USA-Technical Details-Helium used

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

  1. Doug Lord
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    Doug Lord Flight Ready


    Heard from a source on SA who in turn heard from the illustrous "Stingray" that Stingray had talked to Tim Smythe of Core Builders who is reported to have said that there was no helium used.......
    Curiouser and curiouser.......
    The sources I have quoted trump the above by a large margin.......
  2. Paul B

    Paul B Previous Member

    What makes you think there was less internal framing due to the helium?

    I spoke to someone who worked on USA in the US, and was "on call" in Valencia in case his abilities were needed. He said he knew nothing about the use of helium in the boat. He said there was a lot of activity in the pumping system for the drag reduction.

    Of course there might have been a system he did not know about, since that wasn't his area of expertise. He may have known about it but was told to deny.

    He did think about if for a bit and mentioned the amount of volume available wouldn't seem to be significant and the added weight of a bladder or other container would take a good amount of the "lift" out of the equation.

    Remember, if you take a 2 litre Pepsi bottle and fill it with helium it will not lift.
  3. mark775

    mark775 Guest

    To me, It is common sense to use the pressure to strengthen the vessel. I have no way of knowing if these engineers have done this.
    A two liter Pepsi bottle of helium will not fly but a twenty liter one would. More importantly, an atmosphere filled two liter Pepsi bottle will crush in a trash compactor but one with two atmospheres of pressure will displace a lot of cabbage stems and tin cans before failure.
    Looked at another way, If one vacuumed all atmosphere from any hull, would it want to collapse on itself? Yes, to a degree. There would then be 14.7 PSI, (1 Kg/cm) of unopposed pressure on every external surface. Wouldn't doubling the pressure to 30PSI make it that much stronger? If it weren't for losing internal spaces on our boats, they might ALL now be made of polyethylene or have a polyethylene membrain. Dont need to worry too much about a puncture - it's not a mylar balloon.
  4. CT 249
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    CT 249 Senior Member

    Doug, many of us here are fascinated by design, yet we don't care about this development because it is not the sort of thing that is going to be widely used. While there are many amazing things about the BMWO effort, using a gas-tight bladder doesn't seem to be one of them..... after all, it's been done by everyone from the Montgolfiers to homebuilders vac-bagging and to 8 year old kids fixing a bike tyre at the roadside. For decades, many dinghy classes (particularly in the UK) relied on inflatable buoyancy as the world's most popular dinghy still does. There are, as we all know, salvage systems that use air bags. So sailing and gas-tight bladders are ancient news.

    However, the fact that gas-tight bladders are old news doesn't mean that they are always easy. It's just that the difficulties with light bladders tend to be little ones; creating tethering points, making sure that all surfaces are smooth.

    For one of my 12'9" development-class hulls, helium would develop a lifting force of about 367 g (assuming the bladder was weightless) in a sailing displacement of about 110 kg. I would have to fit an inspection port to fit it, at a weight of 94g + fastenings and sealant, then add the bladder - say a hyper-expensive one of 50g. Of course, it would have to be custom built to fit around the CB case, mast etc, and we're ignoring the valve and fastenings.

    So we are saving about .015% in weight. Assuming that (by some unknown miracle of materials science) the custom-built bag for my craft costs just double the same (per L) as the heavy mass-produced Opti bouyancy bags, and the cost will be around $900 Aus, or 10% of a brand-new Turbo-kit Laser....all that to save less than a pair of wet boots weighs.

    That is less than utterly insignificant when considering the cost, hassle, time and other realities of dragging around gas cylinders, adjusting pressure, removing and replacing bladders as necessary, etc etc etc.

    At the other end of the scale, anyone who has been inside something like an ORMA 60 tri or a maxi would know that there is very little spare space that can be used for a bladder.

    Given the tiny effectiveness of the lifting power of hydrogen on 99.999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999% of sailing craft, getting excited about this and putting it among the other major advances of the last "50+ years" seems odd. That puts it in the same category as modern cats, modern tris, racks, hydrofoils, carbon construction, GPS, Loran, modern wetsuits, modern wet weather gear, light chined hulls, mylar sails, kevlar sails, dacron sails, modern ropes, assymetric spinnakers, ratchet blocks, self bailers, fibreglass, plywood, epoxy....

