Submersible hulls

http://inventors.about.com/od/sstartinventions/a/Submarines_4.htm

Robert Fulton - Nautilus Submarine 1801

Robert Fulton's cigar-shaped Nautilus submarine was driven by a hand-cranked propeller when submerged, and had a kite-like sail for surface power. The Nautilus submarine was the first submersible to have separate propulsion systems for surfaced and submerged operations. It also carried flasks of compressed air that permitted the two-man crew to remain submerged for five hours.

 

... and its almost weightless when neutrally bouyant...

It had better be or it's know as a sinker, not a boat! (however, it is still not massless). The efficiency of the vessel is dependent on the size, speed requirement, etc. The idea of submerged cargo vessels has been looked into in the past, but I think that the cost and comlexity of building and operating negate the benefit of reducing drag and staying out of reach of the weather. Just being submerged is not enough to avoid wave drag, the hull must be deep enough so that the pressure field decays sufficiently away from the interface. A submarine can be tracked by its surface wave pattern even when quite deep and slow.

 

Mmmm- visualize the impact and stress on the crossbeam (cabin) to hull attachment points when sailing at 15kts and one hull pierces into a wave and decides to go into submersible mode. Water being 800 times more dense than air. Survive and cycle this a thousand times, and i'd suspect she'd handle like a lumber loaded 53 ford two ton with the king pins gone at 50mph. The stresses on such a craft would be immense.

 

It can also be detected by the "internal waves" it creates. These can be many hundreds of metres high.

 

you say not faster but more efficient. speed is an outcome of efficiency. a car with 100 hp can do 90 mph but a boat with 100 hp might only do 30 mph, that makes the car a lot more efficient than the boat. the subs that reach those high speeds have several hundred thousand horse power, thats not efficient it is brute strength.

 

Interesting.. a whole new meaning for effiency

 

"Windage - Friction ....... " Is this trying to imply there is more friction in air than water ?

If you are talking about cross winds, there are plenty of cross currents underwater.

Whitepointer has got the idea - the best load/speed for fuel consumed - is the most efficient vehicle.

Likewise - the least drag for confined volume would be the formula for the most efficient hull design.

In both cases, subs don't 'win'

 

Yes. that's it...with a sail.

In a sailboat, the effect would really look like something (I imagine) with the first 1/3 of the hull being pushed under the waves by the sail pressure and the rest of the hull remaining above the water slightly.

Comparing a submarine to a sailboat ignores how much energy these waves we smash against contain...waves are waves because they contain energy. It isn't the same as moving thru water like a submarine. Saying a submerged hull is going to have more resistance than a hull on the surface is obvious until we add the effect of smashing waves compared to the calm under the water and the potential reduction in pitching.

Imagine swimming against large waves....then imagine diving under and swimming underwater. On the surface, you might get nowhere. But under the surface, the waves don't effect you.

 

There is a good introduction to the so-called "transport factor" in Chris McKesson's wiki at:
http://www.mckesson.us/mckwiki/inde...ehicles_-_Chapter_10#Kennell_Transport_Factor

 

A short video comparison of a conventional boat and a much smaller SWATH

http://youtu.be/qNwGlp_1560

 

im no engineer- but have studied my submarine physics to some extent--much to the (sarc) delight of my fellow writers on here- have design plans for a civil submarine--that wont be built for a LONG time..if at all...
in this i respecfully disagree --in this case efficency is not a function of speed --in fact i might argue that speed is not a function of efficiency at all. but what you say does sound intuitively correct...the fact is-
that car going 90 miles per hour will use more fuel than a boat going 3 knots with 5 hp...
with subs- they use that high hp for speed true- but its not efficient as say a civil sub which uses aprox 1/4 the hp needed for a boat. research that - if you like.
it takes less energy to move a sub(submerged running) at a given speed as it will a boat..its really that simple.
but go into your bathtub--fill a bottle with water just enough to sink it or neutral bouyancy, then push that through the water--then do it with a rubber duck and see which one is goes farther, is easier to push etc..its a well known fact a submarine hull has less friction -less wave resistance, less windage -blah blah, .....a car can if geared right with a small engine go 4 mph and get 200 mpg's! now thats efficiency..they used to have 120 mpg cars that ran off small diesels..at the direct cost of speed and as you say- brute strength. you cannot tow or climb hills very well..

as soon as you want to add speed--anything becomes LESS efficient.. of course a car is more efficient, there is much less factors. the density of water and the density of air..are two..
the mass of a car..vs the mass of a boat.etc. brute strength will not succeed over good technique anyday. and the same goes with vehicles.. the military can use those high hp's because they have nuclear power.

