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When you plan to build a pressure hull for external pressure, keep in mind that the failure depth depends most of all on the expected failure mode (buckling or non buckling).

When you build in concrete the material gives you the option to build sufficient thick walled that buckling as expected failure mode can be ruled out.

The technique you describe looks possible but sounds expensive as you are building 3 shells instead of one. (inner and outer shell to act as a form).

Keep also in mind that there are limits how deep and narrow the spaces where you cast the concrete in, can be (check concrete casting norms). If the spaces are too deep and narrow the concrete will tend to de-mix in the pour seperating the gravel in pockets.

Keep also in mind that a albacore shape has about 5 times less propulsion need than a surface vessel - this is why a whale swims below the water - not on the surface - in fact no animal swims long distances on the surface because of this difference in engergy efficiency.

Wil
concretesubmarine.com




Design of Offshore Concrete Structures / Construction of Marine and Offshore Structures, Third Edition / The Dock Manual: Designing/Building/Maintaining / Plasticity in Reinforced Concrete

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Basic Concrete Engineering for Builders with CDROM / Design of Concrete Structures / Strength Design for Reinforced - Concrete Hydraulic Structures Engineering Manual on CD / Design of Offshore Concrete Structures / Construction of Marine and Offshore Structures, Second Edition (Civil Engineering - Advisors) / The Dock Manual: Designing/Building/Maintaining / Theory and Design of Concrete Shells / Thin Shell Concrete Structures / design procedures of reinforced concrete shell structures (JGJT 22-98) / Understanding Structures / Concrete Planet: The Strange and Fascinating Story of the World's Most Common Man-made Material / Concrete Construction Manual (Construction Manuals (englisch)) / Large Wind Turbines: Design and Economics / Dynamics of Offshore Structures / Offshore Technology in Civil Engineering / Design of Offshore Concrete Structures / Concrete in the Marine Environment (Modern Concrete Technology)

-- Edited by admin on Thursday 15th of March 2012 09:53:49 PM

Hello doug,

picture a WW2 submarine running on surface somthing like this. The beauty of the "captain nemo float out" is most of all in cruising BELOW the storm in snorkel mode and leave the coffee cup on the table while all surface ships are shaken to the border of resitance.

Snorkel is not popular in military submarines because it is absolutly NOT stealthy, especially if you stick it out some 10m above surface - but for a civil sub the snorkel mode is just perfect to cruise in calm conditions and use the diesel just as a normal surface yacht would do.

Also to benefit from the much lower drag that exists below the surface (factor 5).

 

. . .

When you design your sub as a surface boat with dive capability you also need to keep in mind that you will need a handling and a engine capacity similar to a surface ship.

It is for good reasons why this kind of hullform was abandoned in modern submarines.

Mother nature and submarine engineers agree on whale shapes for good reasons.

Why give away the benefit of whale like snorkel mode cruising for going back to a abandoned historic u-boat concept?

 

 The idea that a submarine should run on the surface is only understandable in the context of early submarines that where built to fit into the context of a fleet and seen as warships in the context of a surface fleet. As soon as navies became more experienced in handling submarines - the submarine started to be "a thing apart" operating apart on its own. This influenced ultimatly in its desing transforming it from a "fleet operation animal" to a "fully aquatic animal" - so in a nushell if you do not plan to have crews in gala uniform presenting fleet parade on deck - just forget surface capability and WW1/2 designs.

 

. .

 

 

 

Dough,

The fact that a whale shaped hull dived at a depth of the hull diameter in snorkel mode will not track the waves like a surface ship does, is the beauty of the concept. This leaves the coffee cup on the table and keeps the crew seasikness free.

Please check:
How deep you need to go for submerged protection

I would recommend a 10m snorkel tube, a good steel tube will work just fine. Hose snorkel workes fine too (tested that with the prototype) but i prefer a rigid tube due to the high camara point and simplicity of handling.

Snorkeling in a sub is different from a diver - a diver must breath against the water pressure that is on the lungs - so the snorkel is limited to 30cm length.

A sub does not expand lungs against the water pressure - air flows trough the hose or tube and is not affected by the pressure, just by the friction on the tube walls - so you can snorkel much deeper than a diver could.

 

/

　

　something like this?

Dough,

I would not start with any military design. Skipyack is a design built for speed exceeding 40 knots - the type XXI is a double hull design built to resist underwater explosions used for u-boat hunting. - non of that fits the needs of a family crusing in the caribbean in a captain nemo boat.

