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Clew Strap for Loose-Footed Main


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#1 thinwater

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Posted 14 April 2014 - 07:53 PM

Any reason not to use a long soft shackle? Seems it would be the easiest sliding option. I'm not interested in immovability--it stays on all year--just simplicity.

 

My last boat had a  ball bearing out haul car. Nice. The prior sail on this boat was attached foot and tough to flatten. On my first sail with the new sail (yesterday) I simply tied the clew down with a sail tie and it worked well enough, but the wind was light. I could put a slug in the track, but my hunch is the friction would be greater.



#2 Estar

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Posted 14 April 2014 - 08:20 PM

Depends on how tight you want to get it to the boom.  The soft shackle requires a little slack in order to put the noose over the stopper.  That's probably fine.  But if you want to get it tighter the normal rope technique is a spectra strop with splices loops with end and then a lashing between the loops.  You can make that up right tight to the boom.



#3 thinwater

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Posted 14 April 2014 - 09:16 PM

^^Is there any reason to get the clew tight to the boom, closer than a few inches? Perhaps some minor aerodynamnics.

 

I would rather stay with a single line, rather than multiple wraps, as it would probably slide more smoothly. A lashing was plan B, and so it may be. I'm not interested in watching Velcro burn in the sun.

 

Most I see are webbing. Other than the ability to attach Velcro, is there any reason?



#4 allen

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Posted 14 April 2014 - 10:39 PM

A long soft shackle should be fine. If you are concerned about the length lost when putting the loop over the knot, you might consider making the soft shackle twice as long out of smaller line and making two wraps.  That would cut the loss due to sliding the loop over the knot probably by a factor of 4 because there would be two loops and the knot would be half as large (2 x 2 = 4 :-).

 

Allen

L-36.com



#5 Alex W

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Posted 14 April 2014 - 10:47 PM

If the clew isn't pulled tight to the boom then the outhaul is another vague sail shape control (like the main sheet) that can control twist or draft, right?.  As you release the outhaul the sail can lift farther from the boom and develop twist.

 

I experimented with this only on a very small dinghy (my keelboat has the clew held to the boom with a slug), but it did make it difficult to get good sail shape.

 

The slug on my main for the clew has less friction than the 6:1 and 2:1 cascading blocks used to control it.  I'm getting a new main made now and decided just to stick with the heavy duty slug instead of switching to a strap.  It also means that I don't need to worry about the positioning of reef blocks mounted on the boom -- a strap would require moving the blocks used for the second reef.



#6 Schnick

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Posted 14 April 2014 - 10:50 PM

If the strap is not tight, the outhaul loads go way up.  If you allow the outhaul to be anything but parallel with the boom, it is then sharing the leech load of the sail and is WAY harder to adjust, and the sheaves/purchase etc all experience higher loads and earlier failure.  I have seen this particularly in the outhaul sheave at the end of the boom on more than one boat.  By keeping the clew strap tight, the clew strap takes all the vertical leech load and the outhaul can just do it's job of controlling draft at the foot.



#7 Bulbhunter

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Posted 14 April 2014 - 11:37 PM

I recall the SF sail maker and racer types found that a very stiff webbing with sewn in velcro for adjusting the size of the loop enabled the clew to slide on the boom and gave you enough adjustment to fit it well. They were racing that sort of set up up and down the coast in the the heavy knarly stuff never heard of it causing issues.



#8 thinwater

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Posted 14 April 2014 - 11:42 PM

If the strap is not tight, the outhaul loads go way up.  If you allow the outhaul to be anything but parallel with the boom, it is then sharing the leech load of the sail and is WAY harder to adjust, and the sheaves/purchase etc all experience higher loads and earlier failure.  I have seen this particularly in the outhaul sheave at the end of the boom on more than one boat.  By keeping the clew strap tight, the clew strap takes all the vertical leech load and the outhaul can just do it's job of controlling draft at the foot.

r

Good point. In my case, the clew is far enough from the boom end that some space won't matter much. But good point.

#9 thinwater

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Posted 14 April 2014 - 11:50 PM

I recall the SF sail maker and racer types found that a very stiff webbing with sewn in velcro for adjusting the size of the loop enabled the tack to slide on the boom and gave you enough adjustment to fit it well. They were racing that sort of set up up and down the coast in the the heavy knarly stuff never heard of it causing issues.


So,which slides better, Amsteel or wide webbing? I can fabricate either easily enough.

Heck, the old sail tie will probably be fine.

#10 allen

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Posted 14 April 2014 - 11:54 PM

I recall the SF sail maker and racer types found that a very stiff webbing with sewn in velcro for adjusting the size of the loop enabled the tack to slide on the boom and gave you enough adjustment to fit it well. They were racing that sort of set up up and down the coast in the the heavy knarly stuff never heard of it causing issues.

^^ All the boats I see now use Velcro loops, many wraps around the boom.  Here it is on a Cal-40 in the Big Boat Series.

