Is rigidity a religion? Amas on the move....

[guzzis3]

Yeah I was an engineer too. If I were having discussion with my piers then I would prefer they speak precisely, but this isn't a work meeting. It's a public forum where all sorts of people put forward ideas. You are discarding their thoughts because they don't have a formal technical background.

Focusing on the language rather than the idea is petty and unhelpful. If it offends you so then offer a friendly correction rather than a nasty criticism.

I make lots of spelling mistakes now. I try to catch as many as I can but now I'm blind and brain damaged I stuff up a lot of things. I guess I have no value now and I should crawl into a corner and wait to die.

Maybe someday you will find yourself in a situation where you struggle to participate. I hope you don't meet someone like you then.

 

[Ad Hoc]

.... It's a public forum where all sorts of people put forward ideas. You are discarding their thoughts because they don't have a formal technical background.....

I am not discarding anyone's thoughts - do not crate a false narrative for a straw man argument.
However, do you mean like this:

I hate to shoot anyone down in flames but I think you are totally wrong.....

Is that the type of disregarding someone's thoughts that you mean?

Every forum is public and full of people with or without technical knowledge. That is a given.. is the raison d'etre of a forum in the first place - to gain help/advice/knowledge from those that can offer such.
There is a big, big difference between someone not knowing the correct terms/meanings....and someone, when pointed out, rather than stating ah ok...i wasn't aware, who just doubles down and keeps on going - out of a sense of not enjoying being corrected. The former, everyone is happy to assist, the later, become cantankerous polemic and poisoning the thread/forum for others. Feeding the later, does not help anyone.

You are conflating the two entirely separate issues simply because you disagree with my approach to extracting information from someone, to gauge whether there is an their understanding of the subject at hand.

.... If it offends you so then offer a friendly correction rather than a nasty criticism.....

It doesn't "offend me" in the slightest, that is you your own interpretation.

Oh, you mean a friendly correction like this:

Water does not flex.

If you or the poster takes offence with that - that is more a reflection of you/them, than anyone else.
It is merely a simple factual statement.

....I make lots of spelling mistakes now. I try to catch as many as I can but now I'm blind and brain damaged I stuff up a lot of things. ...

You have my deepest sympathy for the condition you are in, and I applaud you for being able to still contribute as and when you can, despite your disability.
You have my respect..and admiration.

But your brain is still working very well...and that should not hinder you in your comments or understanding of others!

 

[gonzo]

I believe that using proper terminology is very important. There are many members that do not have an engineering or technical knowledge. In that case, it is even more important to call things by their name. Also, to explain what they mean. Water does not flex, but it flows. Those two terms represent different physical behaviors. It is confusing to transpose them and leads to misunderstandings.

 

[Skeezix]

If the engineers here can see their way to help neophytes like me through the pitfalls of terminology, I appreciate it. I hope I am not misinterpreting or misunderstanding the concept of buoyancy. As I understand it, as the ama of a trimaran is subject to more downward force, it goes deeper into the water, if and until the buoyant force of the displaced water creates sufficient righting moment. It is a dynamic system intended to move toward equilibrium. My point is that because the heeling and resultant buoyant righting force are dynamic, the trimaran structure can, and probably should, be mostly static. Try as I might, I have not seen any refutation of that claim. Perhaps I cannot discern the counter because I am a simpleton befuddled by the jargon.

There, that should have enough verbiage and technical errors for even the most ambitious semantic police to chew upon for a good long while.

 

[Ad Hoc]

Ok, there is a lot in this, but the main points are thus:

...As I understand it, as the ama of a trimaran is subject to more downward force, ....

What do you mean by this…what force, coming from where?

...if and until the buoyant force of the displaced water creates sufficient righting moment....

Not sure what you’re getting at here too….there is always a righting moment as soon as the ama touches the water.

... It is a dynamic system intended to move toward equilibrium.....

The vessel is merely not at equilibrium when a force is applied to the vessel that moves it away from its static equilibrium position, that is all.

Dynamic – I think as you seem to think of it – is what is called dynamic stability, which is simply the work done in heeling the vessel through a given angle. The area above the heeling lever effectively represent the amount of potential energy left in the system, to prevent capsize.

... My point is that because the heeling and resultant buoyant righting force are dynamic, the trimaran structure can, and probably should, be mostly static. ....

You’ve lost me here… what does this mean?
The only ‘dynamic’ aspect is the amount of wind/wave heeling lever being applied – but in analysing the stability of a vessel we ‘assume’ this to be a constant force, for a varying set of given conditions.

Perhaps you should have a read about basics of multihull stability HERE, this may help to clarify?

... There, that should have enough verbiage and technical errors for even the most ambitious semantic police to chew upon for a good long while.

It is not the incorrect terms, per se, that is the issue. It is maintaining them even when corrected, as that is where confusion enters.

 

[Gary Baigent]

Pedants are the real life at parties. I'm sure you have heard this before Ad Hoc?

 

[Ad Hoc]

Pedants are the real life at parties. I'm sure you have heard this before ..

