Code Zero Sails, aerodynamic questions

[sharpii2]

When I look at a big lapping Genoa, I see a large, Low Aspect Ratio (LAR) sail.

I imagine a large, LAR, Bermuda or Boom Lateen sail would have similar virtues and vices. Very few sailing work boats had high aspect ratio sails. And those tended ones used in areas with a lot of wind blockage, such as high river banks.

My understanding is that LAR foils are far less likely stall when the angle of attack abruptly changes. Such changes can be brought about by wind shifts, change in boat speed, and pitching. The last two mentioned are changes of angle of attack due to changes in apparent wind direction.

 

[CT249]

If fractional jibs are all so superior I wonder why these guys are flying an overlapping sail
View attachment 100514


Because a fractional jib can be an overlapping sail.


...or the new foiling Gunboat G4
http://www.boatdesign.net/forums/multihulls/gunboat-g4-uptip-foils-50397.html
View attachment 100515
View attachment 100516


https://vimeo.com/125378004

Interesting that its the mainsail that can't be released fast enough to prevent the capsize of that new Gunboat,...but the code/genoa gets released in plenty of time.
http://www.boatdesign.net/forums/multihulls/gunboat-g4-uptip-foils-50397-7.html#post733502

I thought that is just not suppose to be....those big, bad, genoas are just going to capture the wind and cause the capsize.

I would enter another alternative theory here,...its more difficult to get a sail to spill the wind that is restrained by a multiple-part tackle than a sail that is being controlled by a single sheet line,...a genoa sheet vs the multi-purchase gear utilized on most mainsails.

Those guys are using large overlapping headsails when and where that's the best thing to do for them. Other sailors do NOT use large overlapping headsails when and where they are not the best thing.

Yes, if you are sailing a boat without sail area restrictions, with an enormous budget and mainly for long races, it's logical to use an overlapping fractional headsail a lot of the time, and an overlapping masthead headsail some of the time. Yes, if you are going downwind like the Gunboat in the picture, it's logical to use a larger headsail.

No one ever said that in those situations, a large masthead or fractional overlapping headsail is not faster. We all know it's faster and the reasons are pretty simple - bigger is faster most of the time. But the fact that in some situations big headsails are faster does not mean that big headsails are always better or always faster, so many people prefer smaller headsails that are more easily handled.

Back in the '80s I raced a couple of times with Andrew Buckland, the main creator of the modern assymetric spinnaker and a multiple "world" 18 Foot Skiff champ, on a mono with a roller-furling masthead genoa that set over the normal fractional headsail. The people who owned and sailed that design later dumped the masthead genny because for normal harbour racing it was a complete pain to deal with, and for offshore racing it wasn't really worth the expense and complication. It was a classic example of an idea that works well for oceanic racing on a maxi multi, but which does not work for shorter courses.

Out of interest, have you sailed keelboats with the modern short overlap headsail rig much? And have you been lucky enough to have the experience of sailing the same boats with 150% overlapping headsail rigs, and then after they have been modified to take short overlaps?

With respect to the G4 capsize - can we ask who said "those big bad genoas will catch the wind and cause the capsize"? Even if the headsail was easier to dump in that instance (and that's unproven AFAIK), so what? It's one boat in one situation. When we're racing our fast cat we dump the jib first downwind for good reasons, when we're racing a medium-speed dinghy we dump the main first for good reasons, when you race a skiff you dump the kite first for good reasons. The fact that one boat uses a particular technique doesn't mean it's better overall.

 

[gggGuest]

My understanding is that LAR foils are far less likely stall when the angle of attack abruptly changes. Such changes can be brought about by wind shifts, change in boat speed, and pitching.

Not to mention simple wind speed changes... Yeah, horses for courses again. A big twisty low aspect ratio gaff sail is pretty hideously inefficient in terms of power per square foot compared to a high aspect ratio modern rig. But if you want to belay the sheets and troll along steadily while the crew is handling the fishing gear then that's a damn sight better than a rig which requires two crew to do nothing but constantly trim the sheets and which acts and responds instantaneously to the slightest change.

 

[brian eiland]

... Yes, if you are going downwind like the Gunboat in the picture, it's logical to use a larger headsail.

No one ever said that in those situations, a large masthead or fractional overlapping headsail is not faster. We all know it's faster and the reasons are pretty simple - bigger is faster most of the time. But the fact that in some situations big headsails are faster does not mean that big headsails are always better or always faster, so many people prefer smaller headsails that are more easily handled.

