Best rig for small catamaran circumnavigator?

[RHough]

Originally Posted by BigCat

Despite all of the nonsense through the years about the slot effect, fewer sails is for the best from an efficiency standpoint. The slot effect merely reduces the inefficiency of having two sails working together, it doesn't make them more efficient than one sail with the same CE as the two working together.

This is either gospel truth or pure horseshit, depending on your definition of efficient.

Is lift per unit area the goal or high L/D ratio?

[Alan M.]

Originally Posted by BigCat

Despite all of the nonsense through the years about the slot effect, fewer sails is for the best from an efficiency standpoint. The slot effect merely reduces the inefficiency of having two sails working together, it doesn't make them more efficient than one sail with the same CE as the two working together.

So why do they use leading edge slots, and slotted flaps on aircraft during takeoff and landing? Wouldn't they simply extend the wing area without opening slots, if this were more efficient?

[brian eiland]

Originally Posted by rob denney

As I said, I am not "disputing" the existence of the slot effect, just the basis on which you supported it in this thread

I supported it with a reference to Marchaj's book. Are you disputing this book?

Then how about these references that won't involved you having to go read a book:
Technical Papers by Arvel Gentry
http://www.arvelgentry.com/techs.htm

The Aerodynamics of Sail Interaction
http://www.arvelgentry.com/techs/The%20
Aerodynamics%20of%20Sail%20Interaction.pdf

How do Sails Work
http://onedesign.com/articles/article6-1.html
________________________________________________


On a similar subject, I had submitted this quote, This is another of those axioms that the textbooks have got wrong and have taught us wrong for so many years. But as Tom Speer* noted, “there’s no way to finally put a stake through the heart of that old explanation—it just keeps coming back to life”.

The subject I speak of here is that old description of how an airfoil develops lift. It's another of those descriptions that many just continue to get wrong....but those old explanations just won't go away.

How Airplanes Fly
http://www.allstar.fiu.edu/AERO/airflylvl3.htm
Almost everyone today has flown in an airplane. Many ask the simple question "what makes an airplane fly"? The answer one frequently gets is misleading and often just plain wrong. We hope that the answers provided here will clarify many misconceptions about lift and that you will adopt our explanation when explaining lift to others. We are going to show you that lift is easier to understand if one starts with Newton rather than Bernoulli. We will also show you that the popular explanation that most of us were taught is misleading at best and that lift is due to the wing diverting air down.

[RHough]

Originally Posted by brian eiland

I supported it with a reference to Marchaj's book. Are you disputing this book?

Fact: The air "sees" the sailplan as a single unit.
Fact: Total lift force is a function of angle of attack.

The idea that that the Genoa or Jib provides a greater percentage of the lift than the main is a misunderstanding. If you look at the pressure distribution of the Genoa and the Main and the two combined you will find that the pressure differential is higher on the forward portion of each. The front 1/2 of each sail 'does more work' than the aft 1/2. Since the air 'sees' the two sails as a unit (single flow pattern around the combination), the forward part does more work ... leading to the assumption that the Genoa is a better left producer than the main.

The air 'in the slot' is not accelerated, it is slowed. Placing the mast in this area of reduced velocity can mitigate the drag caused by the mast and reduce it to a value less than one would think it would have in free stream.

The reason that soft sail rigs of Genoa and Main can produce higher lift, is because they can operate at a higher angle of attack without stalling. A hard sail of equal area as the Genoa/Main combination that could operate at the same angle of attack would produce the same lift. This would require a highly cambered wing. Slots and separate flaps on aircraft serve to create such an airfoil.

On sailing craft the lift requirement changes. The sails do not operate at their maximum lift above the design point windspeed. Below the design point the boat can use more power than the rig can provide, above the design point the sails can produce more lift/power than the boat can use. Once this point is reached, drag reduction through reduced camber is the trim goal, there is more than enough power available.

