The case for fully automated sailing rigs

Jib Boom
StaySail Boom
MainSail Boom

I am a firm supporter of the Boom, in fact my design has three booms, so I cannot be accused of animosity towards the boom.

 

Is this from your video game knowledge?

 

Have you now changed your mind about booms? A rough drawing of a rectangle is not a design.

 

You have not demonstrated anything, because headsails and mainsails have different geometry and tasks.

How many boomless-main boats have you sailed or owned? When one has sailed boomless-main boats and owns one in which the boom is an option, it really drives home how well booms work.

1- a boom dramatically reduces mainsheet loads. The vang /traveller take most of the vertical load while the boom itself takes the horizontal compression load. The dramatically reduced mainsheet load allows one to play a mainsail without using a winch in many boats, despite the fact that mains are often much bigger than headsails.

2- a boom ensures that when the mainsail is eased in a gust or reach the whole sail swings outboard while staying flat due to the boom taking the horizontal compression. When the sheet of a boomless main is eased, the sail becomes very deep. This means that it doesn't depower properly in a gust. The clew section of the sail curves back towards the mainsheet's lower securing point and this extremely hooked clew section can create major weather helm problems.

3- with lazyjacks and a stack pack, the boom becomes an excellent way to store a mainsail;

4- the boom offers an excellent way to separate twist, outhaul tension/lower draft, and sheeting angle. This allows competent sailors to optimise sail shape.

5- since heel causes a change in the immersed hull shape and the pressure shifts outboard, most boats generate weather helm when heeled. This makes easing or depowering the mainsail, rather than the jib, the optimum way to react. Therefore the mainsail has a different job to the jib - it is more important that the mainsail can be easily depowered by both shape and angle of attack than the jib.

6- to say that the mainsheet can go to outriggers downwind is to ignore the significant problems with doing that. First, you have to shift the sheeting point from inboard to outboard and vice versa, which is problematic (ie do you have the complication of multiple sheets, or what?). Second, the outriggers themselves are difficult to build strongly. Thirdly, they interfere with coming alongside. Fourthly, they can drag in the water when heeled badly unless they angle up so highly that they permit excessive mainsail twist.

There's nothing wrong with boomed jibs. I've sailed with a few of them - have you? However, they come with their own problems;

1- they are heavily loaded with vertical forces when sheets are eased, which means that they must be strong and therefore heavy. A wishbone takes care of some of that but enforces point loads at the forward end, which are problematic (I've tried);

2- they take up a lot of space. So does a main boom, but the main boom is in a much wider area of the boat;

3- they prevent the headsail from overlapping, which is a very efficient way of gaining area;

4- the fact that they hold the jib out is much less important in reality than in theory (as proven in racing classes) because when running deep the standard jib is collapsed because it is blanketed by the mainsail. Holding the jib out with a boom doesn't improve the airflow in that area and therefore doesn't dramatically increase the jib's power. This is the proven reality.

This is one of the many areas in which it is extremely arrogant to ignore the enormous accumulated wisdom of people who have done much more designing and sailing than one has personally. One can either learn from others, which allows us to gain an enormous amount of knowledge, or sneer at them and remain closed-minded and learn nothing.

Sure, not every boat needs a boom and some sailors choose not to have one. However, picking out an isolated case where a particular boat or person chooses a different design does not mean that design is the optimum one and that everyone else is wrong.

Is that why you cannot see that the stern on this double ended canoe yawl;



is NOT an "imitation" of the stern on this highly competitive racing boat, like you said it was?

 

This thread is going to still pop up for people interested in the idea of the original post.

Chris White's "MastFoil" rig seems relevant to the original post, and where the discussion went, in the current state of technology and design thinking.
(Increased automation. Easy to control. Effective for propulsion, relatively, both downwind and upwind. Design concern given to the loads on the parts.)
[Relatively, and/or at least as claimed, by a source with a good reputation.]

