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Sam.Spoons View Drop Down
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    Posted: 16 Jan 19 at 5:51pm
Yup, that's where I was at too. Proper brain bender it was though, even when I built the mock up I couldn't work out why it was 5:1 even though I could see it there in front of me.......

So I think you are probably right that it should be fitted the other way up to be rule compliant. It's much easier when the dead ends are attached to the fixed end.....


Edited by Sam.Spoons - 16 Jan 19 at 5:54pm
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Posts: 6662 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 5:25pm
Its certainly an odd way to rig the system. But I made a model too and it definitely is 5:1, and I've now realised how I managed to get the wrong answer. To be class legal it needs to be rigged the other way up.

Edited by JimC - 16 Jan 19 at 5:34pm
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Sam.Spoons View Drop Down
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Posts: 3401 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 3:13pm
You are right though, it would not be too difficult to re-jig it for either a class legal 4:1 or 6:1  Thumbs Up

Edited by Sam.Spoons - 16 Jan 19 at 3:13pm
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Posts: 3401 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 3:08pm
No it isn't! I know it's a long thread and, like most people, I can't always take the time to read all the way through myself but if you look back to my post on page 2 you'll see that it is 5:1.

The OP's question BTW was "what is the purchase of this system?" rather than asking how he could 'improve' it. (mozzy in fact who is not exactly inexperienced WRT this stuff).




Edited by Sam.Spoons - 16 Jan 19 at 3:10pm
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Posts: 219 		Post Options Post Options   Quote ohFFsake Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 2:38pm
3:1

Really it's a 2:1 purchase but with the tail led to advantage so the overall purchase is 3:1

Turn it upside down and it would be 4:!




Edited by ohFFsake - 16 Jan 19 at 2:40pm
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 1:31pm
The rules mandate it is 4:1... yet this is how it is supplied by RS / Selden and how nearly everyone in the class has it rigged. 

So somewhere between the supplier and the person who wrote the class rules there has been a mistake. 

Perhaps the class felt the need to specify a purchase to stop people over tensioning the uppers and damaging their masts? I've not been in the boat long enough to know the history. I don't think running more tension on the uppers would be an advantage, so I don't really see the point in the rule.   

But, the current system rubs on the mast. There is a steel protective plate but this comes off all the time. So I was thinking if something kinder on the mast could be rigged up, and that when I noticed the rule.  
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Posts: 476 		Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 12:44pm
Originally posted by Sam.Spoons

Originally posted by PeterV

Goodness me, on the 5th page and a lot of people failing on basic mechanics.  As stated by several a fixed point acts only as a turning point and adds nothing to the purchase, in seamanship terminology this is a tackle 'rigged to disadvantage' so it's a 3:1.  A bit of simple rearranging could easily make it a 6:1.


But we have already established that is it neither 3:1 or 6:1? The tackle drawn gives a 5:1 advantage both in theory and by experiment.



The system as shown is 5:1 but by using the same blocks in a different arangement you could get 6:1 without any change in range. So unless there is a rules mandating a max of 5:1 I don't know why anyone would rig it this way.
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Posts: 3401 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 10:33am
Originally posted by PeterV

Goodness me, on the 5th page and a lot of people failing on basic mechanics.  As stated by several a fixed point acts only as a turning point and adds nothing to the purchase, in seamanship terminology this is a tackle 'rigged to disadvantage' so it's a 3:1.  A bit of simple rearranging could easily make it a 6:1.


But we have already established that is it neither 3:1 or 6:1? The tackle drawn gives a 5:1 advantage both in theory and by experiment.




Edited by Sam.Spoons - 16 Jan 19 at 10:33am
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Posts: 131 		Post Options Post Options   Quote PeterV Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 10:30am
Goodness me, on the 5th page and a lot of people failing on basic mechanics.  As stated by several a fixed point acts only as a turning point and adds nothing to the purchase, in seamanship terminology this is a tackle 'rigged to disadvantage' so it's a 3:1.  A bit of simple rearranging could easily make it a 6:1.
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Posts: 823 		Post Options Post Options   Quote PeterG Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jan 19 at 9:47am
Clearly the person hauling on the caps, , the hull and the mast foot don't move in relation to one another when the system is pulled on. When I'm stood on the deck pulling it on, the mast doesn't slide toward me. The only thing which moves in relation to hull, mast foot and myself is the caps. Therefore, it helps to define a system where those are considered fixed and the caps are moving. 

I hate to admit this, but I think you are right. One end is "fixed" in relation to the applied force, and that's the key to the effect of turning it upside down.
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