My answer to the form question is in the fotos below. It is a autopropelled living space bubble with a living space equvalent of an 68 squaremeter apartment inside, that guarantees leave coffee cup on the table conditions in all sea states cruising at a speed of 8 knots in snorkel mode with the hull 4m submerged.

It is extremly stable at dive, can easyly hang on the snorkel, deep ballast center, high camara point on the snorkel top, a lot of natural sunlight inside due to uplooking viewports, full standing height everywhere in the boat.

Your approach may be a bit different - so best thing to go is ask yourself what you want to get and design it according to your needs - going completly away from what military sub designers do.

 

Videos of the 200 ton submarine yacht hull see here.

-- Edited by admin on Saturday 10th of September 2011 07:20:24 AM

You can run the submarine yacht as a snorkel boat - in this case you handle exactly the same navigation methods as a surface yacht. If you want to handle it as a submarine navigating below and near reefs you will need aditional navigation items like forward looking sonars that allow you getting a "picture" where the boat is and where the reef is. Keep in mind that visual orientation under water is limited to a few meters - even exceptional clear water as in the caribbean will not give you a visual of more than 20m this is very little to navigate at sight with a 20m boat. Somebody compared it to navigate a blimp in the fog in the mountains at sight. On the other hand in practice if you are drifting in the open sea with light in the viewports you will have a awful lot of sealife aproaching your viewports while hanging still.

I understand your concerns. Just consider that the male orca fin is as high as its body diameter  and it does not bring up a drag that would slow down the male orca below the female that lacks that fin.

Imagine a snorkel boat like a orca with a tube on top of the fin - the tube would stick out in the air so would have no drag at all. Only the 4m in contact with water would create drag (comparable with the fin) when in a streamlined fairing.

What concerns submerged navigation in shiping lanes - the only good advice is do not look for ways "how to do it" - just avoid shipping lanes like any other yacht,  handle such sea areas surfaced. Always keep in mind that a ship needs kilometers to stop due to inertia and has no way to change course while navigating a narrow channel- never plan to dive under it - iwould recommend to just stay out of the way like anyone else does.

For a good impression how rigid a snorkel is, check a flag mast  - also keep in mind that drag appears on the foot of the mast - not on top - while snorkeling. If you still not comfortable consider a forestag or a snorkel built like a airplane wing.

 

The hose snorkel worked very well when i tested it with the prototype. You might go for a detachable hose. At the end of the hose you need a buoy and a automatic close valve if the end goes under.

Keep the connection of the snorkel with the hull as strurdy as possible - (cast in) - and put a valve on the inside of the hull for easy valve off when snorkel takes damage .

The two snorkel design you see on the pictures allows a simple automatic ventilation sistem. The boat will tend to have the nose in the wind direction while hanging on a mooring so if you put a 90 degree knee and a funnel on the bow snorkel you force air down the snorkel into the hull leaving it trough the aft snorkel.

This kept the hull absolute condensation and moist free - much better than i have seen it on sailing yachts in the same climate and mooring conditions.

 

Wil--yes thats the guy--his langauge sounds like dutch to me?..but im guessing he must be local. The size of that hull is amazing..when its fitted out it will be beautiful.

 

I have a thoerneycroft 30 hp for my sub..its a 60 tonner i believe(the one in project status)

total immersed volume 1127 cubic feet. so that makes it a 60 tonner i bleieve? displacement about 69000lbs fresh water. concrete will be used to fill the entire rear portion and some of the bow section to bring it down. the rest will be open space ...

the 30 hp -i hope thats big enough or not too big..i chose this because it seemed about right if i needed a bit of emergency power up river ina current or such.

Its running here...

http://www.youtube.com/watch?v=VjUBwsdeR-k

-- Edited by u-boatdreams on Thursday 15th of September 2011 10:57:52 AM

I also want to note to others reading--that the first post for a pressure vessel was not a final decision

we might do it that way or--not...

concrete will be used but likely for ballast. I still acknowledge Wil for his contributions to my project and his influential and pioneering ideas...



a decision on the actual sub method will be made by end of two weeks from today--

i have a business partner and we are going to build it to see what can be done----not to "mass" produce subs(no worries there Wil- not competing with you at all) -but to see what interest there is and to sell one to leapfrog to a better one...I wont be doing concrete that i know of..either steel or FAL which is a ferrocement synthetic morter...different than using standard concrete forms--as in Wils methods.

my goals are to go to the arctic and great alkes -such as superior, and make voyages in it in order to prove what they can do...and to show off a little--yea a bit of ego there maybe-

since i cant wait to pull up in my sub at the boat shows....

