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PostPosted: Tue Nov 05, 2013 3:34 pm 
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aschaffter wrote:
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.


Exactly correct. :-) Did anyone say that mast compression was the cause of the bend? I didn't.

The halyards and sheets do not have to be over-tensioned to bend the mast, the mast is subject to bending moments from normal sailing loads. Mast bend is a normal trim function. I would go so far as to say that if your mast is not bending under sheet and halyard loads you need to tighten things up.

I have no reason to doubt people with 20 years of Hobie sailing experience that tell me the mast bends less and rotates easier. Why would anyone doubt these observations?

Rather than argue that they can't happen, try to find the solution that does not violate the laws of physics that explains the observations.

The disconnect here has always been the assumption that mast compression is bending the mast and that the dynamic improvement noticed by the sailors that have used both systems is due to a reduction in compression loading.

Cheers,

R


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PostPosted: Tue Nov 05, 2013 3:43 pm 
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AntonLargiader wrote:
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.


Your diagram shows only those loads and does not include the loads that balance them. It does not prove anything.

I'm not questioning the change in mast bend or the transfer of loads in the halyard systems that result in the sailing performance observed. I don't doubt that the mast bends less and rotates easier.

I'm saying that the compression in the mast is not the likely cause of the bend. There are other moments with much greater magnitude acting to bend the mast than halyard tension.

If people would stop looking at mast compression as the source of the bending moment they might stop debating.

:-)

R


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PostPosted: Tue Nov 05, 2013 3:54 pm 
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aschaffter wrote:
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.


Alan,

You can not have personally experienced an Aussie rigged Hobie 16.

I am telling you from 37 years of experience sailing the Hobie 16... and both versions of jib halyard... that this system does make a HUGE difference. And this is regardless of rig tension. I am not an engineer and don't need to be one to know this difference clearly is reality. Any qualified sailor would realize this once they try the system. This is also why it is standard equipment on the Hobie 16 and has been for years.

Now... for the engineering guys. Thinking of the bow. A bow rigged with 1:1 can not possibly be bent as easily as one rigged 3:1.

With the original halyard 100% of the halyard load must be strung down the length of the mast between hound and cleat. Original system is a 3:1 bow.

With the Aussie system, only 1/3 of that load is carried between hound and cleat. Aussie system is a 1:1 bow.

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PostPosted: Tue Nov 05, 2013 4:21 pm 
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Matt- you're getting sucked into the abyss. Turn back now while there's still time. :roll: :roll: :roll:

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PostPosted: Tue Nov 05, 2013 4:28 pm 
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Ha! :)

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PostPosted: Tue Nov 05, 2013 4:53 pm 
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I resurrected this thread because it was a big factor in my deciding to spend the money. And I've seen a noticeable improvement in mast rotation.

Although there are probably less and less boats converting, a thread like this can be very helpful, both the engineering and the actual observations.

Short of actually doing engineering studies on the loads in various places, I'm not sure anyone is going to come to a conclusion. And it sounds like Hobie, in coming up with the Aussie haylard, relied on seat-of-the-pants reaction and didn't bother to worry about engineering it. Probably saved them a ton of money, and they ended up with a good product, that depending upon your needs, is worth the money.

Best of luck,

Jim Clark-Dawe


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PostPosted: Tue Nov 05, 2013 5:07 pm 
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Quote:
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.


Alan, you have not been able to substantiate your claims. You are unwilling or unable to show what balances the varying number of Fh forces in my diagram even though you agree that a simple sum of vertical forces is accurate enough. Once I take the external forces stuff out of your posts (you'll have to argue that to someone who disagrees with you, wherever they are) there isn't much left. We're talking internal forces here.

I really wonder if you know what the AH is. I keep thinking that if you looked at one, it would be clear to you.

You're the challenger here, convince us.


R,

The Aussie halyard does not defy the laws of physics. :)

The halyard is nearly coaxial with the mast so the vast majority of its force is represented in the diagram. Even Alan agreed: "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."

If you want to skip straight to the bending, great. That's what this is all really about. But that's not the same as saying there isn't a compression force.

