SPIN . theory, designs, and techniques









First ,-I,m not a sail maker , naval architect, or have any special qualifications ,-just a catsailor who has logged some miles racing with shutes over the years-



To enter the Worrell all catsailors must submitt a sailing resume ,-this is basically it for those that wish to understand the perspective and interest in Formula racing .--

-CatSailing experiences include 6 Worrell 1000 s , a decade or so racing mainly in Hobie ranks winning numerous regional championships and regattas ,also attending numerous National and World {now Continental Championship races, -Races in the Prosail and Ultimate Yacht races as seen on NBC Sports in 88 and on ESPN. Also have races in larger monohull and several dingy classes inc Lasers Interlakes Lighting, which I rebuilt.-I,ve also built 2 catamarans of experimental nature along with restoring , repairing and helping others refitting catamarans over the years.



My first experience with shutes on cats were in the 88 Ultimate Yacht Race events on the then new Hobie 21s,-

shutes were launched off a tramp bag just on an extra set on bridal wires off the bows {no pole} no snuffer. It was quite a learning experience to jump into major competition, many of us had little spin time on cats, and most ran over the shute getting it tangled under the hulls and boards at least once ,--very embarrasing with a t v camera on you in a major event.

All got the hang of them very quickly though, particularly Carlton {great catsailor who the Worrell memorial trophy is in rememberance of} using a fuller HOOD shute ideal for the very heavy cat and its measurements and set up at that time.



-For those catsailors new to assymetrical shutes we use and are standard equipement now on numerous designs and all Formula cats , they are actually just BIG baggy jibs in effect,this is a good way to think of them , and not be intimidated by them . You race and sail with them much the same way you race and sail with the jib by keeping apparent wind flowing around it , reading telltales {if you must } keeping them flowing on both sides while sailing as low downwind as possible without stalling the flow of air on both sides causing stall and making the boat slow down . How precised this low downwind line a team can sail along with proper technique in set up and teamwork will determine downwind speed in various conditions .Most read the curl on the spin as it starts to break , many also add a set of telltails about half way up just above the seam about 12 to 18 inches back from the leading edge.-The one big difference in getting used to the spin is to BEAR OFF , downwind in the puffs to keep from turning over , new catsailors to shutes will instinctively turn upwind in gusty conditions and capsize , again the skipper must immediately pull the tiller and head DOWN wind at the first sence of a gust hitting or preferabley with crew spotting them and counting down their arrival -5-4-3-2-1-bear off slightly ,-

One other very important technique to mention here is the abosulte necessity to keep the mainsheet and main cleated in snug AT ALL TIMES and only use the traveler , The mainsail on most cats acts as a backstay ,if you release the main there is no support to counteract the force on the top mast area and large forces at work on the spin ,-the mast will potentially snap ,as we saw happen to one of the Worrell teams this year during the Hatteras leg in 30 mph gusts and confused seas.

- It is very easy to learn the basics of good spin handling, to master them in all types of conditions is a never ending lifelong enjoyable pursuit.



-Interesting , I gave the H-21 spin to a friend a few years ago who adopted it for use on his Nacra 6/0 ,-It was o k in light air but was just too full for the lighter faster 6/0 as compared to the H-21 it was designed for , in most conditions above 6 mph winds .A flatter more high aspect shute was needed for the 6/0 , it was fun experimenting though, we had a number of shutes including the huge 400 plus sq ft Worrell shutes , the Aussie version mid size ,to the much smaller flatter 6/0 shutes.--

Kind of funny , I gave the huge 6/0 Worrell shute to Matt,s father Bob to use on his hi performance Geogeon trimaran , he liked it so much he ordered one from Randy ,-

-This seems to be the general theory in observation of shutes applied to cat designs through the spectrum over the years of the earlier very heavy H 21s and similar earlier predicesors with big full shutes sailing lower , to the new HI TEC lightweight Formula 18ht debued this year with their 18 sq meter , much smaller flatter hi aspect shapes sailing at much higher hotter angles downwind to achieve the best VMG , or speed to distance sailed downwind fastest to the C mark or beach flag gate in distance racing.-I experienced this sailing angle difference being very noticable evan between the Inter 20 and new 18 hts in sailing the Spring Fever regatta this year on the I-20 in the same start with Randy and Matt on the 18 hts , they sailed much higher hotter angles downwind on the lighter 18hts.