-- Edited by u-boatdreams on Thursday 15th of September 2011 11:53:30 AM

Wil when using saddle tanks- there are issues as i am learning-

 1. where do the viewports go?

2. how does the saddle tank interface with the side of the pressure hull?

3. by what mechanism can you open the induction valves for the MBT's?(in ths case saddle tanks?)I was thinking a kingston valve--or t valve but this must reach through the pressure hull..?

fal has the advantage of also forming to complex surfaces like a uboat design..of course concrete is cheaper--so concrete could make the inner pressure hull surrounded by two 1/2 inch thick walls of fal.

 

 

FAL- yes its  expensive but less  than steel.- would make a good form --you can apply it in patches it sticks to itself so cold joints are no worry. Its about the same as fiberglass in costs  but stronger...and rigid. I would love to know the compression yield of it at 1 inch thickness...hmmm ill likely do a drop test with a small model and see how it goes...

So you suggest to have an emergency saddle tank blow out manouver - without compressed air - on the base of chemical generation of gas like in a car airbag.

http://www.lemurzone.com/airbag/inflate.htm

The car industry went away from compressed air due to the higher long term reliability of a chemical gas sistem. Maybe for a submarine it would be fine to have a smoother and less explosive (dangerous) way to generate the gas. (different chemicals)

Although such a sistem would share the downside of drop weights (use only once) it could be built with very little cost and risk of operation.

A gram of chemical can produce half a liter of gas - means 2 kilo of chemical can produce a ton of emergency buoyancy force.

dive planes are lift mechanisms that can fail in many ways, for example block in a collision, and they fail completly to create lift when the boat stops. Drop weights depend on release mechanisms that left allone in marine ambient during a decade probably will not work when you need them.

A scuba tank can explode with the force of a granade, if you ever saw such a event you would probably not think about the possibility to store such a tank in a way that makes his explosion non-lethal i would assume that a scuba tank explosion inside a sub hull is a sure kill for the complete crew. Scuba tanks need regular inspections to avoid such events, they are expensive, they have expensive valves to control the extreme pressure inside and a scuba tank only contains a gas volume the size of a telephone cell which creates 2 tons of buoyancy on the surface but only a few kilogram of lift in critical depths where you probably will need the emergency sistem most.

So if you relay on blow out sistems you need a LOT of gas to create lift at depth due to the compressibility of gas. This means you need several dozends of scuba tanks each of them with a tight inspection shedule each of them expensive, each of them a kill hazard. So a sistem based on scuba and compressed air is probably more hazard to safety than addition of safety.

Military subs use compressed air as they have such sistem on board anyhow to launch torpedos - so it is not a additional sistem that creates a additional hazard it is a second use for a sistem that is already on board anyhow for military reasons.

Engineering a chemical sistem can be as easy as filling Alka Selzer tablets into a glass bottle and put it into the saddle tank. As soon as the boat goes below a certain depth the bottle will crack water comes in contact with the tablets and produces a amount of gas compareable with a scuba tank. The sistem is simple, free of inspection, free of explosion risk, full automatic, cheap. And you can design it for lots of gas that still give a reasonable lift in considerable depth.

-- Edited by tornado on Saturday 24th of September 2011 06:23:16 AM

One other thing i wanted to mention- i have dabbled in steam engines and boilers- these days fire tube boilers are very safe--it is because they use blow off valves. the pressure in aboiler is much higher than a compressore tank. so it would be easy to set the blowoff vlave at say 200 psi...or evben 150 psi--that way it is sure not to explode. if you put two valves on the tank this is a almost a guarantee it is safe...fact: there have been no marine accidents in the steamyachting world for over 50 years now...no boilers exploding...that i am aware of...to me the tank is the way to go--of course scuba tanks are something like 3000 psi rating i think...they use very high pressure compressed air--i believe around 600 psi...probably not good then if it explodes--

also sadly thje other day i priced concrete prssure pipe- the costs were about 1800.00 u.s. per meter of 6 diameter tube...steel was less expensive at about 9500.00 compared to 15000.00 for the pressure pipe--wil--is concrete going to to not crack under the pressure? if not done like a prssure pipe??? ok i know your sub is 30 inches or somehting like that thick- but whats to keep it from a crack that can make its way through the hull???hairline cracks

 

- but pressure cracks?? don't they go right through the entire pipe?