I sure have, heard it many many many many times before.
Especially by those subverting opinion as fact, ad nauseam..

 

[redreuben]

Enough already

 

[gonzo]

Perhaps the misunderstandings on this thread started with using wrong terminology on the title. There are no rigid materials. Rigid is a theoretical concept used to simplify systems. In an ideal system, we can consider a material rigid when it does not deform more than a predetermined quantity. I think the OP meant stiffness, which can be quantified and calculated. However, that is my guess and could be wrong, which is an example on how clear definitions prevent misunderstandings.

 

[Robert Biegler]

My point is that because the heeling and resultant buoyant righting force are dynamic, the trimaran structure can, and probably should, be mostly static.

I don't think that follows. The forces on a car are also dynamic, especially when the road is bumpy, but that is exactly when you want a suspension. That suspension still restricts movement. You generally don't want the wheel to turn as it rises and falls. That is called bump steering, and generally frowned upon. So allowing some movement might be good, but you have to think about what movement you allow. Were you thinking just of a stiff structure compared to one that is wobbly in every possible way?

Layman's speculation: the Gougeon trimaran Adrenaline was mentioned earlier in the thread. Compare it to a rigid structure. If a trimaran sails upwind, the last part to pass over a wave crest is the leeward ama's stern, inducing some pitch, and roll to windward. And for a short time, as its bow is out of the water, the stern sinks, making the ama move through the water at a pitch angle large enough to increase drag. Then the bows hit the water, and the local water flow is again as if the hull were pitched up. Adrenaline lets the ama pitch down as the hinge goes over the crest, so there is that little less push to make the whole boat pitch and roll, the stern doesn't get dragged through the water, and the bow doesn't pitch down as hard.

I don't know why, despite Adrenaline doing well on the Formula 40 circuit, this feature didn't spread. Perhaps it doesn't play well with foils, and they offer more advantages.

 

[Skeezix]

I don't think that follows. The forces on a car are also dynamic, especially when the road is bumpy, but that is exactly when you want a suspension. That suspension still restricts movement. You generally don't want the wheel to turn as it rises and falls. That is called bump steering, and generally frowned upon. So allowing some movement might be good, but you have to think about what movement you allow. Were you thinking just of a stiff structure compared to one that is wobbly in every possible way?

Layman's speculation: the Gougeon trimaran Adrenaline was mentioned earlier in the thread. Compare it to a rigid structure. If a trimaran sails upwind, the last part to pass over a wave crest is the leeward ama's stern, inducing some pitch, and roll to windward. And for a short time, as its bow is out of the water, the stern sinks, making the ama move through the water at a pitch angle large enough to increase drag. Then the bows hit the water, and the local water flow is again as if the hull were pitched up. Adrenaline lets the ama pitch down as the hinge goes over the crest, so there is that little less push to make the whole boat pitch and roll, the stern doesn't get dragged through the water, and the bow doesn't pitch down as hard.

I don't know why, despite Adrenaline doing well on the Formula 40 circuit, this feature didn't spread. Perhaps it doesn't play well with foils, and they offer more advantages.

For a car, the road is static.

Your description of the leeward ama at different times as it crosses a wave is excellent, thank you. I can see how Adrenaline's swain might be helpful. I searched for more about Adrenaline, but found little.

 

[Skeezix]

Ok, there is a lot in this, but the main points are thus:



What do you mean by this…what force ...

I quit reading as soon as you asked where the downward force on an ama comes from.

 

[gonzo]

That is a pertinent question. There are many forces on an ama. The downward force is not a single vertical vector. Gravity is a vertical downwards vector, but the rest of the downward force is the vertical component of many force vectors.

 

[Skeezix]

It is an impertinent question in the context of my statement. To the degree the wind blows on the sail, the ama is forced deeper into the water until the buoyant force equals that of the sail. Of course all the details of how a trimaran works are far more complicated. None of us need our noses rubbed in that truth. But the basic interaction between the greatest force trying to overturn any sailboat and the greatest force keeping a trimaran upright, and the fact that the water yields to varying degrees in that interaction, is the simple question I asked readers to consider.

 

[Ad Hoc]

I shall ignore the previous asinine comments - since it is clear you do no understand the relationship between someone making a claim and happy to clarify what they mean by it (as the person making said claim) and someone not being able to justify said claim, and thus just speculating. But I do enjoy watching those that have zero idea how to answer such questions, reacting with click bait of likes...it is hilarious and predictable, and very sad too.

.... But the basic interaction between the greatest force trying to overturn any sailboat and the greatest force keeping a trimaran upright, and the fact that the water yields to varying degrees in that interaction, is the simple question I asked readers to consider.

This is the first time your reply has actually made any sense.
It is very simple to answer and most of which, as already posted above, but perhaps your ignorance prevented you from reading the post, is noted HERE.

The waterplane inertia of the hull form provides the "stiffness" and the restoring moment, with the VCG in a given position, to prevent either capsize, and/or the ability to drive/sail harder and faster.