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Robline for downhaul #273375
06/22/14 08:07 AM
06/22/14 08:07 AM
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Kingston SE South Australia
JeffS Offline OP
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Thinking of using Robline on the Nacra 5.8, can somebody explain to me how to splice the cover neatly so it can be continuous sheet. I'm comfortable with the core and have the fids but my cover joins suck


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273376
06/22/14 08:29 AM
06/22/14 08:29 AM
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Jake Offline
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What type? The dingy control is good stuff and holds up to a lot of abuse. I spliced two eye splices in the ends of mine and I connect them with a tiny piece of amsteel blue. They flow through the blocks that way (and you can unrig it). Otherwise, Samson has really good splicing instructions. Here is the end-for-end class II instruction:

http://www.samsonrope.com/Documents/Splice%20Instructions/DblBrd_C2_End%20for%20End_AUG2012_WEB.pdf


Jake Kohl
Re: Robline for downhaul [Re: JeffS] #273387
06/22/14 05:10 PM
06/22/14 05:10 PM
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Thanks that's the info I was after for some reason it didn't come up in my search. Not sure what type yet 4 or 5mm any suggestion? How did you connect the Amsteel Blue?


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273389
06/22/14 06:13 PM
06/22/14 06:13 PM
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South Carolina
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Originally Posted by JeffS
Thanks that's the info I was after for some reason it didn't come up in my search. Not sure what type yet 4 or 5mm any suggestion? How did you connect the Amsteel Blue?


I had 4mm originally but at the urging of my crew, I upgraded to 5mm. The Amsteel (5" of it?) is just looped twice through the two eye splices and closed with a square knot. We have to disconnect our downhaul when de-rigging the boat so that gives us an easy way to do it.


Jake Kohl
Re: Robline for downhaul [Re: JeffS] #273390
06/22/14 08:11 PM
06/22/14 08:11 PM
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Thanks again, I thought 4mm might cut in a bit so I'm with you on the 5mm, I have 6mm spectra now but it doesn't run too well


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273399
06/23/14 07:38 AM
06/23/14 07:38 AM
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Jake Offline
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with the 5mm, if you need it to flow through any 16mm blocks (like I do in the take-up system in my front beam), you will need to put the eye splice in the core and not the cover of the Dingy Control. I did mine both ways as an experiment and not only was brummel splicing the cover a gigantic PIA (it's very tightly woven), it took a while to loosen up and it's still a little sticky getting through the blocks in the beam. On the other end, I did a tuck splice of the cover into the core and then eye spliced the core. That worked well.

The amsteel that connects the two makes a really strong connection so that we don't have to panic if we see it sneaking out of the beam. We still try to keep it out of the loaded part of the line but we know we can tug on it pretty hard without worry. For keeping the square knot fairly reliable, I heat the bitter ends of the amsteel with a torch so that it mushrooms the material. That mushroom will catch in the knot and keep it from coming undone if it slips that far.


Jake Kohl
Re: Robline for downhaul [Re: JeffS] #273411
06/23/14 07:36 PM
06/23/14 07:36 PM
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JeffS Offline OP
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To move my downhaul sheets under the tramp on my Nacra 5.8 I made a bracket to transition out next to the inner fore beam, to minimise friction I used exit blocks, http://www.onlinemarinestore.com/store/pc/viewPrd.asp?idproduct=32897&idcategory=429
it then goes across the deck a bit over a foot and enters the end of the beam so the join has to be free flowing, if I go any bigger with the exit blocks the bracket gets too big, these have a small exit so I cant really whip the line, on the Dyneema I stitched it pretty tight but doubt that will hold too well if it cleats where I stitched too often. I don't have to remove this when packing up the boat and am wondering if the Robline racing sheet would be strong enough if I removed the core at the join and splice the covers as in this video https://www.youtube.com/watch?v=4LbX7jLGkYM

Attached Files
Downhaul guide 2.jpg (26 downloads)

Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273412
06/23/14 07:59 PM
06/23/14 07:59 PM
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South Carolina
Jake Offline
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It would probably be OK for the occasional trip through the cleat if you do an end for end splice like that. Note, however, that I was not happy with the Marlow Excel Control (I bought it for a downhaul line originally). It seems to chafe pretty quickly and although it has high modulous fibers in the cover, it is STRETCHY because the core is fuzzy polyester that compresses. I'm sure that fuzzy core makes that end for end splice easier, though.

Regardless, you are going to be relying heavily on the whipping whatever you do...whip it with a strongly colored thread so you can at least identify it as it starts to get into the purchase system. I would still try to avoid carrying it through the heavily loaded purchase section.

Note; we had that Excel control on a continous furler line on Alan's Mosquito trimaran and it worked magically for that and the end-for-end splice held up to a good bit of tugging.

One other note; getting the core through the cover on the Robline Dingy Control takes a lot of patience because the cover is so tightly woven. I would prepare at least a 6 pack for this splicing job if you are going to extract the core out of that line!


