I have a 1985 H34 with B&R rig. I have roller furling completely covering the headstay, so I set the tension with the backstay and some math. Would someone check this and see if I have gone astray, or if any good other people could use it on their boat. I called Hunter support and they said the headstay was 9/32inch 1x19 wire with recommended tension 20% of breaking strength, which they said was 9400 pounds. My loos tension guage pamphlet says 9900 pounds breaking and recommends 1500 for the forstay. But the forstay is covered up by roller furling; I can't put the tension guage on it. Now I go to Practical Sailor 10, Aug 1 1993. They say you can figure target backstay tension with trigonometry: backstay force=forstay force x (Sin alpha /Sin Beta) Alpha is angle forstay makes with top of mast Beta is angle backstay makes with top of mast I measured these angles from my Hunter Owners Manual rigging drawing, and got 16 and 20 degrees. Backstay force=1500 x .85; =1275 max,319 min (25%) Now the backstay is split into two, so you can't measure the tension of just one wire (too high to reach). So the tension should be half on each lower wire (a physics major assures me): 637 lb max, 160 min What do you think? It seems a little low to me in practice.
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Hale Davidson
Could be...
As a rough starting point, you are probably safe using the method you described. I only have two concerns, neither of which is insurmountable. First you state that the angles you used for calculation were measured from a sketch in the owners manual. If this sketch is drawn to some scale then the angles measured are probably good enough to use in your calculations. If the sketch is for reference only, or has been photocopied, then the angles may be off by quite a bit. (You may want to use some Trig to find your boat's angles using mast height and the distance from your mast base to the fore and aft stay attach points on the deck.) The second thing that may be of concern is using the guide's formula on a B&R rig. With aft swept spreaders there may be some load/tension not accounted for in that formula. I'm using the word "MAY" here because I don't know for certain if the formula can or can't be used with a B&R rig. Does any one else out ther know if this formula can be used with a B&R rig?
As a rough starting point, you are probably safe using the method you described. I only have two concerns, neither of which is insurmountable. First you state that the angles you used for calculation were measured from a sketch in the owners manual. If this sketch is drawn to some scale then the angles measured are probably good enough to use in your calculations. If the sketch is for reference only, or has been photocopied, then the angles may be off by quite a bit. (You may want to use some Trig to find your boat's angles using mast height and the distance from your mast base to the fore and aft stay attach points on the deck.) The second thing that may be of concern is using the guide's formula on a B&R rig. With aft swept spreaders there may be some load/tension not accounted for in that formula. I'm using the word "MAY" here because I don't know for certain if the formula can or can't be used with a B&R rig. Does any one else out ther know if this formula can be used with a B&R rig?
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Joe Bolm
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JoeO
Rig for B & R first
I agree with Hale...the swept shrouds/spreaders share some of the tension/force of the forestay and your calculation doesn't take that into consideration. If you do what you described, you may overtension the rig and add too much mast bend. I think if you check with a Rigger who has some experience on a B & R rig, he'll tell you to set the tension to some minimal value and then use your backstay adjuster to provide mast bend and eliminate forestay sag. I think there's a procedure for rigging the B & R rig either in the archives or on the HOW homepage under references if you want to do it yourself. For my H34, I always use the backstay adjuster to tension the forestay before I unfurl the jib and release it after re-furling the jib. That way the boat is stored with a minimum amount of tension on the rig, thus prolonging its and the boat structure's life.
I agree with Hale...the swept shrouds/spreaders share some of the tension/force of the forestay and your calculation doesn't take that into consideration. If you do what you described, you may overtension the rig and add too much mast bend. I think if you check with a Rigger who has some experience on a B & R rig, he'll tell you to set the tension to some minimal value and then use your backstay adjuster to provide mast bend and eliminate forestay sag. I think there's a procedure for rigging the B & R rig either in the archives or on the HOW homepage under references if you want to do it yourself. For my H34, I always use the backstay adjuster to tension the forestay before I unfurl the jib and release it after re-furling the jib. That way the boat is stored with a minimum amount of tension on the rig, thus prolonging its and the boat structure's life.
