Maintaining Tension on Running Backstays

[Stumble]

Fair enough Ann. I like using permanent markers to a reference point on the boat. But yes marking lines is a great idea.

[transmitterdan]

With 4:1 tackle on the runner you should be able to put sufficient tension on by hand without a winch. That assumes the main length of the stay is a low stretch material (wire or dyneema). All you are trying to do is stop the mast pumping. It's possible your mast doesn't pump anyway. Some designers of cruising boats used an over sized mast section such that runners are redundant. But they included runners in the rigging plan to appease the traditionalists who think they are always required for a staysail.

[GILow]

I'm really glad I posed this question, the various responses have made me think much more carefully about what is actually going on with these stays.

Looking forward to putting it all into practice, and yes, I am starting to see how the winch could turn out to be unnecessary for the setup. I certainly hope so, as it will make for much less work.

Matt

[Snowpetrel]

A big 62 foot charter boat that I sometime skipper just has a 4:1 tackle onto a cam cleat on the runners for the staysail. Seems to work OK though I do worry about their strength. My prefered system is 2:1 onto a winch. Much quicker to release. But pleanty of options. I like to have a tricing line to pull them forward, the tail from the tackle can work. Have you got a photo?

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[GILow]

Tricing line.

I had to look it up. (Blush!) But yes, that was what I was thinking of doing. I already have the required hardware, including some special large radius/light duty blocks to pull the lee stay forward to the main stays without putting a sharp bend in the wire stay.

The highfield levers look strong enough to pull a bulldozer from the mud, and the blocks are the RF1174 series which are rated to 1 ton working load. All of this only added to my sense that great force was required, but I am starting to think it was more a case of the good old fashioned belts and braces thinking that has been applied to the boat throughout.

I think the current blocks with good 12mm dyneema line should be strong enough, but I will take photos, not least of which because the highfields are really quite impressively engineered. They were custom made for the original owner in QLD, very much the outback engineering variety, not pretty, but I would trust them with my life.

Matt

[Stumble]

Gilow,

Don't confuse static tension with absolute load. The amount of tension needed to be applied isn't all that much, but the flex loads from the mast pumping or boat shaking can be orders of magnitude higher than the set tension. I have only sailed one boat with load cells on the runners, and we would typically tension them to ~200lbs. But see peak loads at the cell of over 2000lbs (this was a tripple spreader 115' carbon mast).

[transmitterdan]

Matt,

Stumble is right that the dynamic loads can exceed 10 times the initial tension. I think you are right that 12mm Dyneema is strong enough. I think it has a breaking strength of something like 10 metric tons (check with supplier to be sure). Even accounting for strength lost in the eyes it still should be OK.

[Stumble]

12mm (really 1/2" amsteel) has a breaking strength of 34,000lbs. I probably wouldn't go this size. It's just to big.

For what it's worth I would use a composite system. From the masthead down to a sailmakers eye I would use 1/2 amsteel. Because frankly it isn't that expensive, and oversized isn't going to hurt you much. This line should be about 3' shorter than the distance from the attachment point on the mast to the chainplates. Then run a piece of heavy duty bungie cord from the base of the chainplates to a clip on the eye of the runner.

For the working end of the line assuming you want to keep the 4:1 purchase: use 10mm endurabraid brought down either to a winch or a clutch. I wouldn't trust a cam cleat with this, not because of strength, but because of the possibility of unintentional release. For the attachment between the top block and the sailors eye use a soft shackle made from
1/4" amsteel blue.

The upside of this mood is that the entire system can be stowed without messing with the rig when you don't need it, and can be pretty easily be put into service when you do. The other upside is that the amsteel soft shackle acts like a fuse. Not that you should ever see this much tension on the runner, but if you ever do the shackle should pop at around 8,000lbs. This should be far below working loads, and allow you to save everything else in the event something goes wrong.

[GILow]

If a 115' carbon fibre mast produces peak loads of 2000 lbs, then our dinky little 50' "telephone pole" (thank you Ann) is probably going to produce a hell of a lot less.

That sounds like quite a clever formula for the runners there, thank you Stumble.

I can certainly see the merits of such a system, however in the interests of budget friendliness, I will stick with the current wire stays and RF1174 blocks, thread in the dynema line and see how it all behaves. As Ann points out (in such an eloquent fashion), we really do have a very conservative rig and I think the loads generated are going to be relatively trivial.

The point about the cam cleats being inadvertently released is a good one, I will look closely when I am next on the boat, but given our very wide decks and the placement of the chainplates I am optimistic that they are well enough out of the way.

Thank you all again, looking forward to putting some of this into practice.

Matt

[roverhi]

8mm would probably be adequate, 10mm more than adequate for the standing part of the running backstay. Might want to go with 11mm or 12mm for the tackle part of the line just to make it easier on the hands. The ultimate would be dacron sheathed but that stuff gets real expensive. Dyneema/Technora/Amsteel are stronger than 1x19ss wire so you don't need to go oversize especially for this use. You are only supporting 2/3rd of so the load as a Cap Shround/Backstay that go the masthead. The bare stuff isn't that expensive though proper thimbles can get pricey. I'd change just so I wouldn't have that heavy wire whipping around.

[JPA Cate]

Matt,

For our running backs, Jim used 7 mm dyneema, and for the tackle part, it is 12 mm spectra line. Our rig is 7/8 fractional, 65 ft. Mainsail is 52 sq. m. the genoa is 120%, and Jim worked out the loads before buying.

Ann

[GILow]

Peter/Ann/Stumble et al.,

I must admit, until Peter made the point about heavy wire whipping around I had not realised the merit of Stumble's suggestion.

For now there are so many areas where I could (need to) spend money on the boat, that I think I will stay with the gear I have, and see how it goes. At least I am pretty confident that the current wire stays and blocks are up to the job, all are in good condition. I'll put the dyneema solution on the wish list and if I win the lotto or sell another business software system I will go shopping with happy abandon. Until then it's make do with what I have, but I will certainly report back on how I was able to apply all the other good suggestions.

Thank you all again for the great advice.

Matt

[Stumble]

No worries. It's always good to have a wish list. This way when you walk past the discount aisle at WestMarine you know what to look for. So long as the system you have is working I wouldn't stress it so much, but it's always nice to think of upgrades.

[Snowpetrel]

Hi matt. Many advantages to spectra runners, light weight with no whipping, but even better for us cruisers is the low chafe on the mainsail.

I would be happy with polyester double braid for the 4:1 as long as the tackle is not stupidly long when the runner is set. The little bit of give can help reduce shock loadings when punching into a head sea. Spectra is of no real benefit if its used on a cam cleat. Will slip long before it gets close to working load.

With the cam cleat, I usually put a locking hitch on it, theres a few ways to do this but I normally just use a slipped half hitch with the tail around the tackle above the cam cleat, then another loose locking hitch above that. You can taper the tackle line to reduce bulk eg remove half the core, or splice in a lighter line. Or remove the cover... Cheers

[GILow]

Originally Posted by Snowpetrel

Hi matt. Many advantages to spectra runners, light weight with no whipping, but even better for us cruisers is the low chafe on the mainsail.

Well, you got my attention with that statement. I have just fitted lovely fresh new sails... and I want them to stay that way for ever....

Well, as long as possible anyway.

Matt