Lifting Spinnakers:does it lift the bow?

Yep. The first few pages had posts with substantive arguments and after that it became repetitive, personal or just plain quibbling. I skimmed through every single one of the other posts and read completely any that seemed to offer something new to the argument.

This question cannot be resolved by repetitive opinions, calculations based on assumed values, artists’ impressions of sail lift vectors pointing in arbitrary directions and photos of boats with their bows pointing to the heavens at the moment the photo was taken. If this was something being proposed for the first time I would invoke the rights conferred by my honorary Missouri citizenship*.

There is a considerable weight of opinion but it falls on both sides of the argument and feathers outweigh opinion that is not accompanied by data or observation. So I gave MHO of where we were at and asked if an observation could be made, proposing a method. Of course an on-board data logging system with load cells would be the thing to use and probably exists on Volvo boats, l’Hydroptere and boats of that ilk, but they are unlikely to release their data for all to see.

Don’t take this personally, any of you. Just pointing out that none of this could be admitted into court. I’m not saying anyone is wrong and least of all do I claim Doug is right. Come to think of it, he just asked the question...

* “show me” for the non-US folk ...

 

Terry,

Over the years, I have spoken with so many sailmakers, designers and sailors who use the sails, about this topic and the answers would make your head spin. These were really smart folks with vast collections of knowledge and experience in the sport. The responses have come from all quarters, based on a hundred different variables and active sources of knowledge. Some had charts and numbers up the wazoo. Others could tell you, very precisely, what they feel when sailing in dozens of different conditions. Some of them guessed and some of them will swear to you that they just inherently know.

You know what the sum total of all that data gathering reveals?

There's no real concensus... it depends on the boat and the rig... it's all about sea state and wind conditions... it's all about how the boat is sailed... and on and on it has gone. This thread haggled it to death and reached the same conclusion.

I know that some folks like to feel that there are soild, data driven explanations for the subject. Unfortunately, you're not going to be able to put numbers on it and call it analysed to completion. The moment they do, some one will come along and casually debunk the numbers with real world demonstrations.

Now, if you want to open a real stinky can of worms, which has also been haggled until it bled, show some courage and post a thread about the description of the planing state for monohulls and multihulls. You'll soon find out that this current topic is complete child's play by comparison.

Anyone?

 

- God, no! I don't have that kind of courage. I would rather tell sail-boarders their craft were not truly boats!

 

Why couldn't a spinnaker for a high performance boat be designed similarly to a kiteboarding kite with mods to make it as easy to launch as a "normal" spinnaker? In essence, it would have a more or less rectangular planform and be launched with a halyard ; the control might be with a combination of twin very light, folding poles and a retracting bow sprit. The goal would be to develop more power than a normal spinnaker... Could something along these lines work?

 

No.

You are proposing to make Florida orange juice from a bushel of Michigan apples.

Have you looked at the control systems for kites? They don't use multiple attachment points, all lines return to one point. Even large scale kite implementations (like on cargo ships) the kite is the only "sail" in the air, as the kite needs a clear area without obstructions like masts, shrouds etc. to get in the way.

Since I know it is impossible for you to agree with me, I now fully expect an onslaught of pictures, quotes from the dark corners of the Internet and obscure references from other credible people taken out of context. Tally ho!

--
Bill

 

I don't know enough about kite/spinnaker design to know whether this is possible or not.

 

Is the point of the sail to drive the boat or lift it out of the water?

If you want to drive the boat, you design the sails to do that. It so happens that excess power not used to drive the boat can be used to lift the entire boat, thus lowering it's dynamic displacement and making it easier to drive through the water. There is an optimum relationship between Drive and Lift within the limits of righting moment.

How you get to this is an interesting puzzle. Kites can have very low heeling effect on the boat, and for water born craft where the total drag is very high a kite can operate at an L/D that makes them fast. If you want to sail at high multiples of true wind speed, look at the rigs ice boats and land sailors use ... not kites or spinnakers ... wings.

 

Kitaker

The point would be to make the boat faster. I'm thinking that a "spinnaker" using some of the technology available for kites might be a whole new kind of sail for high performance offwind.

