Laser Clew Tie Down

W

will162878

New Member
As I have said before, my pet hate of the Laser is the clew tie down. The class rules now allow some development of the basic rope strop design:

ILCA Rule 3(g) deals with the tie-down:

Part 1:
The clew of the sail shall be attached to the boom by line or strap around the boom and through the sail cringle or by an
optional quick release system attached to a line or strap around the boom.
Click to expand...

Part 2:
The clew tie down may be passed through simple balls or tube/tubes to reduce friction.
Click to expand...

Shevy has posted a useful article on his website outlining the details of his idea using stopper balls and tubing:

drLaser Clew Tie Down

The science of the tie-down friction is quite straight forward:

The frictional force is equal to the vertical force multiplied by the coefficient of friction.

Therefore we need a solution which decreases the friction coefficient. This coefficient is determined by the materials in contact.

I have investigated the possibility of PTFE (Teflon) tube (ultra low friction) but the cost is prohibitively high.

There are many polymers around which have low friction properties and probably quite a few that have been moulded into balls for a variety of uses. Does anybody know of any easily available plastic balls with low friction properties that could be strung on a 3-5mm line?

I have tried using tubes (science labs at school had some low friction tubing they were discarding) but tubes usually have low firction coatings on the INSIDE and the contact area with the boom is too large.

Any ideas?

I reckon Shevy's design is a very good starting point but should be scutinised and hopefully improved.
 
The fleet I have been sailing with has some folks using the stopper balls and they like them, however the top two are trying a different approach which may or may not be legal

They are using 1/2" spectra webbing as the tie down, with velcro to hold the webbing wrap together (this same setup is used successfully on offshore boats, the velcro holding is not an issue) As far as I can tell, that's fine - where it seems to be in the gray area of the rules, is the 1" wide piece of UHMW polyethelene which is physically attached (glued) to the webbing sitting between the webbing and the boom
 
well, on APS they have the quick realease thing, which works wonders with a Spectra cord tie down, enough for 3 raps around the boom. Spray a little Team McLube, and Viola! a very sweet clew!
 
The tie down can be "a strap" so webbing fine rules wise, regardless of what is glued to it: that is part of the "strap."
 
Is that your opinion or is that an official ruling by the ILCA ? The reason I ask is that what's the difference between using a piece of UHMW under the strap, or a piece of metal or formed plastic as written about on drLaser here
 
If it is attached to the strap there is no reason why you cannot call it part of the strap. There are no limits on the strap design or material.
 
So, how do you turn a webbing strap into a webbing strap with a low friction inner side? PTFE is a thermoplastic so if you melt PTFE tape (as plumbers use) and press it into a strip it could be glued to the webbing?
 
Will wrote:
> There are no limits on the strap design or material.

Except that 1) there is the Fundamental Rule, and 2) the term "strap" has a particular meaning in the dictionary. ILCA has partly re-considered this issue, and has ruled that a "strap" must be a flexible device. Metal sleeves, rings, etc. are OUT. At least until the rules are changed again...

Rules can't be interpreted in a vacuum! You must consider the past rules, as well as other related rules to really understand what they say.

Rule 3(f) used to impose the condition "the clew of the sail (or the quick release hook where used) shall be tied to the boom in any manner, provided no block or any fixed fittings are used" in the clew tie-down design. Now, that's relaxed.

What's different in its new version 3(g)?
- "Tied" is gone, "attached" is in.
- The cordage used that used to be undefined is now restricted to be either a "line" or "strap".
- The restriction of "no block or any fixed fittings" is gone, and is now relaxed to specifically include "simple balls or tube/tubes to reduce friction."

Rule 3(g)ii now explicitly states WHAT is allowed on a strap or line used as a clew tie-down, and does not list any sewn on tapes or ribbons or leather or plastics. In fact, the action now allowed is precisely "PASSED THROUGH simple balls or tube/tubes"...

"Fundamental Rule" is also clear: "No addition or alteration may be made to ... equipment... fittings, type of fittings... as supplied by the builder except when such an alteration or change is specifically authorised by Parts 2 or 3 of these Rules."

Thus (not just IMHO, but as a matter of fact), the clew tie-down reported by Greg Marriner (with 1" wide piece of UHMW polyethelene which is physically glued to the webbing) is ILLEGAL. Until the Chief Measurer rules otherwise (which should not happen unless the membership approves such a rule change, as required in the ILCA Constitution).