 

cal40.jpg



#11 Bulbhunter

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Posted 14 April 2014 - 11:57 PM

I recall the SF sail maker and racer types found that a very stiff webbing with sewn in velcro for adjusting the size of the loop enabled the tack to slide on the boom and gave you enough adjustment to fit it well. They were racing that sort of set up up and down the coast in the the heavy knarly stuff never heard of it causing issues.

^^ All the boats I see now use Velcro loops, many wraps around the boom.  Here it is on a Cal-40 in the Big Boat Series.

 

cal40.jpg

Yes I started seeing them on the Moore 24's and the Express 27's early on never had any issues with them. My U20 main built here in SF had the same set up. I converted my Ericson 28 to loose footed had one of our really respected local guys do it - he did the same deal for that sail. Never had an issue with it and it gives you the ability to really custom fit it once you get the sail back on the boat. No complaints and very simple solution that seems to work with no obvious issues.



#12 Bulbhunter

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Posted 15 April 2014 - 12:02 AM

The trick however is super super stiff webbing sewn up in layers. That loop you see is stiffer than hell to give you an idea if you were to take the main off and stuff it in a bag you would need to sit on the damn loop to smash it flat. Not talking about a soft webbing that will collapse on its self and lay flat if you were to lay it on its side on the floor etc.

 

This stiff webbing strap that holds its shape then slides pretty easily unrestricted on the boom. If the webbing were soft and flexible I think it would grab the boom and not slide easily.



#13 allen

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Posted 15 April 2014 - 12:05 AM

^^ That might be a little confusing.  The ones I have seen are more like a long stretch of webbing with Velcro sewn to both sides.  You feed it through the clew and around the boom and then kind of roll it around until there are 4 wraps or whatever number it is.  It gets its stiffness from the multiple wraps.  There is no sewing through all the wraps.

 

Allen



#14 Bulbhunter

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Posted 15 April 2014 - 12:10 AM

^^ That might be a little confusing.  The ones I have seen are more like a long stretch of webbing with Velcro sewn to both sides.  You feed it through the clew and around the boom and then kind of roll it around until there are 4 wraps or whatever number it is.  It gets its stiffness from the multiple wraps.  There is no sewing through all the wraps.

 

Allen

What he said.; Sorry yes the sewing is the velcro on the webbing with multiple layers 2-3 layers creating the very stiff loop that then will hold its shape under pretty heavy load thus still let it slide across the boom fairly easily.



#15 Estar

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Posted 15 April 2014 - 01:13 AM

Just for discussion:
 
For Velcro brand "Hook 088-0199 Loop 1000" (this is their 'high strength' textile product - there is one higher strength model with plastic mushroom heads) 
Peel Strength 1.0 pound per inch width [1.75 N/cm] 40011
Shear Strength 8.0 pound per square inch [5.5 N/cm²]
 
Let's say a box boom with 8" height and 4" width = 24" circumference,
with 2" wide webbing/velcro = 384lb shear strength per wrap
with four wraps/velcro bonds = 1536lb total shear strength
 
 . . . . but that is with a linear piece - does the 'circular' nature of the wrap cause the sheer strength to be higher?
 
according to the harken calculator, the mainsheet load on my boat in 25kts is 3496lbs (with a zero offset from end of boom, which is where the strap would be)
 
 
EDIT: Another source has a higher rated shear strength for that exact same velcro product: 14PSI . . . which then suggests 2688 lbs shear strength for 4 wraps on the above boom


#16 NoStrings

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Posted 15 April 2014 - 01:22 AM

I've sewn a few dozen of these things, one of which is on my boat. Its a 5-6' length of 1" spectra with hooks and loops sewn on either side. You should get at least 2 passes and there is no way that sucker is popping loose. And yes, it slides on the boom. It was a great improvement over the scattered harken bearings from my outhaul car.

#17 Estar

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Posted 15 April 2014 - 01:49 AM

^^NoString: the harken calculator says a 1339lb load on your boat (Baltic 37).

 

 A 6' long 1" wide strap length =   72 sq in.  X 14 psi = 1008lbs shear strength.  

 

So, there must be some factor in that it is not a linear pull on the velcro.



#18 NoStrings

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Posted 15 April 2014 - 02:05 AM

I just checked while I was flipping the chicken on the bbq, 3 passes. I can't speak for the loads Estar. One of them has done two Pac Cups on a J-125. Now you're making me wonder.

#19 NoStrings

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Posted 15 April 2014 - 02:38 AM

I suspect the bend radius of the boom might have something to do with it.

#20 duncan (the other one)

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Posted 15 April 2014 - 02:42 AM

Any reason not to use a long soft shackle? Seems it would be the easiest sliding option. I'm not interested in immovability--it stays on all year--just simplicity.
 
