Sail area configuration effects on speed

Should be an interesting Worrell 1000 in 03 on the new Jav2- 18 HTs ,--Many would like to see the Worrell 1000 open up to Formula Classes in the near future. Possibly all types of F-18 HTs next year .

An interesting aspect in rules changed in 03 is that all teams will be allowed 2 sets of sails to be interchanged each day,- their option , presume many will have a larger full main and smaller flatter one, --similarly with the chutes.

There are some rumors also of a main reefing system to be put into use, --similar to the 110-ft cats in the RACE, -JUST A LITTLE smaller SCALE. This may be great for distance racing cats.

Another interesting aspect of the 18 HTs is that they seem to have settled into a shorter than max. . height mast allowed per class rules. This indicates a self-limiting factor to achieve the ideal sail configuration through the average range of conditions.
A taller mast and sail in ;aspect ratio{measurement of foot to luff length area inc. roach } generally 3 to 1 or more, --that is the base or foot of sail is one third or less the height.

We see this self limiting feature applied to mainsail aspect ratio and mast height applied in development classes like As and 18 SQs, --Some As sailed in predominantly light wind will have high aspect ratios and do well in light wind conditions, -but fade to the back of the pack as winds increase.
Similarly 18-sq. development went briefly to higher masts and sails but were beaten through the range of higher wind conditions by those with shorter masts and lower aspect sail.

We see many of the older designs like H-16s for example with relatively shorter masts 26 ft and lower aspect sails by modern standards that really excel in as the wind increases. ;We see similar effect in several newer 16s that have similar beam and righting features as longer length boats but have less sail area on shorter masts, --They also excel in higher wind speed conditions. Catamaran design with larger sail areas power up sooner, -but this added area when overpowered turns into aerodynamic drag as the flattened top portion twists off to leeward in high winds.

The ISAF has standard method for measuring {real sail area} ;this is what is used in several classes.
Some use rated sail area, which basically adds sail area to those that measure beyond a certain aspect ratio.

The high-speed record attempting sail craft use very small low aspect sail plans for anticipated high wind speeds required.

Is there an ideal formula for aspect ratio and area for each wind strength?
The question many W-1000 teams will be asking -what is the ideal for the 18 HT in 2 size ranges antisipating some higher wind speed days?

One rated sail area question also, would a 2 windspeed factor approach be a better means of rating sail area accurately, --based on mast height ;luff length, --sail area ;-aspect ratio and C E ;{center of effort}

Thanks
Carl

Some corelation between rating systems in use is needed past and present.

The discussion purpose is to explore concepts and ideas to improve catamaran rating .
-A study of past rating systems and calc and percentage applied factors based on yacht design data is the basis or a factor for all rating systems . -

Do these standard applications vary when applied to design trends in modern catamaran design --
Many previous rating systems applied to yachts where displacement -- single hull stability ---limited beam to length ratios ,--and max. hull speeds of around 6 knots dependant on hull length ,- were main factors .
Stability and sail area vary , 18 sq cat design with 18 ft L -and 10 or 12 ft beam are certainly very different and require a very different means of rating than a similar sized single hulled non planning craft .--Similarly trimarans with more beam than length require a different approach to rating along with their very different basic design features and speeds .


The 60 tris race in class ,-how do these relate to equivilant sized sailing yachts.-

There is a practical self limiting sail area and ideal design aspect ratio for many catamaran classes in existance .
A Class cat design ,-18 sq ,-Formula 18 HTs with variable mast heights have found the ideal to be less than max. allowed in class rules.
It may be best to use actual or real sail area and simply designate an efficiency rating in 2 windspeeds for them .
It would seem greatly simplified .2 windspeed approach would allow effects to be more defined and reflected in them rather than the current sail efficiency factor calc.


Other differences are an ability to change sails --headsail sizes and types ,--also common on yachts are mainsail reefing systems commonly used ,-not commonly used in smaller high speed beach cat design.

Aspect ratio A as a factor is most effecient upwind , less downwind and reaching on non spin rigged cat design.

Downwind current design trends are to spin cat design.
Reliant more on high aspect ratio mainsails upwind ,-and setting the spin down , which are also becomming more high aspect in ratio per area on taller lighter masts with less overlap area on the main .
As most catsailors know the slot area in high speed cats is a key to obtaining max/ speed . This applies to jib slot -or assymetrical high aspect spin .
Catamarans also sail higher hotter angles downwind to keep attached airflow and speed.-This effects sail efficiency again ,-very differently than other sailing craft.

Spin efficiency is currently a non rated factor ,--

For consideration --
Should a revised -updated efficiency factor for sails --both main jib --and spin area be formulated .
Based on a 2 windspeed factor basis .
Sail area effects vary as a total percentage with windspeed.
The relationship between spin-non spin types vary with windspeed .
Aspect ratio efficiency of all sails varies with windspeed .

