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  #31  
Old 07-02-2015, 07:33 PM
sharpii2 sharpii2 is offline
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/\ While I like the "kite as jury rig" idea, would a kite be flying in such light winds, given Quemere's experiences? And wouldn't retrieving a kite that has splashed down also be extremely difficult?
This is why a lighter than air kite is needed.

It can "sleep" already up in the air, waiting for the next zephyr to come along.

Rather than using the more expensive helium, I'd be inclined to use the much cheaper and easier to produce hydrogen (H2).

The kite could have an inflatable frame, which would be filled with the H2.

It would most certainly need an added balloon, unless it was made as an airfoil shaped balloon itself. The H2 would produce about 1.1 ounces of lift per cubic foot, so it would take more than a dozen cubic feet of H2 to do the job, maybe several dozen.

The real problem I see is the zephyr might well pass before it gets the kite into actual pulling position.

This is why it's usual practice to heel a dinghy to leeward, when sailing in light winds.

For a strictly down wind sail, this set up makes far more sense.

The balloon no longer needs to be streamlined in any way, and it needs no control lines either, other than its tether line. It could loft an enormous spinnaker.

As a survival rig for a life raft, a down wind only kite makes a huge amount of sense.

It would be flown only when there was plenty of wind. It needs no frame, making it really easy to stow as part of the life raft kit.

It could, perhaps, double the rate of down wind travel of the raft.

When used with a survival dinghy, which has a keel or a 'board, and some kind of rudder, the down wind kite would offer about 90 degrees of down wind course choice.

One with a balloon could be left up permanently and not have to be reeled in every time the wind slacked.
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  #32  
Old 07-03-2015, 07:28 AM
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Angélique Angélique is offline
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Originally Posted by sharpii2 View Post

[ . . . ] The kite could have an inflatable frame, which would be filled with the H2. [ . . . ]
That's almost what they have in the below kite, only have to pressurize the frames with a light gas instead of air, and maybe make the frames a bit larger in diameter for more volume...

Kite Assist Platform - (link + first pic from post #26, but no text quoted there)
Quote:
Unlike typical kites that have rigid poles made of fiberglass, KAI (Kite Assist Institute) kites have been specially designed with lightweight frames formed by pressurized air-filled bladders that are inflated with a pump or gas cartridge before the kite is launched.

Mechanical adjustment of the kite assist instrument elevation platform in progres: Here Don Montague (right) grips an inflated frame while Joe Brock (left) is cutting a sting.

About Sharpii2's above posted balloon idea's . .

From the above link, they also have a Kite × Balloon hybrid, which they call a ‘‘Kytoon’’ which looks to be perfect for filling with a light gas when 100% sealed.

It would be nice to know what size provides how much power on a wind speed scale from about 0.1 to 30 knots or so . . .

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The Kytoon flying above the ship. It is about 4 meters in diameter.
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  #33  
Old 07-03-2015, 08:01 AM
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Just saw the Kytoon is filled with helium -- link -- link --

It looks to be designed to lift things, propel things doesn't seem to be the aim of the Kytoon.

BTW, if the Kytoon is 4 meters in diameter, then how big are these guys . . .

Quote:
Don Montague and Joe Brock move the kytoon into the tan science van for protection from gusting winds. They have kept the kytoon inflated in anticipation of using it again and to maximize a limited supply of helium needed to replenish it.

Calm conditions and light winds today created the perfect opportunity for the KAI (Kite Assist Institute) team to launch their customized kytoon, a helium-filled kite balloon.

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  #34  
Old 07-04-2015, 08:06 AM
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Angélique Angélique is offline
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Originally Posted by CT249 View Post

While I like the "kite as jury rig" idea, would a kite be flying in such light winds, given Quemere's experiences? . . .
When dismasted I reckon there's wind, so windlessness isn't an initial problem when using a kite as a jury rig. And it's only to reach the nearest port, which still could be a few thousand miles though. So best salvage whatever you can from the original rig to build a jury rig with a mast out of it when needed. But for any jury rig the lower than original mast and the reduced sail area will generate a maybe to low propulsion in light winds.