Jake Kohl
Re: Robline for downhaul [Re: JeffS] #273414
06/23/14 08:36 PM
06/23/14 08:36 PM
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Kingston SE South Australia
JeffS Offline OP
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Thanks Jake I was only using the Marlow video to illustrate what I would like to do with the Robline, I'm happy if it takes a while as long as it's achievable.


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273415
06/23/14 09:35 PM
06/23/14 09:35 PM
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Hobart, Tasmania, Oz.
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Re: Robline for downhaul [Re: JeffS] #273417
06/23/14 10:16 PM
06/23/14 10:16 PM
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Kingston SE South Australia
JeffS Offline OP
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Thank's Dazz that's great info and it looks like that splice would be strong enough for my purpose, how does he stay quiet when he's doing it? I will be ranting , raving and drinking


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273424
06/24/14 07:54 AM
06/24/14 07:54 AM
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Hillsborough, NC USA
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Isotope235 Offline
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Be aware that Marlow Excel Control Line and Robline Dinghy Control Line are constructed differently. The splicing methods for the two are therefore different as well.

Marlow Excel Control Line has the strength in the cover whereas Robline Dinghy Control Line has the strength in the core. For the Marlow, you splice the covers together. For the Robline, you splice the cores. Splicing the wrong part together (on either) will significantly weaken the line.

To make a continuous loop in core-dependent line, I generally do a stripped-cover splice in each end and then end-to-end splice the cores together. That yields a continuous diameter splice, but the core is partly exposed.

If I want a fully covered core and can tolerate a 50% increase in line diameter, I'll end-to-end splice the cores, milk that splice back into one end, and bury the covers at a slight offset.

I hope that helps,
Eric

Re: Robline for downhaul [Re: JeffS] #273427
06/24/14 04:47 PM
06/24/14 04:47 PM
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JeffS Offline OP
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Thanks Eric this is harder than I thought


Jeff Southall
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Re: Robline for downhaul [Re: JeffS] #273428
06/24/14 06:45 PM
06/24/14 06:45 PM
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Hobart, Tasmania, Oz.
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http://specialropes.com.au/index.php?route=product/product&path=79_87&product_id=58

using 5mm liros magic sheet pro on the downhaul and jibsheet. not having any issues with its strength. the boat came rigged with just the cover and no core!


C2 AUS 222 by Goodall design
"Darph Bobo"
Re: Robline for downhaul [Re: JeffS] #273429
06/24/14 06:51 PM
06/24/14 06:51 PM
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Hillsborough, NC USA
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Isotope235 Offline
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On the flip side, you should consider just how much line strength you really need. High-modulus line (such as Dyneema) may be cool, but we (myself included) often get suckered into using the stuff when it isn't really necessary. Hand-tensioned lines don't take enough load for stretch or strength to be an issue. Regular braided polyester is good enough. Plain old 3/16" Sta-Set, for example, has a tensile strength of 1400 lbs. Even if you cut the core and did a cover-to-cover end-to-end splice (like the one shown for the Marlowe line), halving it's strength the join, it still exceeds the working load limit of the (assuming 29mm) blocks.

For dinghy controls, I worry more about picking a line with a good grip in the cleat and a nice hand, than about the tensile strength.

Oh, and if you're happy with your exit blocks, fine, but for in-line exit applications, a block like http://www.harken.com/productdetail.aspx?id=5038&taxid=424 is generally more suitable.

Regards,
Eric

Re: Robline for downhaul [Re: Dazz] #273430
06/24/14 07:06 PM
06/24/14 07:06 PM
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Originally Posted by Dazz
http://specialropes.com.au/index.php?route=product/product&path=79_87&product_id=58

using 5mm liros magic sheet pro on the downhaul and jibsheet. not having any issues with its strength. the boat came rigged with just the cover and no core!


It came rigged that way because the rope that goodall's is designed without a core.

Re: Robline for downhaul [Re: Isotope235] #273431
06/24/14 07:40 PM
06/24/14 07:40 PM
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Jake Offline
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while I agree that the high modulus lines are way overspec from a capacity standpoint, I can absolutely feel the stretch when sheeting or working downhaul. I get much better feedback from a line that has very little stretch (particularly with mylar based sails).


Jake Kohl
Re: Robline for downhaul [Re: Jake] #273439
06/24/14 09:50 PM
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Well, let's compare 3/16 Sta Set (which is not a pleasant line to use) to 3/16 Samson Ultra Light (simply because the specs were easy to find). Both are about the same diameter. Both have about the same tensile strength (1400 lbs vs. 1200 lbs). Sta Set is double braid polyester. Ultra Light has a HMPE core with a polypropolene cover.

Just to make the comparison easy, say you pull on your downhaul line with about 130 lbs force - that's probably about twice as hard as I ever pull mine. At 10% load, Sta Set has 1% elongation. Ultra Light has 0.5% elongation. If that difference (one half of one percent) additional stretch is noticeable and bothers you, then by all means, go for the high modulus line. I myself can't tell the difference by feel. I simply pull until the sail looks good.

Of course, I'd still choose Ultra Light over Sta Set -- because it is easier to grip. For a continuous loop, I'd choose something easy to grip and easy to splice, such as Marlowe Excel Control (which is specifically designed for that purpose).

