Topic : One String System

Can anyone describe the mechanism of the one string system at the thwart going through the cam cleats please ? Is this actually one string or are their two separate strings each going thru a rake forward and rake back cam cleat.
Thanks very much any help you can give me.

Posted: 06/06/2020 08:37:16
The control line is one continuous piece of rope.

Posted: 06/06/2020 10:14:40
By: Chris Martin
Thank you very much Chris. So does the line come out of  the rake forward cleat, loop round and go through the rake back cleat with about 30 cms spare slack for the loop. It's this mechanism and its operation that  I am trying to figure out please. I have built the boat and I am trying to plan the rigging and its operation. I have never seen or done this before.
Thanks again. 

Posted: 06/06/2020 10:27:20
By: Ainslie French
When I set these up I leave about 1.5m slack on each side tensioned by an elastic take up. It goes almost all the way to the back of the boat under the side deck.
If you don't the system will get "stringbound" and will seize up. 
Other that modification it's as you describe. 

Posted: 06/06/2020 10:40:35
By: Chris Martin
Thanks Chris, I think I get the picture. That's great !!

Posted: 06/06/2020 13:22:58
By: Ainslie French
Just re-rigged mine today. Chris M is spot on about 1.5m each side.

I just upped the block size on mine to improve ease of use

Posted: 06/06/2020 19:40:27
By: Gareth Griffiths
Thanks for the added information Gareth.

Posted: 07/06/2020 07:58:06
By: Ainslie French
You can view "Magia Bianca" - "White Magic" awaiting the rigging here : 
At the moment I am working out the forces on the pulley systems prior to choosing the bits and the new mast, boom and mainsail should be arriving from the UK shortly. 

Posted: 07/06/2020 23:00:14
By: Ainslie French
Hi Ainslie,
Glad to hear you are finally getting to the rigging stage!  Keith Callaghan has some fantastic diagrams on his website of how the systems work.

Posted: 08/06/2020 07:43:57
By: Stuart Bates
Hi Stuart,
Thanks for your kind comments and the link. Yes, I have Keith's diagrams showing how the system works and I agree they are excellent. I am just down to the fine detail now, to see how physically all fits together. 
Thanks again.

Posted: 09/06/2020 06:23:34
By: Ainslie French
Ainslie, the key to getting your head round it is that the one-string block has a range of movement, the Jib Halyard on a 2:1 gives you a fixed range that it is possible to move over. The shrouds will move a set distance for the range of rake that the Jib gives you, so the purchase is calculated so that the movement range at the one-string block moves the shrouds the correct amount to match the jib movement.  The shrouds also have a tension system (required otherwise you would never be able to take the jib off) that needs to let the rig tension off sufficiently for you to unhook the jib halyard, but also be able to provide sufficient tension in the system when sailing.  The other systems are also calculated so that the movement range is matched with the One-String block, whilst also being able to be adjusted independently.
I hope that this helps with the understanding.

Posted: 10/06/2020 09:28:43
By: Stuart Bates
Stuart....would you mind elaborating further please? My grammar school physics prowess seems to have left me.
If the one-string block is tensioned i.e. pulled on then the jib halyard tightens which puts forward tension on the mast and releases tension on the shrouds i.e. straight mast? ....and releasing tension on the block takes tension off the jib and adds tension to the shrouds allowing the mast to rake back. Have I got that right? ..... and on my boat the lowers stay relatively tight throughout? This is the last piece if the jigsaw for me :-)

Posted: 10/06/2020 12:33:42
By: Rousey
In terms of the One-String System: Remember that a 2:1 means 2 cm movement of control line for 1 cm movement of block.
Jib Halyard on a 2:1 at the top of the mast then the movement at deck level is around 70cm
This means that any purchase attached to the one string block will have the 70cm of movement at the end of the control line, so the purchases need to reflect that.
Shrouds, these are on a 6:1 purchase (3:1 & 2:1), so the movement at the shroud is 6 times less than at the one-string block.
Lowers, These are on a 9:1 purchase (3:1 & 3:1), so the movement of the lowers is 9 times less than at the One-String
Puller, Should be around 7:1, but some are on 6:1
I hope that this makes sense and if you would like any further details on any part please feel free to message me on Facebook.
There are details of the work I did on converting a Winder to One-String at

