I'm not so sure about this. I heard or read about three efforts to build single handed F16 that would look more like a A cat. I don't know the exact build status of any of those, but compared to current F16 the idea seems to be to move the front beam and daggerboard way back, allowing an higher aspect main. This would also move the center of gravity toward the back, allowing for a smaller bow.

This would probably make the end result look like a widened Bimare X16 with a shorter mast and more sail area (the Bimare uses a beefed up A Class mast).

I'm curious to see the results of those efforts.

I don't know Hans, they sure do look different to me.

And I'm not only refering to the spray rails. That bow height on the Geltek flyer 2 looks to be 250 mm at max. I'll be very surprised if the Wildcat F18 has less then double that.

Summarizing, same hull length double the bow height, no angled down deck and a spray rail.

I am not saying they look the same but as a look a like. I know that some a-cat guru's did involved in the design of the Wildcat and they look at A-cat. A lot of people are looking at A-cat because it is one of the classes where developent is going on and on pretty quick and they take some of the gimmicks like the wave piercing bull because it is nice looking.
If you look from the side to a wildcat you see the same look a like type of nose.

I really have to get back to running some more simulations and writing reports (my reqular day occupation), but I want to glarify this misunderstanding up.

You can't not have a higher aspect sail on a F16 as the boats already have, unless you are prepared to remove sail area. That is because the max sail area, max luff length and max mast height are all limited under the F16 class rules.

So if you want a 15.0 sq. mtr F16 sail (and you do when racing in light to medium winds) then the aspect ratio will always be equal or small then 8.1^2/15 = 4.375

Now moving back the F16 rig by 400 mm (= alot) will be an a par of repositioning a 135 kg crew weight further back by 74 mm or 3 inches. or 130 mm = 5 inches when 1-up at 75kg. Not an earth shattering difference, although that sidestay/daggerboard may now really be in the way while you also develope short boom issues.

Now the designers can do what ever they want to the position of the beams and smaller bows but the end result will not mimic the A-cat. The specs and ratio's of both designs really do not match very well.

We really have got to get away from the myths that are created around the A-cats and look at the hard numbers. Simply making any given design appear more like an A-cat doesn't necessarily transfer any of the benefits. The F16's must look far more towards the F18's for guidance.

Wouter

I'm still pretty convinced that the entire A class package is aerodynamically and hdrodynamically optimised compared to the F16's single handed. I do think there is a distinct difference bewtween single and dual, in my opinion the single handers will diverge toward the A class design and the dual toward the F18's design largely due to ergonomics of two bodies and the extra weight.

Lets only talk for the moment of single handers, in my view the A class are pushing the beam back more and more to get extra bouyancy in the now smaller and smaller bow volume, this suddenly starts to load the dagger board only, hence the dagger board is getting further back and the rudder is becoming tiny on the A's and by effect of only 1 board, less drag and more efficiency.

Now we have the problem on the F16's of when the Spinnaker goes up and the whole lack of aerodynamics of the snuffer and sprit which always is going to be our archilles heel.

Wouter. Utter rubbish, Of course you can have a higher aspect sail on an F16 than are currently built. I think myself (and including all those with GP mainsails) and Hans propbably have the highest aspect minsails at present. Mine is (I think) about 970mm. The A class guys are mucking around with heads around 1100mm. Bigger head in the sail means less sail area DOWN LOW; thus foot length reduces and thus the aspect ratio increases.

Biggest you could go is a head and foot of approx 1.85 and a 8.1 luff, as you say 4.374. BUT no-one has got close to this yet and there are loads of reasons why they would not get that far, possible? maybe, desirable? Prob not.

I also have an F16 design in my head that would look VERY much like the most recent A classes, perhaps even more extreame as the F16 rules allow T foils, you do not NEED volume up front, you can use T fouls to provide the "anti-pitch" when needed.

If I ever get the money to commission a build, the hulls will look like thin rowing 8's (but not as long) very fine bow entry and either thin or planing sterns.

A Hobie 16 with a flat bottom?

I do not have the exact calculations for volume placement but I would be more than willing to bet against that statement. The Viper has huge volume in the middle of the hull near the beams, but a much narrower fore and aft even though the bow is deeper. This would provide the tendency to pitch more pronounced and also make it more difficult on crew position to keep the proper attitude making the boat less user friendly to sail fast.