 

exactly!! this was why i was mentioning one hull--let alone two..submerged, would be very difficult to achieve.
--i agree completely on this post- the stresses would be so great the reinforcement on the cross beams would need to be overbuilt compared to a light tri or mono.
this probably adds much more weight and windage and by the time you do all that- your connection system, which will be lowered by the hulls, end up hitting oncoming waves, or following waves, and waves any higher than 2 ft smashing against those cross arms or connections to each hull, constantly nullifying any gain in efficiency...also consider this: when the hull is under sail --the bouyancy of the sub hulls which would be almost neutral, would be forced down by the sail because there is no righting moment- it is lost due to the almost weightlessness of the hulls. forcing those hulls deep under water..what will keep those hulls from wanting to submerge further?/?

they must be only slightly positive or neutrally bouyant!!? easily forced down even by walking on it if neutral. this requires a complex balancing act to get the weight and the hull in perfect balance--of course then it means you cannot carry cargo or gear because you will affect the bouyancy of the hulls- now you are limited too by what you can carry aboard the vessel..and you cannot use the provisions as ballast- -when you get low on provisions you will raise the waterline of the sub causing it to lose its balance again negating the effcient that was sought in the first place-even a few liters of water would change the way the hull sits in the water...its a sad cycle...

then -think too of the ballast needed to have those hulls submerged--most people have no idea the amount of wieght it takes to sink a given volume- and i can personally assure you- there will be little living space in those hulls...and you wont be able to have a deckhouse...
oh and dont get grounded either--you wont ever get off unless you have a ballast release system.


also rememebr the effect of a keel ? this is now negated.
there is nothing to help those hulls gain speed. a kite might help. it pulls differently than a sail.

now especially for civil subs--one of the reasons i let go of my sub build was it needed a tender vessel in port. now try using sails and rudders on two submerged hulls- have you ever swamped a canoe and tried to push it sideways?(sadly i learned this the hard way!)
--envision this: when you are sailing, trying to tack with two large hulls submerged!- now, the density of the water actually works against you! as the force vectors acting during a tack start to counter your motion. it even might be dangerous...especially in a traffic area where there are many boats...and you cannot turn fast enough to avoid some idiot approaching you when you have the "R.O.W."
and then there are currents..you are really going to be affected by currents of any speed.
- because- they will affect your hulls more than a surface vessel(one thing that a surface vessel has a slight advantage, is in currents -although subs can use the to drift dive so maybe this isnt applicable?)


neat idea -and im utterly radical when it comes to this stuff- ask anyone here- but believe me- even i wouldnt venture down this road...great idea in concept- not in practicality...

 

No, the crossbeams wouldn't be overbuilt...

The hulls would be SMALLER and LIGHTER. We wouldn't be using weighted hulls or something...we'd be using regular wave piercing hulls with several feet of height lopped off...the part of the hull that never goes in the water.

Not only would the hulls be Lighter, but we'd no longer have the stress of pitching in waves and the stress of the added wave resistance....So our crossbeam structure, if anything, could be built lighter, not heavier.

I don't know where you're getting the idea of heavy sunken hulls and overbuilt structure from.

 

me either...if it works-- go for it... happy sailing. if you get it up and running --id like to learn more about it..

cheers!

 

Leo, wouldn't SWATH with skinny supports have near same wetted area

like if the hulls were torpedoes with only razor thin 'pillars' front and back, or maybe just in middle, or just in the front and have upper bridge-deck ride on air cushion at speed, because it would be same displacement as two semi-circles (and mostly eliminate bow wave and keep wetted surface constant).


I thought the problem with SWATH was trimming them, or that to be able to trim you needed excess volume and THAT increased wetted surface.

So I was thinking of SWATH/foil hybrid, where in resting mode it would settle down and rely on some of the bridge-deck sitting in the water, but once at speed the foils would be used to trim it up to SWATH height.