Welcome to the UKWA Home Page Forums Technical muscle box range and rig tension

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  • #3730

    Hi all!

    I’ve just installed a muscle box (power box) onto my mast, and have a question for those who have experience with it:

    If I remeber correctly, the jib halyard should be long just enough to reach the muscle box hook when hoisting the sail. Now could you give an approximation of how far back do you pull the muscle box hook from this ‘untight-hoisting’ position to the position for the maximum desired rig tension? Do you use the full range of the muscle box or less?

    I’m asking this because I used the tension gauge to see what is happening, and was surprised that even about 6cm of pull results in shroud tension well above 160kg specified in the W book as maximum tension for strong wind. Since muscle boxes have range of travel of about 12cm, I thought that it would be ok then to tailor the halyard a bit longer than ‘just enough to reach the hook’ – in order to hook it with less strain when changing foresail at sea….

    Am I wrong at something? I tried to follow the instructions for the tension gauge the best I could, but it might be that I was doing something wrong.

    Thank you + best regards,


    Dave Barker

    Hi Mato,

    I would estimate that we use no more than 8cm of travel on our muscle box.

    Do you have a Superspars tension gauge? If so, feel free to email me to check your method, but I think you’re probably doing it correctly.



    Hi Dave!

    Thank you for your reply. It seems that 12cm of travel is more than enough, so I’ll have another halyard made – a little bit longer than this one, so that I can hook it more easilly.

    Yes, I have the Superspar tension gauge with their instruction leaflet. I’m glad you mentioned this, because, I was in fact sceptical that perhaps this gauge is not precise – as I have seen that there exist far more expensive ones… Now I’m confident that everything is ok.

    It seems that last summer I have been sailing with rig tension of 225kg at the lowest position of my highfield lever (didn’t have the gauge back then)… I’m glad nothing broke….

    Thanks again and best regards,


    Dave Barker


    Did you have to pull very hard on the forestay to tension the Highfield lever? I would think that 225kg is fairly difficult to apply… 😯


    A cheaper option might be to swap one or two of the shackles for the elongated type. I’d be loathe to go getting another halyard made up when the current one is so close to being ideal – you might want to change your mast rake or some other parameter that makes your old halyard right and your brand new one wrong!



    I didn’t pull on the forestay, but it required a very hard push on the lever from almost kneeling under it… I thought it was supposed to be that way…


    Thanks for your hint. But there is another reason it might be a good thing to replace this halyard – I have made this one myself with a hand swager and I don’t know if it is equally reliable as a professionaly made one…

    By the way, getting into DIY swaging was an ordeal of itself. To cut the long story short: I found that it should be done in reverse order – first find the ferrules that you regard as appropriate, then get the swager from the same manufacturer or at least have the ferrule manufacturer recommend the swager. It seems that these things do not conform to a certain standard.

    I have tried five different ferrules, and the best looking results were with Ormiston plain copper ones. Unfortunately I got the swager beforehand from another manufacturer (I wasn’t aware at the time of purchase that they make only aluminium ferrules wich are regarded as inappropirate for marine use), so it is not a perfect match.

    Thanks to both of you + best regards,



    Remember to kick the mast into position against its aft heel stop after pulling on the rig tension, you will find that the rig tension drops after having done this. I do this by kneeling on the foredeck and giving the mast a sharp tug forwards against the mast chocks. Others do this by standing in the boat and pushing forward.


    @matoi wrote:

    I’ve just installed a muscle box (power box) onto my mast,

    AFAIK you have a brand new Wayfarer with a brand new mast. Why did you put the muscle box on the mast? IMHO it is much easier to put it on top of the CB case. 😕 See picture:



    I have placed the box temporarily onto the mast because I wanted to experiment with a line for centerboard up/down hauling from helm’s position. I suppose that it’s probably not worth the complication, but anyway it is all part of the game… Has anyone else ever had control lines for CB?

    Best regards,


    P.S. XXXXXX, I’ve sent you a private message some time ago, could you please take a look. Thanks.

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