Wharram wing sail on a ~30ft monohull

[pironiero]

I was thinking about wharram wing sail on a modern sport-ish monohull, wouldnt it be cheaper with similar performance to modern square mainsails? boom at the top should allow for better sail shape at the top and actual wing shaped mainsail should allow for better wind flow.
Main question is- will it be safe using it on a boat without any spreaders? im talking strictly about 30ft ish monohulls

Am i wrong? Please explain.

 

[Ilan Voyager]

You are not totally wrong. There are already plenty of full battened mainsails with fat heads working since more than 10 years on fast monohulls like the Minitransat.
In fact these mainsails are simpler than the Wharram version which won't be cheaper, nor better. Probably inferior.
There is a lot of experience and data with these square or fat head mainsails. That means also that if you ask a sailmaker with experience on these sails you'll get the best price. None good sail is cheap.

A mast without spreaders, ie free standing or almost, with such very powerful main sail? Surely not safe because of the weight of mast deprived of the support of the spreaders. That will be pretty heavy.
Far too much heavy for the stability of a small 30 feet boat, also extremely costly as a a custom carbon mast will be mandatory. With the price of this mast you can make a second 30 footer.
It will far more interesting to use the well proven solutions used on the Minis and transpose it on a similar 30 footer (it has already be done on a cruising 9 meters round bow sail boat designed and made in France, and it's not an expensive boat).
It's a work for a experienced naval architect as the hull must be in adequation with the rig and vice-versa.
Link for the Revolution 29
Accueil - Afep Marine https://www.afep-marine.com/revolution29-bateau-aluminium-presentation.php

 

[Ilan Voyager]

29 feet. The mas has already 2 pairs of spreaders and have a look at the section of the mast on a cruising boat. Imagine the mast needed without spreaders...

 

[rnlock]

I wouldn't be so quick to write off the Wharram "wingsail". Most masts I've seen must create some fairly awful separation in an important place. I think it's quite possible that a "luff pocket"* as Wharram is using might have superior aerodynamics. If you don't want to use a luff pocket, then it probably pays to have a mast as thin as possible. In that case, and especially if the mast has to be aluminum instead of carbon fiber, spreaders are probably a necessity. I wonder what various racing rules say about luff pockets.

Without actually running the numbers, I wouldn't be so quick to write off a free standing mast. I've been on a 25'6" cruising boat with a free standing aluminum mast that won a number of local races. Some commercially available cruising sailboats, such as the Nonsuch boats, have had free standing masts for some years now. I'd want to run the numbers before rejecting that option. We should remember that the funds that were to be spent on many expensive additional points of failure, otherwise known as turnbuckles, terminals, spreaders and almost innumerable other small stainless steel bits would be available for the free standing mast instead. Also, that a luff pocket probably allows a fatter mast without as much of a performance penalty. Such a mast WILL require a more substantial step, and a deck mounted cantilevered mast is out of the question without a good supply of unobtainium and probably a lot of extra money. Wharram's page on his wingsail does show stays to the top of the mast, in case a pure cantilever is out of the question, and in that case, maybe a deck stepped mast would work. It would allow the lower parts of the mast to be a bit thinner.

I have to admit I'm curious just how those top battens work on the square topped sails.

*Wharram's term. I don't know if it's the same term as everyone else uses.

 

[Ilan Voyager]

I do not write off the Wharran wingsail, simply there is a proven since many years solution, used from windsurfs to racers around the world maxi trimarans. So you have plenty of sail makers having experience with these sails, which is simpler than the Wharram.
I do not see the interest of starting an experimentation of a custom sail plan on a small boat not made for racing, when you have already a proven solution which works well which has been refined for years. The Minis (6.5 meters monohulls) cross the Atlantic at 6.5 knots mean speed solitary, with no assistance nor routers...A racing mini is able of more than 18 knots, and can keep in optimal conditions 16 knots during hours, as seen last year crossing the Channel, and the cruising ones are not far behind.
A friend of mine has since 2016 a Revolution 29. It's a comfortable rather heavy (5.5 tons) sweet cruising boat with a round bow and enormous volume, it's easy to maneuver alone or best for 2 persons who are not athletes. It's a family boat.
But that takes 12 knots easily without efforts with dacron sails, and you keep 10 knots while sipping your Chassagne Montrachet. It's able of 16.5 knots top speed with 25 knots of wind.
The mainsail is very well mannered, rather easy to tune and easy to control. There no complication with running stays. Brief that works nicely for relaxed cruising. The mast when tuned needs only regular maintenance like any mast. That lasts many and many years.