My last boat had a  ball bearing out haul car. Nice. The prior sail on this boat was attached foot and tough to flatten. On my first sail with the new sail (yesterday) I simply tied the clew down with a sail tie and it worked well enough, but the wind was light. I could put a slug in the track, but my hunch is the friction would be greater.

works for me on a dinghy, but I'd be worried about spreading the load a bit more on a big carbon (yacht) boom - with spectra webbing.

#21 Ishmael

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Posted 15 April 2014 - 03:51 AM

^^NoString: the harken calculator says a 1339lb load on your boat (Baltic 37).

 

 A 6' long 1" wide strap length =   72 sq in.  X 14 psi = 1008lbs shear strength.  

 

So, there must be some factor in that it is not a linear pull on the velcro.

 

Is it not the same issue as in multiple passes on a lashing, after a certain number the load on the end is zero?



#22 Estar

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Posted 15 April 2014 - 04:11 AM

^^ yes, I think so, what I don't know/understand is this . . . Say you have three wraps of webbing, that means you have two Velcro bond line wraps. In that case, is the load reduced by 6 (the number of webbing legs) or by 4 ( the number of Velcro bond legs).

I think it is 6, which would make a three wrap really strong.

In either case it makes a three wrap more than strong enough for no strings.

#23 Ishmael

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Posted 15 April 2014 - 04:18 AM

A guess? Because of the unusual bond properties of Velcro, the bond line doesn't sheer abruptly like glue but creeps. Since the Spectra webbing doesn't stretch so the creep is contained, I would guess the load is reduced by more than a 6 factor. Maybe you could break some?



#24 allen

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Posted 15 April 2014 - 05:29 AM

^^ There is a huge compression load on the Velcro that is on the underside of the boom.  The sheer strength there will be much higher than just the spec of the raw Velcro.

 

Allen



#25 SailAR

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Posted 15 April 2014 - 12:03 PM

we have been using the webbing/velcro strops on our main for years... i'm pretty sure they're not anything more fancy than jackline material with vecro sewn on either side... this is for a large roach main (p:39', e 15').  two wraps have never slipped... and I would guess some of the strops were in excess of 6 years old.  Easy to put on and remove and slide well on the boom..



#26 Estar

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Posted 15 April 2014 - 06:03 PM

ok, velcro . . . 

 

This is "genuine Velcro brand, made in USA", I bought at WM, which is not a 3m product, and appears to be weaker than the 3m product.  So, first lesson is that there are differences in strength between the various hook and loop products.

 

I pulled between two shackles.

 

A straight line shear pull (eg no loops) I got 7.5 psi

 

A "2-wrap" I got 45 psi (6X the straight line - I 'expected' a bit more than 4x, and got +2x more)

 

A "3 wrap" I got 70 psi (9.3x the straight line - I 'expected' a bit more than 6x, and got +3.3x more)

 

So, it would appear there is a lot of advantage to the first loop, probably because it puts a compression friction loading on the velcro, and then significant but diminishing returns to further loops.

 

Extrapolating a bit - A 6' webbing piece made into a 3-wrap loop, of the 3m tape, should then be 72 sq in x 14psi x 9.3 =  9400lbs (if the 14psi spec is correct - I have some on order to test/confirm).

 

If I have this right . . . . That's pretty damn strong - surprised these are not used in more applications.

 

As thinwater mentioned the failure mode is also nice . . . a very slow creep, rather than just letting go.



#27 BuggarTheBone

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Posted 15 April 2014 - 10:50 PM

We have used spectra webbing and velcro on our 45'er. This summer running downwind in 40-45knts we heard a loud ripping noise and then found that the velcro had sheered.

 

We had two loops of webbing and the sheer was where the velcro was stitched....ended up with the velcro shredded in strips hanging off the webbing!

 

Discussed replacement with sailmaker who suggested that it was now his considered opinion that 40' is about the limit for velcro webbing.

 

Have now replaced with heavy dyneema strop with spliced loop each end slipped onto each arm of the large D-shackle on clew - works a treat.

Cheers



#28 NoStrings

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Posted 16 April 2014 - 01:10 AM

BTB, that would make sense to me. Virtually every boat that I've made a velcro strop for has been under 40', excepting the -125 which is fairly lightly loaded off the breeze. All of the Express 37s on SF Bay use them.

#29 Estar

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Posted 16 April 2014 - 02:25 PM

We have used spectra webbing and velcro on our 45'er. This summer running downwind in 40-45knts we heard a loud ripping noise and then found that the velcro had sheered.

 

We had two loops of webbing and the sheer was where the velcro was stitched....ended up with the velcro shredded in strips hanging off the webbing!

 

Discussed replacement with sailmaker who suggested that it was now his considered opinion that 40' is about the limit for velcro webbing.

I am surprised by that failure mode. Based on my testing to failure, I would expect the "velcro to velcro" to slip rather than the "velcro to webbing" to fail.  So I wonder about less than perfect construction methods rather than a 'concept' failure. 