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PostPosted: Tue Nov 05, 2013 5:36 pm 
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AntonLargiader wrote:
Quote:
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.


Alan, you have not been able to substantiate your claims. You are unwilling or unable to show what balances the varying number of Fh forces in my diagram even though you agree that a simple sum of vertical forces is accurate enough. Once I take the external forces stuff out of your posts (you'll have to argue that to someone who disagrees with you, wherever they are) there isn't much left. We're talking internal forces here.

I really wonder if you know what the AH is. I keep thinking that if you looked at one, it would be clear to you.

You're the challenger here, convince us.


R,

The Aussie halyard does not defy the laws of physics. :)

The halyard is nearly coaxial with the mast so the vast majority of its force is represented in the diagram. Even Alan agreed: "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."

If you want to skip straight to the bending, great. That's what this is all really about. But that's not the same as saying there isn't a compression force.


No its not. The compression load is there and real. The *ONLY* thing I'm trying to get across is that is is not compression that forces the mast to bend.

One of the goals in rig design for systems that rely on the mast *NOT* bending under sailing loads is to keep the mast in column. This is because compared to a load applied at 90 deg to the mast it takes a metric cr*p ton of load to bend a mast out of column with compression.

I have never questioned the effect of changing to the Aussie halyard system. I have never questioned or argued that the mast reacts differently when that system is changed *even though* the total compression in the mast does not change.

Just stop trying to prove that mast compression is causing the bend that you observe, it cannot be done.

Yes the mast bends.
Yes, when the mast is bent it is harder to rotate.
Yes, the halyard system has an observable effect on how the entire rig behaves.
No, changing the halyard system does not change the total compression load in the mast.
No, it is not compression loading that bends the mast in the first place.

Who have I argued with there?

:-)

R


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PostPosted: Tue Nov 05, 2013 6:39 pm 
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I'm with you. Understand buckling and all of that. And I'm not trying to prove that the compression is bending the mast, just that it exists (and varies depending on the halyard config). The non-axial complement to it is all we really care about.

What do you work on?

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PostPosted: Tue Nov 05, 2013 6:51 pm 
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RHoughVYC wrote:
aschaffter wrote:
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.


Exactly correct. :-) Did anyone say that mast compression was the cause of the bend? I didn't.

The halyards and sheets do not have to be over-tensioned to bend the mast, the mast is subject to bending moments from normal sailing loads. Mast bend is a normal trim function. I would go so far as to say that if your mast is not bending under sheet and halyard loads you need to tighten things up.

I have no reason to doubt people with 20 years of Hobie sailing experience that tell me the mast bends less and rotates easier. Why would anyone doubt these observations?

Rather than argue that they can't happen, try to find the solution that does not violate the laws of physics that explains the observations.

The disconnect here has always been the assumption that mast compression is bending the mast and that the dynamic improvement noticed by the sailors that have used both systems is due to a reduction in compression loading.

Cheers,

R


Lets compare a Hobie mast to a dowel again. Fix the base of the dowel in a hole drilled all the way through in a block of wood. If you hold the block firmly to the table you can cause it to bend with a compressive load or a side load (any load that has a horizontal component)- push the tip sideways. But, unlike the bottom of the dowel, the base of the Hobie mast is not restrained- without stays/shrouds/forestay/jib halyar, the mast can tilt until it falls over. For the mast to bend without a compressive load it requires a pivot or fulcrum somewhere along the mast. Then the force with a component perpendicular to the mast applied past the pivot towards the free end will cause it to bend. Again, that load must be past the pivot point. On the Hobie, the mast pivot is at the tang, so the only force that can cause a bending moment is generated by the small amount of mainsail between the tang and the masthead or load applied by the mainsheet through the boom and sail to the upper mast and masthead. As we know this load also has a component parallel to and through the mast, a compressive load.

Bottom line, the forces on the mast are complex, and bending can be a result of a number of them.

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PostPosted: Tue Nov 05, 2013 11:21 pm 
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AntonLargiader wrote:
I'm with you. Understand buckling and all of that. And I'm not trying to prove that the compression is bending the mast, just that it exists (and varies depending on the halyard config). The non-axial complement to it is all we really care about.

What do you work on?


