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PostPosted: Mon Nov 04, 2013 5:56 pm 
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Maybe just change the description to mast "bend" and leave out compression.

I can testify 100% that the Aussie system reduces mast bend.

With the standard (old) halyard, the bend could be 90% due to the location of the cleat on the side of the mast because... when centered, the same halyard tension will not cause as much bend... until the mast rotates to one side. Then the bend is held more by the halyard tension and resists rotation to the opposite side, and then back again.

With the Aussie system, the mast is easily rotated side to side under normal rig tension.

It works and if I had to choose... I would not use the old halyard system ever again. The Aussie halyard makes tacking in (especially) lighter air hassle free. No more kicking the mast over to force it to rotate.

Salesman? Yes... But sailor first.

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PostPosted: Mon Nov 04, 2013 6:09 pm 
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100% agree, Matt. But first some people need to be convinced that there's a compression before they can imagine a bend caused by it. :D

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PostPosted: Mon Nov 04, 2013 6:48 pm 
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RHoughVYC wrote:
AntonLargiader wrote:
We agree the force at the mast step doesn't change, and we agree that we are both talking about the mast compression between A and B.

Looking at the vertical forces on a section of the mast around B, I don't see how, for a non-zero halyard tension Fh and constant mast base reaction Fbase, that Fab would not be different when you have three Fh (stock), one Fh (Aussie) or zero Fh (cleat at A) forces.

Image


In the image you provided, there cannot be a non-zero tension Fh. For there to be a non-zero tension at Fh you have to include the rest of the system.

You cannot evaluate the load and it's potential effects until your graphic representation of the system has a total moment of 0 around the centre of mass.

Any 2D diagram can only represent the loads in one plane. To evaluate the JibLuff/Halyard - Mast loads you must diagram a 0 net moment in that plane.

The real simple proof is that without a 0 net moment load diagram the mast falls down. So when you try to figure out the effect off the tensions in just the jib luff and halyard you have not considered the other forces that allow the jib luff to develop tension.

The system is much more complicated than the simple arguments put forward here.

Cheers

Randy
the rigger :-)


Concur, this is a three dimensional issue, but for simplicity to discuss mast compression and how the Aussie rig reduces or does not reduce mast compression all you need to look at is the components of all vectors that are parallel to and act through the mast. As I said earlier since the mast doesn't fly into space and doesn't shoot down into the water all forces must be in balance- net force is zero.

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PostPosted: Mon Nov 04, 2013 6:54 pm 
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aschaffter wrote:
all forces must be in balance- net force is zero.


Meaning that as you go from one Fh to three Fh you need to increase Fab to stay in balance? After all, you and I agree that Fbase doesn't change.

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PostPosted: Mon Nov 04, 2013 11:58 pm 
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aschaffter wrote:
RHoughVYC wrote:
AntonLargiader wrote:
We agree the force at the mast step doesn't change, and we agree that we are both talking about the mast compression between A and B.

Looking at the vertical forces on a section of the mast around B, I don't see how, for a non-zero halyard tension Fh and constant mast base reaction Fbase, that Fab would not be different when you have three Fh (stock), one Fh (Aussie) or zero Fh (cleat at A) forces.

Image


In the image you provided, there cannot be a non-zero tension Fh. For there to be a non-zero tension at Fh you have to include the rest of the system.

You cannot evaluate the load and it's potential effects until your graphic representation of the system has a total moment of 0 around the centre of mass.

Any 2D diagram can only represent the loads in one plane. To evaluate the JibLuff/Halyard - Mast loads you must diagram a 0 net moment in that plane.

The real simple proof is that without a 0 net moment load diagram the mast falls down. So when you try to figure out the effect off the tensions in just the jib luff and halyard you have not considered the other forces that allow the jib luff to develop tension.

The system is much more complicated than the simple arguments put forward here.

Cheers

Randy
the rigger :-)


Concur, this is a three dimensional issue, but for simplicity to discuss mast compression and how the Aussie rig reduces or does not reduce mast compression all you need to look at is the components of all vectors that are parallel to and act through the mast. As I said earlier since the mast doesn't fly into space and doesn't shoot down into the water all forces must be in balance- net force is zero.


You are correct about net force being zero. You are not correct about the compression loads on mast section between the tang and the cleat. Forces internal to the mast act on it, not through it.