 

The velcro shear strength is not high (8-14psi) and I would have through it not hard to get the sewing/adhesive strength higher. I was testing with zig zag stitching and adhesive backing. It sounds like perhaps you had straight stitching without adhesive - is that correct?  If so, that would point load the velcro fabric along the straight stitching lines.

 

Also you say you were using a 2 wrap - a three wrap would have given you significantly more strength.

 

Many of the TP52's use straps.  Anyone know if they are sewn slings or are velcro?

 

Attached File  tp52.jpg   123.45K   56 downloads

 

A full main in 40 kts will generate some very significant loads on the strap - harken says 9000lbs on my mainsail at 40kts and 11,000lbs at 45kts. I am not surprised a 2 wrap  failed but am surprised at the failure mode.

 

I am curious about this - anyone else used one of these velcro straps on a +45' boat in strong winds?  Any other reports of failures, and what the failure mode was?  



#30 allen

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Posted 16 April 2014 - 02:41 PM

^^ I question the 9000 pound number.  Aside from the fact you would probably be reefed in 40 knots, let's calculate the sheet load backward.  Assume you have a 50:1 winch on a 2:1 purchase and a very strong trimmer who can exert 50 pounds on the winch and end mast sheeting.  That would be 5000 pounds.  While that is a lot, if you just have a more typical 24:1 system and a 30 pound pull you only get 720 pounds.   What kind of mainsheet system is generating 9000 pounds?

 

Allen



#31 Estar

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Posted 16 April 2014 - 03:03 PM

^^  http://www.harken.co...insheetLoading/   Put in E = 21' 8" and P = 63' 4" (my own rig dimensions) and 40kts, and it says "8953lbs Mainsheet load in pounds".  I suspect Harken is ballpark correct - do you have reason to believe they are not?

 

My mainsheet system was speced by Harken - it's a #53 winch with a 3:1 tackle.

 

I have to say I have never tried to winch the full main in against 40kts.  If I am in that situation I am either turning up and letting the main luff to drop reefs in, or running off and letting it out (not winching in).

 

I have just now 'broken' several two and three wraps.  In all of them the velcro slipped at failure.  In two of them the velcro also tore horizontally at a 180 degree bend around a pulling shackle.  You would not have that sharp a bend around a boom, but compressions on the likily near 90 degree bend might create this failure.  But I have not yet seen a failure of the velcro to webbing bond.  The are 'failing' at very close to my 'estimate/extrapolation formula' above, but I am still using the weak stuff rather than the better 3m stuff.

 

Attached File  web.JPG   318.09K   4 downloads

 

and

 

Attached File  web2.JPG   257K   2 downloads



#32 allen

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Posted 16 April 2014 - 03:15 PM

OK, 50x53x3 is a big load and you could use the traveler to increase the load above that.  Harken says the calculation is not widely accepted as accurate, part of why I questioned it.  My little 36 ft boat has a 5:1 system so I probably can't get more than a few hundred pounds on it.  I also would be letting it out in that kind of wind, letting it bubble or even luff.  Otherwise, the sail would not be seeing the full 40 knots anyway because the sail would be horizontal :-)

 

Could I get some clarification on the test setup?  If you have a 4 inch boom width and 9000 pounds and a 2 inch strap and three wraps, you have 24 square inches of Velcro that has a compression force of over 1000 psi on it.  I think that is going to greatly increase the shear strength.  I would think that is where most all of the strength would come from.  Is that part of the setup?

 

Allen



#33 Estar

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Posted 16 April 2014 - 03:58 PM

^^ On the test set-up . . . as always, it is not perfect . . . I am pulling smallish loops - basically 4" long x 1" wide - I thought those proportions were very roughly right for a box boom.  I am using 1" dia pins to pull.  So I am getting a bit less than 1" "compression" surface.  And then converting to psi so I can scale it, and I am assuming linear scaling with sq in of vecro.

 

Happy to adjust anything you think could be improved.  

 

Since the failure mode is slow slipping, (like with our bends), the precise 'failure load' is difficult to pin down, so we should take them as general ballparks rather than precise numbers.

 

It is all a little sloppy, but the ballpark is meaningful higher than I would have guessed before I started.



#34 allen

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Posted 16 April 2014 - 04:11 PM

^^ If I understand, you are scaling your results assuming that all the holding force is around the boom.  That is a reasonable assumption if the stuff is linear.  You could test that by using a 1/2 inch pin if you can't use a larger one and see if it scales up to your 1" resutls.  You might  be able to secure some pipe to your test setup perhaps with chain or Amsteel if you make sure the edges won't cut the line.  That would get you a larger diameter.

 

Allen



#35 bluelaser

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Posted 16 April 2014 - 06:20 PM

^^ If I understand, you are scaling your results assuming that all the holding force is around the boom.  That is a reasonable assumption if the stuff is linear.  You could test that by using a 1/2 inch pin if you can't use a larger one and see if it scales up to your 1" resutls.  You might  be able to secure some pipe to your test setup perhaps with chain or Amsteel if you make sure the edges won't cut the line.  That would get you a larger diameter.

