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WTCA News>2007>Tasar RCB Stay Slide Option

Tasar ReCirculating Ball Stay Slide Option

A “For interest” comment by Frank Bethwaite, Designer. 6th November 2007

Ethos (Characteristic spirit of a system).

At root, the NS14 - Nova - Tasar thrust was a gender revolt in which we replaced a “Women don’t sail” credo with a “Women are welcome” invitation, and expressed that invitation by creating “a good boat for a man and a woman”.

The research and development which went into that boat is outlined in High Performance Sailing. It was good enough to create, in 1975, the Tasar. This was a boat which in 1975 looked like1980 but which possessed dynamics decades ahead of its time.

For its global spread and more recently its revival I thank many visionaries. Initially there were my Sydney and then Australian friends who promoted it strongly despite Performance Sailcraft falling in a heap. They created a solid Australian centre of strength which gave the Tasar a second chance to spread. From this centre:

• In Vancouver, Mary Paddon’s indefatigable enthusiasm and drive created the NATA
• In the UK, Matthew Wetz organized the scattered owners into a strong TAUK.
• In Japan, Keiji Yoshikawa’s vision and planning created JTA

These initiatives established the Tasar as a strong global class by about 1990. For another ten years the class thrived, then began to decline as it approached the end of its product life.

At this point a new set of initiative appeared. The Melbourne Tasar group sensed the difference between the superficial image which was aging as all static products age in this consumer world, and the continuing strength of the Tasar’s dynamics which remained sound and relevant. They started to promote the Tasar strongly. First they organized team racing throughout a Docklands Boat Show several years ago. This demonstrated the strength of the class’ organization. Interest in the class surged.

A “Future Directions” committee was formed, and focused on improving the image while maintaining or improving the underlying dynamics. Within three years we had the Mylar sails of more modern appearance and lower cost, The Tasar suddenly began to look Twenty first century. Class growth worldwide revived.

Bethwaite Design has pitched in with new moulds, the cast Rudder Stock, the Bethwaite Series regattas, and other initiatives.

When Europe dropped the ball, it was again the Melbourne Tasar group who picked it up. They thought outside the square, organized the 1977 World Championships in an exotic location, and we enjoyed the new experience of the Phuket Worlds. We can now see why the Laser Masters World Championships have become so popular.
As a result of these modernization thrusts, the Tasar is beginning to present as one of today’s boats, with a second and solid life cycle ahead of it.

For some time there has been a strong call, again from Melbourne, to take another step along the modernization-of-the-image path, and allow the use for the stay slides of the light strong ReCirculating Ball (RCB) roller cars now available.

As designer, I deem this justified both at a fundamental level to reduce the physical effort needed to draw the stay slides back and so keep the boat within the strength of a woman to handle, and also as a part of the ongoing modernization thrust. I have therefore undertaken the work needed to get the essential design facts.

My Design Objects.

• No change to mast-pin and stay-position geometry.
• Retain “extreme condition” continuity of strength.
• Retain say 100% margin for routine conditions.
• Must be ergonomically efficient.
• Must be comfortable - no cleats nor bumps where the forward hand swings.
• No change of function.
• Must be visually appealing - No unsightly lumps.

“Extreme condition” Test Program

From time to time sailors get “caught out” in extreme conditions. Usually the first thing to break is the stay. Occasionally it is the mast. The continuity of strength of the existing design is about right.

1. I re-tested the present C-section track and slider arrangement to destruction, to reconfirm what we have been using. (Note; 40 years ago I tested both the smaller and the larger Ronstan tracks, and found the smaller to be the stronger. The larger track distorted under extreme load. That is why we use the smaller track).

2. The Ronstan 14mm roller car arrangement was also tested to destruction.

Apparatus.
The tension from a 49er 6:1 Boat Bender was doubled to give a purchase advantage of 12 to 1.
To measure the friction loss the actual tension was measured by Loos guage up to the limit of the Loos table (which stops at about 40% of the theoretical breaking strain of the wire.)
Friction loss increases with tension, and is less than 15% at 200kg. I have assumed 25% loss at 600kg.

