USA-Technical Details-Helium used

Discussion in 'Multihulls' started by Doug Lord, Mar 27, 2010.

  1. Paul B

    Paul B Previous Member

    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?
     
  2. Paul B

    Paul B Previous Member

    Try the Nitrous instead. It makes everything funny!
     
  3. peterraymond
    Joined: May 2009
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    Location: Colorado

    peterraymond Junior Member

    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.
     
  4. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    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..
     

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    Last edited: Mar 30, 2010
  5. Paul B

    Paul B Previous Member

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

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  6. CT 249
    Joined: Dec 2004
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    Location: Sydney Australia

    CT 249 Senior Member

    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.
     
  7. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ==============
    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.
     
  8. themanshed
    Joined: Sep 2009
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    Location: Palm Beach County

    themanshed Senior Member

    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?
     
  9. Chris Ostlind

    Chris Ostlind Previous Member

    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.
     
  10. Munter
    Joined: Jul 2007
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    Location: Australia

    Munter Amateur

    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.
     
  11. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    I cancelled my proposed post because I thought it was pointless and silly. Maybe I could start a trend :)
     
  12. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    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.
     
  13. mark775

    mark775 Guest

    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.
     
  14. Chris Ostlind

    Chris Ostlind Previous Member

    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.
     

  15. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

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