Spin area applied to cat design is still developing .
It begane with early design used in several classes and has a long history making a comeback for use in the last decade with better asymetrical shapes -configurations and snuffer systems.
Bill Roberts noted Arc designer patened an earlier version,
many have added over the years .
Most new modern cat design utilize snuffer systems and spin ,-they basically double the horsepower -downwind and broad reaching , they are just plain great fun .
Tests for the Olympic Tornado class changes recently and updates to spin use revealed an ideal size and aspect ratio and spin pole length in balance. This size was adopted for use .
In the U S modern type spin development was different , Randy S popularized the spin in earlier Worrell 1000 races using one very successfully on a P-19 ,-seen on the cover of numerous sailing publications.
In 88 the Hobie 21 with spin was used for 2 professional sailing series .-Prosail and the Ultimate Yacht Races -seen on N B C Sports .
Randy moved up to the 40s ,-but a number of excellent sail lofts produced very different spin for use on the 21s -
North --Hood -Smyth ,-Aussie chute ,-and others .
Carlton at that time used a Hood chute very successfully and developed an on tramp retrieval sysytem .
Numerous other spin developments occured ,-some of the most interesting was again by Randy S for the N-6/0 for use in 98-99 Worrell 1000.
By using more extreme mast rake and longer spin pole he developed huge 440 +- sq ft chutes with large overlap areas being sheeted off the back crossbeam location.
Other teams used more moderate sized spin -340 range area and showed to be more versital and as fast or faster in many conditions . The exception was light to moderate wind speed . -
This is very common in the Worrell 1000 with typical lighter seabreeze in the morning slowly building as with most coastal areas with the increased seabreeze as land heats up in the afternoon.
The largest gains in distance racing are actually made in light wind conditions . The time sailed is much greater so the light air days are where most differences in finish times occur.
A little different game in accumulated time, Bret and Rod the Austrailian team ,-Randy.s nemisis would often finish ahead on breezier days but never could make up the larger differences Randy put on them in lighter conditions .
From this some conclude that large chutes are better -faster etc etc . not true .
There are numerous design elements that come intergrally into play .
Aspect ratio is one ,-and slot area between mast and spin is another overlooked aspect .The modern new designs with no jib like the 18 hts that also have smaller high aspect ratio spin design do this for good reason,--it is faster.
Rating spin area for cat design presents some unique problems . Current P rating sticks on a one penalty increase fits all approach wether its a 200 or 400 sq ft spin .
Texel adopted ideal spin sizes per Tornado tests and applied progressive sizes per length categories with added penalty for any sizes over . 4 points are added to each spin rigged cat .
ISAF uses a better approach rating actual spin area as 10 % of total in rating formula equation. It also subtracts r-jib area from spin area .
What is needed is an added spin efficiency rating per aspect ratio also to accurately rate spin rigged cat deasign .
This is proposed in the TIP rating .-
Here are factual historical reasons to change to design measurement based rating --from current P-rating
Per research of Derek Kelsall and John Shuttleworth. Extensive correspondence in the english monthly Multihull International. A.o. in nr. 117 of october 1977. basic rating formulas for multihulls were further established .
In 1985 during a symposium in Annapolis a number of experts spoke about a simple system. A.o. the late Hugo Myers, one of the advisors for the original IOMR system, was an advocate for a formula which had the same general form as the final Texel Rating formula.
In the period from 1982 to 1984 there was a change over from a pure statistical system like the PY handicap system, to a pure measurement system. In the beginning, naturally, the IOMR system has been used, being the oldest one, adopted by the IYRU since 1974. But a period of experimenting started with the english formula of Kelsall and Shuttleworth and other formulas. In 1985, after consulting a.o. the american scientist Richard Boehmer.
When the IOMR and the simple T R formula are both supposed to be good, then it must be possible to express the set of formulas of the IOMR in the form of a simple power formula. Using a multiple regression analysis method on various collections of boats it has been a surprise that it was possible indeed. With such a high correlation between the results, that the simple power formula found, can replace the set of IOMR formulas.
What is said basically means that a formula of a type like the TR formula is a universal formula for multihulls. The formula is easy to adapt for all circumstances.
As the IOMR, the english (MOCRA) formula as well as the TR formula approximate the performance of optimal boats, additional corrections are possible and sensible for designs which are not optimal. That has been done in the TR system in the same way as has been done in the original IOMR (PMA) system in California.
The TR formula is metrical : 100 / (0.99 * RL0.3 * RSA0.4 / RW0.3)
To serve boatowners in the USA where crews use imperial measurements (feet, sq. ft. and lbs) you only need to change the constant factor from 0.99 to 0.3397. Simple and practical.
With the IOMR written as a power formula :
100 / (1.00 * RL 0.311 * RSA 0.42 / RW 0.318)
you only need to change the constant factor from 1.00 to 0.3275. for use in any area where people work with imperial measurements and weights.
--more on the rating development -
There are 4 formulas available to approximate the performance. Bruce nrs (1967), IOMR (1968), KSP since 1976, Texel Rating since 1984 Edmund Bruce, pioneer of Amateur Yacht Research Society, died 1973.
IOMR = International Offshore Multihull Rule (California, 1968).
KSP = Kelsall Shuttleworth Performance. (MOCRA formula, around 1978).
TR = Texel Rating by Nico Boon, 1984, slightly modified in 1993.
8.
IOMR, KSP and TR use length, sailarea and weight (displ.) only..
RL = rated length, RSA = rated sailarea, RW = rated weight. (kg.).
General form of these formulas : 100 / (c * RL p * RSA q / RW r).
Bruce (metr.) =2.5209 * RL 0 * RSA 0.5 / RW (1/3 ).
Bruce (imp. ) = 1 * RL 0 * RSA 0.5 / RW (1/3 ).
MOCRA (metr.) = 100 / (2 * RL 0.5 * RSA 0.5 / RW 0.5 ) .
MOCRA (imp. ) = 100 /(0.5 * RL 0.5 * RSA 0.5 / RW 0.5 ).
TR (metr.) = 100 / (0.99 * RL 0.3 * RSA 0.4/ RW 0.3)
TR (imp. ) = 100 / (0.3397* RL 0.3 * RSA 0.4 / RW 0.3).
IOMR (metr.) = 100 / (1 *RL 0.311 * RSA 0.42 / RW 0.318).
IOMR (imp. ) = 100 / (0.3275 * RL 0.311 * RSA 0.42 / RW 0.318).
IOMR here, is a "translation" into a powerformula of the IOMR formulas.
9.
Above Beaufort 5 or 6, stability of a design is the limiting factor for speed. A rating has to be calculated then by using the smaller sailarea making heeling moment = righting moment. No other formula required..
In very light winds use TR (metr.) with c = 0.89 and RSA ^ 0.5..
(rev.7/96).
---end Texel info -
We can use this base system very easily in N A -
We can modify it to existing conditions in N A
Per existing design and race preferences -
Believe the TIP rating outline addresses these , combining the best elements of Texel -ISAF and Prating .-
The advantages of this system are numerous -
Advantages
Utilizes the best features of the 3 main current rating systems in use ----Tex. Isaf and P. =TIP
Provides an accurate proven rating number for modern cat designs, --no provisional number is needed-
Eliminates the page of modification factors that utilize a one penalty factor fits all approach regardless of the size spin ;jib ;main mast height, -etc.
Provides a much larger base pool internationally of base rating information to help verify rating accuracy.
Integral rating system, more compatible to promote large class racing groups in N A .
--Would enjoy others getting involved to author as a group this improved rating system for use in N A --
Carl
