Absolution 7 Posted July 3, 2009 Share Posted July 3, 2009 I had a Ronstan Orbit block fail rather dramatically at the weekend. Just wondering what other peoples experience with these blocks has been like. I have a few of them on the boat including one on the back stay Link to post Share on other sites
Guest creative suffering Posted July 3, 2009 Share Posted July 3, 2009 I had a Ronstan Orbit block fail rather dramatically at the weekend. Just wondering what other peoples experience with these blocks has been like. I have a few of them on the boat including one on the back stay One word.... HARKEN! actually more words... what loading was on it and what is the MWL of the block? These glorified plastic blocks are prone to uv and heat (black absorbs the most heat) attack! and with no metal between the pin and the attachment to your boat / fitting..they are reliant on the plastic keeping to original manufactrers spec (new) but with UV / heat degradation the will lose strength and not last! in other words ... keep spares or replace them in critical applications(harken) Link to post Share on other sites
Absolution 7 Posted July 3, 2009 Author Share Posted July 3, 2009 Only 6 months old so probably not UV damage. More likely that it just exceed BL. It was being used as part of cascade arrangement for the vang. How much load was on it... not sure but definitely too much! http://www.ronstan.com/marine/range.asp?RnID=343 Link to post Share on other sites
Guest creative suffering Posted July 3, 2009 Share Posted July 3, 2009 Only 6 months old so probably not UV damage. More likely that it just exceed BL. It was being used as part of cascade arrangement for the vang. How much load was on it... not sure but definitely too much! http://www.ronstan.com/marine/range.asp?RnID=343 Actually! other than buying a load cell and testing every fittings "load in the biggest breeze possible" it is very hard for Joe Average to work out loadings on a fitting and then buy the corrrect fitting without going overboard (oversize / overweight / overkill. sure, like many, i have found experience and looking at what the top boats use is good but surely Companies like ronstan would have a chart of loadings relative to sail size / boat size to give the average pleb a good chance of getting the right bit! Link to post Share on other sites
col j 0 Posted July 3, 2009 Share Posted July 3, 2009 had 3 of the black harken ones blow out (left with 3 shackles) so went to these, seem to be holding out ok. have them on kite sheets/braces/tack line on an occasionally very overpowered 727, they have out lived one spinnaker pole and one kite Link to post Share on other sites
wheels 543 Posted July 3, 2009 Share Posted July 3, 2009 But isn't the line supposed to wrap around through the hole at the centre of the block???. Link to post Share on other sites
col j 0 Posted July 3, 2009 Share Posted July 3, 2009 the block pictured would have had a line tied to that for a cascading system i think. that is their design i believe/hope...thats what out main sheet system has Link to post Share on other sites
Absolution 7 Posted July 3, 2009 Author Share Posted July 3, 2009 But isn't the line supposed to wrap around through the hole at the centre of the block???. That's used as the becket is on these blocks. Link to post Share on other sites
Guest creative suffering Posted July 3, 2009 Share Posted July 3, 2009 gee this is hard to say... wh whe wh whee wheel wheels is right! the dyneema / dynax line has togo through the centre hole (as well as the top) to spread the load on to the strogest part (the sheeve) and that has to happen in every application! een if cascaded off ! well spoted wh whe wh wheels! Link to post Share on other sites
Absolution 7 Posted July 3, 2009 Author Share Posted July 3, 2009 I have just had a very positive email back from Ronstan in Aus. They are sending me a replacement and are very keen to help even though the local supplier didn't want to do anything until I could produce a receipt. Link to post Share on other sites
Absolution 7 Posted July 3, 2009 Author Share Posted July 3, 2009 the dyneema / dynax line has togo through the centre hole (as well as the top) to spread the load on to the strogest part (the sheeve) I know some of the high load blocks are designed that way but these ones are designed to have the load on the head not the sheave. According to Ronstan: The Dyneema® Link is produced from FSE Robline SK75 fibre, which is 10 times stronger and lighter than steel, and provides the final connection from the block to the load point. Requirement on mounting point - the Dyneema® Link must be attached to a smooth, well rounded mounting point; without sharp edges or burrs. If in doubt, a shackle should be used. Also see pic Link to post Share on other sites
Guest creative suffering Posted July 3, 2009 Share Posted July 3, 2009 farr out!. i think ronstan hae got that wrong. if the dyneeema rope had been reeved hrough the centre hole it would have bridged the break point and there would have been no problem. i would bail up Ronstan and say you followed thier spec and it failed! and demand a replacement! their diagram is dodgy when you consider the strength gain of running the dyneema through both holes! Link to post Share on other sites
Murky 1 Posted July 3, 2009 Share Posted July 3, 2009 had 3 of the black harken ones blow out (left with 3 shackles) so went to these, seem to be holding out ok. have them on kite sheets/braces/tack line on an occasionally very overpowered 727, they have out lived one spinnaker pole and one kite Interesting. I've got the black Harken versions (carbos) with no problems so far. My instinct was to go for the ones with the stainless cheeks (now called the Classic range) but according to the catalogue, the carbo ones can take a substantially higher load, by 20 or 30%. Visually though, you keep looking for what is providing the grunt in these things. Link to post Share on other sites
col j 0 Posted July 4, 2009 Share Posted July 4, 2009 re the carbo blocks. they did blow after a flog of the kite in about 30 knots (were the 40mm harken, well within their spec sheet, now on 55mm orbit blocks) Link to post Share on other sites
Gappy 9 Posted July 4, 2009 Share Posted July 4, 2009 Depending on the size of the boat the top block on a cascade vang is pretty highly loaded and normally you would use a solid bearing block as these are better under high load and have a high breaking load I know the checks broke not the sheave but those orbits don;t have that high a breaking load and ronstan seem to normally over rate there blocks is what we have found. Personally I would be dubious using them on a vang and backstays. Cheers Gappy Link to post Share on other sites
wheels 543 Posted July 4, 2009 Share Posted July 4, 2009 I wonder? is it a case of over spec, or is it perhaps a case of less headroom between working loads and max load. Another possible.... I find with a lot of these new "space age" materials, the stronger they are getting, the less they seem to like shock. You may be able to place a very high working load on them, and even take that load to well beyond the normal safe working load as long as it is a slow pull/load increase, but hit it with a fast transient load ("shock") and some of these materials fail rapidly. Link to post Share on other sites
Guest Posted July 4, 2009 Share Posted July 4, 2009 You go it Wheels. The loads published aren't 'shock' loads. Link to post Share on other sites
SloopJohnB 322 Posted July 4, 2009 Share Posted July 4, 2009 Then you apply the "Explosvie Factor" like when you drop off the top of a wave. Link to post Share on other sites
wheels 543 Posted July 4, 2009 Share Posted July 4, 2009 Yep you got it SJB. And it doesn't have to be much of a wave either. It is all due to the fact that the stronger these materials become, the less elasticity they have. The less elasticity, the less they can handle the shock loads. The "snap" like carrots. Apart from reduction in weight, I am not sure the hunt for stronger less elastic materials is really the right path forward. There are pluses of course. Like a line simply dropping when it breaks instead of becoming a slingshot and slinging a broken shackle like a projectile that can take out someone in it's path. And the weight saving of course, along with less windage due to being physically smaller. But the failure due to less load headroom is the negative, which simply has to be weighed up against the pluses. Link to post Share on other sites
SloopJohnB 322 Posted July 5, 2009 Share Posted July 5, 2009 Use low friction rings Puma did the vang this way. I cann;t find photos of her setup at the moment. Similar to this http://www.sailingworld.com/sailing-gea ... 72086.html Link to post Share on other sites
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