The Fallacy of Freestanding Masts

Many people believe that freestanding masts are superior to stayed masts, usually arguing that the aerodynamics of the mast is better without the windage of stays, and that there are less parts to fail, so a freestanding mast will not lead to catastrophic failure.  I see these arguments quite frequently on certain manufacturers and designers web-sites as well as boat design blogs.  I believe that they are in error.  The aerodynamic losses, added weight, and excess cost all outweigh the minor benefits of going unstayed.  Here is why…

 I have personal experience having skippered and raced a Freedom 38 with a freestanding mast for the last several years.  I have also raced on board several Farrier 31R’s, including Blue Lightning and Cheekee Monkee with stayed, rotating carbon wing masts and asymmetric foils.  

A freestanding mast is really a giant cantilever.  All the massive healing force of your sail area must be taken by the mast, and kept upright by the partners (where the mast meets the deck).   Stays do contribute some minor windage, this is true.  However, an unstayed mast must be of significantly larger diameter to compensate for the lack of stays.  Perhaps even more critical than the windage of the greater diameter mast, it interferes with airflow over the sail surface and reduces driving force.  This extra diameter mast is at the leading edge of the sail, creating a great big pocket, which causes the airflow to become unattached.   Attached flow is much more efficient and increases driving force, that is why Farrier Trimarans and fast beach cats like the Hobie Tiger have a rotating wing mast, to create a smooth flow on the lee side of the sail.  Pocket luffs on windsurf sails do the same thing.   The large diameter freestanding round mast actually decreases your driving force and slows you down.

Unstayed rigs also cause significant extra weight.  In a day when stays can be lightweight synthetic, a freestanding mast must be much beefier and therefore heavier to accommodate the bending load and stay in column without stays.  The deck and hull surrounding the partners must be significantly re-enforced so the huge lever sticking up in the sky doesn’t get ripped right out of the deck.  This all leads to extra weight, which slows you down. 

Then there is the added cost.  A larger diameter mast takes a larger mandrel, more material and more time to make. Finishing (sanding,  barrier coats, paint, etc.) also take more time and material.  The added re-enforcement of the hull takes time and material as well.  All these things add up quite quickly.

It would seem to make sense that an item with less parts would have less chance of failing, except for the simple fact that these parts are what hold the mast upright.  Although I have not seen any numerical reports on a ratio of stayed mast failures to freestanding mast failures, I have seen enough freestanding masts broken off to wager that the claim of more parts to break is unfounded in the case of masts.  The loads of heeling force and righting moment must be calculated exactly in order to design a freestanding mast with a high enough margin of safety.  Be sure that you will pay dearly for those services and the construction of the mast(s.) I recently read about a 40 footer that spent $600,000 on freestanding masts and sails. Ouch! Yes, the boat went faster, but it went faster because it added roach and sail area, not because of the freestanding masts. Many smaller, prototype, or home-made boats try unstayed masts without the proper calculations.  Most of them have many knobs and bulges from numerous repairs to their mast.  So is your risk of catastrophic failure lower with an unstayed mast?  Perhaps, but only if you’re willing to pay for it.

Did I forget to mention the inability to carry large downwind sails?  Without stays, spinnakers must be small and hoisted only part way up, or their force will break an unstayed mast.  Or the mast must be even larger and stronger and heavier to carry a full size spinnaker. 

Further, windage on your stays is far less of a factor than water resistance and hull shape.  Most boats with unstayed masts are not very efficient through the water.  They are wide, comfortable and heavy.  Spending $600,000 to reduce air resistance when you’re dragging 12,000 pounds of lead through the water on a boat with a length to beam ratio of 3:1 seems absurd to me.  Try a brand new 36’ trimaran for ½ the cost and you’ll go 3 times as fast with stays!  Even on identical hulls, a stayed wing mast with equal sail area will probably go faster than an unstayed rig because of better flow attachment to the sail.

Am I saying unstayed masts are bad? Certainly not.  To some people they look cleaner and less complicated on a boat. They are definitely unique.  If designed properly, they bend off nicely with gusts, allowing you to carry full sail longer.   Just be aware that they will not be faster, lighter, or less expensive. They will add cost, weight and aerodynamic inefficiency to your boat or building project.  That is why we have chosen to use stayed rigs on the Adventure Trimaran.

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