 

Allen

 

Or just cut a piece of pipe that will fit inside the shackle over the pin as a sleeve. do any size you want from there.



#36 Dex Sawash

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Posted 17 April 2014 - 12:46 AM

For dinghies and small keel boats, will a strip of double sided velcro without the webbing be strong enough given a few wraps?

I am pretty sure I can get my wife to show me how to cut a strip off the roll.

And on sewn straps, Soft side to the boom or bristle side in?
Or is first lap of the boom just bare webbing?

#37 Estar

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Posted 17 April 2014 - 01:07 AM

For dinghies and small keel boats, will a strip of double sided velcro without the webbing be strong enough given a few wraps?

I believe the different makes of 'velcro' will vary in basic fabric strength . . . but some 3/4" wide stuff I have broke at 500lbs in a 2-wrap (that's 2 layers of hook and 2 layers of loop).  You can scale that up for wider or added wraps. It is pretty stretchy without any webbing.

 

I think the 3m stuff has more fabric strength.  

 

If you have self adhesive velcro it is super easy to stick to webbing and I can't see any reason not to - sewing helps, but  you get a big strength gain just using the adhesive on webbing (even cheap webbing).

And on sewn straps, Soft side to the boom or bristle side in? Or is first lap of the boom just bare webbing? The most elegant is to cut the velcro so it does not show on the inside or the outside of the finished/in place loop, but soft side in if you are not doing that.



#38 allen

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Posted 17 April 2014 - 01:25 AM

@Estar.  I take it from your posts that our Sailrite sewing machines will sew through the stick on Velcro.  I have not tried it.  You might not know that my old machine, which would sew through as many layers of Sunbrella as my Sailrite, would not sew sticky Velcro with V-62 thread.  It would gum up the needle and break the thread.  This is really not an option for most people, imho.  Non stick Velcro, on the other hand, on a home sewing machine using V-62 Velcro, does work.  BTW, my old machine was very strong, but 100 years old.  I felt that was old enough to justify replacing it. :-)

 

Allen



#39 Estar

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Posted 17 April 2014 - 02:50 AM

Yes, it goes thru webbing plus sticky loop plus sticky hook no problem at all, and no problem with the one sample of just the sticky loop + hook with no webbing - v69 thread (I think).

 

I have not tested it, but my impression is with sticky back velcro is you may only need to sew the ends.  The rest is going to be held in place by compression.  So a hand sewn row at each end is not too hard or too much work



#40 Ocean View

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Posted 17 April 2014 - 04:29 AM

We use a veclro strap successfully.

The strap is bare on the inside where it makes contact with the boom then the velcro starts and we thread it through the clew twice attaching it to itself all the way around and it's never let go - if it's put on properly. :P

 

I wouldn't use sticky back velcro as it will creep under the loads and continuously give problems and eventually the glue will go messy.

Ours is sewn all the way around and in places through the middle so it;s very secure and never creeps or buckles and the last one lasted 10 or so years before decided to retire it.

It's now our spare in case the new one gets lost overboard ;)

 

Only real issue that's ever occurred is if the velcro collects tufts of cotton, wool etc it needs to be cleaned out to work best.

 

and we take it off after every race along with the sail - which removes any UV issues.



#41 Estar

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Posted 17 April 2014 - 11:00 AM

^^ what size boat?

Anyone here using these straps on over 45'?

#42 hdra

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Posted 17 April 2014 - 03:07 PM

North gave us a velcro strap with our new main on a 72'er, but we haven't tried it yet - have the old webbing strop to a shackle still in place.  I'll take a look at how long of a piece of velcro they gave us and see if we can do more than two wraps.



#43 thinwater

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Posted 17 April 2014 - 03:08 PM

I hate Velcro, eliminating it every chance I get, so I did this (34' cat).

  • 7-foot stiff 1" polyester webbing strap (over 5000#) from the left-overs box. Hand-stitiched an SS ring in one end, too large to pass through the clew ring.
  • Wrapped 3 times around the boom, passing through the ring each time, making a nice neat stack.
  • Doubled back the last turn, through the ring, and finished with half hitch. For a neater finish, through a second hitch over it and tuck the tail back through the ring.

I've had it out in a breeze, purposely sheeted harder than needed (as hard as I would EVER winch it in). No slip, easy to adjust the outhaul, Easy to adjust the strap, clean-looking, and no tendency to tighten the half hitch up. It works, based on friction, for the same reason the Velcro works and lashings work. There is very little load on the hitch.

 

No doubt Velcro is cool. This works too. Easy to adjust, would work on any size boat with the right webbing and wrap count. I need to think of a cooler, more releasable finish. But if it did seize, I wouldn't care. The sail only comes off every few years.



#44 allen

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Posted 17 April 2014 - 03:20 PM

^^ The boat I sailed on that used Velcro took the main off after every race.  I think that is part of the idea with the Velcro.  It was a T-10.



