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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 02-11-2010
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Not all tapered composite masts are lighter than thier constant section aluminum counter parts. A great example is on Hobie 16's and 18's. Some dumba$$ raised thier mast into power lines and killed himself. So, part of the lawsuit was to replace the top 3' with a fiberglass non-conductive section. This section is tapered and substantially heavier than the old style aluminum straight masts. The top 25% of the mast is unstayed. I know it is not a direct comparison, but it is a decent analog.

Airplane wings have a very different laoding scenario than masts. Wings (on non-aerobatic planes) are designed for uni-directional loading. The wing will also stall before it is overloaded so the main spar will not break. All airplanes have a maneuvering speed so in turbulence they will fly at this speed to guarantee that the wing will stall before experiencing a catasrophic load. The main driver for removing wires and struts is for speed.
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Last edited by nickmerc; 08-18-2011 at 06:05 AM.
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  #12  
Old 02-11-2010
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While the loads are different on airplane wings, I think more load is experienced on a wing than on a sailboat mast. As for the reasons behind stayless wings - speed, that applies to sailboats as well. Less parasitic drag and about 40% weight saving. Not only is there less drag from a stayless rig, but the upper part of the sail is much more efficient. With a backstay the sail has to come to a point at the top, or almost so. This is very inefficient and without the constraints of a backstay the sail can be shaped much more effectively. Read about it here State of the Art
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  #13  
Old 02-11-2010
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I see the same site has been posted twice, and quoted several times. Of course the site is by a builder of free-standing masts. What would you expect it to say??
Here is a site for a different viewpoint:

The Fallacy of Freestanding Mast

Regarding race rules, not sure if free-standing masts are prohibited by all racing rules. I think there are some open or box classes that allow pretty much whatever works (e. g. moth, A-class cat). And don't Wylie cats race in PHRF on the west coast?

I was under the impression that the big problem of free-standing mast is cost.

Last edited by BigZ; 02-11-2010 at 07:10 PM.
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Old 02-11-2010
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I looked at the link you posted. It is a multihull site. If you had read the material in the link I posted you would have read about the unsuitability of freestanding masts for multihulls. For a multihull the freestanding mast has to have a larger section and this results in a heavier mast. A conventional stayed mast in a multihull can be of a smaller section than in a monohull because its staying base is wider so there is less compression on the rig. This means the weight increase for unstayed masts on a multihull carries a weight penalty. For a monohull however there is a large weight advantage to freestanding masts. Not only does a properly engineered carbon fiber mast weigh a lot less (carbon fiber is 60% of the weight of aluminum and twice as strong) but the mast can taper continually to the top where the load is zero. Aluminum masts are usually constant section, sometimes tapered at the upper end only.
On the link you posted it is stated that "yes the boat went faster, but it went faster because it added roach and sail area, not because of the freestanding masts." It is precisely the lack of rigging that allows this roach to exist. The top of a mainsail on a stayed rig is limited to a shape that no designer would ever choose if he had a choice and with a backstay he has no choice. Airfoils are not pointed as this shape does not produce lift (except on supersonic planes) and the lack of a backstay allows the shape to be designed for maximm efficiency.
Moths and A-class cats aren't your average racer'cruiser. I know of no racing rule widely used for a 30 or 40 foot monohull that allows freestanding rigs. And if they can't race the builders will not build them as the industry is built around the racer/cruiser model for the most part. Some people just think they look funny.
A freestanding rig is more expensive on a smaller boat but becomes viable at 40' and larger.

