Chotu’s Advanced Standing Rigging Thread (lots of pics)

[Chotu]

sorry I’m a little late to the party here. But I’m glad the party got started without me. I got a chance to see the alarming post about 6 mm dyneema and had me worried all weekend lol

I used the following to calculate righting moment:




14,000lbs righting moment comes from these numbers:

Boat cannot weigh more than 18,000lbs without the waterline being submerged. That's the loaded to death, built poorly, maximum displacement. So I used that rather than true weight for safety.

Note: the load is less than 18,000lbs to grab my boat by a single shroud with a crane and hoist it into the air.

My hull centerline to hull centerline is 10ft.

So 18,000lbs x 10ft is 180,000ft*lbs

180,000 ft*lbs is the actual righting moment to be a bit more techno with units.

But once that moment is applied from the mast (centerline of boat) to the chain plate (extreme beam dimension), we have:

180,000ft*lbs/12.5ft = a maximum 14,400lbs of load on the chainplate.

Any higher load means the boat is already upside down and there are more significant issues to deal with than just losing a rig.

NOW: This 14,400 lbs load is also divided up between 2 shrouds as well, so my projection is overkill. They won’t ever see 14,000lbs unless a shroud breaks off prior to the boat capsizing via wind action alone.

So this is where 14,000lbs load comes from. Real loads will likely be what… something like 10,000lbs on the cap shroud and 4000 on the lower?

Shrouds standing up to 14,000lbs is overly strong with the safety factor mentioned on this page AND my safety factor in the calculations.

[Chotu]

HOWEVER:

How should I do the temporary connection then?

I just took everyone through the math on how to do the real connection. But that’s not what we’re talking about anymore.

How do I do the temporary connection now? Very confused.

The mast itself was lifted onto this boat from the last place with a single loop of 6 mm dyneema tied with a bowline.

[malbert73]

Dyneema lashing is fine for temporary right? Loads to keep mast upright at the dock, even if breezy, are much lower than dynamic sailing forces.

[Chotu]

Originally Posted by malbert73

Dyneema lashing is fine for temporary right? Loads to keep mast upright at the dock, even if breezy, are much lower than dynamic sailing forces.

I would think so. I just don’t know how to do it. I’m not sure how many turns to make with a lashing. I really don’t know how to do a lashing. It’s a little bit confusing. I am much more confident about the real connection than I am about knowing what to do with the lashing.

[Chotu]

Thinking the easier route for the temporaries would be just tying a bowline on each end and only enough pre-tension to keep things from cyclical/shock loading when the conditions are rough

[s/v Jedi]

Originally Posted by Chotu

I would think so. I just don’t know how to do it. I’m not sure how many turns to make with a lashing. I really don’t know how to do a lashing. It’s a little bit confusing. I am much more confident about the real connection than I am about knowing what to do with the lashing.

Chotu, I posted details a number of times. 4 loops long 6mm, eye splice to the turnbuckle, tie three loops, then tighten turnbuckles.

It’s super easy.

[s/v Jedi]

Originally Posted by Chotu

Thinking the easier route for the temporaries would be just tying a bowline on each end and only enough pre-tension to keep things from cyclical/shock loading when the conditions are rough

No, the knot isn’t reliable in slippery Dyneema. Why do you keep trying to do it wrong?

[Chotu]

Originally Posted by s/v Jedi

No, the knot isn’t reliable in slippery Dyneema. Why do you keep trying to do it wrong?

Because it was suggested up thread that I could tie a bowline.

So now what? I can’t fit more than three turns per shroud. It takes much more than that to do lashes apparently.

This is only getting worse. This is not getting better.

Actually looking at your post above this last one, which I didn’t see, you are not talking about the right thing right now.

The permanent solution is completely settled. It is exactly what you are describing.

It is the temporary solution that is not settled.

Or maybe you are talking about the temporary solution. I don’t know. I’m getting lost. There’s too much going on in this thread with this particular detail of it.

Are you saying to do an eye splice to the shroud pin, then take my three (4 now??) loops, then tie 3 half hitches around the loops to gather them in?

