Catamaran Sail Plan Variation – Spinnaker

Adding the spin to the Tornado actually settle's it down on the off wind legs. The bows tend to stay up out of the waves more...danger of burying the leeward tip is much reduced.

Mike.

From what I hear about H16's with spin is the sail actually creates lift on the bows and reduces pitch-poling going off wind.

put a long enough pole on the chute and you'll be ok with the bows.

Get a fat kid for the rear crossbeam.

Humm, I think I've met your guy a fews times in the past, a most perculiar persona. He comes with light and vanishes with darkness. And all the time he presents himself unannounced and goes hence without a wisper of good-bye. He always looks me straight in the eye when I gaze at him; never answers back though, or make a sound. Not even when I can clearly see him take a breath and move his lips.

Kind of a flat character though. He has been that way ever since I can remember.

Anyhow, here is the link you are looking for

http://www.geocities.com/kustzeilen/Genaker/

OK....now that was funny.

Does he just "take your breathe away," Wouter?

Trey
N20 314
Layline Rigging
www.velocitysailing.com

Oops, we overloaded Wouter's website. Is there another link?
-Rob

Sorry, all me resources are in the F16 side of things. There isn't another link, just have to wait a few hours and she will come back online automatically.

To Matt : In short

Spi makes boats more behaved on downwind legs, especially so in strong winds.

P18 without a jib can be done, just rake the mast a little bit more forward.

Tacking is more difficult but with the right technique it is should be really doable even under the worst conditions. make sure you slack the main at exactly the right time and that you make a roll-tack. Get these two things right and she will tack relatively well.

Wouter

Well, it is true that everytime I that spend more than a quick glance on him, he is always fiddling with his hair or tie and generally trying to make himself look better then me. At times we have a little bet going on of who can suck in their belly the longest. He is an incredibally competitive guy and never backs down first. But I wouldn't say that he is sufficiently attractive to take my breath away. Poor fellow, maybe he is compensating for something.

Wouter

Haha,

I love your “poems” about “My Guy.” That is great.

Exactly the article I was looking for, thank you.

I am surprised that the spinnaker would lift the leeward hulls; I guess I have to think about that for a bit.

Thank you for your replies.

Matt

It doesn't, but that is not the point. The point is that the spi DOES calm down the boat alot WHICH feels just as if the bows are lifted. Mathematically and physically speaking the feeling is very much correct but the explanation isn't. However, reality only adheres to what truly happens (feels) and not whether our human explanation for the phenomenon is correct or not.

It will be far to complex to get into this in detail and unless you are science junky it would be pointless trying to explain it as well.

Main point still is and will always be that adding a spi will make the boat more controllable downwind and will make the boat feel more resistance to pitchpoling and sure enough with the spi set you do pitchpole alot less often.

The difference, when the spi is handled right, is such than no crew nowadays sails without a set kite on the downwind legs NO MATTER how strong the winds. Personally, I much rather sail SINGLEHANDED downwind in a blow with a set kite than without. That is how much more in control you can feel.

This all has been my experience on both the Prindle 18 that I added a spi to as my new boat the Taipan F16. So my advice to all is to start slowly with the spi and build up skill gratually but also to work consistantly towards a skill level where you can always pull a kite no matter what the conditions are.

Good luck !

Wouter

I agree with you - as long as you sail the boat conservativly the spin works great in big wind. In big waves (which often go with big wind on the ocean) we put the crew back on the tramp and stop heating it up as much. I throw the hotstick back in the water and steer off the rudder arm/cross bar connection which gives more precision and speed - important when you get hit with a header puff.

I noticed that they also threw the hotstick back in the Hans Wallen Tornado video. I have mimicked that on several occasions and it works well. I don't fly a kite on my boat mainly due to budget constraints. I still have a hard time figuring out how it settles a boat down. It seems it will still make you PP, just a few knots faster when you fly over the bridle. I am a simpleton when it comes to physics so I will just do the "I don't know how it settles the boat, but I'll take your word for it" mentality. I've never even been on a kite flying boat yet. Anyone need crew in Panama City?

-Rob V.
Panama City
Nacra 5.2

I confirm your comments.