The problem for a free standing mast is that sail is not triangular or even rounded headed like on a old beach catamaran, the rectangular sail is very powerful with a pretty high center of effort (that explains the unusual 2 pairs of spreaders on a 5.5 tons 29 feet to keep the mast straight). If you want the same surface of sail ie performances of a Revolution 29 on a lone free standing mast you'll have a serious engineering problem on a small 30 feet.
Aluminum has a drawback for free standing masts; fatigue. Fact well known since ages.
So it's better to use a material which has not this drawback. There are 2 contenders: wood and carbon fiber. Wood will be too heavy for the stability of the boat, remains the carbon fiber. Pretty expensive specially on a custom mast for not a sure result. And it will remain too heavy for a 30 feet with so much sail.
The normal bending of the free standing mast will spill out the wind at the head of the rectangular sail which requires a mast as straight as possible. It's finally a useless complication.
The Wharram is a catamaran so with such a width you can have stays without the need of spreaders. That's impossible on a monohull lacking of width, as the angle of the stays is too small.
Simply rectangular sails always needing a straight mast for working are not compatible with free standing masts unless countless complications.
So it's better to stay with a proven solution when you won't name your boat "Regardless of cost" or "Experimental". Mistakes are costly.
Have a look at the pics of the 29 feet, look well at the rigging, sails and hardware and tell to me if you see anything complicated or unusually expensive on this 29 feet. Personally I see a rational system, rather low cost using ordinary materials, nothing fancy. No backstay, no adjustable or running stay, so the mast won't fall because of a mistake while tacking. A simple block on a normal track to control the main sail, a boom vang, 3 winches, 2 for the front sails, one all purpose. It's minimal.
Accueil - Afep Marine https://www.afep-marine.com/revolution29-bateau-aluminium-photos.php

 

[rnlock]

Every time I look at a conventional marconi rig in stainless, I see money. Money I'd rather have in my wallet. I look at that 29 footer and I see all sorts of fancy metal things that cost money. When I've walked into marine stores, I've been appalled at just how much all that stainless stuff costs. It's almost as bad as for airplanes. I've been on boats that don't have all that stuff and sailed fine.

Windsurfer rigs have the "luff pocket".

I think Wharram would argue that his type of sail isn't experimental anymore, though I don't know if I'd agree or not.

As far as what's feasible with, say, a carbon mast, I'd say it's probably the kind of thing one would have to calculate. At least if homemade.

Aluminum fatigue is only a problem if you don't take it into account in the design phase, or if you keep the boat far longer than the engineers intended. If aluminum fatigue was always a big problem, people wouldn't build airplanes out of it. There are ways of coping.

I'll admit I don't have a handle on the loads or the rigidity required, so I can't just sit down and calculate things. I don't know how heavy the rig on that 29 footer is, either. I'll mention again that the luff pocket probably allows a significantly larger mast without a big penalty, so that should help with the weight of a free standing mast.

The idea that there's only one good way of doing things doesn't convince me in this case. Especially when airplanes have mostly gone for cantilevered aluminum structures, rather than the wire braced types used in the past.

 

[Ilan Voyager]

If you buy stainless steel outside a retail marine store you'll see that the price is not enormous thanks to the Chinese. It's the label marine or aviation which puts the high price. You'll be very surprised if you knew the price of an inox hardware item sold by the factory and the price of the same item christened marine by the retail shop. So that depends on where you buy and make your rigging, and, enormous advantage, that lasts for a very long time without corroding. The strength is very predictable, the behavior under stress also. It's a very safe and durable material when correctly worked.
Aluminium planes after a certain age and number of cycles, if not totally rebuilt and re-certified, lose their certification and are sent to the junkyard. The mechanical inertia of the structure of a plane wing compared to its load is plentiful compared to the loads of a poor tube mast compared to its mechanical inertia. If you take in count the fatigue factor of a free standing mast which is pure guessing and if you take a too comfortable margin of security the poor mast will be so heavy that the boat loses all margin of seaworthiness.
Free standing and very bending masts in aluminium have had the bad habit to snap or to show signs of deterioration in just of few years. When it was the fashion of the highly bendable 3/4 masts with lots of stays, running backstays and other amenities after 2 seasons of racing the masts were "cooked". A good sign was the paint beginning to crack showing the stress lines. A proof with magnaflux or similar showed better the coming disaster.
The catamaran British Steel dismantled in the middle of Atlantic because of fatigue of the metal of the front beam which was an aluminium tube. The catamaran Elf Aquitaine began to break by fatigue of the alu mecano-welded front beam. Happily the skipper Marc Pajot could keep the boat from dismantling bracing it with all the ropes he had.

I do not say that there is only one way, as you have at at least the good and the bad way, but there is almost always the simplest, foolproof and straightforward way, not the cheapest but surely among the cheapest ones.
Going down in cost, far cheaper systems hand made in the backyard but with not the same results. That can be perfectly acceptable if you have no illusions about it.
This rigging of the 29 Revolution has more than 30 years of use, improvements and fiddling with.
It works so well at a decent cost, that for the while nobody has found a better rigging for the same almost low price.
That's empiricism and accumulation of knowledge without any hype, going straight for the goal; a performant, simple to use rigging a the best cost using only normal and well known industrial parts found in a catalog, so you can guarantee it.
After, you have the adventurous ways which often end not so cheap after number of modifications, and too often fails miserably. That's experimentation. That can be sometimes good, that can be often mediocre to bad but that needs always a good wallet even on beach catamarans.
I've a long experience of that with racing 18m2 catamarans. I do not complain as I got plenty of good results, including the experimentation of fat head or rectangular fully battened main sails in 1986 or 87. The true initiators of these sails were the sail board guys with the 10 m2 big sails for speed around maybe 1981 or a bit later if I remember well.