The goal being to allow design freedom in sailplan configuration to encourage faster safer design .
If a catamaran can obtain the same speed with a higher aspect 14 sq meter sail as a 17 ,-then the 14 ,not the 17 should be the ideal target for designer ,--then reflected accurately in rating .

In Porthmouth rating tables now with added 4 catagory windspeeds we see rating numbers moving downward with each as speed increases . Typical of the spread is a 3 to 5 pt increase with some exceptions with unusual older design being a reflection of time to distance traveled by current skippers in class. With shorter times around the course this makes sence . What may not as boats are uniformly incrementally adjusted in windspeed is the effects in relation to one another . With aspect ratio difference ,-beam variation ,spin and non spin effect we should see a narrowing of times in relation to one another rather than a uniform upward scale .


Below are Texel and ISAF - abbreviations and efficiency factor calc.


Texel --
Sails
EG = efficiency percentage genoa (jib)
EM = efficiency percentage mainsail
MSAG = measured area jib (genoa)
MSAM = measured area mainsail
RSA = rated sailarea RSAM + RSAG + RSAS
RSAG = EG * MSAG * 0.01
RSAM = EM * MSAM * 0.01
RSAS = MSAS * 0.07
VLM = vertical projection of luff of main : That is the distance measured alongside the mast from the highest point of a normally hoisted sail towards the lowest point reached when the downhaul is used.
VLG = vertical projection of the luff or leech of the jib/genoa. That is the distance between the horizontals on the mast taken from the highest point of the jib/genoa towards the lowest point of luff or leech whatever. It will be measured alongside the mast. In practice :
VLG = luff * 0.94
SMG = distance between middle of luff and leech of the spinnaker.
SF = length foot of the spinnaker
SL1 = length luff of the spinnaker.
SL2 = length leech of the spinnaker

Sailarea : How the sailarea (main, jib and mast) will be determined is described in appendix 1.
MSAG = Area genoa or jib
MSAM = Area mainsail including mast when swivelling
VLM = Vertical projection luff mainsail. That is the distance measured along the mast in a straight line between the highest point of the sail normally hoisted and the lowest point reached when the downhaul is used.
VLG = Projection luff genoa or jib. That is the vertical projection of the luff or leech of the jib/genoa. That is the distance between the horizontals on the mast, taken from the highest point of the jib/genoa towards the lowest point of luff or leech whatever. It will be measured alongside the mast.
Spinnaker and spinnakerboom
Definition of a spinnaker
Each triangle sail not being a mainsail or genoa is a spinnaker. The condition is that SMG, the length measured along the rounding at half height >= 75 % of footlength SF.
Stiffening systems
It is forbidden to stiffen the spinnaker by leechlines or battens.
MSAS = area spinnaker or reacher
Calculation area spinnaker MSAS
The regulations including how to measure and calculate the spinnaker area will be described in appendix 4.
Ratingnumber applied when using a spinnaker.
The lowering of the rating when a spinnaker is used will be described in appendix 4.


The real sailarea is determined by one of the usual methods.
see ISAF rating


Calculation of MSAM and MSAG, area mainsail, area jib respectively. From both data RSA, the effective area, will be calculated by using an efficiency percentage. That requires the determination of the aspect ratio A. This A is the result of the calculation : Vertical height of the sail (VLM for the main and VLG for the jib/genoa) squared, divided by the area. formula :
A = VLM * VLM / measured area
If a mast is used which is swivelling, with a section which is not a circle then the area of the mast is added to that of the main, before the factor A is determined.
Area mast = 0.5 * maximum circumference * VLM
eff. % = 40.1 + 18.31 * A - 2.016 * A 2 + 0.07472 * A 3
RSA = real sailarea * eff. % * 0.01









ISAF RATING SEGMENT --
Ratings, (i.e. time dividing factors,) take as basis measurable datas, warranted by classes, builders or importers, and are calculated using the IOMR formulas described as follows, verifiable by anyone.

C.2 Datas

WC Weight of the crew (for calculation purposes only).
WS Minimum weight of the catamaran in sailing conditions.
AL Maximum overall length.
WL Maximum waterline length.
CM Maximum authorised mainsail area.
VLM Maximum vertical projection of the luff of the mainsail.
CJ Maximum authorised jib area.
VLJ Maximum vertical projection of the luff of the jib.
CSPI Maximum authorised spinnaker area.
CB Maximum authorised board area.
VLB Maximum board depth below the hulls.

C.3 Formulas

All the following formulas use metric units.

C.3.1. Rated Measurements

Rated Length L : = L = WL + 0.3(AL - WL)

Rated Weight W : = W = WS + WC

Rated Sail Area A : A = M + J


M = Rated mainsail Area = CM x ME
J = Rated Jib Area:

*Multihulls without spinnaker : J = CJ x JE
*Multihulls with spinnaker: J =(CJ x JE) + 10% x (CSP! - CJ)

where: ME = Mainsail efficiency* JE = Jib efficiency*


Sail efficiency (%) : SE = 40.1 + 18.31 X -2.016X2 + 0.07472X3