Test No 1
Present C-Section track, slider and stop, and 2.5mm 1:19 wire with thimbles swaged in with Nicopress swages.
Stated breaking load of slider 980lbs; of wire 1050lbs.

The slider was positioned above one 3/16” bolt, so the entire tension was taken by one bolt.

Tension on the rope “tail” was applied through a spring balance, and increased in 5kg steps, i.e pull to 20kg, Hold for some seconds, ease to about 10kg then pull to 25kg and hold for some seconds - repeat.

System held 60kg. Wire broke at about 63kg as next cycle was applied. Thimbles distorted. No other distortion.
A pull of 60kg on the rope tail implies 720kg less friction loss of say 25% so 540kg = 1190lbs on the system.
This is about what I expected. This is what has served us well for thirty odd years.

(Note. The gunwale laminate is simply not designed to accept a half ton point load. A broad and RIGID backing plate of adequate area to spread the load is essential).

Test No 2
Ronstan 14mm roller track and 14mm roller car with tiny 1/8” bow shackle. Again, track bolted with two 3/16”bolts, car positioned directly above one bolt.

System held 55kg, held 60kg for about three seconds at which point the shackle failed. Mode of failure; shackle pin bent then broke at start of thread. No other distortion. Tension on stay about 1190lbs.

(Note I think that the small 1/8” bow shackle had been fitted as part of a self-tacking jib arrangement, in place of the stronger shackle which comes with the car).

I conclude that the 14mm roller system is probably as strong as the present slider system, and would be strong enough if the ultimate breaking strain were the only consideration. But it isn’t.

“Normal operation” design considerations
- The Tasar is designed to sail and race in winds up to 25 knots.
- If you calculate the tension on the shrouds in 25 knots the worst case is the square run with the slides forward when each shroud will be carrying about 500 to 600lbs (depending on wave state).. This is about half breaking strain, so again is about right.
- At this point the 14mm and the 19mm roller (RCB) systems separate.
- Despite its surprisingly high ultimate strength, the 14mm system has a safe working load of 230lbs. This is not enough. For this reason I am not prepared to approve it.

The ultimate strength of the 19mm system is well in excess of anything the Tasar needs. Its safe working load of 600/650 lbs is exactly what is needed. I deem it to be adequate and appropriate for the purpose.
A problem with the 19mm system is that the stopper slides are huge and unsightly, and expensive. A search is underway for a more compact restraint arrangement.

As at early Nov 2007, two Tasars have been fitted with the 19mm system and sailed on initial trial.
Martyn Sly, crewed by Mike Paynter, sailed in Melbourne with a stopper on one side and a cleat arrangement on the other (see photos). Chris Parkinson sailed in Lake Macquarie with the cleat system both sides.

Both found that the pullback and cleat arrangement worked well when the forward hand was sitting on the deck close to the slide and could apply the 50lb tension upwards as the “pull-back and restraint” line was entered into the cleat. But when sitting in the cockpit the system was difficult to operate because of the upward force needed prior to cleating. An annoyance was that the slide moved forward a few mm as the line bedded into the clam cleat.

So, to sum up:

• If the class wants to move to RCB stay slides, I will be happy to approve a system which uses Ronstan 19mm gear, or its equivalent.

• The class needs to encourage inventive sailors to develop one or more neat and tidy and efficient restraint arrangements, trial them in all conditions, and advise me which they prefer.

• From there I can approach the ISAF Technical Secetariat for their approval of the chosen arrangement, and the class can get on with whatever is appropriate to make RCB slides class-legal.

Frank Bethwaite.
Designer

Posted 2007-11-06
Edited 2007-11-08

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WTCA News>2007>Tasar RCB Stay Slide Option