Quote:
. . . And wouldn't retrieving a kite that has splashed down also be extremely difficult?
For small boats not much more difficult than for a kite surfer I think. Larger boats could need a launch (a small mast maybe) and control system, which like the kite needs to be on board if you want to have it on hand as a jury rig when needed.
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  #35  
Old 07-04-2015, 08:28 AM
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Originally Posted by sharpii2 View Post

Rather than using the more expensive helium, I'd be inclined to use the much cheaper and easier to produce hydrogen (H2).
Don't let St. Elmo hear about it . .




British Airways Flight 9 ---> Accident
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  #36  
Old 07-04-2015, 01:50 PM
sharpii2 sharpii2 is offline
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Although Hydrogen is extremely combustible, it needs oxygen to burn.

If the balloon is filled with pure hydrogen, the hydrogen can only get oxygen after it leaves it.

The spectacular Hindenburg fire was caused by the coating dope igniting first, then burning a hole through which the hydrogen escaped, to mix with the air and ignite.

I don't know much about St. Elmo's fire, but I get the impression it is far more light than heat.

Helium is obviously a far safer choice for lifting gas, but its quite expensive and needs to be stored in a high pressure tank.

The hydrogen could be treated as more or less expendable.
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  #37  
Old 07-06-2015, 04:58 AM
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Yes, the choice hydrogen vs. helium is a trade off between risks and costs, also hydrogen is a bit lighter, so it works a bit better for this purpose. My choice would be helium though.

The above red kite with lightweight frames formed by pressurized bladders could be worth some testing as a jury rig for small boats, or as an extra in light airs, or maybe even as sole form of propulsion.

Normally the bladder frames could be pressurized with air, or rigid kite poles could be used.

In occasions there's not enough wind to launch the kite or to keep it up, the air could be replaced by a light gas of choice to have the kite ready up there to catch any zephyr that comes along. That is if the bladders could be made big enough to lift the kite by a light gas.

If depend on the kite for propulsion it would be wise to carry enough spare kites + bladder frames and stuff to repair leak bladders, and also some spare rigid kite poles.
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  #38  
Old 07-06-2015, 05:19 AM
Trent hink Trent hink is offline
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Hydrogen has the advantage that it can be easily generated from water. You could conceivably generate only what you need for immediate use and not have to store any on board.
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  #39  
Old 07-06-2015, 06:11 AM
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Angélique Angélique is offline
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Hydrogen has the advantage that it can be easily generated from water. You could conceivably generate only what you need for immediate use and not have to store any on board.
I think that would need some installation, and a source of enough electricity, what do you have in mind for those . . . ?
a) - In general ?

b) - On a small boat (10 to 20 feet) ?
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  #40  
Old 07-06-2015, 06:21 AM
Zilver Zilver is offline
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Helium can probably not lift a kite. Not enough volume in the kite. I toyed with the same idea and tried to lift some things with a helium filled party balloon. That was no succes.

Also the helium gas tank is heavy, the helium is expensive and the bladder needs to be free from micro pores (helium escapes quickly from a normal balloon for instance).

I'm afraid helium filled kites are too good to be true....but would love to see someone get it working.

Regards,
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  #41  
Old 07-06-2015, 06:48 AM
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Angélique Angélique is offline
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Good points to consider Hans

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Originally Posted by Zilver View Post

. . . the bladder needs to be free from micro pores (helium escapes quickly from a normal balloon for instance).
The same goes for H2 hydrogen and even O2 oxygen. That's why car tyres nowadays sometimes are pressurized with 100% N2 nitrogen because of it's larger molecules, so you won't lose pressure from the escaping of the smaller O2 molecules through the tyre's porosity.

But the filling and refilling of car tyres with air is for free, so I think 100% N2 in car tyres is mostly a marketing trick to charge for something that used to be free . .

P.S. - Dutch link sort of translation about this aside topic.

My conclusion from above link is that 100% N2 to pressurize car tyres only provides the claimed benefits if you don't keep the tires sufficient inflated with air that's for free and standard contains ± 78% N2, ± 21% O2 and ± 1% other gasses.
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  #42  
Old 07-06-2015, 11:18 AM
Tiny Turnip Tiny Turnip is offline
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Originally Posted by Angélique View Post
Good points to consider Hans

The same goes for H2 hydrogen and even O2 oxygen. That's why car tyres nowadays sometimes are pressurized with 100% N2 nitrogen because of it's larger molecules, so you won't lose pressure from the escaping of the smaller O2 molecules through the tyre's porosity.