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Joe Baker
Physics
Since the split backstays are at an angle, their forces add to considerably more than the backstay. A squared plus B squared equals C squared should calculate that for you, assuming that you split the triangle to get the two right triangles.
Since the split backstays are at an angle, their forces add to considerably more than the backstay. A squared plus B squared equals C squared should calculate that for you, assuming that you split the triangle to get the two right triangles.
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Hale Davidson
Here we go!! (In reply to previous)
Oh boy! I was honestly hoping no one would bring this up. You clearly have Physics or Engineering in your background. I do sincerely welcome your input on this board. (I personally often find it difficult to keep quiet when presented with matters of Physics on these boards.) If the back stay tensioner were completely removed, and the two cables split (one to either side), then yes that angle (those angles) would have to be considered when calculating the resultant force(s) on the single back stay. However, the back stay tensioner uses a block with two pulleys that force the two cables to remain parallel as they depart the single backstay cable attached to the masthead. As they are parallel with the backstay their forces can be summed to find the resultant. It's a very complex vector analysis, and without the use of a chalkboard I'll not try to describe it here. The extra force you refer to does exist, but is generated and (removed by) the tensioning system. A complete analysis will show a tremendous mechanical advantage in the backstay adjustment mechanism. The end result is that because the cables are parallel when they depart the single backstay you can use the tension of one of the split stays to estimate the tension of the single back stay. Assume frictionless pulleys, and multiply by two. (A good assumption considering the forces involved.) Any thoughts??
Oh boy! I was honestly hoping no one would bring this up. You clearly have Physics or Engineering in your background. I do sincerely welcome your input on this board. (I personally often find it difficult to keep quiet when presented with matters of Physics on these boards.) If the back stay tensioner were completely removed, and the two cables split (one to either side), then yes that angle (those angles) would have to be considered when calculating the resultant force(s) on the single back stay. However, the back stay tensioner uses a block with two pulleys that force the two cables to remain parallel as they depart the single backstay cable attached to the masthead. As they are parallel with the backstay their forces can be summed to find the resultant. It's a very complex vector analysis, and without the use of a chalkboard I'll not try to describe it here. The extra force you refer to does exist, but is generated and (removed by) the tensioning system. A complete analysis will show a tremendous mechanical advantage in the backstay adjustment mechanism. The end result is that because the cables are parallel when they depart the single backstay you can use the tension of one of the split stays to estimate the tension of the single back stay. Assume frictionless pulleys, and multiply by two. (A good assumption considering the forces involved.) Any thoughts??
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Joe Baker
Too complicated to worry about!!
I am agreeing with Hale that the force down on the back stay adjuster adds to the forces on the split stays to equal the back stay. Hale has also correctly questioned the B&R rig calculations. Later model Hunters, like the 26 we had, achieved head stay tention without a back stay. Toying with my H-34 split stays while sailing over the weekend made me realize that the mast would stand without the back stay(not recommended). Playing mentally with this stuff is interesting but I have decided sailing is better. I hope you find the specs but if not, just put some tention on them and go sailing!!!!!
I am agreeing with Hale that the force down on the back stay adjuster adds to the forces on the split stays to equal the back stay. Hale has also correctly questioned the B&R rig calculations. Later model Hunters, like the 26 we had, achieved head stay tention without a back stay. Toying with my H-34 split stays while sailing over the weekend made me realize that the mast would stand without the back stay(not recommended). Playing mentally with this stuff is interesting but I have decided sailing is better. I hope you find the specs but if not, just put some tention on them and go sailing!!!!!
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Peter Roach
Need more math
I think that since your spreaders are swept to the stern it takes some of the load off of the back stay. I can actually take off the entire back stay and have the rig stand on the boat (don't try this at home). So the shrouds act as a mini back stay. I would be careful in using trig to calculate the forstay tension.
I think that since your spreaders are swept to the stern it takes some of the load off of the back stay. I can actually take off the entire back stay and have the rig stand on the boat (don't try this at home). So the shrouds act as a mini back stay. I would be careful in using trig to calculate the forstay tension.
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