? Marstrom or A2 ?

Wouter,

I said

Simon,

VAT = 17.5% for UK
Import tax = about 1.7 %

M18 => 18.000 * (1.00 + 0.175 + 0.017) + 1500 + 500 + ? shipping = 21456 + 1500 + 500 + ? shipping = 23456 + some extra for shipping. Cheapest way across the English channel = 300 Euro (when you pick it up and drive it to UK yourself). So I think it is safe to say that M18 will cost you at least 24.000 Euro's. = 16.700 Pounds

I can get you the next best thing (incl all) for 54 % of the price of a M18. As good as halve the cost of a M18.

How much extra are you guys willing to pay for 2 minutes extra speed during a 60 minute race ? If it is a handicapped race than doesn't make much difference anyway as the rating just corrects it back and extra speed potential. In M18's case the ratings are even harder on it than on the next best thing. So for more money you are less likely to make a win in handicapped races.

Anybody paying 23.000 Euro's for a Nacra A2 is out of his mind. You will look pretty silly when you can't beat 15.000 euro F18's and 13.000 euro F16's with that boat and in Simons case also not beat 13.500 Euro Spitfires.

I'll say that the A-cats are great boats but they are simply not worth those prices. Their greatness in speed has largely been lost over the last 4 years. Their limited width and single sail setup is holding them back.

Wouter

Simon,

You'll be hearing from me soon, some more input for your excel sheet.

Here is a first bit :

Crossing the British Channel with car-trailer + boat = about 300 Euro's. (round trip).

Wouter

Wouter,

Slightly confused by the 2 minutes in 60 M18 vs F16.

F16 rates at 104 SCHRS (I think) and 103 Texel ?

Surely an M18 rates lower than 102/101 ?

I would expect it to be around 94 to 96 (at a guess), i.e. A class less a bit for the Kite....



My current price roughly agrees with you on the M18, (where you get the import duty from) I believe i only need to pay VAT at 17.5% (but I have not done any proper investigations)

Simon,

>>Slightly confused by the 2 minutes in 60 M18 vs F16.
>>F16 rates at 104 SCHRS (I think) and 103 Texel ?

F16 schrs = 0.98 (solo)
F16 Texel = 101 (solo)

No modern A-cats or M18 in SCHRS
M18 Texel = 92
A-cat Texel = 100

But you are not going to get 8%-9% more speed out of the M18 relative to the A-cat and F16's.

M18 is suffering from two drawbacks in Texel. High aspect mainsail and extremely low weight. The Texel formula is showing increasely big ofsets at these extremes.

I always use additional wetted surface, prismatic ratio and aspect related power calculations to check up on performance predictions. Often these confirm Texel predictions but at these extremes these differ considerably with Texel predictions.

Example. Wetted surface ratio M18/F16 = 96.6 % => (2.5)root of (96.6 %) = 98.6 %
This numbers suggest that M18 sails 1.4% faster in light and medium wind condition due to less weight alone.

Effective sailpower ratio M18/F16 is between 106 % (light winds) and 98 % (strong winds); medium winds will be an rounded up average of these = 103 % => (2.5) root of (103%) = 101.2 %
This numbers suggest that M18 sails 1.2% faster in medium winds due to more sailpower. At maximum it sails (2.5) root of (106%) = 102.3 % is 2.3 % faster than a F16 due to more sailpower alone.

The M18 spi is 15 sq mtr I beleive while the F16 one is 17.5 sq. mtr. This means that the 17 % larger F16 spi has roughly 10 % more sailpower than the M18 spi translating in 5-7 % more overall sailpower downwind. This fully compensates for the higher wetted surface drag of the F16 making both boats about as quick downwind.

Then prismatic ratios (wave-making drag); this is only of limited importance at the high windspeeds where high hulls speeds are attained => strong winds. M18's ratio is way down there 153/5.49 = 28 but F16's = 180 /5 = 36 are not high by any standard take a look at F18's = 330/5.5= 60 even F18HT's = 285 / 5.49 = 52. So these singlehanders are mainly, if not totally, limited by their wetted surface drag. A thing the Texel formula does not compensate for; it says "longer hulls-higher boatspeed". This is wrong as wave-making drag is typically only a small portion of the overall drag. Wetted surface is more dominant. So large savings in wave-making drag tend to have only very limited increases in speed. But lets take the maximum possible gain. 28/36 = 78 %. (2.5)root of (78%) = 90.4 % this leads to 10 % more speed to the M18 WHEN ONLY wavemaking drag is assumed to be THE SOLE factor taken into account. This is absolutely not the case and arguably very wrong as wetted surface drag is at least as big if not larger and so to the aerodynamic drag of the rig itself. I refer to measurements made on Miss Nylex C-class catamaran. Also the high rig of the M18 needs to be depowered more in these conditions than the lower F16's, also because of less righting moment. so again reducing the sailpower in total by 15 % = 5% - 6% speed loss due to less sailpower. If we take these additional factors in account the M18 will be very hard pressed to sail more than 2%-5% faster than the F16 in the heavy wind conditions.