It is possible to size a rig that fully powers the boat in 10 knots apparent wind, it is also possible to design a boat that sails at a multiple of wind speed. A 2X windspeed boat would be fully powered in very light air. Above that very low wind speed, drag reduction becomes the primary goal and single element rigs and hard sails have higher L/D than the Genoa/Main combination.

The problem that most designs face is that a practical rig is not big enough to fully power the boat at less than maximum lift in lighter air. This makes the multi-element rig a winner since it can operate at angles of attack higher than any single element rig that I know of. If you can cram on enough area to power the boat in 6-8 knots of breeze, it would be a better solution than increasing the number of sails.

IMO a good choice for a rig is a full batten main set on a rotating mast with a fractional jib. Off wind sails can be masthead. The jib can be self-tacking, the main/mast combination can be tuned to have correct gust response. If the jib is roller furling, the only issue is how to fly storm canvas. A storm tri-sail track on the mast allows the main to come down, but a provision for a storm jib must be made. For a small boat, a wire luff storm jib with a hoist point at the head of the storm tri-sail might be a viable solution. Larger boats should probably have an inner forestay with the hounds at the tri-sail head so the sheet load and inner stay to not act to take the mast out of column.

[rob denney]

[quote=brian eiland;212961]I supported it with a reference to Marchaj's book. Are you disputing this book?

Then how about these references that won't involved you having to go read a book:
Technical Papers by Arvel Gentry
http://www.arvelgentry.com/techs.htm

The Aerodynamics of Sail Interaction
http://www.arvelgentry.com/techs/The%20
Aerodynamics%20of%20Sail%20Interaction.pdf

How do Sails Work
http://onedesign.com/articles/article6-1.html

G'day,
Am I disputing Marchaj's, Gentry's and North's explanations? No.
Am I disputing whether those references are the complete picture? Absolutely.

None of them makes any mention of, nor allowance for, all the additional weight and windage required to make a sloop rig work the way they say it should. Nor for the reality that sails stretch, wind strength varies, cruising crews are not constantly trimming and few, if any, sails are perfect straight from the loft.

The complexity and loads required to set up a of a sloop rig make these factors much more critical than for an unstayed, wing masted mainsail only rig.

To quote all your sources as proof that the slot effect exists is valid. To blithely jump from there to a slotted rig is superior is totally unjustified without taking into account the cost of achieving it.

Funny how the availability of time and inclination to discuss things varies, isn't it?

Regards,

Rob

[Richard Woods]

Years ago I spent several evenings at Tony Marchaj's house talking about boats and design. (read the frontpiece to his first book and you'll see how I knew him)

He told me that the most "efficient" rig was a single solid wing. Closely followed by an big mainsail/small jib combination.

However this thread is all about rigs for small ocean cruisers. So in practise that means a single mast. It also means a roller reefing headsail (to keep sail locker space to a minimum). Plus the fact that probably the interior layout will influence the choice of rig more than it should.

Lets get back on topic, or start a new one called "Unusual Rigs"

Richard Woods of Woods Designs

www.sailingcatamarans.com

[rob denney]

Originally Posted by Richard Woods

Years ago I spent several evenings at Tony Marchaj's house talking about boats and design. (read the frontpiece to his first book and you'll see how I knew him)

He told me that the most "efficient" rig was a single solid wing. Closely followed by an big mainsail/small jib combination.

However this thread is all about rigs for small ocean cruisers. So in practise that means a single mast. It also means a roller reefing headsail (to keep sail locker space to a minimum). Plus the fact that probably the interior layout will influence the choice of rig more than it should.

Lets get back on topic, or start a new one called "Unusual Rigs"

Richard Woods of Woods Designs

www.sailingcatamarans.com

G'day,

Sorry about the diversion. Back on topic.

Why so adamant about a single mast and roller furling jib for a small ocean cruising cat?

regards,

Rob

[Bruce Woods]

Originally Posted by rob denney

G'day,

Sorry about the diversion. Back on topic.