This is a simple 2D diagram that illustrates the point.
Image

It is absolutely possible to isolate the mast step from halyard loads. The mast step is not loaded by the main halyard, but the mast section is. Any halyard cleated on the mast prevents that load from being transferred to the step.

The external load at the step and the internal load in the mast section are not the same.


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PostPosted: Tue Nov 05, 2013 4:48 am 
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Not sure why your diagram wasn't showing up (for me at least) so I took the liberty of hosting it myself without the space in the file name. Let me know if you want me to remove it.

Image

It shows how the load changes above and below the pulley. Turn the pulley upside down and you have the lower block of the stock halyard system. It would be even more relevant if you left the halyard tension at 100% in the second one, to illustrate that the force on the mast doubles. The stock halyard has three such forces, the Aussie has one.

And I'm not sure who you are disagreeing with here. Your "The mast step is not loaded by the main halyard, but the mast section is" is what I have been driving at. The halyard(s) add compressive forces to the mast between A and B. And because those compressive forces are off-axis, they create a bending moment.

EDIT: re-reading your previous posts I see we're on the same page with all of this stuff. Cool. I forgot that you were more interested in the stretch. I see you were replying to Alan.

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PostPosted: Tue Nov 05, 2013 8:28 am 
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As the issue is becoming extremely clouded, with a number of partially incorrect assumptions and drawings, and who agrees/disagrees with what. I'll just add a few statements-

To Matt M, I never addressed mast rotation, tacking, etc. with an Aussie rig vs original jib halyard but I said, and stand by my original statement that the claim that the Aussie rig reduces mast compression (by 60%?) is totally, flat out, wrong. Nothing I have seen in this thread refutes that.

ALL lines attached to the mast originating or ending somewhere else (bridle, hulls, etc.), that are not perpendicular to the mast, and are tensioned (not slack) or have reactive forces on them (wind, wave action) have a vector component parallel to and through the the mast- these are compressive forces on the mast. Since they are external forces they must be balanced to zero with external forces (from lines or structure.) If not the mast will move up or down, i.e. if you a put force on any unrestrained object (no opposing force), the object will move- a ball, a car, the boat on the water, etc.

As to the block diagram- the diagram on the right is wrong. 50% + 50% = 100% (not 50%), vector forces are additive! You'll have 100% compressive force and 100% countering it at the step! Think about it, adding multiple sheaves doesn't change the original force it just reduces the effort by mechanical advantage. If that block is only rated at 50% you'll have a big surprise if you tension each line to 50% like you show!

The main halyard in fact does impart mast compression too, in two ways- internally from the cleat, through the masthead sheaves to the downhaul cleat (and it is not affected by the number of sheaves on the downhaul blocks). And to a lesser degree by external forces- the weight of the sail and boom, and by wind through the main sheet. This force is shared with the forestay/jib halyard (and upwind shroud). These external forces are countered by the boat through the step/foot.

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PostPosted: Tue Nov 05, 2013 8:42 am 
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AntonLargiader wrote:
Not sure why your diagram wasn't showing up (for me at least) so I took the liberty of hosting it myself without the space in the file name. Let me know if you want me to remove it.

Image

It shows how the load changes above and below the pulley. Turn the pulley upside down and you have the lower block of the stock halyard system. It would be even more relevant if you left the halyard tension at 100% in the second one, to illustrate that the force on the mast doubles. The stock halyard has three such forces, the Aussie has one.

And I'm not sure who you are disagreeing with here. Your "The mast step is not loaded by the main halyard, but the mast section is" is what I have been driving at. The halyard(s) add compressive forces to the mast between A and B. And because those compressive forces are off-axis, they create a bending moment.

EDIT: re-reading your previous posts I see we're on the same page with all of this stuff. Cool. I forgot that you were more interested in the stretch. I see you were replying to Alan.


Your diagram showed up as a broken link for me so we're even. The intertube can be a funny thing; maybe the ISP gods don't like us? :o

I'm trying not to be confrontational and I hope I'm not arguing with anyone! I'm fairly secure with my knowledge and understanding of the forces and moments created in sailing rigs. I struggle to communicate sometimes. :oops:

After reading the first few pages. I jumped in because the mast step load not changing point is true. The reason why it doesn't was not being clarified. I also agree that the description of a 66% reduction in mast compression statement to be obviously incorrect and misleading.

When you combine the observation that the Aussie halyard reduces mast bend with a statement that mast compression is reduced by 66% the logical, but flawed conclusion is that mast compression causes the bend. That is not credible IMO.