I more often than not throw my tiller extension overboard as well and steer by the rudder arms as well. Same reasons plus on my boat the crew is often behind me on these legs where my non-adjustable tiller extension is seriously in her way. But I would throw the extension in the water even if it was adjustable, the control is just better.

Wouter

With regard to budget to fly a spi.

I'm still sailing with my 2003 kite, they can last quite long. The AHPC snuffer system costed me 250 US$ and works like one of the best. Spi itself should costs about 800 US$. Other hardwire and lines should cost no more 400 US$ in total. In short the costs have come down considerably in the last few years.

You can do it even more cheaply if you find yourself some secondhand I-17 or F16 spi. Sure enough these are around especially since the heavy boys in the I-17 class may now use a larger spinnaker ?

Personally, after knowing what I know now about sailing with a spinnaker. I would give it a good try getting one for he budget that you may have.

Wouter

2 years ago I fitted a spinaker-system on 2 Prindle 18's. The age of the boats justified experimenting. The result was that both boats are used with spinaker in alle kind of lessons and courses. The boat stabilizes remarkably downwind when using the spinaker.

I also had the opportunity to try the Hobie 16 with spinaker. Also the Hobie is much more stabile with the spinaker. It could be more stabile but the shape of the hulls prevent it from being more forgiving. Same problem is with the Prindle 18.

Don't be afraid of pitchpoling when using the spinaker downwind on the 16. Actually the spinaker compensates the pressure of the mainsail to the mast (specially the top). If you're looking into the way the wind blows in the spinaker it is clear that the spinaker will cause some lifting abilities to the bow of the boat.

Have fun..

Like I wrote earlier, these are very persistant myths.

Sorry Boomer

Wouter

Wouter, it's not complex at all. If the aerodynamic center is lowered, the boat will be more stable. If (by moving the tack well forward) the the aerodynamic center is moved forward and an upward component is added to the lift vector, the boat will be more stable. An extreme yet logical extrapolation of this is the Kiteship kite. Attach that to the bow and it will be lifting the bow, because it's awfully hard to push a rope.

I tried many times to explain the difference between "pushing the bow down less" and "lifting the bows", but it is remarkable how fuzzy such a distinction is for some (most ?) people.

Anyway.

I'm done.

Wouter

Would the spi work like a kite? Kites lift into the air becasue the string prevents horizontal motion and the angle of the kite is such that the air is deflected downward forcing the kite up.

I have seen on larger boats (mono-hulls) people dangling off the bottom of the spi for fun. Is that spi can lift a person up, why would it not lift up on the end of the spi pole which would lift the bows up too. It would seem that a spi would direct the airflow to the leeward side of the main and jib as well as downward which would lift the bows due to Newton's 3rd law.

Am I understanding ths correctly or am I way off base?

I'm sorry to say but your are making one of engineering rookie mistakes. Much like the example of where the sailors blows in his own sail to propel him along.

The spinnaker does definately pull upwards at the end of the pole. However it very much pulls downward at the mast hound fitting. As the mast adn spi pole are fixed relatively to eachother this means that these forces will largely level eachother out.

This is called systems thinking in engineering. You must learn to regard a fix composition of elements as one whole system where internal forces have no meaning when looking at relations (newtons laws) that are taking over the whole (system)

Wouter

Wouter,

I am not to familiar with a spi as I have never actually sailed one before (budget constraints). I think I will need to get a closer look at one in action to fully understand this.

Which way does the air flow off the of spi? Where is the center of lift on a spi? Which direction, approximate, is the force vector of a spi?

Upon further thought I think I know what is going on with the spi.

My assumptions are:

1) All the forces on the boat act about the center of buoyancy.
2) Forces created by the air acting on the sails can be reduced down to a center of effort and a vector eminating from the center of effort

Now, depending on where the center of effort is on a spi and at what direction (vector) the force is acting from that center of effort will determine what torsion is acting about the center of buoyancy (CB). If that center of effort (CE) is below the major horizontal chord of a circle whose center is at the CB and a radius at the CE, then any horizontal component of that force (in 2 dimension looking at the port side of the boat) will produce a clock wise torque, therefore lifting the bows. Also, any vertical component of the force will produce a much larger clockwise torque.