The general conclusion and concensis seems to be the lighter the cat the more hi aspect ,{measurement of relative girth of spin , a high aspect main in taller and has less width} along with flatter shapes allowing higher hotter angles that best utilize its lightweight speed potential building more apparent wind .

The other very positive effect of the higher aspect shute is the area between the shute and mainsail or SLOT as it is commonly referred to being more open , the absence of a jib on the new 18 ht , A Class cats ,and others with no jib also improves this open slot area advantage ,---As we all know from sailing jib only reaches in higher winds you do not want to close the slot between main and jib or spin ,-it backwinds the main and or stalls the jib flow and slows the boat speed .



Higher aspect shutes do not overlap as much and have much better speed potential as wind increases , much the same reasoning for multiple headsails on Am Cup type sailing 150 genoas to 100 non overlapping etc.

-Again the larger shutes for similar cats have very similar luff dimentions and added area is generally in the lower aspect ratio ,along the foot, and having a further aft spin block attachment point with more overlap reducing the SLOT area .

These larger overlapping shutes are effective in lighter winds when the slot effect is not as much a factor as less wind is being contoured back through it at a lower velocity.

This will definately help heavier boats become more equal in lighter wind conditions ,-spin area in exchange for weight as Formula Classes apply in rules in limited amounts.

The ideal solution in spin design would be to keep similar aspect ratios for larger area , but this would involve a higher attachment point for the spin ,not a good idea -remember the mast snapping problem and recommendations of one third above the stay tangs max. -or the complexity of running backstays from a masthead type arrangment , ading windage weight hardware and complexity.,Increase mast height ,most are already at max.-also not a good solution.

A roller furling jib can be a help in some conditions but your also giving up 50 or 60 sq ft of sail area.

Another option is to increase the length of spin pole , the problem here is balance , as you move the sail forward the C E {center of effort } on the sailplan moves too far forward of the center of lateral resistence { hulls and board areas} which requires the rudders to constantly be correcting this further forward huge side force on the sails acting as a break in effect negating any speed potential increase and making the boat extremely hard to control ,--Some placed up to 15 ft poles on their cats but could not rake the rig back far enough to counteract its negative effects on balance.



Shutes are great fun , now a joy to sail with having great snuffer and turtle systems , along with ready made packages to retrofit spin and snuffer systems to existing designs.The added horsepower and speed they create once experienced in downwind sailing on a cat is hard to describe , but some of my best memories of sailing have been strapped on on the wire ,foot in a strap , flying off the tops of waves at 25 plus ,-{sometimes at night } crancking on the shute with each one as crew or steering though up each wave and bearing off slightly as we accelerate down the backs as skipper,-{sometimes huge ocean swells } just having the time of my life ,grinning ear to ear .



This is just random incomplete thoughts on spin. design and evolution .Others have filled books and videos on the subject all available here on Catsailor . Hope it is helpfull .



sail safe --added -



Many cats are now standard with shutes and snuffer including all Formula cat designs .

The Open Formula 20 class will give numerous catsailors a choise to update their current 20 and restore,refit ,and rebuild a number of excellent existing designs for major distance racing and major events very inexpensively or to purchase a new exciting Formula 20 boat available , Inter 20- Fox- Storm , and others available.



The 270 sq ft shute may prove best over a wide range of conditions for all boats ,but the 300 sq ft option is available for older existing designs weighing 410 Lbs or more ,helping keep them competitive long into the future .



Given the large number of existing 20s in the U S and Canada , the interest and acceptance of Formula type racing , the prospect of new major Formula distance racing and other major events needing fair equal Formula Class racing including 20s with shutes creating new interest and helping grow and promote the sport as many always felt Formula Classes in N A would accomplish , it seems like the right time to join in with the current 16 and 18 Formula Classes .



Current proposed Open Formula rules can be found on the Formula 20 forum here on Catsailor.{just below } Look for a web site up soon.

Carl

Interesting article in the recent Sailing World magazine on the current sailing speed record holder.

It is described as a tri foiler type with wing sail though would call it more of a proa which has a long lever arm {crossbeam} and pod set to windward to house the crew inside protecting them at high speeds.