I've studied another of Hobie Alter's designs, the Hobie Hawk. It is elegant and very well engineered. I find it very hard to believe that his Hobie 16 design uses a mast section that is forced out of column by the halyard load. There has to be a logical explanation that does not require the laws of physics to be suspended whist sailing.

I hope not to make enemies on the interwebz and certainly the Hobie forum members can help me more than I can help them. My understanding of the H16 rig dynamics is 100% better than it was simply from reading this thread and thinking about the system. To sail the boat well all that is needed is to know is "if you do this, that happens" there is no need to get into the mechanics of the rig. This is particularly true on any OD boat where you cannot change many of the parts. I'm just a numbers and rigging geek, so it bothers me to not know. 8)

Cheers,

Randy


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PostPosted: Tue Nov 05, 2013 9:54 am 
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I can solve this.

I'll remove the disputed "66% reduction" text from the catalog. I'm quite sure this was done years ago and someone who simply divided the halyard purchase ratio of 3:1 into 33-33-33... and by having the less loaded... single line down the mast... hey! 66% reduction!

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PostPosted: Tue Nov 05, 2013 10:37 am 
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aschaffter wrote:
As the issue is becoming extremely clouded, with a number of partially incorrect assumptions and drawings, and who agrees/disagrees with what. I'll just add a few statements-

To Matt M, I never addressed mast rotation, tacking, etc. with an Aussie rig vs original jib halyard but I said, and stand by my original statement that the claim that the Aussie rig reduces mast compression (by 60%?) is totally, flat out, wrong. Nothing I have seen in this thread refutes that.

ALL lines attached to the mast originating or ending somewhere else (bridle, hulls, etc.), that are not perpendicular to the mast, and are tensioned (not slack) or have reactive forces on them (wind, wave action) have a vector component parallel to and through the the mast- these are compressive forces on the mast. Since they are external forces they must be balanced to zero with external forces (from lines or structure.) If not the mast will move up or down, i.e. if you a put force on any unrestrained object (no opposing force), the object will move- a ball, a car, the boat on the water, etc.

As to the block diagram- the diagram on the right is wrong. 50% + 50% = 100% (not 50%), vector forces are additive! You'll have 100% compressive force and 100% countering it at the step! Think about it, adding multiple sheaves doesn't change the original force it just reduces the effort by mechanical advantage. If that block is only rated at 50% you'll have a big surprise if you tension each line to 50% like you show!

The main halyard in fact does impart mast compression too, in two ways- internally from the cleat, through the masthead sheaves to the downhaul cleat (and it is not affected by the number of sheaves on the downhaul blocks). And to a lesser degree by external forces- the weight of the sail and boom, and by wind through the main sheet. This force is shared with the forestay/jib halyard (and upwind shroud). These external forces are countered by the boat through the step/foot.


We all agreed pages ago that the total compression load on the mast is not reduced by 66% buy the Aussie halyard system. You can drop that now. :mrgreen:

The discussion is now about these points:
1. Can a compression load in line with the mast exist without changing the load measured at the step? The answer is Yes.

2. Does the placement of the cleat (point that pins the load) on the Jib Stay/Halyard system effect compression in the mast section?
3. Does the placement of the tension adjusting mechanism have an effect on either the compression load on the mast or the compression load on the step?
4. What effect results from these forces?

You are correct about my diagram, it is not a complete representation of the vectors, that is why it was not labeled that way. The force that turns the load 180 degrees remains 2x leg load so the there is still a 100% load at the turning point (and within the mast section). What I was trying to illustrate is that moving only one leg of the system off the mast transfers only that leg's load to the step. If we don't agree on that point we can stop and share a drink.

For clarity, lets look at a single point (the tang) fixed to an infinitely stiff beam. To that point are fixed (shackled) two infinitely stiff wires. The other ends of the wires are also fixed to the infinitely strong beam at a single point and each wire is placed under 100 units of tension with a 3:1 tackle.

The load in the beam is 2x the load on the wires.

Replace the shackles at the tang with a pulley. Does the load on the tang change?

The pulley allows the load on both sides of the system to be equal with only one adjustment tackle.

It does not matter were on the wire or on which side of the pulley the adjustment tackle is as far as static loads on an infinitely stiff system.

How then does the Aussie 3:1 differ from the standard 3:1?

It is obvious that once the tensions are set it does not matter where the adjustment is *if nothing moves*.

