Military recon powerboat concept

[kach22i]

Originally Posted by rambat

I will apply in my new design 2007 composites to save 60% strucure wieght, offer 2x2000 hp gasoline "silenced" engines (short missions) elec stability and eliminate the axle fans and thier mission killer noise. Stay tuned. And feel free to offer any constructive comments.

1. Does the new design have a client or is it speculative?

2. Gasoline? Doesn't the military want to use the same Diesel fuel in everything?

3. Axial fans help prevent "heave acceleration" in rough weather as I understand it. Can't active noise cancellation (speakers) be applied somehow, or perhaps many right angled turns with absorbtion?

4. I have a design on grid/sketch paper which is a little smaller than a Mark-V and hope to build a scale working model of it. The model will take time and money which is short supply right now. Any ideas on how to find a patron or sponsor?

[kach22i]

Originally Posted by GTO

Anyway, if this is basic info everyone here is aware of, sorry to waste the space.

Good information, thanks GTO.

Isn't there a cheap way with a mass model, a high powered flash light or low powered laser in a dark room to get a general idea on what will bounce back?

[Ramius41]

Originally Posted by kach22i

1. Does the new design have a client or is it speculative?

2. Gasoline? Doesn't the military want to use the same Diesel fuel in everything?

3. Axial fans help prevent "heave acceleration" in rough weather as I understand it. Can't active noise cancellation (speakers) be applied somehow, or perhaps many right angled turns with absorbtion?

4. I have a design on grid/sketch paper which is a little smaller than a Mark-V and hope to build a scale working model of it. The model will take time and money which is short supply right now. Any ideas on how to find a patron or sponsor?

1....Probably

2....Name a 2000hp diesel that doesnt weigh as much as a house....and most of the military's uav's arent diesel.

3....Lets try not to overload the craft with weight before they get the actual payload in it!

4....BEG!!!...

[kach22i]

The B.E.G. method....................not that again.

I wonder how old this picture is.


San Diego boat movers..............
Navy air cushion
http://www.sandiegoboatmovers.com/moves_military.htm

[rambat]

Its a 90' 1989 SES hull, surface propelled. Rohr built it. If I can can find my file I'll upload the layout, a very advanced SES for its time, And I think it was used heavily for various task in the US Navy.

[GTO]

Originally Posted by kach22i

Isn't there a cheap way with a mass model, a high powered flash light or low powered laser in a dark room to get a general idea on what will bounce back?

Not really. If you consider a wire, shining a light on it will create a shadow on the opposite side. Hit the same wire with RF energy of the right frequency, and it becomes an omidirectional reflector. Unless you create your model with optical characteristics that mimic the RF energy characterics (which you don't really know, which is why you built the model in the first place) then that wouldn't work. And your model is no longer cheap.

Thats why RF absorbing chambers are popular for design work.

[kach22i]

Originally Posted by GTO

Not really. If you consider a wire,

What if considering an all composite design hovercraft or SES?

I don't think a plastic/composite/fiberglass wire would carry a signal like a metal one, would it?

I guess one would have to avoid using metal ties to secure the rubber skirt with.

[martin k]

Alex, I reckon your boat has zero stealth.
Gas turbines run very hot so your exhaust plume will give you away for a start. And I don't think the boat is big enough to incorporate sufficient exhaust cooling arrangements.
Also, the beautiful domed cowl is perfect for reflecting radar, no matter what the attitude of the vessel is.
If you design a true stealth vessel, then speed becomes a secondary consideration, depending on operations in mind. 60 knots or 30 knots becomes the difference between transporting a team of 5 or 25.
You need to settle on functional targets, then design accordingly.

[GTO]

Originally Posted by kach22i

What if considering an all composite design hovercraft or SES?
I don't think a plastic/composite/fiberglass wire would carry a signal like a metal one, would it?

I can't directly answer your question as it all depends on the materials used in the composite construction. If the materials used had a radar signature for the frequencies of interest, a study would have to be made of the signal interaction between each laminate. Again, the structure has to be analyzed as a whole. Although I would think fiberglass does have a much smaller signature than a metal, you would still have to confirm that as a whole, the signature reduction is good enough.

Mil-spec radars are GOOD and depending on the ROEs in place, a weapons commander might look at an intermittent return and say, "Hell, I'm bored, put a missile on it and see what happens."

[BMcF]

Originally Posted by rambat

Its a 90' 1989 SES hull, surface propelled. Rohr built it. If I can can find my file I'll upload the layout, a very advanced SES for its time, And I think it was used heavily for various task in the US Navy.

ahh, yes..the 'hulk' as she became known in Navy circles. 'Sea Viking' SES SpecWar SES..aborted in mid 80's when completed only to point seen in that pic. Waterjet propulsion, centrifugal lift fans, and a digital vent valve based heave attentuation system (HAS or RCS), built by us.

Only thing that pile-o-aluminum ever did was some limited duty as a radar target for signature testing to see if they had at least been on the 'right track' with the low-signature design..and that was about all she ever did before hitting the scrap pile. Considered an 'advanced SES' by the folks in teh program office (nuff said) she was actually already sunk by the weight of too many combined requirements, well before the construction began...so her ignominious end was actually a blessing disguise..she would have been a total pig in the perfromance area.

