Backstay tensioning

[Pinnacle]

Our boat has twin backstays that run right up to the top of the mast. I want to be able to adjust the tension in the forestay to reduce it sagging and making the luff of the sail fuller as it gets windier. ( Sorry, my dinghy racing roots are showing through! ) I am contemplating having a new backstay arrangement made up as follows;

New single backstay in 1x19 wire of the same dia as forestay, coming down say 50% of the way to the deck. A small triangular plate on its end and then a separate standing 1x19 wire ( maybe one size dia down from the forstay ) down to each existing stainless plate on the transom. Fix a pair of blocks across the gap between the twin backstays and use a multi-purchase block system with a jammer fixed to the transom close to the wheel, so I can pull the two blocks down towards the transom. This will pull the the backstays together and increase the fore and aft tension in the rig.

This is a pretty common arrangement and does have the advantage that even if by mistake I let go of the tensioning rope completely ( or one of the blocks were to fail ) the rig should stay up.

I hope all of the above makes sense!

Questions - when the twin blocks are pulled downwards, they will increasingly alter the straightness of the wire and require it to bend around the sheeve in the block. Will 1x19 be ok for this, or do I need to have the twin lower backstays made from 7x19? Is there a special kind of block/sheeve I should be using?

What does the panel think?

 

[bbg]

If you are going to get a new backstay made up, why not do it properly? Single backstay down to maybe 10 feet above the transom with a block on the end. Then from one backstay fitting, some Dyneema going up through the block and back down to a cascade which is fitted to the other backstay fitting. You can set it up so that even when you let it fully off (with a plastic ball on the tail of the backstay cascade) you will still have a bit of tension in the backstay.
A better and more powerful solution.

 

[Dan the man]

why dont you just tighten the backstay up and leave it? if it is a mast head rig (?) then it doesnt need adjusting, I believe.
But the first reply is the typical way to do it, if it is necessary.
What sort of boat is it that you own?

 

[Danny Jo]

Danny Jo has a masthead rig and a fancy hydraulic backstay tensioner. The only function for it that I can make out is to tighten the forestay. But like Dan the Man, I cannot see why one should not just have a fixed backstay that is tight enough to keep the forestay tight.

Put another way, having tightened the backstay, what circumstances would make one want to loosen it again? People say, you should slacken it off when not sailing to "rest" the rig. Whatever for?

Mind you, I have heard reports of difficulty getting the doors to shut in some GRP boats when the backstay is tight. And there is one circumstance in which a slack backstay is useful on Danny Jo - the extra room it allows makes it easier to fit the boat lift.

 

[oldsaltoz]

I think I retain the twin backstays and set up a single line with a pulley on each end and a ring in the centre, fix a line to the ring and haul down to tighten both back stays evenly as the pulleys on the back stays get pulled the widening angle will apply tension to the forestay.

Just a bigger version of the standard inverted 'V' on many single backstays and often seen on Cats.

 

[BAtoo]

You already have a split backstay so why not just use the blocks on this as you intend to on the new system - you may need them to be a bit higher up but essentially the same system. I would use blocks suitable for wire onto the backstay, normal blocks thereafter.

something like this -

 

[Bosun Higgs]

You already have a split backstay so why not just use the blocks on this as you intend to on the new system - you may need them to be a bit higher up but essentially the same system. I would use blocks suitable for wire onto the backstay, normal blocks thereafter.

something like this -

You will definitely need new backstays to use that approach - the existing ones will likely be too far apart. AQs to whether you need different wire, I suggest you ask Allspars who are very helpful.

I have a masthead rig with an adjustable single backstay. I use the adjustment to take the strain off the hull ie I apply backstay tension when dropping my mooring and release it when picking it up. The backstay tension doesnt just tighten the backstay and forestay but also the forward lowers.

Does it make much difference? I don't know but I am an inveterate sail tweeker so I do it.

 

[Pinnacle]

You already have a split backstay so why not just use the blocks on this as you intend to on the new system - you may need them to be a bit higher up but essentially the same system. I would use blocks suitable for wire onto the backstay, normal blocks thereafter.

something like this -

What I had in mind was exactly like this, save that there would be maybe 12 feet between the blocks b and c.

