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Old 09-02-2013, 21:09   #16
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Re: Running Backstays-What Size?

Hmm - 12mm Spectra has proved to be about right for a 62' masthead, inline rig on a 6.8 tonne racer-cruiser with a deep draft, keel bulb, three spreaders, permanent inner forestay from top spreader level, no babystay. Mast fore-and-aft dimension 200mm or 8".

I think I posted a photo a while back of it carrying a decent sized staysail and nothing else, with both runners set up, in 60 knots true, with no hint of a wobble or wriggle.

So that tallies more with what Dockhead wrote, by way of sizing.

Even when there's no staysail, the runners play a crucial role in keeping the mast 'in column' with in-line stays. I'm thinking in the event of severe loading, such as smacking the mast into the briny, or a flick roll.

And (again I think it was Dockhead) I entirely agree it's all about freedom from stretch: the angles are so favourable that strength is not the factor governing runner choice. A runner fails to do the job not by breaking (unless it's damaged), but by allowing the mast to move enough that the compression load will buckle it.

It's like a heavy bloke standing on a soft-drink can when it's empty, and a bit dented, as opposed to unblemished.


I would argue that differences in the particular layout of the rig, especially such things as the fore-and-aft mast dimension and whether/how much the spreaders are swept, are crucial, and it seems to me that the OP gave us way too little information for us to make a sensible recommendation.

However I think what posters are doing is fine, stating what proven rigs have got away with using long term .... provided we know other things about their rig, like the above.
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Old 09-02-2013, 21:34   #17
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Re: Running Backstays-What Size?

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Originally Posted by Andrew Troup View Post
I would argue that differences in the particular layout of the rig, especially such things as the fore-and-aft mast dimension and whether/how much the spreaders are swept, are crucial, and it seems to me that the OP gave us way too little information for us to make a sensible recommendation.

However I think what posters are doing is fine, stating what proven rigs have got away with using long term .... provided we know other things about their rig, like the above.
OK! Here's some pictures. It's a keel stepped mast with 54' sticking above deck. It's a Z-Spar 601 mast with two spreaders.

I plan to install a removable babystay for sailing above 25 kt of wind. I ran a temporary second jib from the spin'kr boom lift and it balances out the boat really well with the main reefed on it's third reef. But the mast pumped so bad I pulled it down after about 5 minutes. And I really don't like cranking down on the hyd. backstay to bend the mast.

The 40' IOR boat displacement is around 16K with 7' draft and an all lead fin keel, with a large independent rudder.

Hope that helps.
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Old 09-02-2013, 22:23   #18
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Re: Running Backstays-What Size?

12mm Spectra running from T-Balls at the top spreader downto a block and then 2:1 polyester tails to the winch

40ft IOR Admirals Cup, inner forestay for flying staysail or storm jib, mast 60 ft off the water.

Works fine...4 years now...

To the poster that doesn 't have an inner forestay, I wonder why you have runners ?
To the one that does ...why don't you have runners ?

Runners are only there to counter the loads produced by a flying sail on an inner forestay, to prevent the mast pumping and ultimately destroying the rig.

When heading upwind with the staysail sheeted in tight on the leeward winch, the windward backstay is wound tight on on the windward winch ..tacking involves a complete swap from port to stbd....
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Old 09-02-2013, 22:30   #19
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Re: Running Backstays-What Size?

Question: when you guys are saying "spectra" do you mean spectra cored double braid or single braid Dyneema? If the latter, 12 mm seems like way overkill to me... I think that is the sort of diameter folks are using for shrouds which are way more critical for stretch than runners.

Just curious...

Jim
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Old 09-02-2013, 22:48   #20
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Re: Running Backstays-What Size?

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Question: when you guys are saying "spectra" do you mean spectra cored double braid or single braid Dyneema? If the latter, 12 mm seems like way overkill to me... I think that is the sort of diameter folks are using for shrouds which are way more critical for stretch than runners.

Just curious...

Jim
Jim,
When I say "Spectra" I mean spectra cored double braid....its plenty for runners...all my halyards are "Spectra"....better than wire /polyester combos I had before...

Enjoy the Wooden Boat show !

Cheers
Alan
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Old 09-02-2013, 23:07   #21
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Re: Running Backstays-What Size?

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Originally Posted by Albro359 View Post
Jim,
When I say "Spectra" I mean spectra cored double braid....its plenty for runners...all my halyards are "Spectra"....better than wire /polyester combos I had before...

Enjoy the Wooden Boat show !

Cheers
Alan
Yes, that stuff is good for halyards. We changed over years ago, except for the spinny halyard where I like a bit of stretch to absorb the shock loads when it collapses and fills suddenly. As I said earlier, our runners are 7 mm Dyneema 75 with 12 mm spectra cored tails through a 3:1 tackle to Barient 27's and a Lewmar clutch to free up the winch.

And the festival is fabulous... so many wonderful woodies, old and new, and lots of interesting folks to tell lies with.

Cheers,

Jim
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Old 10-02-2013, 05:46   #22
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Lotsa boats have running backstays and checkstays without the inner headsail. Even the inner forestay is optional.

For preventing pumping in a seaway, especially with the main down, I use the runner opposite the spinnaker pole topping lift (tacked to the foredeck) and the checks opposite the babystay. Everything wound or quite tight. Significant mast bend. Perhaps 2 diameters.

Sometimes in lighter sailing conditions the runners and checks are set up a little to straighten the mast for mainsail depth. A big genoa can cause much backstay to get pumped on and that makes mast bend and that makes a too flat main.

Also holds the anchor and cockpit light!
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Old 10-02-2013, 09:52   #23
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Re: Running Backstays-What Size?

Heck, I've had my mast pump while sitting at the dock. It takes about 10 kt and setting at just the right angle but it happens enough that I have to make adjustments to get it to stop.

Daddle, it sounds as though our boats are set up the same with exception of the runners, that I'll be installing.
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