"Hoyt Balanced Rig"

[CapnK]

Interesting concept, makes a lot of sense. Just watched the video, time to ruminate for a bit... :)

http://www.garryhoyt.com/id32.html

I wonder how one heaves-to with this rig? Shortening sail (a *lot*) might work, but I'd hate to have the open end of that furled sail pointing into 50 knot winds... Maybe a 'storm mizzen' mast could be added... :)

[AdriftAtSea]

Of course, you need a free-standing maast to use one. :)

[Fortis]

Unless that flag is made out of some super space age ultralight fabric....it is blowing harder then three knots out there.
My boat behaves like thgat in five knots...though with more fiddling about due to the extra sail.

For all that. I really like this rig and would happily put one onto one of our dinghies (probably the herron) as an experiment.

Hmmm...I wonder what this does to the keel requirements...

What happens to get it to go dead down wind? Will the rig fly a spinnaker? Maybe a deck-rigged kite instead?

Interesting. Thanks for the link.



Alex.

[oded kishony]

<Maybe a deck-rigged kite instead? >

I've never seen one for a crusing sailboat. Are they available? What are the pros and cons?

Oded Kishony

[Fortis]

At the moment they are around two or three times the size of a good kite boarding kiteand provide only a little more pull. The reason is that they are made for stability and "set and forget" performance instead of bleeding-edge power and stunts. You sacrifice a bit to this end, but it seems well worth it.

The unit that one of the Sandringham boats uses has a launch sock that gets run up the mast and it then opens like a parachute from there. Hauling in is easy, as it stays aloft right up to the last moment as it is whisked onto the deck.

The main pros are that it takes way less attention then the spannaker, which is great for cruising, and it catches the air that is way way up above the mast top. air always moves faster the further from the surface you get...So if you are wallowing around in two knots of breeze at the midpoint of your mast...30 meters higher it is likely blowing around 10 knots pretty cheerfully...the kite lets you hook into that.

Final pro is that you do not have to do much to change course, the kite does a lot fo self adjusting and is very forgiving. At its worst, it will not haul your boat around to where you do not want to be or pull it over on its side in the death rolls....it will just collaps and fall into the water where you can retrieve it (hopefully).

Cons are cost, fiddling about repacking it and the fact that a sudden SEVERE gust of wind will send you back to complaining about the cost as you will be lookinbg to replace it.

Still, it is pretty damned cook to watch a hot placid afternoon, when all the other sail boats are bobbing about with the full sail gear just flopping around listlessly...And then Mokume cuts through them doing about 4 knots on the strength of the kite alone, which is up in whatever breeze is actually going on up there (you can get little remote sensors that live on the kite, apparently). 4 knots does not sound like much...but it beats zero knots by at least a factor of four!


Alex.

[oded kishony]

Thanks Alex!

I'm not a physicist nor do I claim expertise in sail technology but it seems to me that there are some obvious shorcomings to the Hoyt sails.

Personally I don't see the advantage to the offset mast, it still creates turbulance and drag.
What is the purpose of offsetting the mast?
The design doesn't seem suited for a stayed mast which limits it's size.
The design doesn't seem much different than a modified cat with a junk sail.
Am I just missing the boat here?

Oded Kishony

[Captain Smollett]

Personally I don't see the advantage to the offset mast, it still creates turbulance and drag.
What is the purpose of offsetting the mast?

The mast itself is not offset.  The sail is.

The most important part of the sail for drive upwind is the leading edge, and here we all put our mainsails behind that big turbulence producing stick.  So, what he's done is use a horizontal spar to move the sail over so that the leading edge is clear.

My personal opinion about this design is that it is (a) VERY interesting, (b) probably really cool for specific applications (small boats, protected water, etc) and (c) not general enough for 'cruising.'  I could be wrong on counts b and c....

I'm just having hard time seeing this work well/be safe (for the rig) in a seaway.  One thing that makes the mast a good trade-off of the efficiency loss is the strength it imparts up the entire sail.  His design has 100% of the weight of the sail+stays+gaff concentrated on that one little horizontal spar projecting out from the mast.  In my mind's eye, I'm seeing that little double-gooseneck as being a major weak point in any but the smallest of boats/mildest of conditions.

Weight aloft?  Isn't that a down side of gaff rigs?  And his weight aloft is off to one side, so it will have a different effect on different tacks.  It doesn't appear to allow lowering of the gaff (which would loosen the stays) like in a traditional gaff rig.

He mntioned as a downside the tip vortex of a triangular sail.  But, uh, the mast is still producing that drag, so we are not losing anything by using a triangular tipped sail.  I could be wrong, but I thought the push for more square-topped sails on racin' boats was increased sail area.

Looking forward to more trials, though.  My guess is this is the first step of an evolutionary process.  A GOOD first step.  Be interesting to see some real numbers on efficiency of the rig in different conditions - lift produced for the same hull normalized to sail area.

(By the way, is what he said true?  I was under the impression that breaking up the sailplan into more numerous smaller sails INCREASED efficiency...certainly helps with sail handling.  Are catboats really more efficient?)

