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  #1  
Old 12-27-2010
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Rotating wing masts

Lately I’ve been reading a lot about rotating, free-standing, carbon fiber, wing masts. By all accounts they’re much more efficient than the usual arrangement. If this is true why don’t we see more of them?

I understand the problems that it would create for racing, but not everyone cares about racing. I also understand that they’d be more expensive, but carbon fiber spars now proliferate all sailing sub-genres. I also understand taht it may not be practical to redesign an existing boat’s rig, but why don’t we see these on more new designs?

I, for one, am always trying to find ways to make my boat more efficient and faster. And I feel like this is a trend among all sailors, even devout cruisers. Why is such an obvious leap forward in sailboat evolution being ignored?
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Old 12-27-2010
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Pretty sure it isn't just expensive, its very very expensive.
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Old 12-27-2010
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I assume that you indeed mean wing *mast* and not the wing sails that proved so devastating in the last America's Cup.

Wing Masts are like many ideas which really well work in narrow applications. Wing masts offer very small gains in performance but with a high degree of complexity. Wing masts work very well on high efficiency, low drag applications. In that mode they offer an efficiency that can actually be used by the vessel. They are great on high speed vessels like ice boats and racing multi-hulls, because these crafr have apparent wind that is almost always from forward of abeam.

But that small gain in efficiency comes at a price; a very big price in terms of practicality when applied to more normal vessels.

For example, wing masts need to be free to rotate, but with their angle of attack controllable, so that they can offer the proper angle of attack for the wind direction. That means that the crew needs to be able to adjust not just the mainsheet, but the mast angle of attack. Around here there are folks who argue against the advantages of a fractional rig by suggesting that it is too hard for the average sailor to learn to use a backstay adjuster. Visualize the average sailor learning to properly adjust the angle of attack of the mast (remembering that a wing mast is only more efficient when the angle of attack is correct, but greatly increases drag when it is improperly adjusted).

Allowing free rotation requires a single axis of attachment for the shrouds or else a cantilevered connection. If a vessel is very beamy then the vertical staying of the mast can be isolated from the bending sideloads on the spar itself, which is part of the reason that wing masts work really well on multihulls or iceboats. But on a monohull this makes staying very tricky without something like the side struts seen on open class boats. If the choice is to use a cantilevered connection, there needs to be adequate fore and aft as well as side to side bracing of the bearing points for the embeded portion of the mast, and either an above deck set of bearings or else a set of bearings at the heel or the mast and at the deck, with the deck bearings being water tight. Proper support of the deck mounted bearing would in all probability require fore and aft as well as lateral bulkheads or knees occupying much of the interior in the area of the mast.

Wing masts have a lot of 'sail area' in the mast alone, at times more sail area than the boat can safely use and so for a cruising boat, which encounters winds of a variety of forces and directions, this inability to 'reef' the sail area of the mast can be a dangerous liability. This can be a significant problem at anchor or tied up at a dock. In the past, vessels with wing masts were generally daysailors and boats which are small enough that the mast could be unstepped at night. There have been experiemental boats with wing masts which have allowed their masts to feather, but that can mean a lot of noise and a lot of vibration.

Then there is the weight versus cost issue. While a wing mast can be lighter than a conventional stayed spar, for the most part, they tend to be a heavier rig, due to the isolation of the side support from the structure resisting the bending of the spar. This can be worked around by using exotic materials but of course this has serious monetary consequences.

And even if these complications could be effectively addressed, the offshore sailing community tends to be pretty conservative. Here we are nearly fifty years after aluminum spars with modern engineering became the norm, and yet the cruising community still argues that deck stepped masts are somehow less safe. So if you can visualize that, now try visualize trying to convince them that a mast supported on a ball-joint with a single shroud lead to a strut on either side makes sense. I don't see that happening any time soon.

In terms of retrofitting a wing mast to a conventional monohull, there would be little to no real gains in performance, but even if there were measurable gains in performance, the costs and complication would be prohibitive, especially since there are a wide range of less expensive alternatives which would be more effective in improving performance.

Jeff
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Last edited by Jeff_H; 12-28-2010 at 07:57 AM.
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Old 12-27-2010
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Red, by 'wing' mast do you mean the aerorig?