This is getting very, very, very confusing. I don’t think anyone reading this thread knows what the heck is going on with this detail. Including me.

[s/v Jedi]

Originally Posted by Chotu

Because it was suggested up thread that I could tie a bowline.

So now what? I can’t fit more than three turns per shroud. It takes much more than that to do lashes apparently.

This is only getting worse. This is not getting better.

Actually looking at your post above this last one, which I didn’t see, you are not talking about the right thing right now.

The permanent solution is completely settled. It is exactly what you are describing.

It is the temporary solution that is not settled.

Or maybe you are talking about the temporary solution. I don’t know. I’m getting lost. There’s too much going on in this thread with this particular detail of it.

Are you saying to do an eye splice to the shroud pin, then take my three (4 now??) loops, then tie 3 half hitches around the loops to gather them in?

This is getting very, very, very confusing. I don’t think anyone reading this thread knows what the heck is going on with this detail. Including me.

What is difficult about a three loop lashing?! It fits, you have the materials, you only need to do it.

[smj]

Originally Posted by Chotu

Because it was suggested up thread that I could tie a bowline.

So now what? I can’t fit more than three turns per shroud. It takes much more than that to do lashes apparently.

This is only getting worse. This is not getting better.

Actually looking at your post above this last one, which I didn’t see, you are not talking about the right thing right now.

The permanent solution is completely settled. It is exactly what you are describing.

It is the temporary solution that is not settled.

Or maybe you are talking about the temporary solution. I don’t know. I’m getting lost. There’s too much going on in this thread with this particular detail of it.

Are you saying to do an eye splice to the shroud pin, then take my three (4 now??) loops, then tie 3 half hitches around the loops to gather them in?

This is getting very, very, very confusing. I don’t think anyone reading this thread knows what the heck is going on with this detail. Including me.

We have an eye splice to the thimble with the dyneema passing through a Colligo terminator completing with numerous half hitches, but the most important part is the frapping knot at the bottom that takes the strain.

[Lee Jerry]

Originally Posted by Chotu

I used the following to calculate righting moment:


14,000lbs righting moment comes from these numbers:

Boat cannot weigh more than 18,000lbs without the waterline being submerged. That's the loaded to death, built poorly, maximum displacement. So I used that rather than true weight for safety.

Note: the load is less than 18,000lbs to grab my boat by a single shroud with a crane and hoist it into the air.

My hull centerline to hull centerline is 10ft.

So 18,000lbs x 10ft is 180,000ft*lbs

180,000 ft*lbs is the actual righting moment to be a bit more techno with units.

But once that moment is applied from the mast (centerline of boat) to the chain plate (extreme beam dimension), we have:

180,000ft*lbs/12.5ft = a maximum 14,400lbs of load on the chainplate.

Any higher load means the boat is already upside down and there are more significant issues to deal with than just losing a rig.

NOW: This 14,400 lbs load is also divided up between 2 shrouds as well, so my projection is overkill. They won’t ever see 14,000lbs unless a shroud breaks off prior to the boat capsizing via wind action alone.

So this is where 14,000lbs load comes from. Real loads will likely be what… something like 10,000lbs on the cap shroud and 4000 on the lower?

Shrouds standing up to 14,000lbs is overly strong with the safety factor mentioned on this page AND my safety factor in the calculations.

14,400 lb is not the maximum possible tension in your shroud(s). What you calculated is the vertical component of the shroud tension induced by that RM, but you have to "correct" for the angle(s) that the shroud(s) has (have) and also the tension in the other shrouds / stays to get the total actual tension. The increase probably isn't huge (I'd WAG it at 15-20%) but also maybe not insignificant.

[Franziska]

Misunderstanding :-) deleted my post.

[Chotu]

Originally Posted by Lee Jerry

14,400 lb is not the maximum possible tension in your shroud(s). What you calculated is the vertical component of the shroud tension induced by that RM, but you have to "correct" for the angle(s) that the shroud(s) has (have) and also the tension in the other shrouds / stays to get the total actual tension. The increase probably isn't huge (I'd WAG it at 15-20%) but also maybe not insignificant.

