USA-Technical Details-Helium used

[Paul B]

I'm no expert at this stuff, but it would seem to me that there are all sorts of serious issues with gas containment.

I think not. Just go on down to the nearest party store and get a couple of hundred Mylar balloons and stick 'em in through the open hatches that are visible in the decks.

You didin't think all those balloons being delivered to the USA compound dailiy were simply good wishes to Mr. Ellison?

 

[Paul B]

On the lighter side I like to inhale helium from balloons it makes my voice funny!

Try the Nitrous instead. It makes everything funny!

 

[peterraymond]

I cannot imagine not filling amas to save wall thickness or interior framing, now that I think of it. If the one to five hundred pounds of air saved was at one atmosphere, double that at two, and subtract a thousand more for reduced framing - starting to add up!

I've thought a little more about this. Some (most?) of the composite materials are better in tension than compression. You probably also need some additional skin stiffness on the lower parts of a float to resist wave action. These are two reasons that the bottom of the hull is probably stronger than the top. When you hit a wave there is compression load on the deck and tension along the bottom. Actually, even at rest there is compresion in the foredeck and tension below.

If you add some internal pressure then you are adding some tension to both the top and bottom. The top is now stronger because the compression in the deck is balanced by the pressure created tension. The bottom is still strong enough, because it's heavier construction to begin with and the skin intrinsically handles tension loads better.

There is a flaw here though. The internal pressure also creates hoop stress and this is a stress that wasn't there before. With composites it means that you probably have to add some fibers specifically to handle this additional stress. Even with anisotropic materials (same properties in every direction) the total stress goes up if you add load in one direction without subtracting it in the other. Also, the cross-section has to be really close to round, or it will start looking round as you add pressure.

So, could internal pressure ever be an net advantage? I don't think the balance of forces in the different directions would quite work, but these are the questions that keep engineers employed and ensure that only people with stupid amounts of money can even think about supporting a team. Even if it is an advantage, I'd be stunned if it was ever consistently used outside the AC. Can you imagine checking your hull pressure before every sail?

Is it a crazy idea? You betcha.

 

[TeddyDiver]

Mark mentioned our rocket scientist so got to my mind that these monsters were relying their structural loads on the pressure in their fuel tanks..

 

[Paul B]

Most of us are still waiting for the photos that confirm the foiling of the AeroSKIFF. We're going on, what, five+ years now and still no imagery to make it all beyond doubt.

We may not have proof that it foiled, but we do have an admission that it did not foil:

 

[CT 249]

Okay...the real naysayer first - maybe I was a bit hard on you guys. "Yes, please do approach any of the AC teams with your ideas" - I was fully tongue-in-cheek at this point and I hope you are, too.
"Being able to pour liquid helium into MRE bags (MRE means "Meal, Ready to Eat) and calling that comparable is also leaning towards funny" - the helium is contained in a giant "Thermos" bottle, cooled by liquid nitrogen for transport and refrigeration to keep it from evaporating (no amount of styrofoam would work). I was merely pointing out that it is not that difficult to work with gas when even dunderheads such as me can work with the cold stuff. Teddy's suggestion of water is better than mine and fool-proof.
"I'm no expert at this stuff, but it would seem to me that there are all sorts of serious issues with gas containment. When one wants to pressure load a gas, composed of the second smallest atomic structure known... into a hull that is going to haul-***, go through huge racking, twisting, pounding, etc., movements, there would seem to be some fairly big problems to overcome just to keep it from leaking out through the tiniest of openings in the composite structure. But, hey, I'm no rocket scientist and there is a guy on this forum who says he is. ;-) Maybe he could offer-up an opinion? Maybe he's even Doug's Deepthroat in a darkened garage?" - yes, it will bleed out over a short time (days), just like a child's balloon. A balloon that costs .03 pennies to make.
I suppose that I am not that up on the journalistic standards but I just hate seeing somebody get picked on. I, personally, would enjoy the forum much more not necessarily sans crack or flaw but, at least, egos. Sometimes I am guilty.
Now, the one who must not have read any posts but mine and responded as if I was knocking the AC designers (CT scanner?)...Read again, then retract or look stupid. I was comparing as if "even I could do it" - not in any way diminishing their abilities. Come on, you can do it...it goes like this; "I guess I misunderstood Mark's intent and barked at him for no reason. I'll come up with another reason because I don't like him or admit that I just wanted to chime in with the big barking dogs. Sorry, Mark."
Where's Doug? Come defend yourself, Doug! - I have to go to work. (can't wait to see him post proof!)