The points I was trying to make for my aft-mast rig with its big genoa is that I was trying to meet a big variety of conditions with a limited sail inventory (my 3 sails are the only ones I have onboard, and are set up to be reduced in size by roller furling, not hoisted or replaced by alternatives).

As such I wanted a good size genoa sail for those often encounter 5-15 knot winds that we would really like to sail in rather than turning on the engine(s). This size sail, in those conditions, should be relatively easy to handle, ...(and when out cruising I would NOT be looking at getting into tacking duals). I was seeking to get the best from this genoa sail by giving it the best help from the 'cutter jib' (mainstaysail as I refer to it), and providing for its best dumping traits as described by Tom.

I'm also quite convinced that modern sail materials such as the tape-drives or these Titanium sails would allow for a very light weight sail that would maintain their shape even in higher wind conditions. These materials should also allow for sailing under a partially furled sail. As I have said before I believe a hefty size ROUND furling 'tube' (headstay) should utilized to negate some difficulties of stalling the sail due to a 'too-sharp' leading edge to the headsails. Combine this type of headstay foil with a modern 'shaped foam insert' in the leading edge, and this sail should set pretty well in the roller-reefed condition. It would be nice to be able to utilize this reef-able genoa up to the 30 knot range.

For storm conditions that we see coming we slip another sail over that furling genoa:
Storm Sail Configurations

With respect to the G4 capsize - can we ask who said 'those big bad genoas will catch the wind and cause the capsize'? Even if the headsail was easier to dump in that instance (and that's unproven AFAIK), so what? It's one boat in one situation. When we're racing our fast cat we dump the jib first downwind for good reasons, when we're racing a medium-speed dinghy we dump the main first for good reasons, when you race a skiff you dump the kite first for good reasons. The fact that one boat uses a particular technique doesn't mean it's better overall.

Sorry I should not have put that 'big bad genoa thing' in quotes, ...nobody said that specifically. But several have posted messages about the lack of a genoa's capability to deal with gust response, ..on this page http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-40.html

To top it all off a stayed sail has the wrong dynamic response to gusts. Once a boat is sailing at its design speed we call it powered up. More wind does not make the boat go much faster, it just heels a mono, or drives the lee bow down on a multi. This is where the sails need to be de-powered. This usually means making the sails flatter (reducing camber) to control heel and keep the boat on her lines. When a gust hits a stayed sail the load on the sail go up. Something has to give. The stay stretches - adding MORE camber and power just when you need LESS camber and power. This requires you to ease a sheet or make some other trim adjustment to keep the boat on her lines. A sail set on a flexible mast can be designed to have the correct response. A gust hits, the loads go up, the top of the mast bends and flattens the sail below the hounds and opens the leech above the hounds ... drive is maintained and the boat does not heel past her sailing lines.

I can't find the other similar postings that all criticized the lousy capabilities of the tops of these headsails to deal with gust, but there were some number of them.

That prompted me to bring up the fact that the Gunboat G4 was able to release the pressure on their code zero/genoa so easily, while not being able to fully release their square-top mainsail's contribution to the flip. I imagine there are some number of other cases of multihull capsizes that might have been prevented had the vessel had a masthead staysail in lieu of a tall unreefed mainsail.

Watch that video one more time, then tell which sail contributed the most to that capsize?
https://vimeo.com/125378004

 

[powerabout]

you cant point with a overlapping genoa or a code zero so you wont see them on around the cans racing.

 

[powerabout]

main on the g4 is hydraulic and the plumbing was so small it released very slowly
code zero was on a winch

 

[brian eiland]

you cant point with a overlapping genoa or a code zero so you wont see them on around the cans racing.

Likely true for the code zero, but not necessarily for the genoa.

BTW, I'm not looking to do cans racing, been there, done that when I was younger.
I'm looking at cruising rigs that can also SAIL in lt-airs rather than turning on the iron sail.

The points I was trying to make for my aft-mast rig with its big genoa is that I was trying to meet a big variety of conditions with a limited sail inventory (my 3 sails are the only ones I have onboard, and are set up to be reduced in size by roller furling, not hoisted or replaced by alternatives).

As such I wanted a good size genoa sail for those often encounter 5-15 knot winds that we would really like to sail in rather than turning on the engine(s). This size sail, in those conditions, should be relatively easy to handle, ...(and when out cruising I would NOT be looking at getting into tacking duals). I was seeking to get the best from this genoa sail by giving it the best help from the 'cutter jib' (mainstaysail as I refer to it), and providing for its best dumping traits as described by Tom.