Also the hulls appear to be more V shaped than some of the others. The width at free water line does not appear to ba any more. Added volume to a hull out of the water provides no benefit. Carrying more crew weight without the added volume already in the water provides no advantage.

If you look at the A they are removing hull from above the water. The under water lines are not varying with the new designs very much. More freeboard and width are required for a heavier 2 up boat, but I would venture to say that dynamics of the A class are the best (more refined than the other cat classes as they have been through the most development) for the part in the water. The Wild Cat and the Falcon both have take queues from this class.

Wasn't the Capricorn and the Wild Cat designed by Martin Fischer? Then the Viper was designed off of the Capricorn...

Has he done any A-cats? Where are those if he has..

I think the WildCat is nothing but a second iteration of the Capricorn....especially since Martin did design it there are way to many similarities.

Why don't you use the formula for aspect ratio that the SCHRS handicap system uses ? As in that handicap system that you are an offical off ?

Or pick one of the formula's used in aircraft design. I don't care, all come out at my number anyway.

A bigger head does NOT increase aspect ratio as that terms is defined in scientific circles.

You really have to check your data and facts before blowing off.


With respect to building an 1-up F16 that closely resembles an A-cat. Well go ahead, I just caution you to not expect much of it.

Wouter

Wouter

Does a sail with a 1mm head and the same area as a sail with a 1000 mm head have the same aspect ratio?

NOT using the SCHRS model as we use a simple method to make measurement easy.

I am quite aware of how SCHRS does it!

Are you suggesting that a sail that is a rectangle is has the same aspect ratio as a triangle of the same luff length and area?

If yes (and I have the feeling you will say yes). Then why do people refer to sails with larger heads "higher aspect?".

Thats an interesting statement and one I do respect as largely what you do write is based on scientific fact, but do elaborate more why you think the single handed F16 requirements and the A Class are so different, I'm as yet not convinced.

Maybe a counter example is welcome here.

Nils Bunkenburg was first associated with the revolutionary Flyer A-cat and then did the Hobie Fox and FX-one. What happened to the last two ? The first failed in comparison to the Nacra I-20 and the second well, even a bunch of upstarts chaired by dear old Wouter could beat that class/design.

Then he was going to blow away the F18's with his Nikita F18; does anyone still remember that design ?

And when was the last time Fisher did a competitive A-cat ?

Hell, when was the last time Greg/Jim (AHPC) designed a competitive A-cat and not buy one of another designer ? The Mark 5 is the answer, back before the turn of the millenium. After that one the licensed the Flyer (Aigner), the Tool (Mercer) and then stopped. The Capricorn F18 rig is completely off Gregs hands and he also modified the Capricorn hull shape before going into production.

Please name me the designers that are renowned in BOTH the A-cat class and F18 class.


I think we are looking for correllations that may well go either way, yet we seem to focus only on the ones we want to see. I know not of one designer that did a succesful A-cat AND a succes spinnaker boat. And yes that includes Marstrom as the Tornado is a Rodney Marsh design and the M18 and M20 are surprisingly unsuccesful.

Wouter

Yes !

Aspect ratio is an enginering coefficient that has no direct physical intepretation or tight relation to a fixed natural process. Much like prismatic ratio or indeed "max hull speed". Such coefficients or numbers can only be accurately applied over either a limited band of values or for a select group of "situations"

You can only use aspect ratio meaningfully when different designs are close enough to one another. With increasing difference in overall shape the inaccuracy of the results increases also. That is engineering as opposed to exact science. Engineers will often reduce far more complex phenomena into simple rule of thumbs or approximations. The concept of aspect ratio is well on the engineering side of this split.

The expressions defined to calculate aspect ratio reflect this.

One of the most dominant definitions is :

Squared Length of span perpendicular to the flow / total surface area.

As both are fixed as maximums per F16 class rules the maximal attainable aspect ratio is fixed as well.

The effect that changes of the shape will have on the overall performance may however change. I didn't make this definition, I'm just reporting the commonly accepted framework

Wouter

But Wouter all the boats you have mentioned in counter example have been very heavy high displacement boats namely the F18's and a lessor extent the FX1. They bare no resmblance to an A cat and require a totally differnt type of hull.

The F16 single hander though is not much heavier than an A and that is the exact point of my argument, that we shouldn't be thinking along the lines of F18's but more the refined A's.

