Idle thought: NAVY Hovertanks?

rallymodeller · Post by **rallymodeller** » Fri Jul 09, 2010 1:35 pm

As I was puttering around with my old, beat-up Cheetah gravpanzer (new engines, some new armament, scale change) I had a thought:

A very efficient hovertank would be really useful for other than land-warfare uses. A fast, hovering vehicle with the armour and armament of a tank would be unbelievably good at littoral (read: inshore) and riverine warfare. Given the right mix of weaponry it could be a modern replacement for PT boats...

Dr. Yo · Post by **Dr. Yo** » Fri Jul 09, 2010 3:07 pm

A grav vehicle could, certainly. Regular hovercraft have been
employed for years by us and the Russians. The downside of any
fan-lifted craft is that it won't float with the engines ideling. I gather
there are some control and handling issues with hovercraft as well,
( I remember this being mentioned in a show on the big USMC
hovercraft landing vehicles. ) but I don't know much more about it.

But yeah, once you've got a anti-gravity, a lot of possibilities open
up. Consider that gravity control might do for buoyancy issues with
submarines, for instance.

Scotaidh · Post by **Scotaidh** » Fri Jul 09, 2010 4:31 pm

Dr. Yo wrote:A grav vehicle could, certainly. Regular hovercraft have been
employed for years by us and the Russians. The downside of any
fan-lifted craft is that it won't float with the engines ideling. I gather
there are some control and handling issues with hovercraft as well,
( I remember this being mentioned in a show on the big USMC
hovercraft landing vehicles. ) but I don't know much more about it.

But yeah, once you've got a anti-gravity, a lot of possibilities open
up. Consider that gravity control might do for buoyancy issues with
submarines, for instance.

Doc's right - it'd have to be a grav tank. For why a hover tank won't work on water, read Rolling Hot by David Drake.

Jagdson · Post by **Jagdson** » Fri Jul 09, 2010 6:49 pm

Suspension method fail aside, there's a larger problem inherent to the concept: "Navy." Amphibious armor ops are a Marine staple.

Wug · Post by **Wug** » Fri Jul 09, 2010 11:39 pm

Real hovercraft work great over water. It's one of the main reasons for their use.

http://en.wikipedia.org/wiki/Hovercraft

http://en.wikipedia.org/wiki/Air-cushio ... ding_craft

This one looks like it means business.

http://en.wikipedia.org/wiki/Zubr_class_LCAC

I think all existing hovercraft that operate over water can float. Commercial operators would never get insured otherwise. However their hydrodynamic shape makes them difficult to tow.

What about vehicles kept aloft by jet thrust? Of course they can fly over water. think about a harrier hovering or a submarine launching a missile. The problem with aerodynes is hey are inefficient. There hasn't been much interest in them since good helicopters became available.

Scroll down.

http://discaircraft.greyfalcon.us/LIPPI ... SEARCH.htm

David Drake is a novelist. He writes fiction.

Mike

rallymodeller · Post by **rallymodeller** » Sat Jul 10, 2010 1:12 am

I suppose I should specify. I was actually thinking about grav-assist tanks used in a Navy fashion, not as ground-support but, as I said, as littoral warfare or riverine craft. Anti-shipping and so forth (after watching the anime "Tactical Roar" future Navy operations are kind of on my mind). A speedy grav tank (300 mph or so, not out of the question for antigrav) could almost be treated like a manned, reusable multi-shot anti-ship missile with heavy armour and built-in self-protection. Inshore, a few of these could seriously maul an amphibious force.

Once I get my digital camera working again, I'll post new pics of the revised Cheetah with it's new anti-shipping fit and some of the fun new features I have added. As I see it, it is to a land-optimized grav-tank as the later Sea Apache concepts were to the standard AH-64.

Scotaidh · Post by **Scotaidh** » Sat Jul 10, 2010 1:38 pm

Wug wrote:Real hovercraft work great over water. It's one of the main reasons for their use.

http://en.wikipedia.org/wiki/Hovercraft

http://en.wikipedia.org/wiki/Air-cushio ... ding_craft

This one looks like it means business.

http://en.wikipedia.org/wiki/Zubr_class_LCAC

I think all existing hovercraft that operate over water can float. Commercial operators would never get insured otherwise. However their hydrodynamic shape makes them difficult to tow.

What about vehicles kept aloft by jet thrust? Of course they can fly over water. think about a harrier hovering or a submarine launching a missile. The problem with aerodynes is hey are inefficient. There hasn't been much interest in them since good helicopters became available.

Scroll down.

http://discaircraft.greyfalcon.us/LIPPI ... SEARCH.htm

David Drake is a novelist. He writes fiction.

Mike

Mike - It is true that Mr. Drake is a novelist, but he does his homework. He also tries very hard to keep things as realistic as possible, within his framework. I think you'll find that his reasons for hovertanks not working over water will hold ... um.... water.

It's also true that all current hovercraft have built-in floatation. However, all attempts to armor hovercraft never get past the stage where the would-be armour applicator does his weight-vs-power sums. Since most experts agree that a tank is by definition armoured ... The few available amphibious tanks are also kinda skimpy on the protection side of their triangle.