Posted: 11/06/2020 10:15:47
By: Stuart Bates
Thanks again Stuart for your generous explanations. I still need to think hard about this.
I dearly hope not to overdo my questioning and exhaust your patience further, but, could you indicate if the "snodger" also has an elastic take up on each side also being about 1.5m long, please
It seems that Laurie Smarts "Smarty Pants" has something similar see in particular the view taken from the stern showing lines close to the sidedeck running aft from the thwart.
Thanks for any help you can give me, 

Posted: 11/06/2020 12:13:41
By: Ainslie French
Hi Ainslie,
On my boat both of the pole downhaul lines pass through a ring between the deck and the snodger purchase that is elasticated away forwards.  This takes up the tension on both lines, but does let both off when the pole is up, meaning that the leeward downhaul is not putting any sideways tension on the sheets.
The Snodger is led back to the thwart on both sides, allowing the helm to tension/release it whilst sat on the side immediately after the crew has the pole on, before the sheet tension makes it harder to pull on. There is no elastic on the end of the snodger line, so that the line does release fully to help the crew.  Some boats have both downhauls led to one purchase and other boats have individual purchases, either 3:1 or 4:1 (I use 4:1) as there is quite a lot of tension on the line when the kite is set.
Don't worry about the number of questions, it's much harder to visualise the systems when you don't have one to look at.

Posted: 11/06/2020 16:00:58
By: Stuart Bates
Thanks a million Stuart !!
As the Italians  would say "Stuart tu sei grande !" - meaning "Stuart you are great !"
Thanks again 

Posted: 11/06/2020 21:57:55
By: Ainslie French
Currently got the control line on mine set up with fee 4mm control line, I’m using harken 22mm blocks everything turning nice and smoothly though thinking of changing to Marlow 3mm core a per most the fleet for an even smoother service...

Posted: 14/06/2020 09:52:12
By: Gareth Griffiths NHRC
Hi Gareth,
Thank you very much for the extra information.
As there are no Merlin Rockets here in Italy  to view and only the photos in the Merlin Rocket Association Gallery to go by, together with Keith's excellent diagrams, I am having to try to work out the forces within the system from first principles.
I have the book "Dinghy Rigging" which is a help since it gives me a starting point with the numbers, but I still have to go through the potential forces in all the attachments, their appropriateness, screws, bolts, lacing eyes etc. 
I also have two parts lists which Keith very kindly supplied me but its getting everything to fit together harmoniously and above all, safely that really worries me.
I want to build a safe boat without the risk of something crashing down in high winds off the Italian coast where there is little or no rescue service if things turn nasty. 
Of course I've made, and will continue to make loads of mistakes along the way, but these are my problems and I don't want to burden you all with them.
Thank you so much, though, for your generosity of spirit.
Best wishes Ainslie. 

Posted: 15/06/2020 11:25:50
By: Ainslie French
Hi Stuart your blog on the Edgar refit is great. Really interesting would be great to get more of these on the website for members to view when doing similar work.

Posted: 15/06/2020 11:44:39
By: Gareth Griffiths NHRC
That's brilliant !
I didn't know it existed.
Thanks very much Gareth and Stuart.

Posted: 15/06/2020 18:53:35
By: Ainslie French
Thanks for the support Gareth, I do need to update the blog with more details of my findings and extra work I have done since.
 Ainslie, the blog is at

Feel free to pm me on Facebook if you have questions that you want to discuss.

Posted: 16/06/2020 12:42:48
By: Stuart Bates
Great !
Thank you very much Stuart.

Posted: 16/06/2020 16:34:46
By: Ainslie French


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