My only doubt about this is the additional loads created by the spinnaker, but even here with the length of pole we have and the lift created by the flat spinnakers and the apparant wind angle we run I have thoughts that this maybe less of a problem than first thought.

My counter example was not a reply to your post Wayne.

The reason I don't see much common ground between the A's and the F16's is because the key ratio's and specs are to far apart to extrapolate results achieved in the A-cats to F16's.

I'm not going to cover all, there are more then enough posts of mine over the years that has discussed each and any of them. I'm not going to repeat those.

But basically the F16's are short and wide platforms with 20% more sail drive upwind and well over a 100% more saildrive when going downwind when in 1-up mode. The F16 solo sailor lacks a pair of hands and there is no such thing on the F16's as an angle of attack on the mainsail beyond 30 degrees (reaching).

The A-cats are long and narrow platforms with very lightweight masts/rigs. They are sailed by a skipper with a dedicated hand for the sheet and a dedicated hand for the tiller and the rig may experience angle of attacks as wide as 50 degrees (downwind).

These difference can easily lead to a score of differences. A Trivial one is the boom height. A F16 sailor really does not want a low boom when gybing under a spinnaker with the main cleated off.

A more complex difference is in the required dive recovery. The F16's have (even) on the upwind 20% more pitching moment then the A's and have 10% shorter hulls that need to withstand that and also have to carry 20% more weight. These three factors combine to require much more volume in the F16 hull over a shorter hull distance. This means that the bow angle is SIGNIFICANTLY greater (+35%) then on the A's; this is an important performance ratio as it determines the relative magnitudes between wetted surface drag and form drag (waves). I will stop here, but it must not come as a surprise that a 35% difference in bow angle makes the two designs alot less comparable then say a F16 to a F18 who both share an almost identical bow angle (100%).

This is actually one of the reasons why I predicted back in 2001 that the F16's would be just as fast as the F18's. Back then hardly anybody took me seriously. However, I knew that all the key ratio's such as the bow angle and prismatic ratio of the hull, aspect ratio's of the sails and others like the coefficient between heeling and righting moments were all identical to those of the F18's. Of course when each was sailed by their target crews. With such a strong similarity on all those factors, the two design could hardly not be of the same overall speed.

Now, all these factors do NOT match up nicely between the F16's and A's. Ergo, making an F16 more like a A-cat will most likely (well almost certainly really) not transfer the vast bulk of benefits. And without these you end up with an inferior design.

The rest I leave up to your own intellectual capacities.

I hope this answers your question.

Wouter

Gosh its is a complex subject and without detailed knowledge which as yet I haven't learnt, its difficult to reply.

Thanks though and keep writing as I am learning a lot as we go along.

Martin did never designed a succesfull A-cat but was involved in some design issues like the Mikan which was not a bad boat.
AHPC did licensed the Flyer but never the Tool. Jim supported Mercer after he stopped with AHPC to help the start up, AHPC never did anything with the Tool they where never involved there.

Pete Melvin did a succesfull A-class design and the Nacra F18 or inter or how they call these things.

Hans

"AHPC and the Tool", I stand corrected there.

I know Melvin did the Inter-18 but the Nacra F18 is by Comyn (spelling ?). Melvin also did the Nacra A2 but wasn't that a single event wonder ? Sanguiet back in 2006 or so where there was lots of light patchy winds ? I remember discussing this with you actually.


But yeah, Melvin would could be the answer to the question if a designer exist who was succesful in both classes. I grant you that. Although, I don't think two boats can be more different from oneanother then the Inter-18 and the Nacra A2. How does one even start comparing those two bow shapes to each other ? This would again bite us back in the tail with respect to how this whole discussion started.

Wouter

I did not think the designer of the Tool or any of the other AHPC boats was the same - ?????

Pete Melvin is likely one of the few that has had both. The I18 was not a success but that has to do more with Nacras messing with it in the early days of the F18 class in the US.

The A2 was very fast in light air and by changing the beams location the A3 was much better. Note no changes to the hull lines.

Pete also has the Infusion, which was after his A class boats and follows a lot of the percentages for distribution used in the A class. Quite a few people racing the Infusion have commented that it is much smoother and easier to drive than the Cap.

I agree an A will not just scale, but especialy with respect to the F16 which is light and can run uni there are a lot of concepts with ballance and developed lift that the A class has tapped that will carry over. Based on what I have experienced with the first few months of testing the Falcon I feel pretty confident they work.