The site I linked to is not the site of a mast builder. It is the site of Eric Sponberg, a naval architect who will design whatever you would like,
freestanding or stayed and he designs power as well as sail. Eric Sponberg did the engineering for the Freedom rigs. Tanton has also designed some very successful boats with freestanding rigs including production boats (Tanton 42).
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  #15  
Old 02-11-2010
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I'd point out that it depends on the type of multihull. Many trimarans, including Chris White's Juniper, have used free-standing masts quite successfully. Doing so on a catamaran, with no hull to anchor the mast to, is a much different proposition.
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  #16  
Old 02-11-2010
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Quote:
Originally Posted by mitiempo View Post
....... I know of no racing rule widely used for a 30 or 40 foot monohull that allows freestanding rigs. And if they can't race the builders will not build them as the industry is built around the racer/cruiser model for the most part. Some people just think they look funny.
A freestanding rig is more expensive on a smaller boat but becomes viable at 40' and larger.

The site I linked to is not the site of a mast builder. It is the site of Eric Sponberg, a naval architect who will design whatever you would like,
freestanding or stayed and he designs power as well as sail. Eric Sponberg did the engineering for the Freedom rigs. Tanton has also designed some very successful boats with freestanding rigs including production boats (Tanton 42).
Can you post a link to the rules that say free-standing rigs aren't allowed? Locally I've seen Nonsuch and Freedoms in the handicap races. And Wylie boats participate in races on the west coast. I can't find anything that says they are not allowed, except for sites like Sponbergs.
I always suspected that unstayed rigs didn't race too often because they couldn't carry a large spinnaker for downwind and they couldn't point quite as high upwind.

Sorry about my misposting about Sponberg. I should have said he is big proponent of unstayed masts, not a builder.
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Old 02-12-2010
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Most rules in the past either did not allow unstayed rigs, rotating masts or both. Or they didn't specifically dis-allow them but other requirements made them less workable. For example both IOR and IMS rules required a forestay. Unless the forestay is attached just to satisfy the rule it needs a backstay to counteract it if it will be of any use. Neither of the above rules allowed rotating masts. The 12 meter rule did not allow unstayed masts and I don't think any of the other meter rules did either. IACC restricts mast section size to an unworkable section for a freestanding rig and does not allow rotating masts. If you're going to be really competitive with an unstayed rig it should rotate as well. Most racing rules follow rules previous fairly closely as well, change not coming easily to conservative committee thinking. Newer rules do allow unstayed rigs but this comes after decades of not being allowed. ACC and IRC rules both allow freestanding rigs. Open 60 allows freestanding and rotating masts as well. PHRF is open to freestanding rigs but this may not be universal in all regions. Freestanding rigs are not the best closed course racers. But the rigs on production boats whether for racng or not are based on the racing rule of the day for the most part.
History is interesting the way things change. If you go back far enough all rigs were unstayed. Then ropes were used to get more performance from them as they became taller. And then rope gave way to wire, galvanized first then stainless. And now that wire is giving way to synthetics (Dynex Dux replacing stainless wire). Masts were solid wood once. Then hollow wood giving way to aluminum. And then carbon fiber for the strongest and lightest material yet. Material availability has helped make this possible for larger boats with its weight saving. The price of carbon fiber is not justifiable for a smaller boat's unstayed rig as it would be expensive and not much weight would be saved. But for a larger boat the weight loss is considerable. The other problem is volume production. There are many aluminum extrusions available for mast use. A designer just specifies one for the stiffness and strength required for a stayed rig. But there are no off the shelf carbon fiber masts as they are custom designed for every different design and its requirements. Hunter (Vision) and others have used spun aluminum for unstayed rigs in the past but carbon fiber is superior on a weight/strength basis.
I don't know if we'll ever see a great number of unstayed rigs. Change comes slowly to sailing. The first large fiberglass sailboat was built in 1950 and for all its advantages it took a long time to catch on. And fiberglass was less expensive than the labor intensive wood it replaced. Synthetic rigging will likely become popular as it offers advantages over wire and actually is not more expensive. But I can't see the more expensive option of carbon fiber unstayed rigs becoming mainstream anytime soon. But there are advantages in handling and performance and some will go this route with custom boats. And maybe there will be another builder or two like Freedom come along.

This pic is of Project Amazon at speed, designed by Sponberg
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Last edited by mitiempo; 02-12-2010 at 12:14 AM. Reason: add
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