I worked at a rig shop in Canada after I semi-sort of retired from my other career. I've picked up a bit of design theory over the years from aircraft modeling and sail racing since I was 10 or so has taught me a bit about that. I've worked on boats from Lasers to 70 ft Swans. If it is made of wire. aluminum, or stainless we would build it or fix it. It was probably one of the best jobs I ever had. We did everything from 1/16" dia wire to 3/8" dia solid rod rigging and masts to about 110 feet or so. I even got halfway decent at wire to rope splices. I'm pretty passionate about wire halyards over rope. So lets not start that thread. :-)


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PostPosted: Wed Nov 06, 2013 12:05 am 
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aschaffter wrote:

But, unlike the bottom of the dowel, the base of the Hobie mast is not restrained- without stays/shrouds/forestay/jib halyar, the mast can tilt until it falls over.

Yes it is restrained. It is pinned in place at the mast step. It is not fixed, it is pinned.

For the mast to bend without a compressive load it requires a pivot or fulcrum somewhere along the mast. Then the force with a component perpendicular to the mast applied past the pivot towards the free end will cause it to bend.

This is exactly what happens at the mast head above the tang. The free end of the beam must move since it is not pinned. The pin at the tang transfers the aft moment at the free tip to a balancing forward moment below the tang.

Again, that load must be past the pivot point. On the Hobie, the mast pivot is at the tang, so the only force that can cause a bending moment is generated by the small amount of mainsail between the tang and the masthead or load applied by the mainsheet through the boom and sail to the upper mast and masthead. As we know this load also has a component parallel to and through the mast, a compressive load.

The load on the leech of the sail is the highest rigging load on the boat. this is why the main sheet has a 6 or 7:1 purchase. It much more highly loaded than the jib halyard.

Bottom line, the forces on the mast are complex, and bending can be a result of a number of them.


The combination of aft loading at the masthead and forward loading at the gooseneck force the mast to bend under very moderate sailing loads. To take a pinned beam out of column with a pure compression load requires a load that is must higher than any load developed by the rig. The crossbeam will distort before the mast goes out of column from compression loads. Masts are engineered to be hugely strong for their weight in compression. They are noodles when side loads are applied.

The more the mast bends the more it resists rotating from tack to tack. The energy stored in the rig has to be released or reduced before the mast will rotate past centre and to the other tack position where the rig loads from the main and boom will bend it again.

Bending the mast with very moderate load and keeping compression to a minimum has been a feature of fractional rigs since the first ones were built. The design intent is to have control of mast bend with out using loads that would crush the structure supporting the mast.

This loading is what gives a well designed fractional rig it's excellent gust response. The gust response is to bend more, release some leech tension and let the sail twist off to shed power. The energy that increased the mast bend is stored in the system. When the gust passes the energy closes the leech and powers the rig back up again. This automatic response make the boat easier to sail.

The design relies on the bend in the mast for performance. Trying to evaluate the halyard on a straight mast in 2D will never get to an understanding of the system. You must consider the whole rig dynamically loaded. This is the condition where the difference is noted. This is the condition your model must use to conclude anything.

Cheers,

R


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PostPosted: Wed Nov 06, 2013 9:02 am 
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RHoughVYC wrote:
aschaffter wrote:

But, unlike the bottom of the dowel, the base of the Hobie mast is not restrained- without stays/shrouds/forestay/jib halyar, the mast can tilt until it falls over.

Yes it is restrained. It is pinned in place at the mast step. It is not fixed, it is pinned.

For the mast to bend without a compressive load it requires a pivot or fulcrum somewhere along the mast. Then the force with a component perpendicular to the mast applied past the pivot towards the free end will cause it to bend.

This is exactly what happens at the mast head above the tang. The free end of the beam must move since it is not pinned. The pin at the tang transfers the aft moment at the free tip to a balancing forward moment below the tang.

Again, that load must be past the pivot point. On the Hobie, the mast pivot is at the tang, so the only force that can cause a bending moment is generated by the small amount of mainsail between the tang and the masthead or load applied by the mainsheet through the boom and sail to the upper mast and masthead. As we know this load also has a component parallel to and through the mast, a compressive load.