Why so adamant about a single mast and roller furling jib for a small ocean cruising cat?

regards,

Rob

From personal experience its so easy to cruise with. Stow the main when the wind goes aft of the beam (cruising), and you now have a rig that is instantly reef-able to any size with the C of E right up near the bow where you want it. One seems to spend most of ones time trying to slow a cruising cat down to a comfortable speed and the roller furling head-sail makes that task so easy. You are more likely to have the correct amount of sail up for the conditions if you can adjust it so easily with a roller furler system hence better passage times. Tacking a cat with head-sail assistance is also easier in the sloppy stuff. Pretty much an impossible maneuver to accomplish with main only on a vessel with such high wind-age and inability to carry much way through a tack. In the rough stuff I can ballance my cruising cat with the two sails and lash the helm slightly to lee and the whole shooting match will self steer to windward all day long. Try doing that with main only.

Regards

[sandy daugherty]

Rob: I love your work, an hope to see one of your masterpieces here on the Chesapeake one day. However:
Skene, Marchaj, North, Wallace Ross, and others did consider, and test with masts, shrouds, sheets and other itty bits, as well as with pure forms. As well, they calculated scale error for air density, motion in a seaway, and other conditions in several of their studies.
Further, sail combinations continue to be studied at the Naval Academy as part of several undergraduate engineering courses.
Moral: Slot effect is real. Slot effect is good. Slot effect is real good. Good enough to make up for all the twitchy complications. Thus sang the fat lady.

I move the original question: What would you suggest someone in Manila could build out of plywood for long distance, non-heroic cruising. Assume pylwood is cheap, glass is expensive, aluminum extrusions have to be imported, hardwood is rare, labor is cheap, but temperatures and humidity are high. Scrounging a mast is probably not likely, and stainless rigging is so expensive it must be limited to the absolute minimum.

Could he really build a wing mast?

Is a Wharram his only choice?

[Richard Woods]

Why not try my 34ft Romany?? designed for comfortable ocean cruising. Safe, fast, lots of room for the amount of work involved, and easy building in plywood.

I even bought one myself!

Anyone who is building away from the normal yachting hotspots can always find someone to make a wood mast and someone else to make the associated metal fittings for gooseneck and hounds. It doesn't have to be a wing mast to be a wood one. After all, all masts were wood until the 1960's. Galvenised rigging wire is available anywhere (cranes, bridges, farmers etc use it) An ocean sailor can sail to say, Australia, using "temporary" gear and upgrade there.

Some of the largest sailmakers in the world operate out of the Phillippines so no problems on that front.

I agree with Bruce's commments above (still no relation!)

I have cruised several thousand miles on an unstayed masted catamaran, and briefly sailed several others.The (professionally built) rigs were much more expensive than a (professionally built) new metal mast, conventionally stayed and massively more than a secondhand mast.

An ocean cruiser has no time to experiment and no inclination to take risks. Rob agreed with me earlier that the bi plane rig still had handling problems, but that one day maybe it would work.

As the current Americas Cup is to be raced in multihulls with no rule restriction one can assume that the designers will be using the most efficient rig.

Will it be a mast aft rig? a Dynarig variant? A biplane rig? A balestrom rig? or a "conventional" rig?

We'll know soon enough

Sorry but I won't be writing on this forum for a bit - we are going sailing, I hope you can all get on the water this summer as well.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

Richard, may you have fair winds and calm seas - - God speed...

[rob denney]

G'day,

Bruce,
Dropping the main to go down wind (and having to hoist it again if the direction or course changes) is not as easy as trimming one lightly loaded sheet on a ballestron rig, or one slightly higher loaded sheet on a una/cat rig.

Roller furling (pulling a string and the sail disappears) is a great concept, until it breaks or jams. Roller reefing (pulling a string and part of the sail disappears) is a great way to destroy a sail shape and will not go to windward any where near as well as an unrolled sail.