So what do we have on average :

Light winds 1.4 + 2.3 = 3.7 % more speed to M18
Medium winds 1.4 + 1.2 = 2.6 % more speed to M18
Strong winds roughly 3.5 % more speed to M18

On average 3.7 + 2.6 + 3.5 = 3.3 % more speed for the M18, much less than 10 % that Texel predicts.

(103.3% * 3600 sec) - 3600 = 3720 - 3600 = 120 seconds = 2 min per hour


>>Surely an M18 rates lower than 102/101 ?

It sure does but can it sail to that rating ? Example F16 (solo) SCHRS rating is 0.98 but I can tell you right now that an F16 can not sail to that rating. Real life data suggest that is about as fast as the doublehander F16's that have 1.02 as a SCHRS rating. Similar things are being said by A-cat guys. The rating systems are off at these extremes. And I
've done quite a lot research on this as I have proposed and worked out a modified system to replace Texel and solve these issues.

Believe me M18 is a fast boat but not that fast. It is still just an A-cat with spinnaker and A-cat are not that much faster than a upgraded F16 (Ashby main etc) without a spi. Ask Ashby himself what he feels about the T4.9 performance. He may surprise you. There are conditions in which he thinks the singlehanded T4.9 is faster. Now imagine that with the upgrades.


>>I would expect it to be around 94 to 96 (at a guess), i.e. A class less a bit for the Kite....

A-cat can't sail to their rating of 100 against the spi boats. These A-cat ratings most slow down. Rough experience over suggest that A-cats are better sailed off 102 or 104 under Texel. Again, the Texel rating gives a rough buty dependable prediction for most boats but deteriorates greatly at the extremes and that is just where the M18 is. F16 so too, but still less so because we've done some clever things in the class rules that limited the hits we would get. I helped that I knew the Texel system (and thus SCHRS system) very well.


>>My current price roughly agrees with you on the M18, (where you get the import duty from) I believe i only need to pay VAT at 17.5% (but I have not done any proper investigations)

UK and European union. European union VAT 17.5 % minimum, some nations have 19 %. Import tax is supposed to be level over all EC nations. A friend payed 1.7 % importduties in 2003. And you can't work your way around these inport duties as Sweden is not an EC nation. So this adds another 310 Euro's. Everything adds up.

Besides I need to know this [censored] because I'm involved as the advisor in the European Taipan F16 group deal. I've done some research on this matter and have some personal experience at it.

I hope this helps.

Wouter

I just can let it go without comment Wouter, although I didn't want to get into a long discussion with you on this topic and yet I am sure that what I am about to say will get a verbose reply from you.
You have stated that "wave making drag" is not of any major factor in circumstances as you have outlayed above, and that wetted surface area is far more critical! Well I am sorry to disagree, but from my own calculations based on figures and quite thorough practical testing conducted by C.J.Marjac, many years ago, when it comes to the practical application of drag factors for craft of small dimensions, of which can be included all of the sort of cats that we refer to roughly as "off the beach", wetted surface area produces such a minimal difference in drag between ANY/ALL of these sized cats as to not be of relative consequential variation to be used for the "static" calculations of differences in hull performances
Whereas there is a huge difference in drag (and therefore potentual performance) between cats with hulls of equal length, weight, and having the same "driving" power applied, but of different "wave making drag" design efficiency or lack there of. The practical "observations" of this are many and plain for all to see.

>>Well I am sorry to disagree, but from my own calculations based on figures and quite thorough practical testing conducted by C.J.Marjac.

Marchaj and Bethwaite both looked at this and have done many years of research and are both highly respected authors with heaps of proven credit. Yet their views are (apparently) 180 degrees opposite of eachother (according to you). They can't both be right so at least one of them is wrong. Personally I've read Marchaj and I do not recognize that Marchaj wrote anything that would place wave-making drag over wetted surface drag in lightweight beach catamarans. I have the new, updated, 1990 version of his work. I do have some serious misgivings about how Marchaj compares boats. Here he picks information that eventually will suit his own prejudice regarding the fact that no serious improvement in design have been made over the last 100 years. But still I think it is you who is intepreting the results differently.