Hyperlink: Chris White Designs MastFoil discussion

Quote from Chris White about his design which speaks to the themes of this thread:
Why do you think this is such a big deal?
-The MastFoil rig solves many sail handling problems faced by cruising sailors. Because its so easy to reef and un-reef, cruising sailors will be more likely to do so frequently rather than toughing out a squall or waiting for the lull to pass. And being able to easily carry the appropriate amount of sail has obvious safety and performance advantages. Cruisers, even when sailing shorthanded, have the chance for higher daily average speeds, and greater comfort and safety.
-When struck by a violent wind gust, whether from a squall or topography, the MastFoil rig can be quickly and completely depowered by easing the sheets. There is nothing in the way to prevent the sails and foils from luffing, even when deep reaching. Try reefing or even dropping a conventional mainsail with 50 kts of wind behind the beam. It can't be done, at least not quickly. That is not particularly safe and has contributed to numerous sailing accidents.
-In strong weather the foils provide most or all of the necessary drive and they do it so easily. There are extremely low heeling forces, extremely low loads on the "sheet" and low loads in the mast when the fabric sails are furled.
-The foils can be gybed conventionally which is quick and easy, and they can also be gybed around the front of the mast, which in severe conditions will eliminate a lot of stress, both mental and physical.

 

It's interesting and would be easy to handle, but to counterbalance the sales talk from the website there's several issues. Please note that I'm not claiming to be an expert and not saying the rig is no good; I'm just discussing design which is what the forum is for.

1- Actual area is intrinsically low for a given boat length. That probably doesn't matter much in the nice, light and long Chris White multis which would generate lots of apparent wind but it would in other craft.

2- Aspect ratio of the rig is low, which impairs upwind performance compared to a sloop, for example.

3- Accepting the probable loss of performance is fine, but it does mean that the Mastfoil has to be compared to other rigs that also accept a loss of performance. Chris criticises the handling issues of normal roachy mains on sloop rigs - but if one is prepared to accept a loss of performance to go for an easily-handled Mastfoil cat ketch, then one could also accept a loss of performance and go for an easily-handled version of the standard sloop rig - perhaps a "pinhead" main which would alleviate some of the problems Chris mentions.

4- Chris' claim that "sailing upwind, the mast - at the aerodynamically critical leading edge of the mainsail - robs a great deal of its power" just doesn't stand up to modern aerodynamics. Many of us are primed to believe that masts cause drag because of old sources like Marchaj, but his "tests" are arguably bad science because they used ludicrously over-sized masts of poor section.

For example, years ago on this forum where was a conversation between sailmaker Mikko Brummer, who does interesting CFD work, and the late, great Tom Speer, designer of Boeing wings and America's Cup wingmast sections. Mikko noted that "the mast is not just a drag-device but contributes significantly to the driving force of the sails. In a recent CFD study on Star sails, the mainsail drive was 10,2 kgf, jib drive 6,7 kgf and the mast drive 1,2 kgf (that's in the positive, forward direction for the mast as well)."

Tom agreed and noted "The leading edge suction on the mast is a significant contributor to the drive of the whole sail rig."
Another poster here brought up a quote from Prof Jerry Milgram, who said"significant amounts of lift are developed by the mast, which is probably why big old fat IOR masts are never quite as bad as we expect them to be"

I found this very interesting because we have seen in real life, time and time again, that designs intended to cut down the alleged massive drag of a mast did not work like theory says they should. I have five wingmasts and a bunch of other aerodynamic mast fairing devices, and they do NOT have the dramatic effects that olde-school theory says. So we can bin Chris White's claim that conventional mains lose a great deal of their power because of the mast. It's wrong.

There's a pretty obvious contradiction between Chris' claim that the mast robs the mainsail of power and his failure to acknowledge that a furled jib also has a dirty big cylinder at its leading edge.