So, do I take it I need the 7x19 wire?

 

[bbg]

Can't provide any advice on which wire to use, but if you are going to use this system, use a strop from the two A blocks to the B block. You don't need a purchase that's 12 feet long.

 

[Bosun Higgs]

So, do I take it I need the 7x19 wire?

As I said, ask allspars. Personally ( and my background is in stainless steel manufacture) I would be nervous of the thicker strands being bent but it does rather depend on the radius of bend, frequency of adjustment etc. It's not ideal

If it were my boat I would think about replacing the twins with a single down to within say 15 ft and then running either a flexible stainless wire or better still Dynema from one chainplate through a block at the end of the backstay to the tackle attached to the other chain plate.

 

[bbg]

If it were my boat I would think about replacing the twins with a single down to within say 15 ft and then running either a flexible stainless wire or better still Dynema from one chainplate through a block at the end of the backstay to the tackle attached to the other chain plate.

Good idea. Wish I'd said that.

 

[yoda]

I have a tensioner on just one of my two backstays. Yes the second goes slack when applied but not worried about that. Works fine for me but my transom is quite narrow and the pull only just off centre. The twin block approach should also be fine provided you don't bend the wire through too big an angle even with 1 x 19 wire. What boat is it on? That will help with the response we can provide.

Yoda

 

[flaming]

Some interesting replies. I think it depends on the rig, if it's an inline, or nearly inline masthead rig, then I would stick with the failsafe "pulling wires together" approach, as the backstay is actually needed structually downwind. The more modern Dynema approach (of which I'm a big fan) is normally only used on fractional rigs, where if the backstay is released it's unlikely that the rig will come down, as the swept back spreaders take most of the load, and the backstay is only really there for bending the mast.

The issue of why you would want to ease the backstay is one of sail trim. A looser forestay (the only real effect with a masthead rig) will provide more power to the genoa, so enabling you to sail in lighter winds, or just go faster when reaching in moderate winds. if your forestay is just bar tight the whole time, you'll really struggle to make the boat go in light winds.

 

[Bosun Higgs]

The issue of why you would want to ease the backstay is one of sail trim. A looser forestay (the only real effect with a masthead rig) will provide more power to the genoa, so enabling you to sail in lighter winds, or just go faster when reaching in moderate winds. if your forestay is just bar tight the whole time, you'll really struggle to make the boat go in light winds.

Dont see that Flaming. You can adjust the foresail curve through the halyard withoput adjusting the forestay tension. All you will do by slackening the forestay in light winds and hard on the wind is bu**er up the angle of attack which will be right in some places but not others,

 

[Pinnacle]

Some interesting replies. I think it depends on the rig, if it's an inline, or nearly inline masthead rig, then I would stick with the failsafe "pulling wires together" approach, as the backstay is actually needed structually downwind. The more modern Dynema approach (of which I'm a big fan) is normally only used on fractional rigs, where if the backstay is released it's unlikely that the rig will come down, as the swept back spreaders take most of the load, and the backstay is only really there for bending the mast.

The issue of why you would want to ease the backstay is one of sail trim. A looser forestay (the only real effect with a masthead rig) will provide more power to the genoa, so enabling you to sail in lighter winds, or just go faster when reaching in moderate winds. if your forestay is just bar tight the whole time, you'll really struggle to make the boat go in light winds.

Well, it's a straightforward masthead rig and I too favour retaining the twin wires. At the moment, the two backstays go from the masthead to the chainplates bolted to the extremes of the transom, so the angle between them is quite shallow. Any adjustment of the forestay tension can therefore only be achieved by doing something with them both at the same time.

This is what the masthead looks like;

Having read all the responses, i think the best way is to replace the existing wires and have two new ones in 7x19 made up and have a twin block bridal of the sort suggested made up with a single line down to a multi-purchase system that can be controlled from the helm. That way, if the blocks or rope give way, the mast wont come down!

Thanks for all the comments and suggestions.