But the filling and refilling of car tyres with air is for free, so I think 100% N2 in car tyres is mostly a marketing truc to charge for something that used to be free . .

P.S. - Dutch link sort of translation about this aside topic.

My conclusion from above link is that 100% N2 to pressurize car tyres only provides the claimed benefits if you don't keep the tires sufficient inflated with air that's for free and standard contains ± 78% N2, ± 21% O2 and ± 1% other gasses.
... So... assuming no losses through the valve, when your air filled tyre goes down, it is the 21% oxygen that is escaping, and when you pump it back up, 78% of it is nitrogen, so it will deflate less and less each time until your tyre is nearly 100% nitrogen anyway, and has filtered out all the oxygen!
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  #43  
Old 07-06-2015, 11:42 AM
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That was my thought Tiny, thanks for writing it down . .

Good to mention possible valve losses, which of course also could be a cause of pressure loss, but there also the smallest molecules have the biggest chance to escape . .
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  #44  
Old 07-06-2015, 01:34 PM
Skyak Skyak is offline
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Could be a good idea

But I think it would require a different kite design since the normally with air filled float might try to fly at the upper side when it gets filled with Helium.
Awful lot of speculation with too little support.

To get in the ballpark estimate a LEI kite has a main tube ~9inch diam. and 25 ft long for an 18 to 20Msq light wind kite. section A=.44 V=11cf=0.31 CM

The weight of standard air is 1.2256 Kg/ Cubic Meter
The weight of hydrogen is 0.0857 Kg/ Cubic Meter

1.14kg/CM lft from H2
Note all of this is at 1 ATM

So our theoretical LEI kite could get 0.355kg lift by filling to 1 ATM. There is one more problem in that LEI kites use gas pressure for structure and shape so they are at ~1.5 ATM. Weight increases, volume does not so lift is 1.1kg/cM @1.5 ATM. So our theoretical kite would get 0.34 kg lift from H2 @1.5atm.

My conclusion is that if you just use a typical LEI kite filled with H2 it will not float in dead air.

An eyeball estimate that a very good foil shape could be made with a section 3X greater than today's LEI gets me to 1 kg -still not enough to float the big kite let alone a large amount of line. Additionally H2 is much harder to contain than air so the kite will need to be heavier. All this leads me to conclude that you would need a low drag balloon to get enough volume to lift the kite. This leads to questions about performance that don't fit on a napkin so it's the end of my estimates.


----End Calculation, Begin Rant!--------

The kiteboat is brilliant in perfect conditions for two talented crew to achieve performance comparable to conventional performance sailboats. Light air, even for a few seconds puts the kite in the water and likely adds half a kilo of water weight. Presenting a typical windsurf kite on a boat as something safe for cruising and better than sails is a lie. It is like proposing to pull a five tone trailer with a sport bike motorcycle because it has 150hp and saves all the weight of a standard truck. Engines that produce 150hp continuously, economically weigh more than the motorcycle, ditto wheel sets that can control the load.

Using hydrogen balloons to hold the kite up adds more complexity and cost for unproven return. My view is simply that sails don't pay when there is no wind. Kites are just extra expensive sails. Hydrogen can be produced from pure water ~7.5cf/kWh but that takes a lot of fuel or solar panels and that H2 leaks away in the kite. If you consider using that fuel or solar to propel your boat it looks brilliant in comparison. If there is wind up high you could just do what children do to get it up -RUN to make your own wind. 4KW should provide enough speed to get the kite up in 15min (1KWh).

If the kite has any value it is that it stores away and does not weigh much but can provide propulsion in very limited conditions.

You want to know the best way to hold the kite up in light wind -a very tall stick -we'll call it a "mast!".

You still want to hold up your $3000 kite with a $1000 balloon? I have two words for you 'wind shear'. You have your rig up somewhere in the middle of an ocean one evening as you sit reading. The boat is starting to move when Yoink! Then nothing. You go on deck to find the frayed ends of your lines in the water and all your expensive gear going an a world tour and eventually becoming hazardous pollution or wrapped around the prop of some freighter you need to come and save your sorry butt.
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  #45  
Old 07-06-2015, 04:32 PM
sharpii2 sharpii2 is offline
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Originally Posted by Skyak View Post
Awful lot of speculation with too little support.