6- Chris' claim that "the large roach area of the (conventional cat mainsail) contributes to significant weather helm which slows the boat and can make steering more difficult" appears to be a bit odd - it's only a major problem if the designer stuffed up the CLR calculations, which is hardly a fair basis to criticise a rig in general.

7- Despite the remarks I quoted above, Tom Speer thought the Mastfoil idea was good. However Tom also found some of Chris' claims to be dubious; edited here for brevity with Chris' claims of the time in blue.

"I think the concept has a lot of merit. However, some of the statements on his website are rather doubtful, to say the least. Among them are:

"The MastFoil never stalls." - Any wing will stall at a high angle of attack.....

"Pinned to the dock by a 30 knot wind on the beam? We think that by trimming the MastFoils opposite each other that enough sideways lift can be created to actually pull the boat away from the dock!" - This is rubbish.....

"If you are running off in a storm the MastFoil can function as a "air drogue" by providing stern-ward thrust to offset the windage of the hulls and deckhouse." -..... "it's true that the wings could slow the boat for a range of offwind angles. But it's more akin to sailing backwards than it is to deploying a drogue. There will be a heeling moment associated with it, and it won't work when sailing very deep.

As for the behavior of the wing in a storm, just because the wing's aerodynamic center is behind the pivot axis doesn't mean that it will weather vane to zero lift or to minimum drag......Dynamically, the mastfoil needs to have its pivot axis at or ahead of the quarter chord for static aerodynamic stability, and it needs to have its center of mass on or ahead of the pivot axis for dynamic stability. If the first condition isn't met, the mast won't try to weathervane, and if the second condition isn't met, the mast may flutter or be swung about in a seaway. Either outcome could result in more windage than a conventional mast, to say nothing of the violence a fluttering mast can do. It's not clear from the illustrations how these considerations are being handled.

Even if the wings are aerodynamically stable and mass balanced, the dynamic response of the wings to rapid gusts in a gale needs to be carefully considered. ..... the dynamic behavior would have a low natural frequency and be lightly damped. The wing may be slow to respond to a sudden gust and tend to overshoot and oscillate. If it is out of phase with shifty gusts, the lift and drag on the wing can be enhanced, not neutralized. The wing would be trying to weathervane, but it may be constantly playing catch-up instead of maintaining the zero angle of attack envisaged."

This is all speculation on my part, and I don't mean in any way to disparage the Wingfoil concept. I have a lot of respect for Chris White's designs (after all, my own boat is a Chris White designed trimaran). I just wonder to what extent these considerations have been engineered into the design."

Tom also noted wind shear means that even a feathered wingmast can be creating heeling moment.

8 - From cruiserforum;

"A close friend of mine was aboard for the delivery of hull #3 (I believe) from the plant in Chile thru the Panama Canal to S.E. Virginia......The more important problem developed later when the boat lost a mast while sitting in its slip at our yacht club. Because of the rotating foil design, the mast is supported at the bottom and top only, with no rigging support anywhere else. One day a moderate squall blew thru and the wind velocity was just right to start the front mast pumping a bit, which quickly developed into a harmonic and it caused the mast to buckle in the middle and collapse forward over the front beam. Of course this caused a good bit of concern in the Chris White organization. The exact same thing happened a second time later when the boat was on the hard for winter storage.
I believe the “fix” for the failures was beefing up the section of the mast for stiffness and perhaps also shortening the mast a bit in future production. As I understand it, the same failure also occurred on at least one other vessel."

9 - Personally I've noticed how even small section wingmasts seem to be more of a hassle to step because of their windage, and when windsurfing and luffing a "wing-style" rig one really notices how real-world turbulent flow increases their drag when feathered compared to the way they work in a wind tunnel's steady flow.

As noted, this is NOT decrying the mastfoil, just discussing it and in particular, bringing up the thoughts of an expert and highlighting that the claims about masts harming mainsail aerodynamics are incorrect.