Rallymodeler, thanks for the clarification. I think you're correct, but with this caveat - at 300mph (or even 'kph') a 60+ tonne object will have very large turn radii, yes?

rallymodeller · Post by **rallymodeller** » Sat Jul 10, 2010 2:35 pm

Scotaidh wrote:
Rallymodeler, thanks for the clarification. I think you're correct, but with this caveat - at 300mph (or even 'kph') a 60+ tonne object will have very large turn radii, yes?

Heh. Already thought of that. Sea-based grav vehicles can use something land-based ones cannot -- drag brakes.

Picture it. You are in your Abrams-sized gravpanzer, skimming above the water at, say, 200mph. You need to make a tight turn to port. Out of the portside bottom of the panzer pops a thick steel plate on a ram -- right into the water. The drag of the plate "digging in" pulls the tank to port, or more accurately the tank pivots around the plate.

The plates can either be used symmetrically as a "crash-stop" option or differentially to aid in turns. It doesn't take much surface area to be able to create an incredible amount of water resistance -- the scoops on a CL-215 water bomber are about the size of the palm of your hand but the bomber has to scoop at almost full throttle because of the water drag. So make 'em big, brace them really well and give them a giant ram -- and you can do 180s on a dime.

As I am fleshing out the idea I am realizing that my concept has the tank being less like a hovercraft and more like a WIG vehicle with antigrav in place of the wing-generated air cushion.

HWR MKII · Post by **HWR MKII** » Sun Jul 11, 2010 6:19 pm

shouldnt this be in the "practical aspects" thread?

DOMENECH1776 · Post by **DOMENECH1776** » Mon Jul 12, 2010 11:02 am

Scotaidh wrote:

Mike - It is true that Mr. Drake is a novelist, but he does his homework.

Homework is overrated. Well, off to McDonalds, today I start working the fryer!

Dr. Yo · Post by **Dr. Yo** » Mon Jul 12, 2010 12:45 pm

Drake is also ex-military, so I don't think he's just whistling in the dark
here, either. I happily admit to being wrong about about hovercraft
floating, though the point Wug made subsequently, that they
would be a drag to tow, is as valid. As 'Gosh-Wow' as hovercraft are,
you'll notice the armed forces of the world haven't exactly been
clamoring for them. Our own experience in Viet Nam demonstrated
that their downsides outweighed their mobility advantages. Nowhere
in my post did I state that "They don't work over water". Granted,
they're loud, and produce enough spray to be visable from twice the
distance of any ordinary seacraft of about the same tonnage, but
hey.

Anyway, Rally makes a good point. As I pointed out in an earlier post,
past a certain point, grav vehicles become pretty much all-purpose.*
It occurs to me that being able to vary your mass, or negate its
effect, would be very useful for subs, as well.

* And the thought was hardly original with me-I was refering to the
old Traveller role-playing game.

Kylwell · Post by **Kylwell** » Mon Jul 12, 2010 12:51 pm

HWR MKII wrote:shouldnt this be in the "practical aspects" thread?

yeah but my meager Mod abilities won't allow me to merge it.

Old Wombat · Post by **Old Wombat** » Tue Jul 13, 2010 8:13 pm

My take on this;

A "tank" is a land vehicle, once it becomes a seagoing vessel it becomes a "ship" or "boat".

Anti-gravitational devices basically make any such powered vehicle an aircraft.

Air cushion vehicles over water are subject to water displacement, as are other water craft. A tank is a heavy, dense object lacking a sufficient base area to stay afloat. Unless the fans can displace 50/60/70 tonnes, which is 50/60/70 cubic metres of water below the tank it's going to sink. This can, to some extent, be negated by constant high speed motion but this means that the "sea-tank" can neither slow down nor stop, making it next to useless for most maritime roles.

A "repulsor" type lifting device vehicle is, basically, the same as an air cushion (hovercraft/ground effect) vehicle and has a displacement effect.

[Note:- I've also put this in the "Practical Aspects" thread]

mike robel · Post by **mike robel** » Tue Jul 13, 2010 9:24 pm

LCAC (Landing Craft Air Cushion) can carry a single M1A1 Abarms or a passel of smaller craft.

http://en.wikipedia.org/wiki/Landing_Craft_Air_Cushion

Lightly armored hovercraft were used in Viet Nam as riverine craft

http://www.hoverclubofamerica.org/forum ... wtopic=532

Old Wombat · Post by **Old Wombat** » Tue Jul 13, 2010 10:14 pm

Well?

Is a tank the size of an Abrams sitting on a base roughly the size of a LCAC (about, what, 8 times the base area of the Abrams?) a practical vehicle?

The PACV's massed about 7 tonnes operational with a base area of about 81m^2 [0.086t/m^2], an Abrams (for example) masses over 60 tonnes with a base area of only 29m^2 [2.07t/m^2].

That's a surface pressure 24 times greater than the PACV.