windage

I'm curious. How significant is the aerodynamic drag(and possibly hydrodynamic drag in chop) from the mid-pole snuffer when an F16 is going upwind? It seems that racing this boat in light air solo against sloop rigged non-spin boats might be a disadvantage.

There is some drag there, no doubt, but what would you do instead, launch the spin off the tramp like in the dark ages? That would be a tuff snuff if you were racing solo!

There are a few thoughts to this:

Testing the TAIPAN 4.9 with and without the spinnaker (snuffer) it has been noticed to be slower up wind with a snuffer. However this was at the upper end of the wind range, and the testing had it's limitations.

A much more accurate test was done in the US on the Tornado's. Back when they where testing to figure out the best position to place the snuffer, there was extensive testing done to see whether the drag on the snuffer was a major disadvantage. The result was there was drag but it was so minimal they would be better focusing on other improvements.

Those "case studies'" aside the physical of the problem is:

The drag force is much higher at higher wind speeds. For the mathematically minded - the drag raises to the square power relative to wind velocity. This means that there is more drag in higher wind ranges, but then you have more power to over come this.

I would be very surprised if you're losses up wind where more than your gains down wind. If you are loosing out around the course, I would say it it something else apart from the snuffer.

I have been told that an open mouthed snuffer (The opening facing more toward the tack than the head)compared to a closed mouth snuffer (opening pointing towards the head of the kite when set) is equivalent to carrying an extra 3kgs or 6.6lbs due to the additional drag.

That would depend on the windspeed of course. Would be very interesting to know how somebody calculated that, even if outside the topic.

Hi Rolf
I used the term "drag" in the post above and this probably isn't strictly correct. Wind resistance could have been more accurate. How this ex World Champ, Engineer and Foil manufacturer amongst other things came up with 3kgs is beyond my comprehension but I still have no reason to doubt him. However, I have yet to amend the angle of my snuffer mouth to reduce wind resistance but that doesn't mean to say it wont stay on my 'to do list'.
Every time I look at my avatar photo it reminds me

Hakan did some work in this; I think he said he wored out he lost about 2.5% going upwidn with his snail-house for thre Spi.

But you gain so much more down wind :-)

It has been suggested to me that the weight of the spinnaker, snuffer and pole when wet has an affect on the boat pitching more when sailing upwind in a chop. the pitching slows the boat down.. but how would you measure that???

Increased windage is a factor, all testing and calculations indicates so. In the beginning (2001) the classic Tornado was still faster than the new rig Tornado upwind with the top Tornado teams sailing both boats. This was at the multihull evaluation event arranged by ISAF at the time and removed sailor skill quite well from the equation.

I just stalled a bit on the 3kg number as there must be a lot of intermittent steps between increased windage and calculated weight on the boat. That was all that was behind my question and it was not intended as a loaded question.

Dazz, only way I can see to do that would be two boat testing or some creative numbers games and a calculator. I guess it is more a question of feel and we certainly agreed when we switched from the classic to the modern Tornado. Going out on double trapeeze and trapeezing downwind more than made up for it in sailing pleasure we thought.


Greg, you are sailing under a yardstick system I guess. To stop people from removing their spi gear the day of the regatta everybody here have to declare at the time of signing up for the event wether they will sail with or without spi. If they dont say anything, it is assumed that they will sail with their boat set up like it is for the boats measurement certificate. This is enforced and if you race without spi, you are still scored as if you used the spi. I think that is a good system.
Even in light winds I much prefer sailing downwind with a spi compared to without

C'mon guys - 6lbs of additional weight?
Not that I am disagreeing about there being some VERY minor efect from windage, but most of it has to come from your head if is is noticable.

The hoop and sock on these boats is in line with the water and moved down to be close in plane with the tramp and beams. Those would be hard to remove from a boat and provide aerodynamic drag anyway. Most drag effects, like this do not become mathmaticaly significant untill the wind is high. And the advantages of the spin off the wind are undeniably significant.

The general concensus seems to be that additional volume and freeboard are good things, but both of these have a pretty significant negative effect on the windage drag also. In a solo application with light air and flat water, the current F16 designs are far from being optimal, as they have to be able to do 2-up and rough conditions equally.

I've lost twice that and it doesn't seem to matter!