What if he used that areodynamic sleeve around the mast, then simply set the sail abaft of that, but still hung on the mast?  In other words, smooth out the airflow before projecting it along the leading edge of the sail.  Could something like that be a happy middle ground?

[Bill NH]

The offset mast doesn't disrupt the laminar flow around the sail, which increases the sail's lift by reducing turbulence.  The mast still creates it's own vortices, thats what the tapered sleeve over it is designed to reduce.

I also noticed that the "gaff" can't be lowered, although it's probably alot lighter than the heavy wooden gaffs of yore...

The development of square-headed sails has been very much driven by fluid mechanics, not greater sail area... (if greater sail area was the driver, longer booms and shorter masts would do the trick with less heeling).  Reducing vortices at the end of the foil and making the orientation of the foil (curve) more vertical results in more forward driving force...  That's why the foil is always totally vertical on those experimental rigid sail craft...

I briefly owned a Freedom 25, an earlier "think-out-of-the-box" Gary Hoyt design that had a freestanding cat rig, rotating CF wingmast and a high aspect full batten mainsail.  Fast, very easy to sail -with some modifications the P.O. took it to Bermuda singlehanded.  Only problem was that like all wingmasts, the boat tended to sail itself even with no sail set.  One had to stall the mast when at anchor...  On later boats they simplified it to a round, non-rotating CF mast with the mainsail on a sleeve like you describe.  It was less efficient but less of a headache for the average boat-buyer...

I like Gary Hoyt's ability to get beyond the conventional... he has definately expand sailboat design thinking. Once when commenting on unstayed masts, he pointed out that planes used to have wire stays on the wings but modern design and materials eliminated them many years ago, and that there was no reason that we couldn't be doing the same thing with boats...  Makes sense!

[CapnK]

Re: kites - to me they make great sense as downwind propulsion systems, and if I can, I'll try one out on my boat eventually. Speaking of kites, one could be used with this rig, a small one flown from the stern, to heave-to, kinda sorta answering my own question. :)

Bill and Smollett are correct in their analyses regarding the effect of the spar on airflow, and the square-headed mains. Actually, yesterday morning before seeing this rig, I was at my brothers house, and picked up one of his flying magazines that had an article on how to reduce drag on an airplane. Part of the article was specifically about how much drag round things produce, and how much it saves to put a foil on them. The cumulative effect of all the round things on our boat poking up into the windstream produces enough drag that eliminating it would be something that would show an immediate benefit. And "poking up" means that the wind they poke into is *much* stronger - since windspeed increases exponentially with height.

So here's another million-dollar idea that someone can develop (and I only want a small percentage...) ;D :

Produce a small plastic extrusion, symmetrical-foil shaped (opening at the back end), that can snap over existing standing rigging, and which will pivot around said rigging freely when mounted. Sailors could buy a spool of it, cutting it to exact length for their own rig, and self-install in a matter of a couple hours. It would decrease drag, perhaps quiet the rigging down in a blow even. Racers would buy it up like crazy. It could be made cheaply, I bet, cheaply enough that it could be sold at affordable prices while still making a mint.

Last - regarding the upright spar - if they could sharply rake the spar but *not* necessarily the sail, I bet it would work even better. For example, a windsurfer: at low 'hull' speeds, regardless of the windspeed, the spar is vertical. As hull speed increases, the mast gets raked aft, and the pull of the sail on the spar (as propulsion) becomes a *push*, which is more efficient (which is why most of Bert Rutans airplane designs are pushers, not 'tractors' which have a pulling propeller).

Also, something that might factor for lightweight boats, is that a windsurfer rig when raked is producing a vertical component with it's lift, allowing it to come more up onto the surface of the water, and planing. While that is not possible with a keelboat, it still might have a small benefit, in that the effective weight of the boat would be lightened, allowing the hull to rise, making for less wetted surface. Most likely a neglible amount, but like the lightweight backpackers say: "if you watch just the ounces, the pounds will take care of themselves". :)

Food for thought and discussion. :)

[AdriftAtSea]

A Brit tried to do an Atlantic crossing west to east a few years ago in a Kite powered boat, and had to be rescued by the USCG not to far out there... Here's his website...

[Captain Smollett]

(if greater sail area was the driver, longer booms and shorter masts would do the trick with less heeling).

Okay, I hear ya, but...

Pointing ability favors larger aspect ratio - long leading edge, short foot, no?  So, if I'm understanding this correctly and we wanted to increase sail area AND maintain that long leading edge for pointing, the only way to do it is to square off the sail - blow out the roach near the top.

I'm Just thinking out loud as to why I would not want to add area by going to a small aspect rig, assuming my assumption is correct.

[CapnK]

Pointing ability is a function of the shape (depth/width) of the foil - not of the planform of the wing (the outside edge shape).

Ie; a long skinny wing (high aspect) with a given foil will stall (stop producing lift) at the same angle to apparent wind that a short stubby wing with the same foil would stall.

