CarpeDiem 430 Posted September 6, 2017 Share Posted September 6, 2017 Hi folks, I am rebuilding the vang on a Cookson 47 that I am racing on out of Australia occasionally. The vang was repaired after a breakage and I am trying to calculate what the current mechanical advantage is of this setup. I don't know how the formula works when a compound pulley system is connected to an intermediate cascaded system. In the attached diagram the dotted line is confusing me and I don't know how to calculate it. I am probably not going to rebuild it like this, I just want to know what the advantage is, because it's adequate and I don't need more or less. Thanks Quote Link to post Share on other sites
RushMan 31 Posted September 6, 2017 Share Posted September 6, 2017 7 x 2 x 2 .... 28:1 (less friction) After more thinking.... If the compound pulley system finished at the top triple block it would be 7 x 2 x 2 but as it finishes on the boom it might be only 6 x 2 x 2 Quote Link to post Share on other sites
CarpeDiem 430 Posted September 6, 2017 Author Share Posted September 6, 2017 So it makes no difference that the compound 7 is linked to the load as well? I don't understand this, why doesn't some of the force from the 7 get distributed away from the 4 and directly to the load. What if the dotted line was attached to the second pulley from the top, would it still be 7 x 2 x 2, or would there now be some equal or unequal distribution of the 7. I totally get that if the dotted line was attached to the block of three, then it would deffinitely be 7 x 2 x 2, but I am not understanding why it would be still 7x2x2 when one leg of the 7 is connected to the to load. Thanks Quote Link to post Share on other sites
RushMan 31 Posted September 6, 2017 Share Posted September 6, 2017 Instead on finishing on the boom is it an option to finish at the top triple block? Are you looking for less or more purchase? Quote Link to post Share on other sites
CarpeDiem 430 Posted September 6, 2017 Author Share Posted September 6, 2017 Instead on finishing on the boom is it an option to finish at the top triple block? Are you looking for less or more purchase? I can build it anyway I want, I just kind of want to know what the advantage is, cause it's got me stumped. My guess was it's somewhere between 24:1 and 28:1... Thanks Quote Link to post Share on other sites
madyottie 82 Posted September 6, 2017 Share Posted September 6, 2017 I think the movement of the top block is going to be so minimal as be unnoticeable. Isn't it just going to increase friction by a similar negligible amount? I'd just call it 28:1 Quote Link to post Share on other sites
RushMan 31 Posted September 6, 2017 Share Posted September 6, 2017 I can build it anyway I want, I just kind of want to know what the advantage is, cause it's got me stumped. My guess was it's somewhere between 24:1 and 28:1... Thanks Call it 26:1 and time to rip the top of a cold one Quote Link to post Share on other sites
Ed 143 Posted September 6, 2017 Share Posted September 6, 2017 25:1 by my calc, 24:1 through the Cascade, plus 1 extra fall 1 Quote Link to post Share on other sites
Black Panther 1,584 Posted September 6, 2017 Share Posted September 6, 2017 I get 24;1 Quote Link to post Share on other sites
Adrianp 120 Posted September 6, 2017 Share Posted September 6, 2017 25:1 by my calc, 24:1 through the Cascade, plus 1 extra fall I get 25:1 too by imagining 1kg of load applied to the yellow line and then adding it up a 6x2x2+1 for the anchoring of the tail on the final cascade block Quote Link to post Share on other sites
Black Panther 1,584 Posted September 6, 2017 Share Posted September 6, 2017 Yep, missed the +1, 25. Quote Link to post Share on other sites
madyottie 82 Posted September 6, 2017 Share Posted September 6, 2017 I'll go with the 24:1, should have turned the phone sideways for a better look. Not sure how to work out the extra part. Just do a practical test, set it, measure it, shorten the whole thing by say 50mm, and see how much line it uses. Good way to test all our thoughts. Quote Link to post Share on other sites
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