Errr, Mark, if you don't like people being attacked, should you declare that someone will "look stupid" and that we are "a mean spirited bunch"? Those look rather like personal attacks.

Yes, maybe the understanding between us was not clear. Maybe I got the wrong end of the stick, or maybe your writing was not particularly clear (which is not knocking you, I know I certainly write posts quickly and often obscurely). You've been misunderstood by C.O. as well, so it's not just me.

Your passage about how you "could build a like-sized vessel that weighs less than the BMWO that could survive thirteen knot winds as long as nobody had to enter" followed by "if amas or other specific vessels (contained areas) are not being designed this way, why not?" can fairly easily be read as if you were saying "I could build it myself, so it must be easy". In fact is that the structural design of these boats to "survive" 13 knots without collapsing under the huge loads is NOT easy. Implying that it is (which is how your post and it's "why not" passage can easily be read) does seem very disrespectful of the creators of the AC boats, and that's what I objected to.

When it was followed by "perhaps being very constrained by a requisite for substance leads to stagnation" (which still seems unclear - what constraints, what substance?) your post can easily be seen to imply that design in sailing is stagnant, which is far from the case. If that's not your meaning and you don't like attacks, why attack once more?

You may also want to read the history of the people here. For an example, I gave a factual reply (using publicly-available information) on one of Doug's thread's yesterday and his reaction was to partly admit that I was right, but also to slur my honesty yet again. Only one person has ever done that. In the same thread, Doug had posted something that was not only untrue, but which he could not know to be true, yet he continued to attack others.

 

[Doug Lord]

Where's Doug? Come defend yourself, Doug! - I have to go to work. (can't wait to see him post proof!)

==============
Hi Mark, how was work? I've already provided 100% proof-for those that don't accept that-well,they have a problem, not me.

 

[themanshed]

Good thing they still do not make gang planks anymore! But I can see somebody made to walk the bow sprit. I'll stick to building boats....Anybody for a grog?

 

[Chris Ostlind]

Just for the heck of it, I did some Google searches under this general topic and the only thing that shows-up even remotely connected to this discussion, is.... this discussion.

Not a peep on Sailing Anarchy, nothing out of Europe or NZ or Australia, nothing anywhere. At least I can't find it.

In a world where Google can tell us what bathroom tissue is being used by the neighbor, it's decently interesting that not one other person has anything to say on the topic.

 

[Munter]

Regardless of the credibility of the source, the use of lighter than air gasses makes for an interesting area for thought.
From what I have read above there are two thoughts:
1. Use a lighter than air gas to reduce displacement
2. Use a gas to pressurise a hull (or a bladder within a hull) to make better use of composite material's high performance in tension in comparison to performance in compression.

In the first case I guess you would want to displace the air only and use as little replacement gas as possible to minimise the weight. Given the relatively low volume in the hull and floats and the constraints that this would add to the operation of the boat (ie - no easy internal access) and the limited benefit I think this option seems unlikely. I guess its possible but would have thought there were many other things you would do before resorting to this.

In the second case (a pressurised bladder for stiffness), it seems similar to a RIB or perhaps a kitesurfing kite's leading edge bladder. Cloth is terrible in compression but stretching it tight can mean that when forces are applied it they simply vary the extent of the tension. I can see this being of benefit, particularly in the long, thin floats that don't require human access. As noted by others, a bladder will want to become cylindrical when inflated so hull shapes deviating from this form will be subject to additional panel forces trying to push any flat surfaces into round shapes. Again though, it seems rather extreme.

I hope the discussion progress on these topics without undue hyperbole.

 

[ancient kayaker]

I cancelled my proposed post because I thought it was pointless and silly. Maybe I could start a trend

 

[rasorinc]

Most race cars use helium in their tires. Not for weight though. The molecues are larger and under heat and pressure less helium escapes then air.
So it is better in keeping pressure constant.

 

[mark775]

Nitrogen. A nitrogen molecule is three times as large as an helium molecule. It is not about air escaping, anyway. It is about less thermal expansion for better control of tire pressure.

 

[Chris Ostlind]

Well, it is about the gas escaping, among many reasons

Air passes through the rubber compounds far more easily than does clean, dry nitrogen. Maintaining pressure settings is far easier if you are not experiencing gas volume losses.

It's also about corrosion of the metal components in the tire and the wheel.

It's also about the fact that Nitrogen does not burn and air is a key component to many fires. Racing tires, for instance get incredibly hot and with an air volume under pressure, it's just a fire waiting to happen. Nitrogen has no such characteristic.

 

[rasorinc]

Thanks Chris and Mark for expanding on that. I forgot that it didn't burn. Seem to forget more these days.