Calling all Navy types regarding LCAV

[MillCreek]

I am watching an episode of Modern Marvels online.  I am inspired to ask a question and I cannot find the answer online.  Can a LCAC float if the hovering capability is not working?  I was watching a LCAC go motoring over the seas for an amphibious landing, and I wondered what would happen if they had a total engine failure and lost lift.

[dm1333]

I've been out of the Navy since 1988 but I'm going to say yes it can as long as Archimedes principal isn't violated.

[AJ Dual]

I'm not Navy, nor even ex-mil of any kind, nor have I slept at a Holiday Inn Express lately, but I've seen the LCAC's floating without the skirts inflated several times on the various technology/military cable shows.

No idea what a bunch of cargo on one would do without the skirts inflated though.

Most recently, the Smithsonian channel had some hovercraft racing thing on last week, and they did a bit on the LCAC's and showed one just floating in the ocean at rest without the skirts inflated.

http://www.smithsonianchannel.com/sc/web/show/131739/hover-racers-flying-on-air

[ArfinGreebly]

I just spent thirty minutes trying to locate any discussion of the LCAC floating on water, landing on water, stationary on water, engine failure, failure modes, and so on and so forth.

Nothing.

Every single discussion of "floating" uses the term in its "stationary flying" meaning (i.e. floating four feet off the water).

"Landing" is likewise only used in its "to come ashore" meaning.

After a while it gets kinda frustrating to see video after video, picture after picture showing the LCAC either in motion over water or sitting on a beach, with not a single image of the LCAC sitting motionless (and floating) on the actual water's surface.

That'll teach me.

[BobR]

bob

[MillCreek]

I just spent thirty minutes trying to locate any discussion of the LCAC floating on water, landing on water, stationary on water, engine failure, failure modes, and so on and so forth.

Nothing.

Every single discussion of "floating" uses the term in its "stationary flying" meaning (i.e. floating four feet off the water).

"Landing" is likewise only used in its "to come ashore" meaning.

After a while it gets kinda frustrating to see video after video, picture after picture showing the LCAC either in motion over water or sitting on a beach, with not a single image of the LCAC sitting motionless (and floating) on the actual water's surface.

That'll teach me.

I am heartened to see that someone smart had the same results as I did.

[birdman]

Yes.
There is a hollow portion (buoyancy box) below the deck that will keep it afloat.

Remember, while big, the total mass isn't that much.  A box 30x30x6ft woud easily support the entire thing, and is way smaller than the overall space.

[MillCreek]

Yes.
There is a hollow portion (buoyancy box) below the deck that will keep it afloat.

OK, that is interesting.  I had looked online for LCAC schematics and the ones that I found did not have enough detail to answer this sort of question.  I wonder if the box is hollow and air-filled, or is it packed with styrofoam or the like.

[birdman]

OK, that is interesting.  I had looked online for LCAC schematics and the ones that I found did not have enough detail to answer this sort of question.  I wonder if the box is hollow and air-filled, or is it packed with styrofoam or the like.

Hollow.  Don't know if its cellularly divided or not, but its not filled...why add weight?

[French G.]

I did 5 years amphib but not too much LCAC exposure, we were an an LCU ship. I did make some nifty hydraulic lines for some poor souls crewing one that hitchhiked across half the Indian ocean because I was the best support option. LOL, now that's when you know your life is crap.

I'd hate to be stuck in heavy seas with no power with a max load on. Say, an M1A1. LCAC can carry 1, LCU 2, or 3 in emergency conditions.

Neatest thing LCAC wise was a test platform designed to be a beach obstacle penetrator. In the cargo area was mounted a self-contained pod with a GAU-13 30mm cannon and a multiple rocket launcher. Plan was to drop the bow ramp and blast said obstacle. It did a dandy job of disassembling large concrete structures. Probably useless, since the idea of opposed beach landings is hopefully out of fashion.

[AJ Dual]

Neatest thing LCAC wise was a test platform designed to be a beach obstacle penetrator. In the cargo area was mounted a self-contained pod with a GAU-13 30mm cannon and a multiple rocket launcher. Plan was to drop the bow ramp and blast said obstacle. It did a dandy job of disassembling large concrete structures. Probably useless, since the idea of opposed beach landings is hopefully out of fashion.

Yeah, that would be neat as hell to see.

However, if the Navy only had something that just flew through the air and could drop a bomb on something like that, such a project would be obsolete immediately. 

[Tallpine]

Yeah, that would be neat as hell to see.

However, if the Navy only had something that just flew through the air and could drop a bomb on something like that, such a project would be obsolete immediately. 

It would never work.  Big guns on battleships are the only way to go.   

[MillCreek]

It would never work.  Big guns on battleships are the only way to go.   

I will still be interested to see the Advanced Gun System on a Zumwalt-class destroyer.

[birdman]

I will still be interested to see the Advanced Gun System on a Zumwalt-class destroyer.

Look at the videos of the crusader prototype doing a max ROF demo...same gun (basically, the AGS is 3ft longer) and the same ROF (10rpm).  Which is kind of odd from a muzzle horsepower basis, the current 5" gun can deliver ~40% more shell weight to target (20rpm with 70lb shells vs 10rpm with ~95-100lb shells).

The big advantage was common ammunition, more diversified ammo set, and bigger punch per shell...and the magazine size in terms of ready rounds (300 for the AGS vs 20 in the 5"...however, the crew can revload the 5" from magazine at at least 10-16rpm, supposedly, so that difference is somewhat moot).

The AGS does have better range though, and for really long term sustained fire (like half an hour) will perform better, due to cooled barrel, etc.

[280plus]

The latest version of the AGS "reads" the shell being chambered and sets the gun accordingly. They used to have to do it manually which made firing mixed shells difficult. Now they can just load whatever in any order and the gun sets itself automatically. Pretty cool I thought. They're also capable of firing rocket propelled rounds that IIRC will travel beyond the horizon. I don't know squat about the LCAC, sorry.

[Rusty Paul]

To answer the question does the LCAC float, yes it does. LCAC is a complex machine but in essence consists of a  1) hull system,  2) skirt system, and  3) superstructure. The hull system consists of two major assemblies, the deck and the flotation box. The skirt system is attached to the flotation box and the superstructure modules are fitted on the deck.

[AmbulanceDriver]

Look at the videos of the crusader prototype doing a max ROF demo...same gun (basically, the AGS is 3ft longer) and the same ROF (10rpm).  Which is kind of odd from a muzzle horsepower basis, the current 5" gun can deliver ~40% more shell weight to target (20rpm with 70lb shells vs 10rpm with ~95-100lb shells).

The big advantage was common ammunition, more diversified ammo set, and bigger punch per shell...and the magazine size in terms of ready rounds (300 for the AGS vs 20 in the 5"...however, the crew can revload the 5" from magazine at at least 10-16rpm, supposedly, so that difference is somewhat moot).

The AGS does have better range though, and for really long term sustained fire (like half an hour) will perform better, due to cooled barrel, etc.

Question - everything I'm seeing about the projectile for the AGS (the LRLAP specifically) shows a projectile weight of 225-230 lbs.  So I would imagine that the AGS would have significantly more "oomph" than the Crusader's gun?

[Sergeant Bob]

To answer the question does the LCAC float, yes it does. LCAC is a complex machine but in essence consists of a  1) hull system,  2) skirt system, and  3) superstructure. The hull system consists of two major assemblies, the deck and the flotation box. The skirt system is attached to the flotation box and the superstructure modules are fitted on the deck.

Thanks for the info and welcome to APS!