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Old 12-28-2010
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Jeff, thanks for the excellent (as always) explanation. I think all of your points are very valid and make perfect sense. I’d be interested to hear your thoughts about this design that I just stumbled upon while researching wing masts. To my very untrained eye it looks like it would be a very efficient rig, but based on what you've said above it would be more trouble than it's worth, and for that hull it wouldn't add much in the way of preformance.

Globetrotter 45

Copa, I'm referring to a mast with a cross section similar to a wing. Not a wing sail or any other rig anomalies.

Last edited by redstripesailor; 12-28-2010 at 09:06 AM.
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Old 12-28-2010
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Thank you for your kind words. As I read this thread, there are two separate unanswered questions here. The first is "What can be done to make my Triton (I assume that is your boat) sail better (more efficiently)?" and the second seems to be, "What do you think of Eric Sponberg’s Globetrotter rig or rigs like this?"

To begin with the Triton question, all boats behave as a system, and on any given boat, the limitation on sailing performance will often come from pecific components of the design and no matter what else you do, the limitation on performance will come from those components.

In the case of the Triton, the limitations on performance come from several basic sources. Off hand these would be as follows:
  • Low hull-speed due to a short waterline length relative to length overall,
  • Displacement hull form,
  • Comparatively low stability, and
  • Comparatively high drag (especially relative to stability).
As I am sure that you know the hull speed limits the overall theoretically maximum sustainable speed of the boat. The Triton, like most racer-cruisers of that era, has a comparatively short waterline relative to its overall length and since hull speed is proportionate to waterline length, it’s achievable maximum speed is somewhat limited as well. And while it is true that the waterline length grows when the boat is heeled over, on boats like the Triton, the gain in speed is not proportionate to the gain in waterline length. In other words, even the heeled hull-speed is slower than that of a similar length boat which has a waterline length, which is proportionately longer.

But hull speed is not the best predictor of relative passage speeds. A second and perhaps more significant predictor of passage times, is the percentage of the time that a boat is at or near its hull speed and to a lesser extent, whether it can actually routinely sustain speeds above its hull-speed.

The first aspect of this (i.e. the percentage of the time that a boat is at or near its hull speed) is where efficiency comes into play. For a boat to be at or near its hull speed for a large percentage of a passage, the boat will need a combination of being able to either easily hold it’s speed at or near hull speed and be able to sustaining speeds in excess of its hull speed to offset the time that it is below hull speed. In order to easily hold speeds at or near hull-speed, there needs to be adequate drive to overcome the boat’s drag.

Hull forms like the Triton's generate a lot of drag. Their long keels and deep canoe bodies have a lot of wetted surface. Long keels generate a lot of dynamic drag well, as does their short waterlines, and blunt entries. While Tritons are better than many shorter waterline boats, the typical short waterline boat’s blunt entry especially generates a lot of drag in a chop where the bow is repetitively colliding with the wave train. So it is that boats like these need more drive than a more efficient hull form. And displacement hull forms, like the Triton’s do not lend themselves to planing or even to the kinds of reduced wave making that is associated with the current generation of semi-displacement type hulls, and so are not capable of sustaining speeds in excess of hull speed. In other words, they are pretty inefficient in terms of needing a lot of drive relative to their overall displacement.

The efficiency of their hulls can be improved some by fairing the bottom, using low drag bottom paint, and keeping the bottom clean and smooth. There may be some further reduction in drag achieved by going to a ‘Constellation’ type rudder which is a triangular rudder with a larger portion away from the hull or by simple expedients like using a two-blade prop and locking it off vertically in the aperture when making a long passage or racing.

In terms of generating enough drive, there are a number of components that come into play most notably;
1. There needs to be adequate sail area,
2.The rig needs to be efficient in terms of generating drive relative to its wind resistance and relative to the side force it generates across a wide range of wind speeds and angles,
3. The rig needs to produce the drive without inducing too much weather helm as use of the rudder to resist weather helm creates more drag,
4.The boat needs to have adequate stability to stand up to the sail plan while it is producing the required drive, and perhaps the one most often overlooked,
5. The boat has to have a motion which minimizes disruption of the air flow across the sail.