#45 solosailor

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Posted 17 April 2014 - 04:02 PM

Another case of paralysis by analysis…..      I've used spectra webbing with sewn on velcro for many, many years on several boats.    2.5-3 wraps.   Or sans velcro as mentioned with a loop in each end and lashed with spectra on larger boats > 45-50ft..



#46 thinwater

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Posted 17 April 2014 - 05:31 PM

Another case of paralysis by analysis…..      I've used spectra webbing with sewn on velcro for many, many years on several boats.    2.5-3 wraps.   Or sans velcro as mentioned with a loop in each end and lashed with spectra on larger boats > 45-50ft..

 

We don't move forward using old answers. The old best practice has a way of becoming mediocre. To me the thrill of sailing is to really understand the gear and forces.

 

But yeah, this is a pretty damn simple problem... like a soft shackle, which we beat completely to death until, suddenly, a few guys teamed up and improved it on this forum.



#47 walterbshaffer

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Posted 17 April 2014 - 08:44 PM

about a month ago I inquired about this as well and ended up with 5 passes of 1.5" wide "industrial grade" velcro which barely fit through the clew ring around the boom with the loop side towards the boom as it felt less friction on the boom than the plastic hooks side did.

 

the previous set up had been 1' wide around the boom 3 times but that had been sewn onto a sail tie type webbing



#48 Estar

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Posted 17 April 2014 - 10:00 PM

By the way  . .  .adhesive . .  .this stuff: http://www.sailrite....=T#.U1BOAfldXuM is pretty good.  It drys fast, and is then still flexible but not sticky (like the PSA is on the adhesive backed velcro), will not cause much problem with most sewing machines (I think).  I don't know if it is 'needed' (in fact I know it is not with proper zig zag sewing) but it cannot hurt to spread the load, and this adhesive should be stronger than the velcro grip.

 

 
 

North gave us a velcro strap with our new main on a 72'er, but we haven't tried it yet - have the old webbing strop to a shackle still in place.  I'll take a look at how long of a piece of velcro they gave us and see if we can do more than two wraps.

Interesting . . . I would be interested in some 'specs' (length, width, number of wraps), and a photo or two if you can do it.  They should have enough big boat experience to know that it will work.
 
Thinwater, I generally agree with you about velcro.  I have mostly tried to avoid it.  Hate it on clothing.  But I have been surprised by how strong and quick these strops are.  They do seem like they have a place in the tool kit.  I am just not sure yet what sort of place.


#49 thinwater

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Posted 18 April 2014 - 12:23 AM

I've eliminated Velco from a number of "safety" items, like the LifeSling cover. A neat solution can be a number of short webbing "tubes," sewn on alternate sides, like the loops making up a hinge, with a fiberglass tent pole section as the pin. A bit of red 9/16" tubular webbing is slid over the end of the pin as stop, flag, and handle. MUCH stronger, less prone to working open on its own, faster to deploy, and obvious. It takes a few seconds longer to reset, but that's fine.

 

There are certainly more applications, where a pin can be used to release a lashing.

 

I'm assuming you have all seen this approach as well, the father of the "new" Glow Fast release.

http://en.wikipedia...._release_system

 

About the only place I'm stuck with it is certain mosquito netting, since it follows deck curves much better, and those damn flies find the smallest holes.



#50 hdra

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Posted 19 April 2014 - 12:26 AM

North gave us a velcro strap with our new main on a 72'er, but we haven't tried it yet - have the old webbing strop to a shackle still in place.  I'll take a look at how long of a piece of velcro they gave us and see if we can do more than two wraps.

Interesting . . . I would be interested in some 'specs' (length, width, number of wraps), and a photo or two if you can do it.  They should have enough big boat experience to know that it will work.

I'll try to get some pics tomorrow - too dark tonight and we've got to put the galley back together before bed : )



#51 Estar

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Posted 19 April 2014 - 12:20 PM

^^ if you can, please get a close up of the stitching pattern.

#52 hdra

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Posted 19 April 2014 - 10:15 PM

Hey Estar,
Here are some pics - Looks like it's just 3 lines of straight stitching, one down each edge and one in the middle, with the ends stitched down as well.  2nd pic of our current webbing strop to the shackle, 3rd pic I tried running the velcro - goes about 2.5 times around.  They didn't measure our boom size or anything, just came along with the new sail, so I suspect there was not a whole lot of thought put into it.  The velcro webbing is about 2" wide.
 