:-)

R


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PostPosted: Tue Nov 05, 2013 11:12 am 
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RHoughVYC wrote:
How then does the Aussie 3:1 differ from the standard 3:1?


Take a look at my diagram where you have three instances of Fh acting on the A-B section of the mast. If you move that pulley up the mast to A, two of them no longer act on A-B. The Aussie halyard moves the pulley up to the tang and then out to the end of the pigtail, leaving only one Fh behind to act on A-B. That's the 1/3 compression thing (which as we know is actually just 1/3 halyard-induced compression).

As to how much it matters... Fh is not insignificant. 3*Fh is equal to the jib luff tension, which as you know is the entire forestay tension. Think about the 5:1 or 6:1 main sheet force trying to crank the mast backward, and its greater leverage on the rig. Forestay tension is big, and ALL of that comes back down the mast on the old setup. When I have time (maybe next year) I'll try to measure the mast bend induced by the halyard alone.

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PostPosted: Tue Nov 05, 2013 1:00 pm 
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Okay, it may not seem obvious, but it sounds like y'all have converged on something like this (which is my conclusion as well).....

If the two systems have the same overall rig tension, the ONLY difference is that, on the Aussie system, the load on the halyard between pigtail turning block and the halyard cleat is 1/3 of that load on the older system. Assuming the boats are rigged properly and have the halyard cleat on the side of the mast and neglecting mast rotation, this is the only load that acts on the short axis of the mast cross-section. This load will therefore induce less side to side bend with the Aussie system since more of the overall load is on the longer (fore-aft) axis of the mast cross section. The overall mast compression is the same, but the compressive force induced by the Aussie halyard between the upper block and the halyard cleat (the force that can cause side to side bend) is reduced 66%.

And a couple more observations....

I used to rig my older style system with a turning block at the bridle and tie it off there. Sort of a PITA, but it put more tension on the long axis of the mast (less side to side bend) and prevented the infernal batten on jib halyard hang-ups. (Pretty sure this isn't class legal if that matters to anyone.)

Also, note that the newest H16s have the halyard cleat on the front of the mast. I expect this is to further reduce bend, even with the Aussie system.

Okay.....if that's settled, now lets argue about whether more righting moment is produced if one runs their righting line over (as opposed to under) the upper hull on a capsized cat! :lol:

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PostPosted: Tue Nov 05, 2013 2:01 pm 
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Quote:
How then does the Aussie 3:1 differ from the standard 3:1?

It is obvious that once the tensions are set it does not matter where the adjustment is *if nothing moves*.


But in FACT... there is a HUGE difference. Not even a small one.

So, you engineers quit trying to explain away the reality that the Aussie system does indeed make mast bend less and therefore rotation MUCH easier.

This is not sales. This is quality of sailing.

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PostPosted: Tue Nov 05, 2013 2:10 pm 
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rattle 'n hum wrote:
Okay, it may not seem obvious, but it sounds like y'all have converged on something like this (which is my conclusion as well).....


That's roughly how I see it. But - dare I say it - terminology needs to be very clear :) so I would revisit a few things:

Quote:
the load on the halyard between pigtail turning block and the halyard cleat is 1/3 of that load on the older system


The tension of the Aussie rope is 1/3 of the tension on the old system's wire but the same as the old system's rope. Saying "load on the halyard" could be ambiguous.

Quote:
This load will therefore induce less side to side bend with the Aussie system since more of the overall load is on the longer (fore-aft) axis of the mast cross section.


There's less side load because there's less halyard load. I don't think it's about where more of the load is (at least I haven't seen that discussed).

Quote:
The overall mast compression is the same


I'm not sure "overall mast compression" is a clear term to use for anything at this point. Maybe "mast step load" or something like that.


And Matt, we're cleaning up now... this is good news!

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PostPosted: Tue Nov 05, 2013 2:20 pm 
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mmiller wrote:
So, you engineers quit trying to explain away the reality that the Aussie system does indeed make mast bend less and therefore rotation MUCH easier.

This is not sales. This is quality of sailing.


Unfortunately, since in reality, there is no difference between compressive force created by the Aussie rig and original style jib halyard, there is no difference in the ability of either to cause the mast to bend. I suspect with many sailors who report severe mast bend they are over-tensioning both jib and main halyards, both of which can cause mast bend. Once you get the slightest bend from whatever source, increasing the tension on either will cause the mast to bend farther and easier- kinda like a long bow- the initial amount of bend may take a lot of force, but from then on it takes less and less.

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