Ooof. That’s a good catch, Lee Jerry. And thinking through the forces on the triangle for 5 mins leads me to another force that isn’t readily apparent in this diagram. The opposition of the forestay!

Not even included.

THAT is why Jedi worked backward from the size of the current metal rigging to the size of the dyneema. Because it’s a way to quickly account for all forces on the shrouds.

The calculation model I chose is not valid!

We must bring the post/thought process of Jedi‘s reverse calculation to the foreground to proceed. I have to find it…

[Chotu]

Here it is!

Originally Posted by s/v Jedi

Wire breaking strength is 25,000lbs. Pretension will be 5,000lbs.

6mm Dyneema is 8,360lbs. One turn is 16,500lbs.

15% of 35,000 is 5,250lbs

35,000 / 16,500 = 3 loops.

So it stays three loops because I first thought you had 14mm shrouds and the rest goes into overbuilding this as you can see in my wild rounding to stronger above.

Let’s check from the three loops starting-point: 3x 16,500 = 49,500lbs so that’s double of the wire and 3.5x your peak load.

15% of 49,500 = 7,425lbs which is 1.5x expected static load. Three turns will be fine.

Jedi used this method because it’s foolproof and accounts for all designed forces on the shroud without having to do any structural or righting moment analysis.

I have 1/2” 1x19 stainless shrouds.

The breaking strength and working load limits of 1/2” 1x19 are very well known:




So for breaking strength of the 1x19 we see 21,400lbs. Working load limit is 4,280lbs but that doesn’t seem to apply.

15% pretension is 3210lbs with this chart.


On to the Dyneema loading:

6mm Dyneema breaking strength is 8360lbs

1 turn of 6mm dyneema (one loop with 2 legs) is 16,720lbs

We are looking at doing 3 loops. 3 loops is 50,160lbs breaking strength.

3 loops of dyneema have a 50,000lbs breaking strength
My existing 1x19 standing rigging has a 21,400lbs breaking strength.

The 3 loops of 6mm dyneema are essentially twice as strong as the current metal rigging in ultimate failure.

So… regardless of my righting moment, which doesn’t account for the shrouds opposing the forestay or for the force acting at an angle, the 3 loops of dyneema is right.

[s/v Jedi]

Originally Posted by Chotu

Here it is!

Jedi used this method because it’s foolproof and accounts for all designed forces on the shroud without having to do any structural or righting moment analysis.

I have 1/2” 1x19 stainless shrouds.

The breaking strength and working load limits of 1/2” 1x19 are very well known:



So for breaking strength of the 1x19 we see 21,400lbs. Working load limit is 4,280lbs but that doesn’t seem to apply.

15% pretension is 3210lbs with this chart.


On to the Dyneema loading:

6mm Dyneema breaking strength is 8360lbs

1 turn of 6mm dyneema (one loop with 2 legs) is 16,720lbs

We are looking at doing 3 loops. 3 loops is 50,160lbs breaking strength.

3 loops of dyneema have a 50,000lbs breaking strength
My existing 1x19 standing rigging has a 21,400lbs breaking strength.

The 3 loops of 6mm dyneema are essentially twice as strong as the current metal rigging in ultimate failure.

So… regardless of my righting moment, which doesn’t account for the shrouds opposing the forestay or for the force acting at an angle, the 3 loops of dyneema is right.

Exactly. Also see how I rounded to the safe side, i.e. the wire to 25,000lbs instead of 21,400 to create extra room and also make the math easier (I was going for 20% instead of 15% pre-tension at the time, before we saw that Selden owner say 15% is better for a cat).

There’s more: the math/analysis you did doesn’t work well for multihulls. In the past when they did this, there were rig failures (they don’t do the rounding I do but go for the absolute minimum required because of lowering cost).
The solution was to take it as a starting point, go up to the next size wire because of the failures and test to see if it is durable enough. This all came from dynamic loading, not the static heeling force. A monohull absorbs most of the peaks by heeling while the multihull resists that, increasing the forces on the rig. This is why multihulls have much beefier rigging

I learned all this from reading but don’t remember exactly which book. Probably Dashew’s encyclopedia because he started with multihulls so has that design experience.