IMG 3107
IMG 3108
IMG 3110


#53 thinwater

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Posted 20 April 2014 - 03:56 AM

I've been playing with a few variations on my new sail (nothing more interesting than what is posted in the thread) and have a few observations an questions:

  • The reason Spectra is best is stretch. Just like sewing webbing, if the webbing stretches the force is maldistributed. The same is true here for the friction on the Velcro. In fact, Velcro can actually break when used on nylon webbing (I've seen it); the webbing stretches more than the Velcro tape.
  • Friction. I'm assuming we all have the loop size toward the boom. Originally I did not, but I slide a length of that in there (self-adhesive) and it was much better. But I wonder what the loops do at high psi? I will never see more than foot-pressure, but big boats are going to smash it. Is that going to reduce the slide function quickly in time?
  • Does the slide effectiveness vary with the type of Velcro?
  • Do we need to design for a maximum PSI on the boom because of this? Breaking strength may not be the critical factor.
  • Stitching. Since the Velcro operates by increasing friction (a lot) the stitching is going to see no more shear force that that friction value. I'd bet lunch that 2 rows of any stitching will do and last as long as the Velcro.

Interesting.



#54 Bruce T. Shark

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Posted 23 April 2014 - 10:52 PM

North Sails has been supplying my main on my 36.7 with the straps...never had a failure, including the down the bay race last year in sustained 30kts with gusts to 40...

Was also on the Main on my MP30 (Mighty Pearson 30)...a lot easier for wife to handle outhaul from the pit on both boats..

Your mileage may vay..

 

^^NoString: the harken calculator says a 1339lb load on your boat (Baltic 37).

 

 A 6' long 1" wide strap length =   72 sq in.  X 14 psi = 1008lbs shear strength.  

 

So, there must be some factor in that it is not a linear pull on the velcro.



#55 equivocator

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Posted 29 April 2014 - 05:39 PM

Probably depends on the size of the boat. On the SC70, North Sails provides a webbing band, presumably spectra, with velcro. This makes a servicable strop, but it disappeared in nano-seconds when the outhaul puller line broke on SF Bay back in the 1990's.

 

I now prefer a spectra line long enough to make several passes around the boom, spliced on both ends, with a lacing line to adjust the tension. The goal is to get the strap tight enough to keep the clew ring close to the boom, and loose enough to slide when the outhaul is adjusted. But here in SoCal, most boats, even big ones, use the velcro bands.



#56 hdra

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Posted 29 April 2014 - 10:38 PM

Equivocator, I was thinking about doing something like that when we retire the current spectra webbing strop on our Challenge 72 - out of curiosity, what size spectra are you using for the lashing on the SC70?  we're a lot heavier, but would be interested to hear about a similar sized boat.  Our mainsheet is a 5:1 purchase to a winch, so can get some good tension on it when we need to.  I may try out the velcro strap from North on our passage to Bermuda here in a few days, leaving the old strop on as a safety - I'll let everyone know if we break anything : )



#57 Estar

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Posted 29 April 2014 - 11:14 PM

^^ I can tell you, from the sewing perspective, from my webbing sewing tests, that the key is to not try to just sew simple 'end loops' in a 'one part webbing'; but to to wrap the webbing back and forth a couple times  and then sew the middle section down (thus forming multi-part end loops).

 

This is what I originally used to hang mainsheet blocks.  I later switched to a couple wraps of 10mm dyneema with spliced loops.  You could lift the boat with either - which has been my basic strength criteria for most all the important rigging parts.



#58 fatcat1111

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Posted 10 June 2014 - 11:08 PM

Probably depends on the size of the boat. On the SC70, North Sails provides a webbing band, presumably spectra, with velcro. This makes a servicable strop, but it disappeared in nano-seconds when the outhaul puller line broke on SF Bay back in the 1990's.

 

I now prefer a spectra line long enough to make several passes around the boom, spliced on both ends, with a lacing line to adjust the tension. The goal is to get the strap tight enough to keep the clew ring close to the boom, and loose enough to slide when the outhaul is adjusted. But here in SoCal, most boats, even big ones, use the velcro bands.

 

Why loop it multiple times? I would assume that the distance between the clew and the boom was just a matter of the length of the line.



#59 Bulbhunter

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Posted 10 June 2014 - 11:13 PM

Probably depends on the size of the boat. On the SC70, North Sails provides a webbing band, presumably spectra, with velcro. This makes a servicable strop, but it disappeared in nano-seconds when the outhaul puller line broke on SF Bay back in the 1990's.

 

I now prefer a spectra line long enough to make several passes around the boom, spliced on both ends, with a lacing line to adjust the tension. The goal is to get the strap tight enough to keep the clew ring close to the boom, and loose enough to slide when the outhaul is adjusted. But here in SoCal, most boats, even big ones, use the velcro bands.

 

Why loop it multiple times? I would assume that the distance between the clew and the boom was just a matter of the length of the line.

My guess is that by making more than one pass you then can use the lacing line to more effectively snug it down tight. That and it spreads the load some, however given its a single line looped / passed through the clew multiple times and around the boom it would still have the same risk of failure as a single line. But I suspect that is not the concern and the multiple loops are to create a little larger surface area / loading on the boom.



#60 Islander Jack

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Posted 11 June 2014 - 12:16 AM

I'm still trying to figure out what's wrong with a slug sewn just below the clew, sliding in a boom track.



#61 Dex Sawash

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Posted 11 June 2014 - 12:27 AM

I'm still trying to figure out what's wrong with a slug sewn just below the clew, sliding in a boom track.



