stayed vs. unstayed

[man308]

what is the difference between stayed and unstayed mast. If you can, please explain in detail

[gonzo]

An unstayed mast is self standing like a lamp post. A stayed mast has several wires attached to the hull for support.

[spank]

I should add that the engineering of each mast is quite different. While the stayed mast is in compression for the most part, and unstayed mast deals with all kinds of bending forces.

[Eric Sponberg]

I prefer the term "free-standing" which I first used when I published a technical paper on free-standing mast design for the Chesapeake Sailing Yacht Symposium in 1983. "Unstayed" has a definite negative connotation, whereas "free-standing" is much more positive sounding.

Please go to my website, www.sponbergyachtdesign.com, hit the link to free-standing masts, and select the first article, "Some thoughts on the state of the art." This is brand new, just published within the last month or so. It gives a fair bit of insight into the design of free-standing rigs.

Thanks for allowing me to give a little bit of self-promotion. I don't usually do that, but the subject just begged for a mention.

Regards,

Eric

[Lew Morris]

poo poo the Blue... HAIL PURDUE!!!

No animosity intended Eric, just couldn't resist making a comment on your t-shirt... great portfolio

Another BigTen Alumni whose found a warmer place to reside.

Lew

[Matthew]

Hello,
I read your article, and its an interesting website.
How has Project Amazon (or Tin Can) done since 2001 by the way?

One thing I think you might have forgotten to mention when explaining the disadvantages of the stayed rig is the drag caused by all the wires in the air. Or is this not really a big component of overall drag?
Also that the main reason for all the wires on any yacht rig is to hold the forestay tension, and people like headsails because they are conservative. (Or possibly they produce more drive per sq ft than other sails - discuss...?!)

One thing I was wondering about is that you say for smaller boats an unstayed mast is too expensive? I don't understand. The strength calculations for an unstayed mast can pretty much be based on sail area and righting moment, and so can be simplified quite a bit, so I wouldn't have thought there was too much work in specifying a wall thickness in alum, or an overall diameter in wood, to make a free standing mast for a little boat. And the forces being so much less make it cheaper I would have thought, than all the rigging wire and extra hull strength required to take the compression loading of a stayed rig?
Perhaps we are talking about different sorts of sailboat - I am thinking along cruising/dayboat/dinghy style, where performance is important but not everything.

Would be interested to hear you thoughts on this. Great website.
Matt

[Eric Sponberg]

Hail to the Victors Valiant, Hail to the conquering heros.......!

Wish we could do better in the Rose Bowl.

To Matthew's questions:

Yes, drag is a component of the aerodynamics, and it probably makes up about 20% of total drag in the rig. This is parasitic drag--drag that offers no lift. Yup, get rid of the wires, and you get rid of lots of drag. Induced drag is still a bigger component of drag, perhaps on the order of 50% of total drag.

Cost of free-standing masts: I should clarify--my comment was based on carbon fiber construction. Generally, for smaller boats, the cost of the carbon fiber and the process to build the mast is larger for smaller boats because of the fixed costs involved in the process. Compare this to aluminum or wood stayed masts for the same boat including the wires for the rigging, and the cost for the free-standing rig is generally higher.

However, with smaller boats like dinghies and daysailers, then the strength of wood and aluminum is adequate, as well as cheap, for the application. So on relatively small boats, you can still have economical free-standing rigs, and made out of more common materials.

Eric