    EDITED: Yes, Doug, I did write hydrogen accidentally, because I was referring to a page with the values of helium and hydrogen while I posted. If you want to get ridiculously pedantic; you failed to put a space at the brackets in your next post's first line, you threw an extra "l" into let's not get into nit picking each other's spelling and punctuation, shall we?)

    All those major advances I wrote about were used first among the high-performance boats of their day, so they were advances in high-speed sailing.

    BTW, I'm interested how you can know that the possible use of helium was so amazingly advanced - maybe they just got some balloons and strapped them into a section of the hull where they couldn't be punctured? We've all vacuum bagged, making an airtight seal hasn't been new for a few centuries. It's just that the maths show that it's not worth the hassle.
  5. Paul B

    Paul B Previous Member

    Since the claim was the use of helium would help fly the hull it seems using compressed gas would be at odds with the goal.

    What does a 20 litre bottle weigh?

    PE has far too many issues in boatbuilding that will keep it from being the "go to" material in my lifetime.

    Of course PE is also still a semi-permeable material, so when we use PE film for wrapping food items we always include a layer of a better barrier film in the matrix. I would assume if someone wanted to keep their helium purchases to a minimum they would too.
  6. Doug Lord
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    Doug Lord Flight Ready

    1) Actually, it doesn't have to be widely used to qualify for this statement(the one I made as opposed to the one you paraphrased):

    UPDATE: this is fact and is one of the most exciting, incredible developments in design and construction of high speed sailboats that I have run into in my 50+ years of studying design and sailing. Monumental is not too strong a word!!
    This is the first time in history that helium was used as a key element of a successfull Americas Cup Challenger and that is incredibly significant mainly because of the difficulty of the application. The "how" of this story will be very interesting. The fact that the Team was able to make it work in a critical role for every race is simply amazing-the fact that it was required is even more amazing. To presumptively dismiss the lessons from this innovative technical solution before you know the whole story-especially the "how"-is a shame.
    2) I know facts, at least details, are not your strong suit but really "hydrogen"-come on CT read the material!
  7. CT 249
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    CT 249 Senior Member

    I'm no engineer, physicist or designer, but I think you're looking at the wrong sort of strength, and not enough of it.

    The main stresses on a performance boat include compression from the mast in the order of many tens of tons for an AC boat. The mast jack on the little Melges 32 is used at 3,500 to 4,000 psi. Given that the boat can already take that sort of load, increasing the internal pressure by 30 psi is negligible.

    Secondly, the physics don't work as far as I can see. The problems with racing boats are deflection of the skin (under slamming loads of 80psi and more) and maintaining overall shape under those vast loads, and inflatable structures of all sorts are notoriously liable to gross deflection. So inflating the boat does nothing to assist deflection. In fact, while the difference would be minute, it may even increase deflection, because the internal pressure would want to change the shape to a sphere which has more volume.

    A pressurised hull also probably does nothing for sheer strength, probably worsens against many tension stresses, and does nothing good for rig, rudder and keel induced stresses. There's a reason inflatables normally sail slowly!

    The physics also don't work (AFAIK) because gas pressure is extremely bad at maintaining the rigidity of its containing structure and this goes up dramatically as the volume increases. The problem, simply, is that a hull has so much volume that even if it was crushed to 90% of its volume, the 30psi would only go up to 33 psi, which is still so light that it would have almost no effect when it comes to withstanding the loads of wind and water, as far as I know.

    I just walked over to my racing bike. I run time trials at 120 psi, and yet I can easily deflect the tyres of my bike with my fingers despite the fact that the depression I therefore create is significant compared to the volume of that skinny tyre. In contrast, I can't come close to depressing any of my boats or boards (even the polyethylene ones) by a comparable amount.

    Basically, boats are built to such high loads that the additional "strength" formed by air pressure isn't enough to do anything to resist the problem loads. On the other hand, pressure CAN cause problems because boats aren't built to withstand it. A windsurfer built of low-density foam is magnitudes stiffer and stronger than my bike tyre at 120 psi, yet the windsurfer can blow apart due to air expansion on a hot day if the pressure-release valve isn't undone. Interestingly, the skin blasted off the core by such air is much FLEXIER than an intact skin, and the board is close to structural failure.

    Inflatable surfboats around here seem to run at 4.5 psi max (12.5-ish for the highrisers of a Thundercat) and even the national IRB champ used to be as floppy as all get out. If inflating a boat to become rigid was that easy and efficient, why don't racing IRBs and Thundercats do it?

    Basically, the high pressure idea seems to fall foul of basic physics.