Fortunately, we received permission from DoD to re-sell the HAS package (protected/retricted military technology at the time) to a Norwegian company for a prototype high-speed ferry SES and it was launched in Hyen, Norway (and still in service.in Malta now, I belive) in ..86?..as the 'Fjordkongen'. 'Fjordkongen' was about the only thing that ever made any use of the residue of the 'Sea Viking' that I was aware of.

BTW..noting an earlier comment in this same thread.axial lift fans were 'abandoned' for lift fan use in the late 70's..too complex and too susceptible to unrecoverable total stall, where centrifugal fans are not. And..axials made heave resonance and acoustic resonances worse than a centrifugal too...

[kach22i]

Originally Posted by BMcF

BTW..noting an earlier comment in this same thread.axial lift fans were 'abandoned' for lift fan use in the late 70's..too complex and too susceptible to unrecoverable total stall, where centrifugal fans are not. And..axials made heave resonance and acoustic resonances worse than a centrifugal too...

I've read that the axial fans on some early British hovercraft exploded from the heave pressure load of wave impact and cushion variation which heavy seas presented. These axial fans were replaced with centrifugal fans without further incident.

Request For Information (RFI):
Does anyone know of a hovercraft or hovercraft model using a "Mixed Flow" fan? From my reading it might be the best compromise between an Axial Fan and a Centrifugal Fan. Would kind of look like something off a hair blow dryer or floor cleaning vacuum fan. The first version or prototype of the Jeff (A) may of had these, replaced by somekind of right angle axial impeller, replaced by split thrust (one for lift, one for roof mounted directional thruster) centrifugal lift fan.

Axial Fan Note:
In the book...........
Theory and Design of Air Cushion Craft (ISBN: 0340676507)
Yun, Liang Bliault, Alan
http://www.abebooks.com/servlet/SearchResu...76507&nsa=1

There are several large Russian hovercraft which use axial fans for lift. The Brit's and Chinese favor centrifugal lift fans. There is a chart in the book listed above. PM me and I might get around to sending you (any of you) that page.

I don't want to post copyrighted materials which I've scanned myself.

[BMcF]

The Jeff-A used mixed flow lift fans, IIRC. They were purched later by Gentry, intended for use in his aborted trans-Atlantic record attempting SES design that Chris McKesson and John Connor were developing. They had some serious blade cracking problems when initially produced for the Jeff test craft..again if the old memory serves me right. Chris will probably see this thread and set me straight on that one if I erred.

The use of axial fans in hovercraft is more prevalent and less problematic...because the leakage is inherently much higher than that of an SES and always a lot of leakage present at all times when on cushion (why the 'less leaky' but non-amphibious 'sidewall hovercraft', later 'SES', was invented in the first place after all) and thus provides a 'relief valve' that makes stall less likely.

The old SES-100 A could be lift-stalled and that then required that she be set back down on her bottom again so that the fans could recover from the stall..as an example of why axials were evantually abandoned. In the short term..several operational restrictions and additional stall prevention venting mechanism were added to the 100A so that she could complete her trials programs through about 1980 or so.

[kach22i]

Originally Posted by BMcF

Considered an 'advanced SES' by the folks in teh program office (nuff said) she was actually already sunk by the weight of too many combined requirements

Did the weight of the engines have anything to do with it being overweight?

http://ntlsearch.bts.gov/tris/record/tris/00691346.html

Principal particulars are: Length oa 82ft 6in; Breadth 35ft; Draught on/off cushion 5ft 4in/8ft 4in; Max. full load displace,ment 116t. Propulsion is by a pair of 1800 bhp diesel engines driving twin cp propellers.

[BMcF]

Originally Posted by kach22i

Did the weight of the engines have anything to do with it being overweight?

http://ntlsearch.bts.gov/tris/record/tris/00691346.html

Not really...all 'like' vessels produced afterwards use, or used, similar diesels. And I goofed..it was a successor design to SWCM that used jet propulsion..although I thought jets were substitued for the CP solution late in the Sea Viking design phase..

The problem with Sea viking is the same as has plagued nearly every Navy attempt to build a high-speed surface craft (witness the PCs..witness very soon the first LCS..nuff said again)) where too much 'stuff' gets piled on a very weight-senstive hull technology..whereupon its no longer 'fast' at the end of the day, most often resulting in total abandonment during the design phase.

[kach22i]

Just to clear up a long standing confusion on my part;

1. The "Jeff-B" (EDITED; I meant to say Jeff-B not "A", had to look it up- oops LCAC prototype) lift fans which are tied into the bow/stern thrusters were originally "Mixed-Flow Impellers" - right?

2. Were they axial or radial?

3. Were they single or dual on a common axle?

4. These were the ones which you could see straight though when spinning at speed, right?

5. The mixed-flow fan(s) were drawing in air from the port and starboard as well as the cargo well area, right?

6. The mixed flow fans worked fine but were switched to higher pressure centrifugal fans when the military once again stuffed 10 lbs of organic fertilizer into a 5 lb bag, right?

7. I mean to say that the Navy raised the system requirements (added weight) and even larger mixed-flow fans would not fit, or that centrifugal fans had some kind of other advantage yet not discussed.