Narrow Boat Knots

Narrow Boat Knots

History of The Hovercraft

As so many Famous events and People were Born, Lived and worked in Portsmouth over the centuries I thought it would be a good idea to tell the story of the invention of the Hovercraft in 1955.

The idea of using an air-cushion as a means or aid to acceleration and reduction in (hydrodynamic) drag was first explored by Sir John Thornycroft, a British engineer, who, in the 1870′s built some experimental models on the basis of an air cushion system that would reduce the drag of water on boats and ships.

In 1877 he successfully patented the idea and his theory was that if a ship’s hull was given a concave bottom, which could be filled – and replenished – with air, it would create significant additional lift. And so the air cushion effect was born.

Decades later scientists and inventors were still busy with his ideas but without any practical applications. With the coming of the airplane however, it was noticed that additional lift was obtained if the plane flew closer to land or water, creating a “funnel effect”, a cushion of air.

The air lift that this funnel effect created differed with the type of wing and its height above ground. The effect was strongest if this height was between one half and one third of the (average) front-to-rear breadth of the wing. Also known as “chord”.

The next two decades saw little interest in air cushion development.

The successful use of the air cushion effect was not lost on engineers after World War 2 was over and in the early 1950′s British, American and Swiss engineers started to rethink Sir John Thornycroft’s problem.

The Englishman Christopher Cockerell, commonly seen as the father of the hovercraft, being retired from the army, settled into boat building where he soon got captivated by Thornycroft’s problem of reducing the hydrodynamic drag on the hull of a boat by using some kind of air cushion.

His theory was that, instead of using the plenum chamber – an empty box with an open bottom as Thornycroft had devised – air was instead pumped into a narrow tunnel circumnavigating the entire bottom, it would flow towards the center and form a more effective air cushion. This peripheral jet would cause the air to build up enough pressure to equal the weight of the craft and, as it would have nowhere to go, the pressure would force the craft up, clearing it off the ground altogether.

Cockerell successfully tested his theory and filed his first patent in 1955. The year after he formed a company called Hovercraft Ltd. He further envisioned and partially worked out other problems of the hovercraft principle that still have to be fully exploited by modern hovercraft builders. One of these was to re-use the air for greater overall efficiency.

Thinking that his air cushion vehicles would be eminently suitable as amphibious craft he approached the British Ministry of Supply, the government’s defence equipment procurement authority with his findings. Soon after, in 1956, the air cushion vehicle was classified as “secret” and a construction contract was placed with a British aircraft and seaplane manufacturer. The result was the SR.N1 in 1959.

The first SR.N1 weighed four tons and could carry three men. Its maximum speed was 25 knots (1 knot = 1.15 miles or 1.85 kilometres per hour) on calm water. It had a 6-inch (15 cm) rubberized skirt to make it easier to contain the air cushion on uneven ground.

Significant wear and tear of the skirt through friction with the water at high speeds made it necessary to use more durable material and a rubber and plastic mixture was developed by 1963. The length of the skirt had also been extended to about 4 feet (1.2 m).

Early interest in hovercraft enjoyed a peak in the early 1960′s as everyone jumped to take advantage of this amazing vehicle. However, by the end of the decade only the British had produced a range of feasible and practical craft.

The problems inherent of the air cushion vehicle, such as Cockerell and others had foreseen, regarding steering control, noise, salt and skirt erosion, caused many countries to abandon their hovercraft development programs in favour of other, more established multi-function vehicles or to use different vehicles specialised in each terrain or function.

Since the 1970′s however, and especially over the last decade, a renewed interest in the hovercraft as (passenger) transport, military transport and weapons carrier and exploratory vehicle has taken ground, solving many of these problems in their development.

Technology in general made large steps forward during the past twentyfive years, enabling organisations and governments, as well as many enthusiasts at Hovercraft Clubs to enjoy the hovercraft vehicle in its many forms including the very popular Remote Control model size hovercraft!.

As far as hovercraft and their spinoff technology is concerned the future looks ever brighter.

Please visit my Funny Animal Art Prints Collection @ http://www.fabprints.com

My other website is called Directory of British Icons: http://fabprints.webs.com

To visit the list and links to my other Blogg articles: http://bloggs.resourcez.com

The Chinese call England “The Island of Hero’s” which I think sums up what we English are all about.

1. 1. 1. 1. 1. 1. Copyright © 2010 Paul Hussey. All Rights Reserved.

About the Author

Please visit my Funny Animal Art Prints Collection @ http://www.fabprints.com

My other website is called Directory of British Icons: http://fabprints.webs.com

To visit the list and links to my other Blogg articles: http://bloggs.resourcez.com

The Chinese call England “The Island of Hero’s” which I think sums up what we English are all about.

Copyright © 2010 Paul Hussey. All Rights Reserved.

Will a 12-metre long, 2-metre wide power catamaran be stable in bad conditions?

My crazy plan is to build a super-long power cat for commuting to work through a large harbour; it has to be that long in order to allow me to cruise at 12 knots, because all boats that are shorter than that are not allowed to go any faster than 5 knots (that’s just the law, and if I went that slow in a small boat, it would take too long to get to work, hence the length).

It sounds like an interesting plan. I really think it depends how bad the conditions you’re talking about are and how good you are at piloting the thing. Considering it’s about the shape of a chopstick, you’ll need to put some good reinforcement through it just to make sure it doesn’t snap in half. When using it, you’ll also have to be careful you go directly into our out of the waves, because if you go sideways to them they may tip your boat over very easily (although of course it would depend on the depth of the keel). Honestly, I’d make it wider if I were you, or at the very least make it a sort of outrigger.

There’s also another possibility. Depending on the legal definition of a boat long enough to go 12 knots, you may be able to use a standard boat and make only a very small, thin hull extension sticking off the front and/or the back, that would serve no real purpose (not even flotation) besides making the boat longer.

Tugmans Hitch

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