Furlers are a nightmare in a seriously big breeze when you have to remove all unnecessary windage, but have to unfurl it to do so. They are also expensive, as are headsails and the winches and stays required to support them.

Tacking a cat rig is no problem with a correctly designed hull. There are many examples of these, and a few examples of ones that are not.

Balance is not a problem with a single sail as long as it is in the correct location.

Sandy,
Glad you like the boats.

I would appreciate some references for the work done on the cost of achieving the slot effect. Specifically how it applies to cruising boats with stretched sails, crew who don't constantly trim the sails and overbuilt rigs which are not set up with the care racing sailors use. Then add in the cost of the stays, winches and hull beefing up to get it all to hang together and any performance gains are quickly negated. In actual use, the sheer hard work and vigilance required for a sloop vs an unstayed una/cat rig makes it a far less pleasant option for cruising.

Can a wooden mast with gal rigging and cheap fastenings be built? No problem. This was the standard before alloy and ss. On passage you need to check it every day, and before and after any bad weather. Ideally climb or remove the mast every month or so to make sure all is well. Expect to replace the rigging and paint the mast every few years and replace any rotten bits if you are not careful with your checking.

Can an unstayed wooden mast be built? Certainly can. It will need almost no maintenance (no holes in it, no fittings to break or cause rot) and should last forever. You only have to buy one sail, which never flogs so it lasts much longer, the first reef is automatic as the mast bends in strong wind and is easier to handle as it is held on two sides. The sail can be hoisted and lowered, easily, on any point of sail in any breeze. It will be heavy, but the cog will be quite low, possibly lower than a stayed masthead alloy rig.

Carbon is not the expensive material it once was, and there are easier and cheaper ways to build from it than the aircraft crowd use. If you are able to use a vacuum pump, you could easily build your own carbon mast, and it would be cheaper than a good quality timber one, and way cheaper than an off the shelf alloy one. I could send all the materials from Australia, and at the moment they would be a very similar price to buying them over the counter in the USA, depending on import duty to the Philippines. Let me know the boat weight and the centre to centre beam of the hulls and I will give you a ball park price.

Richard,
Rigging a boat, sailing a couple of thousand miles and rerigging it is probably not the cheapest, nor the safest option.

The mindset which uses the AC boats as a reason for a sloop rig on a small cruiser is the reason why so few advances have been made in multihull cruising rigs for the last several decades.

Enjoy your sailing.

regards,

Rob

[sandy daugherty]

Fair winds and reliable weather reports, Richard!
Rob: You've peaked my interest; can you recommend some reading on carbon masts? Its off the wall, but I would like a masthead platform that did NOT rotate when the rest of the mast does.

[rob denney]

Originally Posted by sandy daugherty

Fair winds and reliable weather reports, Richard!
Rob: You've peaked my interest; can you recommend some reading on carbon masts? Its off the wall, but I would like a masthead platform that did NOT rotate when the rest of the mast does.

G'day,

All the carbon mast stuff I know about is for expensive manufacture using heat and high pressure for money no object results. Google carbon masts and you will see what I mean. Any questions on low cost options, feel free to ask.

How big a masthead platform? A tricolur light can be kept fore and aft with a rigid tube up the inside of the mast. A crows nest would probably require a bearing and at least one line to the boat. However, unstayed masts are pretty flexible, it is not much fun being at the top of them, especially in a seaway

[masalai]

I seem to feel that randy quimpo who started this thread may well be disappointed at the direction this thread has taken....

My 2cents, - would be rig for absolute simplicity, easy repair-ability whilst at sea and a robust design and build.... **** happens, and to reduce that risk is (should be) the prime and only concern...

Efficiency and all the fancy go-fast add on stuff will only complicate matters.... Don't piss into the wind - stand side on and with a bit of luck you won't even get blow-back... The same sensible thought should be applied to setting up your boat for ocean crossings.....