    1) We DO have to get inside boats, for sail and gear storage, control lines and wires, masts, maintenance etc.
    2) Maintaining internal pressure requires gas-tight construction which adds weight and/or finishing labour.
    3) Internal pressure puts load on all areas of the container, whether or not they need "reinforcement" by pressure and whether or not they can take it.
    4) The pressure container is neither weightless, costless or hassle-free.
  8. Paul B

    Paul B Previous Member

    Almost 30 years ago there was an attempt to do a beach cat that was an inflatable with an aluminum exoskeleton for rigidity.

    I was asked to quote on the metal bits while Randy Smythe was looking at doing the sails/tramps/etc.

    The thing sailed horribly, even with additional aluminum bits added in an attempt to stiffen the structure. The hulls would deform anywhere there was a load.

    A giant failure.
  9. mark775

    mark775 Guest

    Jeez, I just spent an hour doing this on the AGW thread. <removed> For now, you just go ahead and get a little shut-eye in an ama and dream of a like-weight vessel with better strength and rigidity than a pepsi bottle.
    Paul, it would have to weigh less than about twenty grams to float. I have no idea of the weight of the plastic but just a point I was making - that at some size, it would fly. I hear about the permiability but does it really matter to people spending 20 million on lawsuits over whether they race in seven knots of wind or thirteen, and such? I contend that just about any composite structure would hold a pressurized gas for a race. If they are not building to standards that could prevent helium from leaking out for a day, they should be - Besides, for a compartment that requires entry, bladders for specific zones make sense. You also said "Since the claim was the use of helium would help fly the hull it seems using compressed gas would be at odds with the goal." Not if the structure could be built lighter by filling with pressure. g'night
  10. CT 249
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    CT 249 Senior Member

    The aggressive one is surely the person who is (1) telling the world's naval architects they've got it wrong and (2) making personal remarks about anyone who dares to hold a different opinion.

    And I fail to see where the aggression in a post that starts "I'm no engineer,physicist or designer but I think" (ie not KNOW, but THINK) and includes cautions like "don;t work as far as I can see", AFAIK (As Far A I Know) and others. You, in contrast, started by being aggressive to sailors as a whole, calling them "a mean spirited bunch" and others "boneheads. Dunno how that isn't far more aggressive than anything said by most of the rest of us. Or, on the AGW thread, writing about "bloated academia", "an Über-F'ed up Nobel "Society", "someone with a brain that didn't have the synapses singed in their youth" , "occasional academic professional... who have NEVER held a real job".

    That's aggression. Talking about psi and slam loadings, complete with cautions about the fact that one is not an expert, is NOT aggression.

    Anyway, when helium starts becoming a major factor in high-performance boating (power or sail) I'll gladly admit you were right. Until then, sayonara.
  11. Doug Lord
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    Doug Lord Flight Ready

    Jeez, CT: if USA hadn't used helium they would have been disqualified. Is that a "major factor in high performance boating"?
  12. Chris Ostlind

    Chris Ostlind Previous Member

    A truly lovely use of a threat laden statement within the language available.

    You've singlehandedly elevated the discourse.
  13. Paul B

    Paul B Previous Member

    Can you prove this statement?

    There are many ways to shorten the static waterline a few mm in measurement trim, if that was required.
  14. Paul B

    Paul B Previous Member

    Close enough, at just over 22g it would be bouyant neutral.

    I have some idea of the weight. For example, a one litre Gatorade PE bottle weighs about 20g. So for a 20 litre version to fly we would have to stretch the material to hold a volume about 20x the size.

    Actually your point that "at some size" isn't really the point. A two litre Pepsi bottle can fly, as can a one litre Gatorade bottle, depending on how light we make the bottle. This is true regardless of size.

    I would think it matters greatly if enough material escapes so the result is less than "measurement trim".

    If you are looking for "lift" from the gas you would not pressurize it, and any "composite structure" is going to be heavier than a blow molded PE bottle, so would be heavier than the offsetting "lift".

  15. evandepol
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    evandepol New Member

    I don't quite understand what's so controversial about a pressurized hull providing more rigidity: the atlas rockets from the 1960s that literally launched the US space race relied on it. That design solution provided stronger/more rigid hulls for less weight.

    Now, that doesn't mean that it's easy to pull of, or even dangerous. But it's been successfully done 50 years ago in extremely demanding environments. So why not.
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