For lightwind the contradiction is easily proven away. Below theorectical hullspeed (Froude law = 1.54 * sqrt (waterline length), wave making drag is of no serious importance in boats. This is a well established fact in Naval engineering. Hullspeed for 5-6 mtr boats (16 to 20 feet)is about 6 to 7 knots. So when a boat is travelling at 3.3 mtr a second (11 feet/sec) the wavemaking drag is less than a fraction (15 % or so) of the total hull related drag. This means all the way up too medium sailing conditions when sailing upwind and downwind without a spi in 0-10 knots of wind. The reasond for this is because the energy is given back to the hull by the bow wave rising back again before it reaches the sterns. This is so fundamental in Naval engineering that it must be common knowlegde. So my light to medium calcs must be right.

As Froudes law suggest above theoretical hull speed the drag of a hull rises drastically and very quickly (on heavy monohulls) as a result of the wave-making drag increasing drastically. This is a result of the fact that the bowwave system is now laying at the stern or behind it and the hull can't recouperate the energy that is lost in it. Now here our views start diverging I'm sure. I definately belong to the camp where the opinion is that Froudes law doesn't accurately describe what happens to catamarans and skiffs when they pass the theoretical hull speed. The fact that both skiffs and lightweight beachcats reach multiples of their theoretical maximum hullspeed in stable conditions is at least a clear sign that something different from what Froude's law predicts happens. But you can also see it. How big is the wave system thrown up by a A-cat / F16 or even Tornado at 7 knots boatspeed when compared to say a 20 foot monohull day/weekend cruiser ? Then the cruiser stays there with increasing winds while the skiffs and cat accellerate to 15-20 knots with increasing winds. This at least indicated that weight per length has a big role to play as both designs have the same the theoretical hull speed. Arguably the wetted surface of both boats can't explain this sudden divergence at 6 knots, only differences in how the wave-making drag is behaving can explain this. Froude's law accurately described what happens to heavy yachts so the fault can not be found there therefor it must be wrong predicting what happens to truly light weight yachts.

But you ahve not refered to Froude's law and only to your won experiences :

>>many years ago, when it comes to the practical application of drag factors for craft of small dimensions, of which can be included all of the sort of cats that we refer to roughly as "off the beach", wetted surface area produces such a minimal difference in drag between ANY/ALL of these sized cats as to not be of relative consequential variation to be used for the "static" calculations of differences in hull performances.

Than please explain how your results allow for a 14 foot catamaran with less sailarea to outsail larger boats as you have claimed yourself about your own 14 ft designs. This boat has nothing going for it according to you ; less sailarea and less waterline length. If anything this boat should be slower. Still these perform the same. How can that be ? According the theorem of less waterline length it should be slower. Unless the generally accepted waterline length theorem is simply wrong in these cases; as is long known to designers of military fregates and destroyers as well. These do breach theoretical hull speeds by multiples as well and with limited engine power.


>>Whereas there is a huge difference in drag (and therefore potentual performance) between cats with hulls of equal length, weight, and having the same "driving" power applied, but of different "wave making drag" design efficiency or lack there of. The practical "observations" of this are many and plain for all to see.

Boats of same length, weight and driving power can have huge differences in drag ? Now I think 90's A-cats and 00's modern wave-piercer A-cats look very different in their hulls but their performance seem to be within 5% of eachother. Look at Inter 18 hulls and Tiger hulls, very different yet about the same speed during the 90's. Where is the huge difference in drag ? Same applies to pretty much all Formula classes. And what happens when an F16 hull is just a scaled down F18 hull ? Surely non existant differences in hull design can't by used to explain anythig away. Remember we now have a Blade F16 and a Blade F18 designs that are performing the same as other F18's. What explains the equality when the hulls are arguably similar and the 16 has less waterline length and less sailarea ?

The answer can only be weight. You probably say that this reduces wave-making drag considerably while I say that this mainly reduces wetted surface drag. For a long time this divergence was still possible. We only need to find a counter example that disproofs this. I present F16's to F18's. Actually the prismatic ratio of F18's and F16's hulls is identical (strongly linked to wavemaking drag) with the F16's being shorter. Even the rigs are a scaled down version of eachother. An F16 hull is nothing more than a scaled down F18 hull meaning it has exactly the same wedges and pushed water a side just a quickly as an F18 hull at the same speeds. Only the F18 pushes more aside as its hull is wider and goes deeper. Still these boats perform equally with the F16 being noticeably shorter. Which has the higher wave-making drag you think ? This can only result in the situation where the F16 is having less (hull)drag together with less waterline length. A direct contradiction with the common accepted waterline related drag believe which states that more waterline length reduced (wave-making) drag. Now I can see how wetted surface is reduced by making a hull shorter leading to less hull drag of such a hull, but there is no easy way to explain how making a hull shorter will make wave-making drag less as well. There are only two ways out of this situation :

-1- Wetted surface related drag is much more dominant than wave making drag in these designs. So that any increase in wave-making drag is completely dwarfed by the reductions in wetted surface drag. The descreases in one more then compensates for the increases of another.