As a heads up, this issue is not covered by the F16 class rules and therefore must be in the NOR or SI's to be binding. Gentlemen's agreements are well and good but we all know people are people and regardless of an agreement reached on the beach if a rule hasn't been broken a gentlemens agreement really doesn't mean much for some people. Besides, if it's formalized you don't run the risk of souring an otherwise very pleasant weekend.

Just my 2 cents, I'm leaving now.

David,

this is just how things are done under the national handicapping system, it have no reference to the F16 class or any other classes. But those racing under the system know that these are the rules, and it is specified in the NOR for larger events. For the wednesday night races, it is usually not specified but people are so used to it that nobody ever complain about it.

F16 clas rules state what an F16 is.

AS long as the boat conforms tio the class rules, it's an F16. Exactly the same is true of an F18 i'd expect, unless your class rules are different from the norm.

If this is NOT the case then the boat is not an F16.

No issues with class rules within the F16's.

Okay before this goes off on a tanget that was not intended, my response to Rolf was created with the assumption that teams would be pulling off their spin kit during the regatta which was CLEARLY NOT what he was saying (my bad).

The events where this could be an issue it is handled by the NOR and SI's. It's all good.

Crap! I just made a big bag of popcorn.

If you enter an event as an "F16" or "F18" or "Tornado" or Hobie 16, if your boat starts the regatta conforming to the class rules under which you entered and then mid regatta you change something that takes the boat out-of-class, you should get protested and DSQ.

Class rules simply define what boats of common name "look" like.

This is more like it. I didn't know you guys ate popcorn.

IMHO Tikipete was responsible for a lot of the windage around here. :-p

I have this theory that windage is more important than what we think as the speeds of the F16's and others such as the F18's are becoming nearer the 20knot mark than the 10 knot mark. The higher the speed the greater the effect becomes, the faster we go in the boat the faster the apparant wind.

Certainly in other sports such as gliding, wire struts and anything superficially that sticks out has long been done away with, certainly as speeds have risen.

Yes we do need to consider windage, not only the F16's but all boats with snuffers. I think Swell Catamarans have spent many an hour thinking about this and looking at their boats they are always very clean and aerodynamic compared to other manufacturers. The Shadow a prime example and part of why it does so well on handicap.

The race is on then! Who can come up with the sexiest, most aerodynamic, all carbon lifting foil/snuffer? Oh! Keep it under $5k and 1.5 oz.

SNU has some smooth lines, and don't weigh much. At least compared to the factory Hobie hoop.

You guys are great. I mean that. This is such an active site with lots of smart, experienced sailors willing to share their years on the water. I think those F14 guys are on the verge of going postal.

If you are considering windage of the snuffer, then you should consider windage of what you wear on the water too. A person sticking out the side of the hull is a rather blunt instrument.

Did you see the austrians at the 2004 games, with their red jumpsuits? They obviously thought the same thing. Data is inconclusive though as they did not repeat their performance in 2008.

Are beer bellies or swollen heads slow?

Depends on the wind condition. At some point the righting moment of the beer belly and swollen head is going to compensate for the loss in drag.

Following that logic a sailor with a swollen head have a distinct advantage.

Forget the logic a swollen head is only good for one thing.....Impressing the woman you love!

But then we have Mark, lowering the bar:

I dont think I've ever seen Mark LOWERING a bar.

Trying to drink one dry; maybe.....

Why would you lower a bar? No more service if the bar is leveled or beneath the official norm.

Rolf, It's a term that is used to saythe bar will be closing soon (or not)

"The bar will be closing soon" = it's closing
"The bar will be lowering soon" = It's closing
"The bar will be closing soon, but not lowering" = The bar is closed if someone official asks, but in reality we will be open until we decide it is time to lower the bar.

So the "lower" term is from the curtain they lower or close to really shut down serving. Pretty funny term.

That's strange I thought lowering the bar meant lower the standard.
I never realised it had anything to do with a wet bar and more importantly stop tap.

That's what I thought too. I was thinking the same as Mark, so if I'm already at the same level, does the bar actually need lowering?

Karl! Load up! http://www.juanaspagodas.com/RegattaNews.htm

Yes it means lowering the standard. Making it less than it should be. Something most of us don't want.