Well that is just fine if you're Johnny Oldtech.

#62 Bulbhunter

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Posted 11 June 2014 - 12:42 AM

I'm still trying to figure out what's wrong with a slug sewn just below the clew, sliding in a boom track.

Tracks wear out - and many upgrade booms are carbon which generally don't work so well with stuff drilled into them.

 

Even for the old school boom with a track on it I found the strap worked better than the slide in the track anyway.



#63 Islander Jack

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Posted 11 June 2014 - 01:11 AM

Ah.  I get it now.

 

I thought aluminum was an upgrade.   :-)



#64 DDW

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Posted 11 June 2014 - 01:49 AM

^^ what size boat?

Anyone here using these straps on over 45'?

I guess I missed this discussion originally.

 

I have a spectra/velcro strap holding the clew down on my 45'. But it is cat rigged so the mainsail is pretty big, 960 sq ft. square head. The clew downhaul strap is 82" x 1"  but the velcro is only 55" - no need for around the inside or outside where it does not mate. (Actually the fuzz is 3" shorter yet, because of the spiral geometry and you want it to look neat!) It is installed with three wraps. It does not creep or slip, and seems under no particular strain to do the job. I have a second strap on the clew providing the outhaul loads (there is no adjustable outhaul), again three wraps and 1" wide. There are two additional similar straps wrapped under the boom to take the reefing blocks for 2nd and 3rd reef. In my unique single line reefing arrangement, a single part Dyneema line comes from the reef cringle, through the reefing block, aft to the boom sheave box. So the strap takes a bit more load than just the downhaul loads. These straps had been used for 4 years, I finally had some new ones made because chafe had made the velcro a little ratty looking (which is why I deleted the extra as mentioned above). I have carried the full main in 33 knots maximum, that I can recall. 

 

I believe Harken's mainsheet load formula overestimates loads. For my main it predicts 4600 lbs. @ 30 knots. Doyle's own software predicted 4000 lbs. Due to my odd rig, I can estimate the load with reasonable accuracy: the mainsheet provides almost no down force on the boom, nearly all of which is instead supplied by the hydraulic vang. To reach 4000 lbs at the clew, it needs to be pumped to its max working pressure of 3000 psi. I have never had to pump it over 2000 psi, more normally 1800 and then it is time to reef. That suggests that the actual load is only about 60% of what the Harken formula predicts - at least for my boat.

 

The reefing lines aren't run correctly in the picture, but you can see the straps.

 

Straps_zps8c6a5ddf.jpg



#65 USA190520

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Posted 11 June 2014 - 07:29 PM




We have used spectra webbing and velcro on our 45'er. This summer running downwind in 40-45knts we heard a loud ripping noise and then found that the velcro had sheered.
 
We had two loops of webbing and the sheer was where the velcro was stitched....ended up with the velcro shredded in strips hanging off the webbing!
 
Discussed replacement with sailmaker who suggested that it was now his considered opinion that 40' is about the limit for velcro webbing.

I am surprised by that failure mode. Based on my testing to failure, I would expect the "velcro to velcro" to slip rather than the "velcro to webbing" to fail.  So I wonder about less than perfect construction methods rather than a 'concept' failure. 
 
The velcro shear strength is not high (8-14psi) and I would have through it not hard to get the sewing/adhesive strength higher. I was testing with zig zag stitching and adhesive backing. It sounds like perhaps you had straight stitching without adhesive - is that correct?  If so, that would point load the velcro fabric along the straight stitching lines.
 
Also you say you were using a 2 wrap - a three wrap would have given you significantly more strength.
 
Many of the TP52's use straps.  Anyone know if they are sewn slings or are velcro?
 
tp52.jpg
 
A full main in 40 kts will generate some very significant loads on the strap - harken says 9000lbs on my mainsail at 40kts and 11,000lbs at 45kts. I am not surprised a 2 wrap  failed but am surprised at the failure mode.
 
I am curious about this - anyone else used one of these velcro straps on a +45' boat in strong winds?  Any other reports of failures, and what the failure mode was?  
I know exactly what is made of as I' was on that 52 pictured, that's my hand reaching for the starboard primary, we're about to tack in that pic- it's 4' of 1 1/2" spectra webbing with Velcro sewn on both sides-

The strap is goes around the boom/clew twice. It's important to get it as tight as you can otherwise you change the angle the outhaul trims from resulting in difficulty controlling leech tension, very much like having your jib leads too far aft.

#66 Jim H

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Posted 12 June 2014 - 01:53 PM

Been using velcro straps for years on the IMS40 Boats, Swan 45 and Swan 42.  As mentioned about I have seen either 1.5" or 2" Dyneema webbing with velcro sewn on.  Wrapped around the boom 3-4 times.  Thousands of miles sailed including doing Bermuda and have never seen an issue with a velcro strap.

 

 

Cheers,

Jim






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