Spinlock clutches are the de facto choice for halyard holding in racing boats. For holding and releasing lines at deck level theres nothing that comes close in holding power, controllability and the durability of the gear. That said, it’s a pretty common job for a rigger to try to eliminate the slipping that occurs as the line slides through the cam. Much of this is due to the way clutches and cam cleats work; the cams move out of the way in the direction of the winch when the line is being tensioned, and then when the tensioning is complete, the line moves back towards the sail, taking the cam with it until the cam is completely engaged and the line held fast.
Spinlock XCS with 8mm Crystalyne
Above, we have a Spinlock XCS clutch with the test rope, a piece of 5/16″ Crystalyne. The cam is the toothed gray metal piece just above the line. It’s hinged where it meets the cam arm, which is again hinged where it meets the base plate. When the clutch handle is open, the line can move in either direction since the cam is lifted away from the rope. When the clutch handle is closed, the cam presses against the rope, which in turns presses against the base plate. When this happens, the line can only be pulled “with” the cam, away from the load (to the right in this photo) This means that when loaded (moving to the left) the line jams between the teeth on the cam and the baseplate and is held in place. In order for the holding of the line to occur, the line has to move towards the load a little bit, which engages the cam. This is where we get our initial clutch slip; it’s an inescapable part of how the clutch works, but it can be limited.
Here is a quick look at clutch slip: the lines loaded to ~470lbs, then released. There are two things to note here: if you look at the cam under the clutch handle you can see it drop as it grabs the line, and also, thats a LOT of slip! Video: Clutch Slip
Another thing to note in the cutaway view of the clutch is that the line is flattened a bit where it is held by the cam. Since rope is just a round braid of fibers, when it’s loaded from the side it will deform, getting flatter and wider. This is an important bit of data to use when trying to minimize clutch slip.
The tests are being done with clutches provided by Spinlock. In talking to them about the test, their expectations mostly revolved around proper sizing, as well as quality of the line. Spinlock has done their own testing and wasn’t surprised when the best performance came from better quality lines using higher tech materials. Even among similar constructions, you can tell a higher quality line as it’s generally firmer, with less slop between cover and core. The size helps in that the gap between the clutches baseplate and cam can be greater before the line is captured, and the firmness helps in that the line will flatten out less, and therefore accomplish the same thing.
The problem of slip has paradoxically increased as cordage has gotten higher tech. As we’ve gotten stronger fibers and treatments, downsizing line has become common so as to reduce weight and windage. There are 35′ boats using 8mm line, where as a few years ago they may have used 12mm. This means that the same load (or higher as sail technology improves alongside cordage) on a much smaller cross section. Those same higher tech sails are also far more sensitive to losses in tension caused by slipping, so solving slip is all the more important.
This first test concerned a very common line, 5/16″ Yale Crystalyne. I consider this to be lower/middle of the road for a vectran cored line. It generally works fine, and is quite easy to splice. That ease of splicing does indicate that the cover is relatively loose to the core. It’s the cheapest vectran cored line commonly used in the US, and you can find it at just about every regatta. The 5/16″ sample I have actually measured 7.1mm under load, a bit under spec. It’s the smallest line that’s going to to be tested, and in addition to trying it “bare” it was tested with two sizes of core bulking, as well as a cover addition. The clutch is a Spinlock XCS fitted with the smaller of 2 cam sizes, the 0610 (6mm-10mm)
Core bulking is the addition of extra material inside the core (duh) which yields and increase in the overall diameter of the line, as well as a firmer line. If done properly, the core insertion is tapered at both ends to prevent a hard point in the line and to eliminate any potential snag points. The line for this test was bulked with a 1′ section of it’s own core, which increased the diameter to 8.5mm. After the initial rough draft of this test, I was curious as to how a max diameter core bulk would work, and added a piece of 5mm dynex dux to another section of the same rope, which brought the finished diameter to a very firm 10.2mm.
Cover addition is taking a piece of cover and sliding it over the halyard, and splicing it into the halyards cover in the area of a clutch. If done properly (the extra cover must be tight to the existing cover) , it firms the line, as well as increasing the diameter. It’s a bit more time consuming than the core insertion, and does result in a stiffer line with 2 hard spots where the extra cover tapers into the core. I have seen past failures of this type of treatment (in the cover) on older halyards with lower quality splices, so I do think of this as less reliable than core additions. I used a piece of small New England ARC cover here, which brought the diameter up to 9.3mm.