Just found this: http://www.ralfgroeseldesign.com/parasailor.html

http://www.seateach.com/Parasailor2.asp

 

Think about it Doug.

This is a sail for slow boats. Boats that sail with the apparent wind aft of the beam. Boats that sail slower than the true wind.

Can you imagine the conversation I had with these ****** at the last boat show I worked?

They could not answer any technical questions, they were selling snake oil to idiots. They were very happy when I left.

How does it set at high VMG angles?
Huh?
What is the range of AWA's that the design is superior to conventional sails?
Huh?
How high can you reach with it?
Huh?

Crap for idiots. an easy to trim sail for sailing DDW ... just fine for mom and pa kettle that can't figure out how to trim.

Gosh ... horizontal energy is what drives the boat and this wonder produces LESS?

 

The thing that intrigues me is that with all the research done on kiteboard kites there might be someway to incorporate some of those elements in a sail that could be set and doused on a boat-not flown like a kite. The biggest problem I see,so far, is the asymetrical shape of the kite which would make it very difficult to use.

 

Doug:

Rather than spend the time to outline the many problems with this theory, perhaps you find time within your busy schedule to actually walk the two blocks to the beach and watch someone using a kiteboard.

The kite can't fly until the shrouds are fully extended, the kite oriented properly to inflate and the control lines and frame are held in the right positions. None of these issues have anything to do with asymmetrical shapes. Kites are bilaterally symmetrical (like Victoria's Secret models & 505 spinnakers).

This discussion is pointless without you taking the time to observe the issues firsthand. Since you live about 45 seconds from the beach in Florida, go fly a kite! Five minutes of real-world first hand data collection sometimes is worth far more than days & weeks of Internet speculation.

--
Bill in Ottawa

 

While the planform of a wing could be said to be bi-laterally symmetrical each side of a line running fore and aft thru the center of the wing, convention more frequently defines a wing/foil as asymmetrical or symmetrical based on the wing section. That is the definition I used in defining kites as asymmetrical because the leading edge and trailing edge are different and the top and bottom of the kite(and the kite section) are different. In considering whether a modern kite section might work for a settable and douseable sail it seems that either the section would have to set on each gybe asymmetrically like an asy spin does(using a flexible symmetrical section?) or the sail, as I envision it, would be good on only one gybe. Best I can tell now, a symmetrical section that set asymmetrically would probably not be much of an improvement except perhaps with a relatively high aspect planform requiring a unique attachment to the boat at the top and bottom of the sail.
A more or less rectangular planform asymetrical might be a simpler solution but not by much-it would still need a new method of attachment/support top and bottom.
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Some spinnaker design ideas(see the referenced patents): http://www.freepatentsonline.com/5095837.pdf

 

Kites most certainly are symmetrical on a bi-lateral axis, Doug. You may have confused the term with longitudinal symmetry.

Help yourself to this page of definitions and get back to us...

http://www.google.com/search?hl=en&source=hp&q=bi-lateral symmetry&aq=f&oq=&aqi=

If one puts a matching set of control lines on each side of one's field of vision,(it does take the opposing sets to control a modern kite such as those used by a kite surfer) and one then looks at the kite, it is decidedly bi-lateral in its symmetry.

Here's a photo, in case all this is confusing.

 

Jesus Doug, when you go back and re-write your posts to retroactively make yourself look less wrong, you could be more honest and just say "I was wrong", instead of incoherent babbling ad nauseum.

When you caught me in a calculation error last year, I owned up to it publicly, didn't change the mistake in my post, and apologized while acknowledging that you were correct on that one issue. I'm an adult and I accept responsibility for what I write.

Getting things back on topic, I think the idea of using a kite-style airfoil on a boat in combination with a standard rig to decrease displacement and increase speed downwind is impractical.

How is your build going? From your hints it seemed like an early 2010 launch was the target. I'm done for the season working on Tom's boat - it is now too cold in the garage to work and epoxy cure times are unworkable.

Seasons Greetings,

--
Bill

 

Well there were two mistakes that I see: your misunderstanding of what I meant by asymetrical kite and my misunderstanding of what you meant by "bilaterally symetrical". I trust that is cleared up.