This ban on gluing or sewing parts together is in consistency with the old "no sheet or line shall be attached to another sheet or line. Each sheet or line shall be of one continuous length of uniform diameter" philosophy that existed between 1971 and 2001 (prior to the multi-line systems now allowed for the cunningham, vang and the outhaul ONLY).


Will asked:
> So, how do you turn a webbing strap into a webbing
> strap with a low friction inner side?

drLaser web site has a second article Will fails to mention: Please read the article titled "Humphris Teflon Clew Tie-down" on drLaser first. This article raises serious questions about the suitability of pure Teflon with respect to its "compressive strength".

As for the Teflon tape suggestion of Geoff Sobering, again, caution is required before jumping the gun!

Teflon tape is generally used for wrapping the threads of pipes, adapters and valves to provide a leak-proof, easily removable seal. Its tensile strength (longitudinally) is sufficient (around 700 psi), which is great. But other than the Teflon coating having low compressive strength, ordinary teflon coated tape typically has a HUGE (75% to 100%) elongation! That's no good for a clew tie-down!

Teflon is just a coating in these "tape" applications. It's the cloth or plastic underneath that gives the tape its critical elongation characteristic. Those made from woven fiberglass or carbon cloth offer some amount of dimensionally stability (up to 5% elongation) under wide temperature ranges, but that is still too much elongation for a clew tie-down.

Read and research (ask APS) before acting.

To date, there is no "more elegant" long term, maintenance free solution than the one that combines the low stretch of certain Spectra/Kevlar lines with plastic balls with low coefficient of friction and minimum contact areas.

Best,

Shevy Gunter
 
Thank you Shevy! You mention carbon fibre. Graphite is a natural dry lubricant (electric motor contacts etc) due to its layered atomic structure. Does carbon fibre woven cloth possibly with a resin finish on the outside offer any useful materials choices? Any ideas?
 
I have tried sourcing PTFE tubing as it is required for our use in the UK but to no avail. I have only found teflon tubing with low friction inner surfaces. Another point is that a teflon coated strap will nto suffer the compression problems which tube experiences as it is already flat?
 
Shevy wrote:-

> Please read the article titled "Humphris Teflon Clew Tie-down" on drLaser first. This article raises serious questions about the suitability of pure Teflon with respect to its "compressive strength".

I have now used teflon tube over the tiedown cordage for over a season (with my Radial rig) and there is no real sign of wear. I believe, based on this, that Shevy's concern re " compressive strength" is not an issue.

I have been using a Harken hook in conjunction with this and although this has been reliable and very quick to rig/unrig, it does suffer from having about 15mm clearance between the sail and the boom. As the skipper to boom underside clearance is limited, particularly on tacking with heavy vang pressure, I am experimenting with alternate quick rig/unrig alternates.
 
> I have been using a Harken hook [...] it does suffer from having
> about 15mm clearance between the sail and the boom. As the
> skipper to boom underside clearance is limited, particularly on
> tacking with heavy vang pressure, I am experimenting with
> alternate quick rig/unrig alternates.

As a 6'4" and too-heavy sailor, I would be very interested if you (or anyone else) comes up with an alternative; I like the quick-release nature of a clew-hook, but evey mm of clearance is important. 15mm doesn't sound like much, until it's the difference between air and the back of your head! (or life-jacket).

Cheers,

Geoff S.
 
For a quick release, use your existing rope/tube system but attach a ball like on Shevy's tie-down. Tie a loop to the other end and place the loop through the clew grommet and over the ball. Then all you have to do is release the harken hook and take the loop off the ball.
 
> I have now used teflon tube over the tiedown cordage for over a
> season (with my Radial rig) and there is no real sign of wear.

Thanks, Clive! Good to know. The PTFE tube must be compressing, but due to its el;astiocity, must be regaining its original shape.

Now, the only thing we need is some details about the composition of the particular Teflon tubing you used. [From the article: "...the physical characteristics of PTFE tubes are to a large extent influenced by the working processes and the powder employed during manufacturing. There are literally dozens of different virgin or (carbon, glass) filled PTFE products in different grades...."]

Shevy
 
I have a friend at a gas analysis lab and they use this stuff by the reel so he was able to let me have a small pre used length. In searching the web on prior occassions I have found sources that will sell short lengths. If that doesnt work let me know.
 
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