail is rolled away inside the mast and unrolled or unfurled as required.


  • It’s really easy to unfurl and furl the sail. With an appropriate rig it can be done with just one person and without leaving the cockpit. Very useful if you solo sail and have an auto-helm.
  • You aren’t limited to 2, 3 or 4 reef positions. You can choose exactly how much sail you want out to suit the wind, sea state and characteristics of the yacht.


  • The main sail is permanently hoisted so it doesn’t matter whether it’s fully unfurled or heavily refeed the centre of gravity of the yacht doesn’t improve.
  • The furling mechanism is a collection of moving parts and can be complex so it’s another point of failure and maintenance.
  • In-mast main sails are unlikely to have horizontal battens that can improve the sail shape and its performance – especially helpful as it ages.
  • Whilst the sail is being furled and unfurled it may rub inside the mast increasing wear and tear and decreasing the life of the main sail - maybe and maybe not!
  • If the sail jams whilst coming out or going back in it could leave the yacht in a vulnerable situation as well as leading to damage to the sail.

What does this all mean?

It sounds like in-mast furling is generally a bad idea, but the reality is more complicated. When used correctly in-mast furling is reliable and effective. Across our training yachts it’s roughly a 50/50 mix of main sails that are in-mast furled and slab reefed. This gives students who are with us for more than one course the opportunity to learn on both types of sail.

Interestingly, if you are a bit of a sailing nerd - and everyone at Jolly Parrot is - we haven't experienced increased wear and tear with in-mast main salis versus slab-reefed mail sails. Our experience is the opposite. Our slab-reef main sail yachts need a replacement main approximately twice as often as our in-mast furling yachts. We think this is because there is less flogging when unfurling, reefing and furling - a flappy sail is an unhappy sail! We have seen damage to the tack more often however and this is likely to be caused by the outhaul being over-tightened whereas the outhaul on a slab-reefing sail is adjusted far less often.

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