-- Edited by u-boatdreams on Saturday 24th of September 2011 08:32:50 AM

Hey Wil- actually i wasnt thinking of using a steam plant for propulsion although the idea has crossed my mind- because the fuel: wood, could act  as ballast--but the space requirements are too much to hold  the large amount of fuel--

of course a smokestack is a bit of a problem because of the diameter needed and the extra drag created

and the heat generated from the boiler- up the smokestack would melt the rubber valve seal.

 

ill look at the salt concept you mentioned... i used steam boilers as an example;

 i was trying to inform people that pressure tanks, if safety valves are installed, are safe. and can be used for ballast blows.

 

 I thought if running  a compressor off the main shaft and as well a generator head too. this would give me electricity and also ballast blow in an emergency. for battery recharge--ill use windmill dc generators.- the  more rpms- the more charge power they create. they create a lot of voltage and current at low rpms about 500 produces about 24 volts.  so idling my 30 hp would give lots of charge power.

 

  I am quite happy not staying on the ocean  floor too long--i prefer short dives. im not claustrophobic but a 6 ft diameter tube is not my idea of a fun time..the uc3 nautilus is the same diameter. ill need lots of viewports to not feel couped up...but 6ft dia. is as large as i want to go....too costly-other wise-

 

 

presently my business partner and i are making negotiations for a 6 ft dia. x 40 ft(aprox 12.7 m.)long used propane tank. rated at 200 psi-of course this is a safety factor..and i bet itll go to 1000 psi at over 1/2 inch thick..its solid! cost less than 2500.00 euros. about 4700.00 u.s. or about 4500.00 cdn.should this pan out--this will become the pressure hull..ill reinfoce it..--i did look at concrete--im very fearful that it may crack under pressure...it wont buckle, but cracking -and cyclic loads my weaken it..the mold process is beyond my understanding in concrete....im not prepared to build a 90 tonner, so my goal is 67 ft x 6 ft diameter. max, i did think that ferro-cement would be a great alternaitve with impact resistance over 20 000 psi. and high compressive strength--again cracking the problem is:

i dont want to go down in the pressure hull, the hull cracks- and when water starts to come in fast under pressure- i lose very quickly the subs positive bouyancy of course this is where the mergency blow comes in--but if the water coming in is too fast--then its catastophic failure--the 1 atm is lost and i get the bends even if it does resurface..

how did you reinforce your walls wil?..i suppose that a layer of fiberglass and epoxy might solve cracking issues--but how then do you know there is a crack?

-- Edited by u-boatdreams on Saturday 24th of September 2011 12:23:21 PM

...presently my business partner and i are making negotiations for a 6 ft dia. x 40 ft(aprox 12.7 m.)long used propane tank. rated at 200 psi-of course this is a safety factor..and i bet itll go to 1000 psi at over 1/2 inch thick..its solid! cost less than 2500.00 euros. about 4700.00 u.s. or about 4500.00 cdn.should this pan out--this will become the pressure hull..ill reinfoce it..--i did look at concrete--im very fearful that it may crack under pressure...it wont buckle, but cracking -and cyclic loads my weaken it..the mold process is beyond my understanding in concrete....im not prepared to build a 90 tonner, so my goal is 67 ft x 6 ft diameter. max, i did think that ferro-cement would be a great alternaitve with impact resistance over 20 000 psi. and high compressive strength--again cracking the problem is:

i dont want to go down in the pressure hull, the hull cracks- and when water starts to come in fast under pressure- i lose very quickly the subs positive bouyancy of course this is where the mergency blow comes in--but if the water coming in is too fast--then its catastophic failure--the 1 atm is lost and i get the bends even if it does resurface..

how did you reinforce your walls wil?..i suppose that a layer of fiberglass and epoxy might solve cracking issues--but how then do you know there is a crack?

------------------------------------------------------------------------

Dough, you must be aware that the pressure rating for a propane tank is for inside pressure - its capability for taking compression force is almost cero - as it will fail in buckling mode.

What you should fear in compression load is the arch failure in buckling mode not cracks.

Cracks even if there is one filtering a bit of water on the surface will stop filtering under compression they will not lead to a early unexpected failure in a thickwalled (buckling free) concrete hull where the compression strength of the material and wallthickness versus hull diameter geometry are the important factors.

On the other hand in a thin walled hull that can not stand as an arch but fails in buckling mode - the failure point is almost arbitrary and unexpected early almost inpredictable.

Please keep in mind that before going to make design decisions that you have a clear picture what you should fear, what you should not fear, how compression load is different to inside pressure, and why pressure vessels must be completly different designed when taking inside or outside pressure.

