The use of air

Would not pushing the water down with air only result in airpreshure that is equal too the preshure the water would apply and then the ice would still be there???

I think I read somewhere some icebrakers have proppelers or pumps sucking away the water under the ice resulting it to brake by it's own weight.

Howercrafts should be good at ice braking if the ice is thin and large surfaces off ice is neaded to be broken up.

I noticed on the picture I can see the Norwegian, Danish and Sweedih flag and the logo is the one belonging to Scandinavian Air Shutle.

Where did that picture come from? I heard one that someone tryed out howercrafts in Norway, but I gues it did not make anny sense since narow fjords is not the best place to land a howercraft.

I did not know that SAS was involved, I thought they sticked with airplanes.

I would supose thet is in the baltic sea or oslo fjord since it's the only places I can think the waters are calm enought to make ice like that.

Anny info? annyone?

 

Link to picture:
http://www.hoverwork.com/get.php?f=expl

Hovercraft can break ice up to 40 inches thick, that's over a metre for you international folks.

If you suck away water it will be replaced by more water, that is unless you supply air at a greater pressure and rate. These are similar conditions for the icebraker with pump and the hovercraft.

The reason that you may see hovercraft more often breaking thin ice than thick ice is several fold.

1. Range; if you want to go very far from your home base a convential icebreaker car carry more fuel than a hovercraft.

2. Hovercraft skirts may be torn from jagged or "rough ice" and should stay away from such natural formations.

3. Hovercraft typicaly break up the ice in large sheets as they don't use impact forces. This means large areas which may take time to clear are covered more efficiently than narrow wagon train or caravan style paths of conventional icebrakers.

4. Hovercraft are used to break up ice in shallow but often wide rivers so that the ice flows down river, helping to prevent all the ice melting at once in one area which may cause flash spring time flooding.

 

To get back to little bubbles and warm liquid water, the UT-Battelle approach is a variation on an established drag-busting theme. For example, Speedo produces rough-surfaced swimsuits based on shark skin. Small irregularities on a surface break up the large eddies that otherwise form around an object moving in air or water and which slow it down by rotating against the surface of the object and applying force on it from behind. Presumably what works for a surface/displacement craft will not necessarily work for a fully submerged craft (or fish), and trapping air bubbles in surface irregularities will work differently than pumping air onto a smooth surface. Maintaining a significant amount of air on the surface of a hull will of course provide additional buoyancy, but I suspect the amount of air involved in the UT-Battelle method is miniscule. Here's an interesting article on the subject: http://www.livescience.com/technology/050715_shark_skin.html

 

Re my previous post and the comment about buoyancy. I am assuming that the UT-Battelle approach involves trapped air bubbles, which I would expect to work (however minimally) as would air-filled balloons or sponsons. Free-flowing air that is contiguous with the atmosphere above the water is a different matter.

 

I did not know this, thanks.

Something strange about the picture though.



This was posted in another boatdesign.net thread.

NASA RIBLETS FOR STARS & STRIPES
http://www.nasa.gov/centers/langley/news/factsheets/Riblets.html

 

I am seriously thinking of having a go, very seriously.

I have a 44 foot power cat with semi displacement hulls and surface props . My present speed is 24KTS flat out but 17 all day long. At 24 its like driving a fork lift truck( all back end movement). displacement 14 tons.

The hulls are like fat torpedos and raises only inches when on the plane. Possible 3-4 inches its hard to tell from where I stand.

I am thinking that I will make 2 fibreglass cones that fit over the bulbous bows but have them about 1/2 inch away from the bulbs standing on 3 legs.

I would then feed air down a pipe from the surface that is only 10inches up. I would assume that at 20KTS there would be a helluva depression behind the cones and air will be brought down a 1 1/2 PVC pipe wich would also be the leading edge of the upper portion of the hull. Could even put some bleed holes there too.

This would as I see it supply the 2 hulls with air bubbles. If theres any thing in this theory ---at all-- I should see something of an improvment.

