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Standing rigging - stress calculations
Does anybody know how to go about calculating the stresses in standing
rigging. I have an masthead sloop rigged 50 ' FRP boat. 4 lowers, 2 intermediates, 2 uppers, head & back stay. All inboard rigging. I'd like to know the tensions in the various stays - vs the tensile strength of the wires. Any ideas on how this is done? ----------------- www.Newsgroup-Binaries.com - *Completion*Retention*Speed* Access your favorite newsgroups from home or on the road ----------------- |
Standing rigging - stress calculations
Get a copy of Brion Toss's Rigger's Apprentice. The process takes a number
of steps but it is not really complicated. The main thing is to know your righting moments which can be hard to find if you don't have the original design specs. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com wrote in message ... Does anybody know how to go about calculating the stresses in standing rigging. I have an masthead sloop rigged 50 ' FRP boat. 4 lowers, 2 intermediates, 2 uppers, head & back stay. All inboard rigging. I'd like to know the tensions in the various stays - vs the tensile strength of the wires. Any ideas on how this is done? ----------------- www.Newsgroup-Binaries.com - *Completion*Retention*Speed* Access your favorite newsgroups from home or on the road ----------------- |
Standing rigging - stress calculations
The theoretical calculation is by determining the center of buoyancy,
the center mass of ballast and calculating the righting forces that would react at the top of the mast ... when the mast is pulled over to a heel angle of 45 degrees. You can do the same experimentally by restraining the boat (so that it can roll unimpeded) and by pulling horizontally (or calculating the trigonometric difference for other angles) from the top of the mast until the mast is at a 45 degree angle to the horizontal ... then MEASURE the stress/strain in the wire (cap shrouds). The induced/ forced 45 degree heel would develope the maximum static loads in the wire (by the magic of trigonometry). This would establish the max. 'actual' target load in the wires .... and (important) then make everything 4 times as strong for 'offshore', 3 times as strong for 'coastal' and twice as string for 'inshore'. I prefer a higher Factor of Safety (FS=6 ... many of the reknown 'offshore' designers tout FS=4 but when you backcalculate their work I find FS 'well above' FS=4) for offshore. Simple answer .... your designer probably knew what he/she was doing in rigging selection by adding the proper safety factors after calculating the max. theoretical shroud loads ......... and typically (on a purely mathematical basis) the cap shrouds would be tensioned for a 12-15% load (mast/boat not heeled) based on the ultimate tensile strength of the exisiting wire, ditto forestay/backstay and all the other shrouds would then be trigonmetrically calculated based on the 12-15% of the caps and backstay. Very simple answer .....12-15% on all shrouds, then go sailing to see if the mast stays perfectly in column while on a heel approaching 45 deg. Intermediates .... probably next to worthless from a stress standpoint. Do the trig. calcs. and you'll see that they react with extreme tension to the chainplates because of their very shallow intercept angle with the mast (hounds) .... use runners instead of intermediates for better mathematical solution and less stress/strain as developed on the intermediate chainplates. ;-) |
Standing rigging - stress calculations
On Jan 31, 6:09 am, wrote:
Does anybody know how to go about calculating the stresses in standing rigging. I have an masthead sloop rigged 50 ' FRP boat. 4 lowers, 2 intermediates, 2 uppers, head & back stay. All inboard rigging. I'd like to know the tensions in the various stays - vs the tensile strength of the wires. Any ideas on how this is done? -----------------www.Newsgroup-Binaries.com- *Completion*Retention*Speed* Access your favorite newsgroups from home or on the road ----------------- If you're doing it yourself I'd suggest _The Principles of Yacht Design_, Larrson & Eliasson now in its third edition. It has worked examples using accepted guidelines. While I'm a Brian Toss fan, too, Larrson & Eliasson is much better for this kind of thing. Any competent rig designer will be able to get the answers for you, too. -- Tom. |
Standing rigging - stress calculations
On Jan 31, 1:39*pm, "Roger Long" wrote:
wrote Does anybody know how to go about calculating the stresses in standing rigging? Yes. http://home.maine.rr.com/rlma/Boats.htm#Barque -- Roger Long So how tight did you set the cap shrouds on Dimillo's Restuarant??? Love the shear line of that barque !!!!! .... true art-form. |
Standing rigging - stress calculations
On Thu, 31 Jan 2008 09:09:42 -0700, wrote:
Does anybody know how to go about calculating the stresses in standing rigging. I have an masthead sloop rigged 50 ' FRP boat. 4 lowers, 2 intermediates, 2 uppers, head & back stay. All inboard rigging. I'd like to know the tensions in the various stays - vs the tensile strength of the wires. Any ideas on how this is done? ----------------- www.Newsgroup-Binaries.com - *Completion*Retention*Speed* Access your favorite newsgroups from home or on the road ----------------- From scratch? Find the forces on the mast. Find the dimensions of the mast attachments and the angles that the rigging makes. Then the trig is straightforward. Finding the forces promises to be the difficult bit. Off the top: one way I suppose would be to attach a line at a strategic point on the mast, and attempt to pull the boat to a 45 degree heel or so. Measure that force and angle, and that might provide some basis for a reasonable estimate. Good luck. Brian Whatcott Altus OK |
Standing rigging - stress calculations
And what am I not seeing here - information on calc stresses??
On Thu, 31 Jan 2008 13:39:59 -0500, "Roger Long" wrote: wrote Does anybody know how to go about calculating the stresses in standing rigging? Yes. http://home.maine.rr.com/rlma/Boats.htm#Barque ----------------- www.Newsgroup-Binaries.com - *Completion*Retention*Speed* Access your favorite newsgroups from home or on the road ----------------- |
Standing rigging - stress calculations
On Jan 31, 12:10 pm, "Roger Long" wrote:
... Rich was pointing you in the right direction. The stress on the rigging is strictly a function of the stability of the hull. Actual wind velocities are irrelevant except as distribution of loading may change as sail is reduced. ... This isn't strictly true for headstays and backstays in a masthead sloop. While wind loads on them will be limited by stability actual tension will be limited by hull stiffness and available tackle. -- Tom. |
Standing rigging - stress calculations
On Jan 31, 12:47 pm, "Roger Long" wrote:
... there are limits to degree of precision that can be expected in newsgroup posts. I should have said "loads in addition to pre-tensioning and weight". ... I believe that shrouds are sized to about 3x the expected static load per wire at 30 degrees heel and headstays around 15 times. This seems to put the two types of stay into noticeably different categories when doing stress calcs. I'm with you on newsgroup expectations, of course. Though, as I mentioned before, there is a very complete discussion of how to do these calcs including a worked example in Larsson & Eliasson's book. -- Tom. |
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