Re: Robline for downhaul [Re: Isotope235] #273447
06/25/14 06:57 AM
06/25/14 06:57 AM
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Originally Posted by Isotope42
Well, let's compare 3/16 Sta Set (which is not a pleasant line to use) to 3/16 Samson Ultra Light (simply because the specs were easy to find). Both are about the same diameter. Both have about the same tensile strength (1400 lbs vs. 1200 lbs). Sta Set is double braid polyester. Ultra Light has a HMPE core with a polypropolene cover.

Just to make the comparison easy, say you pull on your downhaul line with about 130 lbs force - that's probably about twice as hard as I ever pull mine. At 10% load, Sta Set has 1% elongation. Ultra Light has 0.5% elongation. If that difference (one half of one percent) additional stretch is noticeable and bothers you, then by all means, go for the high modulus line. I myself can't tell the difference by feel. I simply pull until the sail looks good.

Of course, I'd still choose Ultra Light over Sta Set -- because it is easier to grip. For a continuous loop, I'd choose something easy to grip and easy to splice, such as Marlowe Excel Control (which is specifically designed for that purpose).


Compare the Marlow Excel control. I'm telling you, maybe it wears in and settles down but it's almost like a bunji off the roll. Tie a 15 foot piece to a fixture (trailer hitch) and pull on it...it's pretty surprising. Also worth considering, the Samson ultralight is a blended core - not a true high modulus line.

When we're hitting the limits of the downhaul, you start to feel a wall of resistance. That wall is much easier to feel with a line with less stretch. This is a bit of an over-simplification, but if you have a 16:1 purchase downhaul system with 18 inches between the blocks, a 0.5% elongation at 10% load translates into that line stretching about 1.4 inches between the cleats. the 1%, 2.8 inches of stretch. That said, I've found some conflicting information that even amsteel blue has elongation figures near that...and I'm not certain that elongation is the right type of measurement to evaluate the "springiness" of a line. We're also getting into the distinct territory of opinion, but I can definitely feel the difference and the higher modulus lines on the high purchase or long length (spin sheet) lines. Whether or not it makes a performance difference is certainly debatable.

But - I do recommend securing a long length of different lines and comparing how they stretch over a distance by leaning away from them and hanging on. It's pretty dramatic.


Jake Kohl
Re: Robline for downhaul [Re: Jake] #273452
06/25/14 09:41 AM
06/25/14 09:41 AM
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There are two types of elongation: elastic and inelastic. Elastic elongation occurs when you tension and then de-tension a line. The amount that the line springs back when tension is released is the elastic elongation, which is also called "stretch". Inelastic elongation occurs when a line is first tensioned (when new, or after a period of disuse). The amount that the line lengthens but does not return when tension is released is the inelastic elongation, which is also called "creep".

All cordage has some degree of both stretch and creep. The amount of each varies with the composition of the fibers and the construction of the rope. Nylon, for example, is quite elastic (which makes it good for anchor line, but bad for control lines). Polyester (Dacron) is relatively inelastic. HMPE (such as Dyneema/Spectra) is much less elastic than polyester. HMPE, however, is very slick. Even in braided lines, the strands will slip against each other under load (tightening the weave). It has a lot of creep - much more than polyester.

Have you ever noticed that your shrouds (even 1x19 wire rope) feel tight at the start of the season? Or that they seem longer after a heavy-air day? If so, you've experienced creep. On the last jib I made for myself, I decided to try substituting 1/8" Amsteel Blue (Dyneema) line for the wire in the integral forestay. It is light and plenty strong, but it crept like crazy. The stay is only about 20 feet long and after the first use, I cut it down and respliced it 6 inches shorter. By the end of the season, it had elongated another 4. I'm building another jib now and will go back to a wire forestay.

Marlowe Excel Dinghy Control line has a blended fiber cover over a polypropolene core. Given that the cover will elongate by itself, and will lengthen more as the core compresses, I'm not surprised that that it has lots of initial creep. That's the price you pay for line that's easy to put in a constant diameter fully covered end-to-end splice. Tension it well (with a block and tackle between trees) to pull out the creep before splicing.

My mainsheet is an example of the opposite end of the spectrum. It's a piece of 5/16" Samson Trophy Braid. Now, Trophy Braid is one of the stretchiest double-braid polyester lines available. At sheeting loads, it might experience an inch of stretch but I can't feel it as I play the sheet. I use Trophy Braid because it has a soft, fuzzy, easy-to-grip cover that holds in the cleat very well. The main downside is that it retains water (which adds weight). I'm occasionally tempted to replace it with Robline Racing Sheet Pro (which has an easy to strip cover) but I honestly don't think that would make my boat any faster. In fact, I did make myself a set of Racing Sheet Pro jib sheets, sailed with them once, and went back to my polyester jib sheets.

In the end, most any modern cordage is strong enough for dinghy/small cat running rigging, so the final choice of line comes down to other factors including spliceability, one's tolerance for creep and stretch, cleating security, grip, and ease on the hands. And yes, many of these are matters of personal preference. I agree that it's nice to look at and feel the different brands of line (if possible) before buying.

Regards,
Eric

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