The key to a multihull type craft wrestling the speed record away from boardsail type craft is the effect of beam and righting movement to relative weight and sail area, -obviously the multihull with its much larger beam and righting lever arm has the advantage, unless someone finds a way to attach an extended crew pod racks or wings off a sailboard.

This was actually attempted in effect nearly 30 years earlier here in MI by the Geougeon Bros, -known for West system boat building epoxy, with their run at the sailing speed record with their planning hulled similarly conceived proa SLINGSHOT . Crew would scramble out from the main hull towards the pod some 30 feet away as pressure on the sails and speed increased giving the righting lever arm and weight measured in ft lb. to counteract the forces on the sail.

One main difference is the course, the foiler requires a perfectly flat water condition with no wake and perfect alignment to wind direction, The Slingshot trials took place on Lake St. Clair, part of the great lakes filled with ocean going sized ships, ore carriers, and large powerboats of all types, -quit a difference but very similar concepts using the proa configuration and large righting lever arm and huge effective beam . . .



-Catamarans similarly have a huge advantage over monohulls partially for this reason, added beam. Some planning type skiffs with large racks or wings for the crew to provide this similar lever arm is the exception but same speed theory along with weight to sail area and hull planning capability and other aspects of proper design.. The lever arm of added beam and ft lb. of righting moment are measured by taking the beam, or distance and weight from the center of buoyancy or leeward hull. In cat design even adding one and a half feet of beam say from 8.5 to 10 ft of beam, one would add the weight of crew 300lbs and partial hull and boat weight 100 lb. { just fictional average } at 400 lb. times 1.5 = an additional 600 ft lb. of righting moment over the same crew and similar weight cat with an 8.5 beam as soon as the cats begin to fly a hull, quite an advantage as the wind increases in speed potential having the additional 600 ft lb. driving the boat forward on the 10 ft beam cat. .The most noted real life example of this larger beam effect on potential speed was during the last Olympic boat trials in selecting Olympic Classes and catamaran design for use in the 04 Olympics. The Tornado with its 10 beam sailed away from all 8.5 cat designs in the 15 mph. Av.winds.





-One of the most interesting experiments I saw in relation to added beam and its effects of catamaran speed was during the 87 and 88 Worrell 1000 , / World 1000 –open to any 20 ft cat. Two different boats were entered with 10 racks mounted, one on a traveler on an extended N-5/8 which became the 6/0, very interesting looking, but do the math, a 200 LB crew out an added 10 of effective beam adds up to 2,000 ft lb. of added lever arm counteracting the force on the sails helping drive it forward, ---no wonder this boat was over the horizon from all others within an hour of leaving the beach with its added huge lever arm and beam advantage.



The other most easily understood example of beam effect of cat design are the Supercat Arc and RC series of larger cat designs by noted designer Bill Roberts , these large powerfull cats with larger beam hold most major distance race records and have for some time. I had the pleasure of talking with Bill briefly this year as he stopped by briefly at Jenson Beach during this years Worrell 1000 just before the start . I also own a Supercat and am a big fan of his design work and development of so many good ideas applied.

Evan he ,with his jet engine engineering background will jokingly tell you –{you do not have to be a rocket scientist to understand the effects of larger beam and its positive effects on increasing potential speed in cat design. }



Have fun and sail safe

Carl

Hi Carl



What does your observation say about the future of 20 foot 8"6" wide beam boats. If you don't increase the beam, won't you be just a little faster then a 18 ft 8"6" wide boat?



Marstrom chose 9"6" for his M20 (still not legally trailerable) and not the 10 foot beam of the Tornado to account for the double trapeeze. He argued (second hand info) that the leeward hull would be over leveraged if the boat were wider, causing it to bury and increase wetted surface and ultimately be slower.



I am curious if there is another point of view on beam for a 20 foot boat?



Likewise, are the larger boats necessarily physically more demanding then the 18 footers.



Take Care

Mark

Breaking several new records this year in the Worrell 1000 most experienced catsailors will tell you they are fast enough , and will make the basis of an excellent Open Formula 20 class geared for some very exciting future events like the Tybee Formula 500 being planned and now talk of a more organized Formula Circuit .



Have fun

Carl