wanzap1
Well-Known Member
How simple or difficult (expensive) Is it to have running backstays switched out on a fractional rig?
Thanks
Thanks
Running backstays
- Thread starter wanzap1
- Start date
Tranona
Well-Known Member
Can you explain what you mean by "switched out"? Are you trying to remove them or add them?
Whatever it is you have not given enough information to enable anyone to even guess at an answer - and anyway if the designer of the rig specified running backstays it will be because the rig needs them. Not necessarily all the time, but still needed. Therefore any changes will require a redesign of the rig.
Whatever it is you have not given enough information to enable anyone to even guess at an answer - and anyway if the designer of the rig specified running backstays it will be because the rig needs them. Not necessarily all the time, but still needed. Therefore any changes will require a redesign of the rig.
Venus1
Well-Known Member
Agree with Tranona.
However if you are referring to a commonly undertaken rig change of removing the need for running back stays on a fractional rig (eg when an old racing yacht is bought cheaply to become a cruiser), it needs (as Tranona says) a considerable redesign - usually starting with changing to swept back spreaders which means moving the chain plates aft and hence a new bulkhead or other strong attachment point for the cap shrouds. Not a minor project!
However if you are referring to a commonly undertaken rig change of removing the need for running back stays on a fractional rig (eg when an old racing yacht is bought cheaply to become a cruiser), it needs (as Tranona says) a considerable redesign - usually starting with changing to swept back spreaders which means moving the chain plates aft and hence a new bulkhead or other strong attachment point for the cap shrouds. Not a minor project!
William_H
Well-Known Member
I have a friend with a 30ft with running back stays he hates them and we discuss at length how to get rid of them safely.
His problem is that the cap shrouds and chain plates are abeam the mast. He needs to move them aft or fit additional chain plates aft of the abeam the mast. The cap shrouds then provide a pull aft at the top of the shroud/ top of the forestay. This I imagine is the primary role of the running back stays.
Or add chain plates and move the running back stays to them in a permanent way. Now your runners probably have a branch to pull the middle of the mast aft as well. So intermediate shrouds should also go to the new aft chain plates. Or fit additional intermediate to the new chain plates.
So now we have effective aft support (pull) to the top of the forestay and the middle. You really need to have support (push) to the middle of the mast also. This is usually done by having stout spreaders which are angled back so that they press on the top shroud.
As you might guess all these functions are variable in their power or strength. So new chain plates further aft more power. However that then causes chafe on the main sail when running. More aft sweep of the spreaders gives more push forward which must be counteracted by the aft pull of the intermediate shrouds. Their power depending again on how far aft the chain plates are.
Now all these comments are predicated on how a classic fractional rig is supported. ie on a fairly flimsy mast. In the case of my friend I suspect that the mast is quite solid and it could cope without runners. Much depends on the fore and aft dimension of the mast. So your rig may depend on runners to keep it standing up or the runners may be just to improve up wind performance by adding tension to the forestay. As for my own little boat which came with runners I just removed them no problems.
Now you will obviously keep the back stay. The dimension then or fraction of the rig above the forestay will affect the amount of mast bend and tension you can get on the forestay.
So a whole lot of variables. You perhaps should consult a rigger or rig designer or failing that just look at lots of sail boat rigs and just try to compare your rig to theirs. Then eventually it will be a leap of faith to remove the runners. good luck ol'will
His problem is that the cap shrouds and chain plates are abeam the mast. He needs to move them aft or fit additional chain plates aft of the abeam the mast. The cap shrouds then provide a pull aft at the top of the shroud/ top of the forestay. This I imagine is the primary role of the running back stays.
Or add chain plates and move the running back stays to them in a permanent way. Now your runners probably have a branch to pull the middle of the mast aft as well. So intermediate shrouds should also go to the new aft chain plates. Or fit additional intermediate to the new chain plates.
So now we have effective aft support (pull) to the top of the forestay and the middle. You really need to have support (push) to the middle of the mast also. This is usually done by having stout spreaders which are angled back so that they press on the top shroud.
As you might guess all these functions are variable in their power or strength. So new chain plates further aft more power. However that then causes chafe on the main sail when running. More aft sweep of the spreaders gives more push forward which must be counteracted by the aft pull of the intermediate shrouds. Their power depending again on how far aft the chain plates are.
Now all these comments are predicated on how a classic fractional rig is supported. ie on a fairly flimsy mast. In the case of my friend I suspect that the mast is quite solid and it could cope without runners. Much depends on the fore and aft dimension of the mast. So your rig may depend on runners to keep it standing up or the runners may be just to improve up wind performance by adding tension to the forestay. As for my own little boat which came with runners I just removed them no problems.
Now you will obviously keep the back stay. The dimension then or fraction of the rig above the forestay will affect the amount of mast bend and tension you can get on the forestay.
So a whole lot of variables. You perhaps should consult a rigger or rig designer or failing that just look at lots of sail boat rigs and just try to compare your rig to theirs. Then eventually it will be a leap of faith to remove the runners. good luck ol'will
wanzap1
Well-Known Member
Thanks for your comprehensive reply - this is exactly the information I was looking. Thank you.
Chanquete
Well-Known Member
With swept back spreaders you get a horizontal bow stern mast support at the expense of generating a important additional mast compression force (usually more than 5 times the horizontal force) which may cause buckling problems.
lw395
Well-Known Member
Some fractional rigs avoid using running backstays by having 'jumper' or 'diamond' stays on struts. The struts are at or near the hounds, angled forwards, with the stays running from the masthead to some point lower down. This can support the mast both fore and aft and sideways. A bit '1960s' perhaps, but still valid, and seen on dinghies in reverse, where the struts are angled back to resist the pull of a big kite.