The load on the leech of the sail is the highest rigging load on the boat. this is why the main sheet has a 6 or 7:1 purchase. It much more highly loaded than the jib halyard.

Bottom line, the forces on the mast are complex, and bending can be a result of a number of them.


The combination of aft loading at the masthead and forward loading at the gooseneck force the mast to bend under very moderate sailing loads. To take a pinned beam out of column with a pure compression load requires a load that is must higher than any load developed by the rig. The crossbeam will distort before the mast goes out of column from compression loads. Masts are engineered to be hugely strong for their weight in compression. They are noodles when side loads are applied.

The more the mast bends the more it resists rotating from tack to tack. The energy stored in the rig has to be released or reduced before the mast will rotate past centre and to the other tack position where the rig loads from the main and boom will bend it again.

Bending the mast with very moderate load and keeping compression to a minimum has been a feature of fractional rigs since the first ones were built. The design intent is to have control of mast bend with out using loads that would crush the structure supporting the mast.

This loading is what gives a well designed fractional rig it's excellent gust response. The gust response is to bend more, release some leech tension and let the sail twist off to shed power. The energy that increased the mast bend is stored in the system. When the gust passes the energy closes the leech and powers the rig back up again. This automatic response make the boat easier to sail.

The design relies on the bend in the mast for performance. Trying to evaluate the halyard on a straight mast in 2D will never get to an understanding of the system. You must consider the whole rig dynamically loaded. This is the condition where the difference is noted. This is the condition your model must use to conclude anything.

Cheers,

R


Sorry for my terminology- the base of the mast can rotate, but can not move in a horizontal direction. If it weren't for the stays and forestay/jib providing support it would just fall over (as some have unfortunately discovered when rigging the mast :o ), unlike my dowel.

Though I may have understated the bending forces generated by the sail leech, I think we agree on the other points. I must confess you did a much better job explaining it.

It looks like this thread has come full circle- everyone (including Matt) now agrees that the Aussie rig does not reduce compression on the mast by 60% as originally claimed (or by any amount for that matter), and that while compressive loads on the mast can cause bending the primary cause is wind on the sail and resulting pressure on the leach.

I would like to offer one other cause of mast bend I have observed- Many years ago at Hobie 16 Worlds it was either the Aussies or the Puerto Ricans introduced the concept of extreme mast rake with the main sheet almost block to block just above the rear cross bar, and they did quite well. That appears to have become standard race rigging. I have noticed on many occasions, however, that some recreational sailors have not adequately adjusted the mast rigging to achieve what is, or what they feel is the proper rake to go fast. Instead they use excessive force on the main sheet so the main sheet blocks have minimum separation. Of course they are achieving that by bending the mast.

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PostPosted: Wed Nov 06, 2013 10:38 am 
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AntonLargiader wrote:
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.


In the second half of that sentence, I intentionally used the word "system." The tension in the line on the older system is indeed the same as the Aussie, but since there are three lines, the force is three times more in the described part of the older system.

AntonLargiader wrote:
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).


I do, and that was the point I was trying to make, albeit my terminology may not have been completely accurate! :D If the sum of all the forces is zero, and the force in that section of the Aussie halyard is 1/3 of the older system in that section, then there has to be more force in the other components attached to the mast (pigtail and shrouds). The forces in these components, though, are acting more on the longer (fore-aft) axis of the mast cross section and therefore causing less side to side bend.

And I submit to RH's point that it's not compression that causes the bending. Since the halyard is located outside the mast column, it's actually a moment with a very short arm, no?

AntonLargiader wrote:
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.


Hold on.....wait for it......I agree! :lol:

Matt M: I agree 100% that the Aussie system works better......and I wouldn't worry too much about the terms Hobie uses to market it. I do however think this is a good discussion for understanding why it works better (for those of us who can endure it)!

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Last edited by rattle 'n hum on Wed Nov 06, 2013 2:11 pm, edited 1 time in total.

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PostPosted: Wed Nov 06, 2013 12:27 pm 
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Wow ...

Time for a group hug? And maybe a keg of beer on the beach while we debate the slot effect?

:mrgreen:


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