To get in the ballpark estimate a LEI kite has a main tube ~9inch diam. and 25 ft long for an 18 to 20Msq light wind kite. section A=.44 V=11cf=0.31 CM

The weight of standard air is 1.2256 Kg/ Cubic Meter
The weight of hydrogen is 0.0857 Kg/ Cubic Meter

1.14kg/CM lft from H2
Note all of this is at 1 ATM

So our theoretical LEI kite could get 0.355kg lift by filling to 1 ATM. There is one more problem in that LEI kites use gas pressure for structure and shape so they are at ~1.5 ATM. Weight increases, volume does not so lift is 1.1kg/cM @1.5 ATM. So our theoretical kite would get 0.34 kg lift from H2 @1.5atm.

All very true.

My conclusion is that if you just use a typical LEI kite filled with H2 it will not float in dead air.

Most likely not.

An eyeball estimate that a very good foil shape could be made with a section 3X greater than today's LEI gets me to 1 kg -still not enough to float the big kite let alone a large amount of line. Additionally H2 is much harder to contain than air so the kite will need to be heavier. All this leads me to conclude that you would need a low drag balloon to get enough volume to lift the kite. This leads to questions about performance that don't fit on a napkin so it's the end of my estimates.

Your estimates are similar to mine.

----End Calculation, Begin Rant!--------

The kiteboat is brilliant in perfect conditions for two talented crew to achieve performance comparable to conventional performance sailboats. Light air, even for a few seconds puts the kite in the water and likely adds half a kilo of water weight. Presenting a typical windsurf kite on a boat as something safe for cruising and better than sails is a lie.

Not everyone here is claiming it is. Some of us think that it might be a useful solution in some cases.

It is like proposing to pull a five tone trailer with a sport bike motorcycle because it has 150hp and saves all the weight of a standard truck. Engines that produce 150hp continuously, economically weigh more than the motorcycle, ditto wheel sets that can control the load.

This is a bit of an exaggeration, wouldn't you say? Kind of like a negative political ad.

Using hydrogen balloons to hold the kite up adds more complexity and cost for unproven return. My view is simply that sails don't pay when there is no wind. Kites are just extra expensive sails. Hydrogen can be produced from pure water ~7.5cf/kWh but that takes a lot of fuel or solar panels and that H2 leaks away in the kite.

If you consider using that fuel or solar to propel your boat it looks brilliant in comparison.

I doubt that is true. It is true the H2 will leak away, but how fast? Some materials contain it better than others. The balloon can be "recharged" when need be. Also, the H2 can be produced chemically, using no electricity. The solar, if there is any, could be used to add supplemental propulsion.

If there is wind up high you could just do what children do to get it up -RUN to make your own wind. 4KW should provide enough speed to get the kite up in 15min (1KWh).

If the kite has any value it is that it stores away and does not weigh much but can provide propulsion in very limited conditions.

This is the best reason to consider it.

You want to know the best way to hold the kite up in light wind -a very tall stick -we'll call it a "mast!".

You still want to hold up your $3000 kite with a $1000 balloon? I have two words for you 'wind shear'. You have your rig up somewhere in the middle of an ocean one evening as you sit reading. The boat is starting to move when Yoink! Then nothing. You go on deck to find the frayed ends of your lines in the water and all your expensive gear going an a world tour and eventually becoming hazardous pollution or wrapped around the prop of some freighter you need to come and save your sorry butt.
I guess this depends on the design of the kite/balloon. It can be designed to be quite resilient. Also, for mostly down wind sailing, the line can have some stretch to it.

I really don't understand the reason for a rant.

We're all mostly just brainstorming here.

Most likely a simple kite, or a kite with a balloon, would be a supplemental sail rig.

I also doubt that the kite is that much more expensive than a conventional rig of the same quality, once you include spars and rigging, unless the latter is bought at a discount price. Area for area, it most likely is, but the kite can be presumably smaller on the principle that it will be in more abundant wind, higher up.

For everyday sailing, the conventional rig gets my vote, hands down. but there may be circumstances where a kite an/or a kite and a balloon might be useful.
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