-2- Wave-making drag is NOT directly linked to only waterline length but to some other ratio like Weight/length (which I used in my other post) or Width/length where reductions in wave-making drag are possible when a hull is shortened.

Combinations of both are possible as well as I used in my earlier post.

So Seriously Darryll, I fail to see how Marchaj or any other person with experiments can disproofs what I've done in my other post. My theory explains what happens in a few very important cases where their theories simple predict a different outcome.

We can still decide we believe one system over another knowingly that it fails in certain key comparison but than we enter the realm of believe systems instead of science.

I hope this explains the background to my earlier post a bit. There is way more but it will take far too long to write all that down.

Best thing I can say is that no-body believed the F16 claims in the beginning. With regard to equality to F18's. Among which the US rating committees. Now we know better. Daniel won his class at Westland cup in 2004 at an F18 rating, Jennifer won a first in first-in-wins-racing in 2004 in a mixed F16/F18 fleet and is also Alter Cup qualifier Area D and Spitfires are all in the top 20 at Texel 2004 with a 104 Texel rating (F18 = 102). All things not possible under commonly accepted waterline length reasoning.

With kind regards,

Wouter

In my spare time I will look up the Miss Nylex data. Google can't find the webpage containing this info anymore, but I have a hard copy. Somewhere.


Wouter

For a very very simple example Wouter, a knike blade run through a fluid sharp edge leading, offers very little resistance to the motion of the blade, BUT turn it at ninety degrees and run it through the same fluid in the same way and the resistance is very very noticable! Same knife, same surface area, same motivation, different drag induced, fairly obvious that a hull that is "finer" through the water offers less resistance to forward motion than one that is "fat"???

What does all this discussion have to do with the availablity of an A2?
I have given up trying to get any pricing and delivery on the A2 and have a Flyer on order.
As far as if the A boats are worth the price, you have to look at it in the context of racing within the class. For Portsmouth you have just as much a chance of winning on corrected time with a 20 year old Hobie 14 Turbo as you do spending money on the latest hot boat.

When it comes to boats of smaller length out performing others of longer length WOUTER there is such a thing as "efficiency" that comes into the equation, it should be obvious that of two craft of differing size, a craft designed smaller BUT more efficient WILL out perform a craft that is moderately larger but incorporating a greater amount of inbuilt inefficiencies (all other variables being equal). You use a lot of formulations gleaned from various places, but you seem unable to combine them into an accurate, logical result for other than that which suits your purpose at the time, this is not a criticism, but purely a personal observation.
Have you not noticed that an ice yacht far outperforms sailing craft (on liquid water) of ANY size and power, by many times? All the principles of aerodynamics and hydrodynamics apply equally to both. The ice yacht is sailing on water in its solid form but it is still sailing IN water in its liquid state due to the pressure of the blades on the surface of the ice at point of contact. You could be a little less reserved when intimating that “smaller should in some way be slower”, Smaller IS slower when ALL other relative factors are equal, but only when they are equal, and that could perhaps explain why there exist the differences between a “Tiger” for example and an “A” class, their differences far outweigh their similarities. To even try to compare different class’s of cats “theoretically” is fraught with “pitfalls” due to the HUGE amount of different related variables between them. To take only a small “few” of these differences and try to say “this is why”, no matter how many established principles and “theories” you try to apply is invariably going to lead to incorrect or at best, subjective conclusions.
As to Marjac or Bethwaite, I have to confess that having been personally familiar with Bethwaite for over 40 years, and having applied Marjac’s “theories” with success to my own commercial designs, I have to say that when it comes to “originality” and accuracy of experimentation. I have to give Marjac top marks and Bethwaite rates somewhat considerably lower.

Your right GISCO, the thread does seem to have wandered, and I apologise for my part in that, and I think that your point is well taken that it really all boils down to personal choice when buying a cat to compete on and not a matter of “mine is better than yours” like two kids at school competing to see which one can “piss” the highest in the school toilet!

Go to post

http://www.catsailor.com/forums/sho...ew=expanded&sb=5&o=14&fpart=

and lets continue this discussion there.

If you think that I'm pissed off then you are right. I am, I didn't spend all that hours passing University examens and studying through other sources like Bethwaite and Marchaj to get dusted by somebody who believes that I'm wrong because he just very much believes that.

Counterargument on a scientific basis please, not some "personal observations" or "dislike for Bethwaites way of doing experiments".

I challenge you !

Wouter