Topic : Shroud movement

Can anyone help me with an idea of how much the shrouds move when raking a deck-stepped mast? I'm nearing completion of the redecking and restoration of my NSM 2 (3285) and wish to assess where to run the various sections of the purchase systems within the various spaces I have available. For instance, if the shrouds only move 60mm I have enough height in the kingpost; if they move more I shall have to arrange a cascade along the centreboard case, etc. etc! I shall have the same dilemma with the lowers but would guess that they move less? Any help gratefully appreciated.

Posted: 05/07/2006 09:50:51
By: RichardS
They don't move very far, although did you mean 60 mm or 60cm, as I don't think 60 mm is enough for the shrouds, I would guess closer to 15-20cm. Most boats have the shroud/lowers pulleys on the frame that runs up in front of the tank and then up/down the king post. 

See picture. The pink rope the is under the toe strap is the shrouds.

Posted: 05/07/2006 12:22:26
By: Alan F
Thanks Alan - Yes I did mean 60mm (2.3 inches?). 20cm is about 8 inches in old money - do the shrouds really get shortened by that much? My problem is the space up/down the kingpost as, although the layout of the boat is very similar to your linked photo with the centreboard case running full-height up to the tank bulkhead, my kingpost seems much shorter than the one in the photo. This means I have only about 180mm (7 inches) travel at the kingpost. This in turn means I need to be careful about the amount of purchase I use where the shrouds come through the side deck. My thinking was this: if the shrouds only needed to move 60mm, I could put a 3:1 along the tank frame, a 6:1 up the king post and a 2:1 along the centreboard case, making 36:1 in total (but it all depends on the throw of the shrouds or I shall run out of movement at the kingpost - sigh!!)

Posted: 05/07/2006 13:07:33
By: RichardS
I am sure they don't move a whole 8 inches, but 2.3 doesn't sound enough. Put it this way, with 4 to 1 and a full height king post can only just get the tension on when fully raked. Some basic school boy maths could approximate but invloves tans and cosine and stuff that I have long forgotten

Posted: 05/07/2006 13:48:44
By: Alan F
I was going to post something here but realised that what you actually need is the true figure from someone who has gone and measured his/her boat and a guess isn't good enough.  My guess FWIW is about 3 inches in old money, will measure at weekend if you have no better answers

Posted: 05/07/2006 16:19:12
By: Andrew M
I think he means the actual shroud itself moving 60mm before any pullies.

Posted: 05/07/2006 16:22:56
By: daveF
You're absolutely correct. I would be very grateful if someone could measure next time they rig their boat, and yes I DO mean how much the shroud moves before any pulleys (in other words how much of the shroud disappears down through the side deck!). This information would enable me to design the pulley system to fit the space and still have about 36:1 which is what I see on most boats.

Posted: 05/07/2006 18:25:16
By: RichardS
Not sure if this helps but on my Tales (3489), I have a coarse adjustment and a separate fine adjustment that both work on the same set of purchases.  If you look at this link (and ignore the fact that it is talking about spinnaker setup), you can see the fine adjustment as white stringed Y running down kingpost and then to purchases under shrouds while the coarse adjustment can just be seen running from these purchases horizontally along tank top (just above thwart in pic) - they then go around a pulley on tank top and back along centreboard casing.
I will look to see if I have a better picture and can anyway send you some measurements at the weekend as boat will be back home on Friday.

Posted: 05/07/2006 18:25:37
By: RichardT
Movement at the shrouds equates to rake.  

How much rake do you want, or how much do you think you can live with? If you are after the mast head being over the transom, then you will need substantially more than 60 mm at the shrouds.

When I deck stepped my NSM 1 I just used the space under the mast step (high bow tank, therefore full height available from hog to deck).

I had to set the limits of 'active' adjustment (i.e. your 60mm max) and then fitted rigging links above deck level on the shrouds. Light winds, I lengthened the 'static' length of the shrouds - strong winds, shortened them. I could still adjust the rig, but couldn't get it fully upright in strong winds - a small price to pay at the time for an 'Automatic' raking rig system conversion which cost less than £100 to fit.

In short, if you can live with a limited rake, stick to your maximum 60mm shroud movement for simplicity of rigging.

Posted: 07/07/2006 08:29:08
By: The Old Trout
While I think about it, Lowers:

I rigged them with fixed ends at the gunwhales, up to two turning blocks attached robustly to (actually, through) the mast at gooseneck level, and then attached them both in front of the mast to the adjustment purchase, which was also led down to the hog.

That way I only had to buy one set of expensive adjustment blocks, rather than having a set on each side of the hull.

You can tell I was on a tight budget...

Posted: 07/07/2006 08:35:37
By: The Old Trout
Thanks Old Trout! Some useful thoughts there.

Posted: 07/07/2006 10:43:59
By: RichardS


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