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