Doug

I always thought "lowering the bar" was a play on the more popular "raising the bar" as used in track and field meets, where you raise the high jump or pole vault bar as the better atheletes go higher and higher.

I was a pole vaulter in my younger days, so I know something about having them "lower the bar"...when it was my turn!

Or, as my Officer Evaluations used to say back when I was in the Air Force, "Lt. Bohan sets low standards and consistantly fails to achieve them."

So, who is going to invent the retractable spinnaker pole? That's all we need right? Extend it at the A mark and suck it back under the tramp at C mark, it could even double as a righting pole if done right! ;^)

I dont think the retractable pole is allowed under the rules?

Depends if you're the person trying to "step over" the bar.

Sure it is, you do not even have to have 1, it just can not exceed 3.5m if you do.



And I always though lowering the bar was an aid to help those who were too drunk to stay on the stool but still wished to continue.

Straw?

Hey guys, lowering the bar has nothing to do with drinking bars, nor sheep baas, nor gold bars, but all to do with raising the bar, wait for it, the high jump bar and by insinuation raising and lowering the standard.

Getting back on topic fat boys with big profiles are going to be less aerodynamic, at a real disadvantage in light air, sink the boat down to far on its water lines, unable to move around the boat like the whippets, and we carry the same handicap as the 70 kilo skinny bloke, I vote we allow fat blokes to have the same handicap as a dual hander and be allowed to carry the jib as well, tis only fair.

Talk about lowering the bar...

Sailing is about weight placement and ballancing the boat, not so much about how much weight. Strapping on some fixed lead to the platform just to make the fat lazy guys who do not move on their boat feel better is BS.

*plunk* (sound of Matt stepping on a lot of toes)

Who pissed in your Wheaties! I'm sure Wayne was just kidding anyway.

But now that you mention it. . .

Nobodies toes I have not stepped on before. If I am allowd to carry the weight so it moves where I need it then OK. (Although this may present some issue to catch up with a few of you guys ) Dead weight strapped to a platform is NOT an equalizer. That is my point and it has been the source of many a heated debate, which I am sure you all have heard from more than me.

The weight issue for the F16 is why I chose to get into the class, (Crew more than the platform). I would be racing F18 now if not for their crappy weight handling.

Sorry for being pissy this early in the AM

Wayne we will let you rig up the jib solo when you hit 130kg, which is where I end up doing it 2 up

For those tossing out suggestions on alternations to the class rules, I'll lend you my steel tipped safety shoes when you go into action. Step away

Assuming that everybody who are heavy also are fat and lazy is where you can get into trouble with toes

I object to the lazy part! However, I am living proof that working out at the gym on a regular basis has nothing to do with weight loss! Still, I could probably touch my toes if I could find them.

Life is good, especially pork chops and mashed potatos.

I agree that adding weight to the platform to compensate for a crew too light is a dumb idea. It's better to give them lead weight to carry so it helps the righting moment. Until the crew goes overboard...

But that's not what Wayne proposed. He asked for more sail area to compensate for his weight instead. Fat (no pun intended) chance

Wayne and I are in the same weight range, I'm 93kgs. For the record we both know *where* to place our weight on our boats.

Matt, do you REALLY want to go down this road?

Ding, I stand my my statement and for me it is true. (essentaily there was no F16 available when I wanted to go spin but the issues above with F18 pushed me to building 1)

You and I HAVE been down this road and are pretty familiar with eachothers points. I would be more than happy to discuss it with anyone else - just bring beer or rum

What was the specific practical issue you had with the F18 you where sailing at the time?
How much do you and your crew weigh?

I think Matt's issue with the F18 is easy to understand: he mention his crew weight was 130kgs. How many teams at the F18 world where using the small jib and small spin? The number I've heard is None. Nada. Zero.

It is a clear indication that if your crew weight is less than 140kgs, you are not competitive in the class. And even at 140 you have to carry 10kgs of lead to qualify for the big rig.

Matt, it's your choice of words not the content. I have absolutely no issue with the F18 not being right for you. But don't make your point in such a way "crappy weight handling" that it is directed as a slight at my class. Don't trash the F18 class because you want to make a point about weight in your class.

Do unto others Matt.

