mainsheet diameter

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paulburn

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I am planning to upgrade to Harken equipment for my mainsheet - 4:1 system on a Beneteau 27.7. The blocks which look suitable in size have a max rope diameter of 10mm which I am worried will be too thin to hold easily in strong winds. The next size up blocks (max rope diameter 14mm) seem enormous. Any advice please on what rope diameter is appropriate for a boat of this size ?! Thanks.
 
its all about comfort, bit of a twitch and just do it by hand but any more and its the winch so size doesnt matter, for what its worth my bene 351 has a 12 mm fl uffy on it, nice and soft to the hands.
 
i don't know your boat specifically but it depends a lot on the main sheet set up. The extremes are a main sheet set up on the cabin roof and attached to the boom only about 1/3 the way from the gooseneck. The loads are huge but the amount of rope needed is not so great. A traveller system may be fitted but perhaps of limited range. The other extreme is end of boom sheeting to a horse over the tiller. Here a huge amount of rope is involved but not such great loads. I hope yours is somewhere between the extremes.
As already mentioned a main sheet can be mostly left cleated if you have an efficient traveller system to ease the boom in or out. This can make a very good sail shape. Of course in a jibe you may need to ease the main out then pull in rapidly to minimise the boom swing over shock, then ease out again rapidly to minimise knock over.
I have been on boats recently where this manouvre is quite difficult for me an old guy on the mainsheet. On my own boat with a relatively large main I am happy to let the boom swing. on my friends farr40 fractional an uncontrolled jibe is a fearfull thing with thoughts of major damage. The Farr has 6 part purchase with a trimming tackle added. It takes a lot of pulling the sheet in and then letting out to acheive a gentle boom swing over. Likewise with a friends 27 fter, heavy masthead, the sheet traveller is on top of the cabin and so not conveneient for the pull in and let out. The weight on the sheet is too much for me with 4 part purchase in a wild jibe.
So there are all sorts of considerations to main sheet, the size of the rope being one. The strength of the rope is not normally the consideration but the size for handling is important. Unfortunately too thick a rope will not run out so easily. Nevertheless the 10 mm sounds about right.
good luck olewill (what a load of wafffle)
 
I find 10mm is about right, but suggest that you try and get a single braid for it. The single braid lines are lighter and more supple, and generally easier on the hands. Even though they have lower swl's, the mainsheet system is unlikely to be anywhere near the swl on any suitable line.
 
You will be fine on 10mm polyester. Jusy done the same on my 38s5 & going to use 12mm max but might drop to 10mm Spectra. Gone for Harken Carbo Blocks which look tiny compared with the old Goiot ones but have a high breaking strain.
 
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