Plain Crystalyne (top), bulked to 8,5mm, ARC covered to 9.5mm, bulked to 10.2mm
The test was conducted on the prestretching bench, which had a Spinlock XCS clutch mounted in the middle. Tensioning was performed with a winch on one end of the bench, from there the line ran through a snatch block at the other end of the bench, then through the clutch in the middle where it was tied to a piece of 3/4″ nylon on the “load” side of the clutch. The nylon line was used so it would stretch, and provide some pull on the Crystalyne as the clutch slipped. After being tied to the test rope, the nylon line ran through _another_ snatch block on the other end of the bench, then back to the opposite end, where it was tied to a hydraulic cylinder on a load cell. All this mess was there in order to provide a long run of line to tension against, as the first time I tried the test the clutch the tension on the line would drop dramatically after the winch was released. This was because there was only a few feet of line on the load side of the clutch before it was dead ended to the bench. Without load behind the clutch, the cams won’t engage.
To test the line, each section was brought up to 1000lbs or so and left to sit for around 5 minutes. This should remove constructional and bending stretch, as well as make sure any stretch was pulled from the other components in the system. For the test numbers, I took the line up to 600lbs, about appropriate for a 10m boats jib. Once it was there, I released the line from the winch, and measured how much the line moved, as well as how much the line had compressed under the clutches cam.
First the stock Crystalyne. The actual size of the line under load was around 7.1mm, and in three tests is averaged 26mm, or just over 1″, of slip. The pressure was dropping quite a bit, going from around 600 to the high 300lb range. If this were on a boat, I think the result would be quite a lot of change in the draft of the sail, and scallops off the hanks and/or wrinkles. Really interesting was how much the line flattened out where the cams held it; down to under 1/4″!
The next test was with the core bulked by adding a cut piece of the Crystalynes core. This made the line firmer and larger, to around 8.5mm under load. This is a pretty typical change CYR would make to a line thats been slipping, and I’ve had good results and reports from customers. The slip was reduced around 40%, at 16mm or ~5/8″. This would be a big improvement over stock, but would still show up in the sail. In three tests the pressure dropped from 600 to between 430 and 480lbs, and the line under the cam shrank to 8.1mm. Better, but not perfect by any means.
With an extra cover of New England ARC (great product!) the line was firmer yet, and measured at 9.3mm, or just under 3/8″ This is a pretty big increase, and I was expecting this to be our top performer, as in addition to the size we had the extra grip of the ARC. It did improve, to around 11mm or 7/16″. The line barely deformed under load, being 9.2mm where the cam gripped it. Pressure dropped to an average of 510 lbs over 3 tests.
I’d done the initial test with those three lines, but wanted to try again with a more extreme treatment, and used a piece of 5mm Dynex Dux inside the line for a bonus test. This is NOT something I would recommend actually doing, as the line is incredibly stiff, and I think theres a good likelihood of it jamming over a sheave or through a turning block. Additionally, when bulked it was over 10mm, which is the max line in the clutch. This meant that even when the handle was open, the line still dragged over the cams a bit. Oddly, using an actual 10mm line didn’t result in this, which makes me think that the incredible stiffness of this bulk was keeping the line from moving properly through the clutch. This would slow releasing the line, as well as wearing more quickly over the bulked portion. I believe the braid of the core was distorted a bit as well, so there may be a commensurate loss of strength with this goofy bulk. It did perform well though, as it saw just over 6mm (1/4″) of slip, and the pressure only dropped to 565lbs. The line didn’t shrink at all where it was in the cams. Again, I wouldn’t actually recommend this bulk, but it does illustrate the core (heh) result of this test.
The takeaway here is that the more material you have in the line, the better. Bigger helps, but firmer is just as important. The negative effects of the cams action are minimized with a good core bulk or cover addition, and getting as close to the max size the cam allows is key.
Based on this, I’ve modified the specs I’ll use at CYR for bulking halyards. Typically, I’ve used the same size core for core additions. In the future it’s going to be larger sizes of core, as well as prestretched pieces to make for a firmer core addition. The goal I think, should be to get to just below max cam size for best performance, but not to make the line so stiff or large that it impedes the release through the clutch. It’s been quite helpful to learn what the targets should be for this sort of work, and it’s going to improve the quality of the product I turn out. Coupled with CYRs extensive database of boat measurements, we can now provide halyards that outperform bare lines and other treatments. Contact me at email@example.com today to discuss this and other ways to get the most out of your rigging.
While doing the first draft of the test, I also encountered a few tricks that can help you on your boat while racing. Both involve getting cam to grab the line more efficiently as the line is released from the winch. First, once you’ve tensioned the halyard, but before releasing from the winch, open and close the clutch handle, then open again and physically push down on the top of the cam. This will better seat the cam against the line. Then, when releasing the line, let it off the winch smoothly and slowly. This keeps the relatively slick cover of the line from sliding over the teeth of the cam. These techniques helped most with the untreated line, although they were still nowhere near the performance of the core and cover treatments.
The first test generated a ton of interest, as well as “you shoulda”s, so feel free to keep them coming, as well as any ideas for other tests on stretch or break testing. The rigging season has started in earnest with the warm weather, but I’ll take the best ideas and give them a try on slow days and get the results up here. Thanks for reading!