[quote=David Ingram
Do unto others Matt. [/quote]

Sorry Dave,

I did not mean to single out the 18 class. It was that was my logical choice of potential platforms when we were looking to go spin. The weight issue is crap across any number of differing classes and it is my opinion and I stand by it. (The 18 class does at least have the differing sail plan)

What we really need in cat sailing is some corrector for height that has a lot more impact in performance than weight on a modern spin boat. The short guys are considerably dissadvantaged in righting moment.

Wider platforms for short people.

The following is not aimed at Matt, I just use his last post as an opportunity.

Weight, height, a body like knitting pins with a swollen head.. It is all the same argument.
Accept that the world is not tailored for you and learn to live with it. It is most often not your body that makes you go slower than optimum on the regatta course. It is what is inside your head. Most other reasons for poor performance are excuses made up by your ego to avoid admitting that other sailors know more about the game and trained harder than you did.

If somebody desperately feel that they need to gain weight or loose weight, there are eating strategies to fix that. Few are willing to study enough and accept the habitutal changes neccesary to have success with it.

Matt:

I agree 100%. I could not tell you how many races I won at 310-320 when we raced the H-16 back in the 80's., when most everyone was around 295. As you said it is all about boat handling and weight placement and how you move around the boat. I can't wait to get on one of your Falcon's.

Doug

Doug,

have you ordered a F16 Falcon?

Nothing like diversion to get off of a sensitive topic (LOL)! BTW string bean, it is "height challenged".

Shorter sailor(s) would be less windage? A book from the 90's talks about keeping crew and skip close to minimize windage, a la road biking.

If a snuffer bag has that much windage that it causes a cat to run deeper then one without, what about the higher bows of the Viper versus the Blade. Would a Blade sail higher because the bows have less windage?

Gilo, I beileve that is part of the "concept" behind all the new cut back bows we are seeing on the newer A cats, F16's and F18's. Some call them wave piercing, but in fact, every bow is wave piercing, right? So it must be to reduce windage while out of the water.

Not only the reduced height but also the egdes of the hulls as the wind pass over them. Sharp egdes give more drag than well rounded egdes.

Welcome to the world of boat design. Every feature and descision is compromise. Big volume and high freeboard provide more wave drag and windage. Lower of these can cause beam slap and increaded wetted surface.

The list of compromises is imense. Most boats have gradualy drifted into a minor range varience where the whole thing works pretty well. Changes to stuff like this is really nit picky and of such marginal difference between plaforms as to be ridiculous. I doubt there are more than a couple sailors in the world who could actually tell a difference.

It all goes back to the ballance thing as Rolf said. Nothing you can do or change on the boat will equalize things exactly. Get it close and go sail.

If you worry about it, then it is slow no matter what. If you think it is fast then it is.

I definately agree 100% on that!

Rolf - You get your ticket to come over for the Global Challenge yet? We will find you a spot to rack up.

Lottery company have not called me and confirmed yet

(it is a money issue, and nothing else)

Rolf, I have never seen sharp edges on the bow of any boat/cat. They are blunt enough not to stall and generate lift when sailing upwind. So cutting them away for aerdynamic reasons is not as clever as some people think. You will find a chapter in Marchaj's book about some of the effects involved.

I have a furling genaker on my boat. I sailed the boat with and without it, never realised any difference, so I don`t care even if it is an easy exercise to calculate it. I wouldn't care about the drag of a snuffer as well, maybe about the blocked airstream to the trampoline. But only if I am bored and want to invent problems
Maybe somebody else has tested his boat with and without snuffer and can us tell the difference?

Cheers,

Klaus

I have the same Promlem.

Would love to come; Dosh precludes.....

Since everyone is racing with basically the same setup, does it really matter at all? Fugedaboutit and sail fast!

No, got to do the catering circuit for a year and get the internet business going. Hopefully next season. Being boatless is KILLING me.

Doug

So who died and named you spokesmen for the class?...

What a tetchy useless piece of drival, why is it that people can't see the lighter side of the internet and its forums, this is supposed to be a good natured humour filled piece of reading not a bun fight because someone is all pissed about dissing their particular class of boat.

Go back to the F18 Forum and play there before we all start dissing the F18 for bit of good wind up banter.