It will cost nothing as I am hauling out for an anti fould job any way and if its crap a hammer and a grinder will remove it in minutes.

However of all the years water skiing I cant honestly say that when I ski over aireated water ( wake etc) I felt any less resistance to the ski. Only at very high speed did the wake feel easier, but I think that this was because the ski was out of the water most of the time.

But that is a point, ski racers ski in the wake, dont they?--in the bubbles, is there a reason for that?

 

Russian Super-Torpedo "Shkval", supercavitation

I thought I remember seeing this technology on a new super torpedo developed by the Russians.

...here is one brief discussion from a googled site

Russia has developed new submarine-launched torpedos that travel at incredible speeds – perhaps as fast as the speed of sound underwater. Scientific American reports in its May edition that these supersophisticated weapons have been linked to the sinking of the Russian submarine Kursk last August, and even to the arrest and imprisonment of Edmond Pope.

Pope, an American businessman, was charged by Russian authorities with spying, specifically that he had sought to buy plans for the "ultrahigh-speed torpedo."

The magazine reports that "evidence does suggest that both incidents revolved around an amazing and little-reported technology that allows naval weapons and vessels to travel submerged at hundreds of miles per hour – in some cases, faster than the speed of sound in water. The swiftest traditional undersea technologies, in contrast, are limited to a maximum of about 80 mph."

The new technology that allows for these incredible speeds is "is based on the physical phenomenon of supercavitation."

The 6,000-pound Shkval rocket torpedo has a range of about 7,500 yards and can fly through the water at more than 230 miles an hour. The solid-rocket-propelled "torpedo" achieves this high speed by producing a high-pressure stream of bubbles from its nose and skin, which coats the weapon in a thin layer of gas. The Shkval flies underwater inside a giant "envelope" of gas bubbles in a process called "supercavitation."

 

Your source obviously doesn't know its *** from its elbow. Supercavitation isn't the same as injecting bubbles, although the end result is the same - friction reduction. There's a pretty good thread in this forum that discusses the shkval and its plusses and minuses.

 

Informed Discussion of Shkval

I simply 'googled it' for a quick reference as I did not remember exactly where I had seen the info, nor the validity of the info....so much for my source.

So why didn't you reference the webpage address of that more informed discussion?? (sorry I didn't either)

300Kt Torpedo
http://boatdesign.net/forums/showthread.php?t=10574

 

Because this thread isn't about the torpedo.

 

personally speaking I would think that airiated water and supercavitation on torpedoes is just two different ends of the stick. One being the start of it and the other being the extreme ulimate.

Both methods if not the same have 'the use of air' or gas.

 

Use of Air or Gas

That's the way I thought of it as well
Brian

 

I am at present glassing up 'false bows' that I propose to fit in front of the bow and bulbous bow. However a thought that I was sure about is becoming unstable and that is I am no longer sure that air will be drawn down into the depression of the 'false bow' does any one have any thoughts on using this approach rather that pumping air down that in actuall fact would be necessary on a conventional displacement hull.

I am trying to distroy the friction and 'bow down' effect that I have over 20TKTS, and to increase speed by what ever I can. I am in now way expecting ridiculous figures

An increase of 5% would be wonderfull.

As soon as the fibre optic cable is repaired in Tiawan I shall be searching the internet dilligently.

 

A photo of what you have now and a sketch of what you have in mind might help.

Do you presently have bulb bows?

Not sure what you mean by "air will be drawn down into the depression of the false bow" ??

 

I think I understand the false bow comment, a laminated sheet which allows an air acvity behind it to remain open. This cavity is then fed high pressure air which then escapes through holes, perforations and nipple or dimple like nozzels.

I would suggest that the holes be a equal or neutral in direction as possible. I say this because you may not always desire forward thrust from the air jets, not if you are turning or trying to slowdown and stop. Then again if the holes do face back/stern they will not act as little water inlet scoops upon forward motion. This cheese grater may help you picture the surface I'm thining of.



See the large holes up front, but spaced farther apart.