There are rigs which have runners, but you only need to use them when sailing hard in waves, or if you want a tight forestay to get the jib shape right, without bending the mast too much. Or if you're setting a spinnaker in lots of wind.
There are other rigs where the runners are absolutely crucial.
There are rigs which have runners, but you only need to use them when sailing hard in waves, or if you want a tight forestay to get the jib shape right, without bending the mast too much. Or if you're setting a spinnaker in lots of wind.
There are other rigs where the runners are absolutely crucial.
KellysEye
Well-Known Member
From what I've seen running back stays are normal on a fractional rig, I assume there is a reason for that.
Tranona
Well-Known Member
Once again a load of rubbish. You clearly have not looked at fractional rigs so have no idea how they work. Suggest you read the earlier replies, particularly from William_H which will educate you.
The vast majority of fractional rigs DO NOT USE running back stays. The most common arrangement is swept back spreaders to offset the forward pull of the foresails to avoid running backstays.
dom
Well-Known Member
Quite correct, and sweep them back enough one doesn't even need a backstay
reeac
Well-Known Member
I don't understand. Jumper struts point diagonally forwards and stiffen the upper mast against backwards loads produced by the mainsail. Running back stays point diagonally backwards and stiffen the mast against forwards loads. I had an 1895 designed dayboat with this arrangement and once lost a jumper strut and so made two new ones from best quality oak. Each strut had a vertical groove at its outer end with a small transverse stainless steel bolt buried there to provide an anti-splitting compressive load and also a surface for the rigging to bear on.
flaming
Well-Known Member
To be honest, somebody proposing to remove running backstays based on the advice from a random person on the internet who has never seen the boat, and not consulting a rigger in their local area should probably not be too surprised if their mast later falls down...
Even if the random person is as sensible as Willam_H has proven himself to be over the years!
Consult a rigger.
Even if the random person is as sensible as Willam_H has proven himself to be over the years!
Consult a rigger.
wanzap1
Well-Known Member
I'm not proposing to remove the running backstays based on advice on this forum. I asked if was a big task / expensive. Of course a rigger would be employed.
dom
Well-Known Member
Only after consulting a naval architect first for the righting moments, hull loads, etc. He in-turn might need to contact the spar manufacturer. Prob easier to just buy another boat!! In any event, fractional in-line setups had a fairly short life; it would be useful if the OP told us what the boat was.
lw395
Well-Known Member
Using jumper struts and stays not only stops/limits the leech tension bending the mast, but also transfers the backward pull of the permanent backstay to the hounds, so it reacts against the forestay.
You are quite right, the leech tension can be significant in tightening the forestay. There might not even be a backstay, you could have swept back spreaders and the shrouds behind the mast. I.e. add jumpers to a typical dinghy rig.
AIUI XODs got rid of their runners and acquired jumpers some time before I was born?
Chanquete
Well-Known Member
The mote you sweep back your spreaders the less will be the aditional compression forces on the mast.
But other problems arise.
But other problems arise.
lpdsn
Well-Known Member
As already said, a lot depends upon the boat and how crucial the runners are to the rig staying up. I've seen it done on what was originally an IOR boat to get its IRC handicap down, but a new mast was designed and fitted. On other boats the runners aren't so crucial and are just used to fine tune the rig. For conservative cruising you could do without.
Or in summary, it depends...
You'd need more than a rigger - as already said too I believe.
William_H
Well-Known Member
I seem to have omitted to mention the possibility of fitting jumper struts to the front of the mast. (rushing the reply)
The jumper struts 2 spreaders facing 45 degrees to centre line 90 degrees apart typically about 1/3 the length of the main spreaders mounted near the forestay attachment. Wires are tensioned from the top of the mast down to typically the base of the main spreaders. This wire structure makes the top of the mast stiffer so that any load on the backstay at the top is transferred down to the top of the forestay. ie it does what running back stays do.
However running back stays as said often have a branch to provide pull back of the intermediate point. (the main spreaders). Jumpers will not help here and only aft of abeam mast chain plates and intermediate stays can provide that pull back. (then to do it properly you need the aft swept spreaders.) Again all depends on the fore and aft stiffness of the mast.
As said of course so many variables including the stiffness of the boat which dictates rig loads.
So yes of course we are discussing factors involved in removing the runners. But ultimately the safety of the rig can only be calculated by an expert taking all factors into consideration. ol'will
The jumper struts 2 spreaders facing 45 degrees to centre line 90 degrees apart typically about 1/3 the length of the main spreaders mounted near the forestay attachment. Wires are tensioned from the top of the mast down to typically the base of the main spreaders. This wire structure makes the top of the mast stiffer so that any load on the backstay at the top is transferred down to the top of the forestay. ie it does what running back stays do.
However running back stays as said often have a branch to provide pull back of the intermediate point. (the main spreaders). Jumpers will not help here and only aft of abeam mast chain plates and intermediate stays can provide that pull back. (then to do it properly you need the aft swept spreaders.) Again all depends on the fore and aft stiffness of the mast.
As said of course so many variables including the stiffness of the boat which dictates rig loads.
So yes of course we are discussing factors involved in removing the runners. But ultimately the safety of the rig can only be calculated by an expert taking all factors into consideration. ol'will
Kukri
Well-Known Member
Alternatively, look at simpler ways of handling runners.
Highfield levers are one such.
Highfield levers are one such.
geem
Well-Known Member
I love'my runners. What's the big issue?