The Triton’s factory rig was actually a very efficient rig for its day. It was a fractional rig which had about as much sail area as the boat could stand up to, it balanced reasonably well, and the mainsail was reasonably well proportioned. If you wanted to make the rig more efficient and money were no object you could replace the mast with a taller, tapered slightly bendy carbon fiber spar, increase the fore-triangle height a little, eliminate the jumper struts and stays, change to non-metallic shrouds and backstay, add an efficient traveler and an adjustable backstay, go to slightly fuller-roached, more powerfully cut sails made from a low stretch fabric and use mast-bend and forestay tension to blade them out in a breeze. This mix should allow you precisely adjust the drive, weather helm, and heeling to the conditions and so improved performance will come more from being able to use the rig efficiently than from reduced air drag or increased sail area.

But ultimately you will come up against the limits of the Triton, which is its lack of stability relative to drag. The Triton’s narrow beam, slack bilges, low ballast ratio, and shoalish draft mean that these boats just do not have a huge amount of stability, at least as compared to more modern designs. And so it is hard to carry enough sail area to overcome the proportionately large hull drag mentioned above. At best you will improve the sailing ability just so far. It will be noticeable but it will not make the boat sail at similar speeds to more modern boats of similar displacement, and it will be wildly expensive to achieve this added performance.

The other item is the Triton's motion. While the Triton has softer accelerations than many boats this size, they tend to roll and pitch through comparatively wide angles and these wide roll and pitch angles disrupt the flow across the sail as compared to designs which have been intentionally designed to have a slow roll and pitch rate as well as small roll and pitch angles, which is the current trend in hull and foil modeling.

To be frank, if performance or efficiency is important to you, I would suggest that you start from a more efficient hull and keel and then optimize from there. But then again, most sailors like to tinker with what they have and ask insightful what-if's.

As for the Eric Sponberg ketch that you linked to, I see this as a one trick pony gimmicky concept. It is a rig that should be pretty efficient as a reaching rig and is well coupled with the somewhat inefficient hull, but it would not represent an improvement over an optimized version of the Triton’s original rig, and frankly it would be wildly more expensive.

Respectfully,
Jeff
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Last edited by Jeff_H; 12-29-2010 at 07:02 AM.
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Old 12-29-2010
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One of the worlds main developers of Wing masts for yachts is I believe based near me in Inverness,Scotland and there are several examples to be seen locally-one in particular fitted to a big catermaran(suspect this might have been the test bed)
Can be very efficient in large scale commercial applications.

Last edited by ffiill; 12-29-2010 at 03:34 AM.
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Old 12-29-2010
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Wow, Jeff, quite an explanation! I pulled the motor out of my boat and glassed over the aperture, thus I'm completely at the mercy of wind and tide. I've spent many an hour on light air days either drifting or swinging on the hook contemplating ways to improve my rig. I have concluded precisely what you've said above, that it's just not worth all the trouble and expense for such marginal gains in performance. I bought my Triton because it was the best boat that I could afford at the time. And since I've had her I've identified many traits in her that I do not wish to have on my next boat. If I get any wild hairs to make major rig modifications I will wait to do it on an appropriate hull.

I was curious about wing masts because they seem like they would offer many advantages over traditional rigs when married with appropriate hulls. I wanted to know that if this was indeed that case, why we didn't see more of them. Jeff, you've more than answered my question and I really appreciate your insightful responses.
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Old 12-30-2010
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You are very welcome....

I tip my hat to you sailing a Triton without an engine. I should say that I too enjoy that unique aethetic to sailing an engineless boat, and admire the skill required to do so with a boat like the Triton. (I did the same thing with a Folkboat back in the 1970's) You learn all kinds of tricks and you really become one with the boat (or else spend a lot time in trouble).

Jeff
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Old 01-04-2011
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Thanks Jeff. I totally agree with you about becoming one with the boat. I used to work as a sailing instructor for Outward Bound’s Hurricane Island sailing school where we did a lot of engineless sailing. It was always amazing to watch inner city kids who’d never even seen an ocean before deftly handle their vessel after just a few weeks. It was also interesting to see them form an affinity for a craft that dealt out much more pain than pleasure.

I thought a Triton would sail like a hotrod compared to the schooners and dumpy OB boats I grew up sailing. Man, have I been disappointed. My next boat is going to be quite different; light air performance is now my number one criteria (hence my initial posting). I used to moor in Woods Hole and the current there could best my little boat 50% of the time. Now I’m out of NC’s Cape Fear river and I spend about 40% of my time getting skunked.
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