There is some references to pratical experience on sailing without spi gear earlier in the thread and on the F16 class forum. I think we can agree that there is a difference and that the difference is due to increased drag.(AAGH! I got to stop connecting drag with The Adventures of Priscilla, Queen of the Desert)

About bows and drag. You should know..
John Shuttleworth had an article about how he loocked at minimizing drag from wind passing over the hull in his Tektron and Dogstar designs. He reported that the optimalization done was worth the effort as far as I remember. The articles I read about the design and build phase of Cogito said similar things. They looked at minimizing drag from the platform.
Minimizing exposed area and rounding off surfaces sounds like a logical thing to do to reduce drag? Please do share your thoughts. Interesting topic and something that we can adjust as compared to drag from our bodies while trapeezing.
Is this drag tiny compared to going the wrong way or not knowing how to trim the sails.. Indeed

Doug,
hope you succeed and get finally get that F16

Built one successful before. I will be back up again...thanks Rolf. It is killing me not to sail...Although Ike took away our local place to sail. 1 1/2 hrs drive now

Doug

Rolf,

I am always very careful if people tell me something about minimising drag. I don't want to have a boat minimised for drag. I rather want to have a boat optimised for speed or efficicncy or whatever. To make it clear, a boat optimised for drag is a boat without a sail, or even better: no boat at all. And it should be clear that this should not be the target for any trade.

Yes, bows generate drag, and no bows generate no drag, however bows generate also some lift (like a sail) if sailing upwind, and as with sails, bows with higher aspect ratio are more efficient than bows with low aspect ratio. Apart from that hulls accelerate the flow at the low part from the sail by displacing a volume of air and reduce the tip vortex (at the boom) around the sail. As mentioned this is explained in Marchaj's book.
Last but not least, the hulls of a beach catamaran help to make the flow around the trampolin more efficient, hence it generates more lift and less drag (this effect might be offset with a spinnaker kit). The lift of the trampolin lifts the boat (slightly) and reduces hydrodynamic drag.

All of these effects are of secondary order. But it shows that optimising a single component (the bows) of a boat for a single reason (aerodynamic drag) doesn't guarantee an improvement of the whole system (which includes much more than just aerodynamics).

Regarding the drag of the sailor traping out: The same sailor would have about the same drag while sitting on board, but he interfers less with the sail when trapping out (although I don't know if this is good or bad). Again this is a second order effect.


A bit off-topic: When building your rudders and boards, you shoudn't round the tips. Maybe you know that already.

Cheers,

Klaus

Klaus,
Can you explain your comment on not rounding the boards and rudders. My blade boards are cut straight at the bottom with the same cord from top to bottom. I think the falcon's boards taper a little from the trailing edge at the bottom. The infusion's boards round from the trailing edge down to a straight leading edge and the wildcat tapers from both the leading edge and the training edge. I am just trying to get an idea of what each design is trying to achieve hydrodynamic-ally. Thanks.

Hi Chris,

I meant rounding the tip edge of the rudder, not the planform. The planform is what you see from your rudder, if you lay it flat on the ground. The wing tip edge is best seen if you look from the leading to the trailing edge (e.g. front view). If you make it round, you help the tip vortex, which is always there, to be stronger and hence more dragy. If you make it sharp, you hamper the vortex a bit. Hence rountig or fairing the tip edge is not good. A simple cut is better, just have a look at modern aerobatic aircraft (which have a symmetrical foil as our rudders).

In terms of planform you have some degrees of freedom from an aerodynamic point of view, many shapes are possible. Some people "believe" in elliptical shapes, however a simple taper ratio of 0.4 is as "good" (depends largly on your figure of merit, which is not only drag) as an elliptical shape, but much simpler to fabricate. There is a small "improvement" possible if you have rounded leading edge on the last 5% of span, as you can see on many airliners when not equipped with wingtip devices. Again second order effects, most important parameters are area, span and the section shape(s).
It is difficult to judge these rudders unless you know what are the most limiting factors (stalling at low speeds, cavitating at high speeds, structural strength), what are the design targets (optimising lift/drag) and what is design philosophy (rotating or sliding kinematics, designed to be loaded or unloaded when sailing straight) , etc.

When we broke the rudder of my friends T, we decided to keep the same area and span, but went for staright leading and trailing edge and designed a new section shape, which should have less cavitation, slightly less drag and better structural stability than a conventional NACA 4 digit section.

Cheers,

Klaus