The main reason for the square-head on sails is to basically reduce (wing)tip vortices, from what I understand. Done properly and with a little twist-off up there, you'll have a foil throughout your sail shape that flattens as it gets to the top and has a lower angle of attack, which is a more appropriate foil config for the higher wind velocities up there, when compared to down lower on the sail.

[Captain Smollett]

Pointing ability is a function of the shape (depth/width) of the foil - not of the planform of the wing (the outside edge shape).

Do you have a citation for that?  I know I've read in multiple places (sail design books, sail aerodynamics web sites) the opposite - luff length matters.  Aspect ratio is not defined as Luff:Foot, but Luff^2/SailArea and from everything I've read, this design metric is paramount to upwind performance.

Offered only as the result of a quick Google search and not intended to be authoritative:

if you lengthen the boom and shorten the mast, to end up with the same mainsail area, the following happens:
- the aspect ratio of your mainsail planform is reduced a bit, which will only be detrimental to performance when you sail upwind.

From a discussion on BoatDesign.net

I wish I could find my sail design book...but I've misplaced it.

[CapnK]

OK, I see what you are thinking now. What I was referring to is that "pointing ability" is the ability of a sail to produce lift at a given angle to the true wind.

Look at foil shapes - slower plane foils are fatter (Piper Cub) and have a higher optimal angle of attack, than faster foils which are thinner (F-16) and have a lower AoA relative to angle of incidence: "the angle between the wing's chord and the longitudinal axis of an aircraft" (or boat in this case). Thus a thinner foil works at closer angles to true wind, ie; when pointing higher.

So I think that Angle of Incidence is what you meant when you were talking about "pointing ability".

I think the reason for a tall, skinny sailplan (or a glider wing, in case of an airplane) producing more lift is that for a given area of sail, more of that area is cambered towards it's leading edge, and producing lift.

[Oldrig]

I'm really intrigued by this video--thanks for posting it.

I've spent many years sailing one-sailed boats, and like Gary Hoyt, I've spent many wonderful hours on a Marshall catboat.

While I can't really add to the technical discussion, this looks like it should work. (Interestingly enough, his sketches show a catboat hull, and this sail would surely eliminate the scariest part of catboat sailing: downwind.)

I'd love to see one of these up close.

My biggest aesthetic objection would be the way the sail operates off the center line, but Hoyt's examples seem to verify that it's possible to sail quickly and efficiently without worrying about centerlines.

--Joe

[Captain Smollett]

Yeah, I was thinking in terms of a specific speed at a stated angle of incidence rather than stall angle.  The taller rig (normalized for sail area) will generate more lift at a given hull-to-true wind angle.  Right?  We on the same page?

I'm wondering if it is because of "more camber" or if it is because you have more surface area producing lift.  Upwind, lift is produced in the first bit of sail.  If you consider a strip of sail, let's say 10% of chord length back from the luff and calculate the area, the tall sail will have a much higher area represented by this strip than a low sail, of same TOTAL area.

In other words, I *THINK* that if you set up 'wings' with the same parametric camber in that critical strip, ie the same shape sail, and the same total area, but they differ only in aspect ratio, the taller sail wins in terms of lift production, simply because that critical strip is larger.  Upwind, the lower aspect sail has more wasted sail area.

Boundary layer effects are a whole other discussion, of course, which I *think* would again favor the taller rig, which you mentioned before.

[Bill NH]

A good analogy to what happens at the head of a sail is what happens down at the keel.  When sailing upwind, your keel is actually moving through the water at a slight angle, not slicing straight through (due to your leeway).  This creates high pressure on the lee side of the keel and a lower pressure on the windward side.  This is what gives a keel its lift.  However, a fluid will flow from high to low pressure, and the water does this by "sneaking" around the bottom of the keel, creating vortices and reducing some of this lift-producing pressure differential.  This phenomenon is exactly what the Aussies designed the wing keel to prevent...

This same "wrapping around" of vortices happens at the head of the sail as well, and research has shown that the fathead sail will have smaller losses than a triangular shaped sail.

I don't know a whole lot about planes, but haven't I seen planes with "winglets" (for lack of the correct term) at the wingtips that do the same thing as a winged keel?  Or are they for something else?

[macdiver]

What if he used that areodynamic sleeve around the mast, then simply set the sail abaft of that, but still hung on the mast?  In other words, smooth out the airflow before projecting it along the leading edge of the sail.  Could something like that be a happy middle ground?

James Wharram and Hanneke Boon have done this for their catamarans.  They call it a Tiki wing sail or just the wing sail.  It first appeared on the Tiki 21 in the early 80's.  There is information about this sail on Wharram's website.  Also the multihull forum has information about it.  From what I can tell from reading the available information is that it is a good performer at a low cost.  Wharram's implementation does not have a boom.  The sail fabric wraps around the mast.  Halyards run up the mast sleeve to the gaff. 

Since this sail has been around for a while, my guess is that it does not offer extreme performance or it would have been adapted by the racers.