I'm also quite convinced that modern sail materials such as the tape-drives or these Titanium sails would allow for a very light weight sail that would maintain their shape even in higher wind conditions. These materials should also allow for sailing under a partially furled sail. As I have said before I believe a hefty size ROUND furling 'tube' (headstay) should utilized to negate some difficulties of stalling the sail due to a 'too-sharp' leading edge to the headsails. Combine this type of headstay foil with a modern 'shaped foam insert' in the leading edge, and this sail should set pretty well in the roller-reefed condition. It would be nice to be able to utilize this reef-able genoa up to the 30 knot range.

For storm conditions that we see coming we slip another sail over that furling genoa

 

[powerabout]

code zero great for light air but you need to be a few degrees off and the more wind the further off
The old mast head big overlapping genoas are good in light air on a cruiser no doubt.
from the days of giant genoa and small main, now its the reverse

 

[brian eiland]

Overlap Genoa Size on my Aftmast Rig

Somewhat surprisingly I never did bother to calculate the overlap % of my genoa on the aftmast rig I proposed. I just did it by dropping a straight line down from the masthead in my drawing, then measuring that "J' dimension, then divided that length into the luff perpendicular (LP),....standard method.

Guess what I came up with?.....slightly less than 104%.
Surprised even me, as I had just guesstimated it at 110-115% for years.

 

[brian eiland]

Double Headsails on America’s Cup Catamarans

I was recently sent a link to a NY paper with lots of photos of the recent trails held up there in preparation for selecting teams to challenge for the next America’s Cup. What struck me so vividly was the number of these photos that had these hi-tech machines sailing with double headsails,….in fact double headsails set on two parallel headstays.
http://www.nydailynews.com/new-york/iconic-america-cup-sailing-competition-new-york-city-gallery-1.2629557?pmSlide=1.2629540

To bad I could not make a few copies of these photos and post them here, as I have found in the past that links to newspaper articles soon fade away and can no longer be accessed.

I then sought out some videos of this racing action, and found these vessels to be quite adapt at utilizing their two headsails on and off during the racing, and mostly in a roller furling manner.
And using that dbl arrangement more often !
https://www.youtube.com/watch?v=5C2whBVxQEE
https://www.youtube.com/watch?v=Mp574MSXkao
https://www.youtube.com/watch?v=_4QyKx8eMj0
http://www.boatdesign.net/forums/multihulls/35th-americas-cup-foiling-multihulls-48428-18.html


Now you might ask, ‘why was I so surprised’?? Well you see I’ve been touting this double headsail arrangement for a LONG time, and in opposition to many nay-sayers, who go as far as to denounce most headsails as secondary items,…secondary status. :?:

 

[CT249]

Aren't they just the Code Zeros? No one's ever said that if you can get 'free' area or extra area, you won't use it at times - especially if you have essentially unlimited funds, enormous crew expertise, and a professional pit crew. We also know that the AC boats sometimes go faster without a jib.

The fact that AC guys (like IOR guys, Metre boat guys, CCA guys, Volvo guys, shorthanded guys etc) use multiple headsails and big headsails sometimes is surely all the evidence that anyone needs to prove that there is little if any unreasonable "denouncing" of headsails. Everyone knows there is a time and place for multiple headsails and big headsails. The issue is how they fit into a particular time and place.

 

[CT249]

By the way, I just found this old pic of a mast-aft concept. The pic is from the Australian National Maritime Museum, the boat is on Sydney Harbour, but no other details are available and I can't recall reading about the boat.
https://www.flickr.com/photos/anmm_thecommons/8570700962/

 

[brian eiland]

Can't quite tell where the mast is on that photo?

 

[Stumble]

CT,

Yes the AC45's are using very small jibs with Code zero's. They are also pretty much one design, the current rules have basically eliminated any changes to the rig or sails, since for this evolution at least there simply isn't much gain to be made there. The OD rig means more development money is getting poured into foils, where the real gains (at least for now) are, and everyone gets to save money.

Brian,

Everyone accepts that a big headsail is fast downwind, but upwind it can hurt vmg. If you are looking for more examples of this strategy take a look at the TP-52's, the big Maxie's, heck even fast dingys. The faster the boat is down wind the bigger the main tends to become, the smaller the jibs, and the tighter luff the asymmetric spinnakers are.

 

[brian eiland]

....
The faster the boat is down wind the bigger the main tends to become, the smaller the jibs, and the tighter luff the asymmetric spinnakers are.

:?: Did you post this correctly?