If the CE is above the major chord of the circle described above, then any horizontal component of force will produce a CCW torque about the CB while any vertical component of the force will still produce a CW torque.

In my above explaination the vertical and horizontal components I am referring to are of the force that is perpendicular to the cirlce described above. This force is a component of the spi's overall force vector. I hope this makes sense to you all. In my head it is perfectly clear.

Since I don't know where the CE is on a spi I can't be sure if this is why everyone thinks it creates lift.

Now, as to why a spi "settles" the boat down on a reach. Take the same perspective looking at the port side of the boat. I knwo for a fact that the CE of the spi is out in front of the CB of the boat. This means that the spi is dragging the boat forward versus pushing it. As you know it is easier to pull something in a straight line than it is to push it.

I guess I should have taken that technical writing course as an elective instead of wine tasting. This is much easier in person with a pencil and paper.

Let me know if I need to clarify anything or if I am making absolutly no sence at all.

Wout, pull on the end of the pole is vertical, or a tiny bit aft of vertical. Pull on the hound fitting is far more forward than down, thus the net effect is that the spin generates forward "pull". Tell me if I'm wrong, but the lift of a sail flying free is perpendicular to its luff. This image of an 18 skiff, admittedly with an exaggerated pole length and luff angle compared to most cats, shows the general orientation of the kite to be maybe 35 or 40 degrees aft of vertical. This will clearly degrade the amount of forward thrust available to pull the boat through the water. However, the total thrust or pull generated by the kite is unchanged. If the vertical component is greater than the "tripping" component of drag caused by the greater speed, then the kite will without doubt lift the bows.

Andrew,

We are talking about common spinnakers on beach catamarans here, not extreme examples that really have no application on beach catamarans. Sure enough you and others could device a contraption where the spinnaker will lift the bows, although this is much more difficult than you think, but that still doesn't say or proof that spinnaker setups as commonly used on Cats actually lift the bows or not.

Also one of the documents sciencific analyses was done on the Cherub skiff boats. A monohull with a long spinnaker pole and an angle back spinnaker. Still the numbers showed a setup that didn't lift the bows despite the fact that these boats ride with their bows high in the air as many other skiffs.

Also from my own experience; I could get my bow to fly on a 49-er just be placing our weight way back on the wing. Under spinnaker it flew less high when the weight was similary placed back.

But lets stick to the catamarans setups.

Wouter

I haven't studied your post in all details but the theme enclosed in them is correct. In the end, as I think you say, the spi creates one overall force that can be devided up into 3 components. In summary these are :

-1- a horizontal force along the centreline (drive)
-2- a horizontal force perpendicular to the centreline (pushes the boat to lee)
-3- a vertical force

These three forces create in turn 3 moments around the CE of the hull and daggerboards becuase the CE of the spi sail isn't at the same place as the CE of the hulls and daggerboard.

Force 1 and 3 result respectively in a counterclock wise moment (when looking at the boat from port) and a clockwise moment. Wether the bows are lifted or pressed down in absolute sense dependent on which one of these two moments is larger than the other. On beach catamarans the moment linked to force -1- is bigger than the moment linked to force -3- and so spi doesn't lift the bows in an absolute sense although the vertical force does lift the whole boat out of the water a little bit. To makes things simpy right !

If this is what you were getting at then yes I think you are correct.

However as we discussed elsewhere this is only part of the story that explains what sort of effect adding a spi has to a catamaran

Wouter

I installed the Hobie Cat snuffer system on my H16. It's incredible! The bows get lifted and you just take off. We've used it on deep reaches and down wind legs and have just flown by other H16's. My wife, normally afraid to pitch poll (that's another story, I should say stories) is pleased with the spi's affect. I don't recommend using it in wind lighter than about 8mph when racing under portsmouth. You'll take a hit of about 3mins to the hour.

cincy kid

Well,

I'm glad Wouter is done, now we can go on exchanging our experiences with the spinaker on the Hobie 16.
MY experience is that the "diving capabilities" of a H16 diminish when using a spinaker downwind.
I suggest giving it a go with the spinaker. It is fun.

Although for a lot of H16-diehards adding a apinaker is a bit of defiling (correct word ?) the H16-class.......