A good way to understand how a propane tank will fail is to watch the following video - this is just 1bar ( =10m depth) pressure (video) - this is a failure by buckling ! from atmosphere perssure of a tank. You can avoid this only by a internal rib structure as military submarines have. Even so failure by buckling remains a serious problem. A thick walled concrete hull solves this elegant - it is thick enough to stand as an arch.

Wil

concretesubmarine.com

-- Edited by admin on Saturday 24th of September 2011 01:13:12 PM

-- Edited by admin on Saturday 24th of September 2011 01:16:40 PM

wil, can you send the video link please?

You have catastrophic buckling failure for a tank in 10m depth - and you have 1430m destruction depth for a concrete cylinder (see study below).

This paints the picture ...

---------------------------------------
Paper Number 3011-MS
Title OCEAN IMPLOSION TEST OF CONCRETE (SEACON) CYLINDRICAL STRUCTURE
Authors Roy S. Highberg and Harvey H. Haynes, Civil Engineering Laboratory
Source

Offshore Technology Conference, 2-5 May , Houston, Texas
Copyright 1977. Offshore Technology Conference
Language English
Preview ABSTRACT

An ocean implosion test was conducted on a pressure-resistant concrete cylindrical structure to obtain the depth at implosion. The structure was a reinforced concrete cylinder with hemispherical end caps, twenty feet (6.1 m) in overall length, ten feet (3.05 m) in outside diameter, and 9.5 inches (241 mm) in wall thickness. The structure was near-neutrally buoyant having a positive buoyancy of 12,000 pounds (5.4 Mg) for a hull displacement of 85,000 pounds (38.5 Mg). The implosion depth of the cylinder was 4700 feet (1430 m). A predicted implosion depth, using an empirical design equation based upon past test results, was 16 percent less than the actual implosion depth.

INTRODUCTION

A pressure-resistant, reinforced concrete hull was constructed in 1971 as part of a Seafloor Construction Experiment, SEACON I. The structure was placed on the seafloor at a depth of 600 feet (180 m) for 10 months. Figure 1 shows the SEACON I hull prior to its ocean emplacement. Since its retrieval in 1972, it has been located in the open air about 150 ft. (50 m) from the ocean. In the summer of 1976, the structure was returned to the ocean for an ultimate load test, that is, the structure was lowered into the ocean until implosion.

SPECIMEN DESCRIPTION

The cylindrical structure was assembled from three precast, reinforced concrete sections. The straight cylinder section, 10.1 feet (3080 mm) in outside diameter by 10 feet (3050 mm) in length by 9.5 inches (241 mm) in wall thickness, was fabricated by United Concrete Pipe Corporation. The concrete hemisphere end-closures, 10.1 feet (3080 mm) in outside diameter by 9.5 inches (241 mm) in wall thickness, were fabricated in-house. Tolerances on the sections conformed to concrete pipe standards of not to exceed to ±0.75 inch (19 mm) for the inside diameter or minus 0.5 inch (13 mm) for the wall thickness.

Steel reinforcement in the amount of 0.70% by area was used in both the axial and hoop direction. Reinforcing bars of 0.6 inch (15 mm) diameter were employed throughout the structure. A double circular reinforcement cage was fabricated for each precast section; the concrete cover on the outside and inside reinforcing cage was 1 inch (25 mm). For the cylinder section, hoop rebars had a spacing of 27.25 inches (692 nm) and 31.25 inches (794 mm) for the inside and outside cages respectively.

The hemispherical end-closures were bonded to the cylinder section with an epoxy adhesive, no other attachment besides the epoxy bond was employed (Figure 2). The gap between the mating surfaces of the hemisphere and the cylinder was less than 0.13 inch (3 mm) for 75% of the contact area. Prior to epoxy bonding, the concrete surfaces were prepared by sandblasting and washing with acetone.

Source: http://www.onepetro.org/mslib/servle...011-MS&soc=OTC

Wil--these sections would be a great way to build a sub--the thing that would be hard would be- how do you make all those sections watertight??

 

i am guessing you would use pipe installed into the mold to give holes to connect them...

is it possible to do a hull this way and make it watertight and one solid monolithic structure?

thanks Wil, i had planned to reinforce any steel pressure vessel i bought...the deal  may or may not go through--and my biz partner and i are going to look at concrete as an alternative. wanted to ask you what youi think of shotcrete???

 

 my idea of a splithull--seems to be the best way to go..but we will make three models if we don't get the 6 ft x 40 ft tank--the problem  is that the tank might not be 6 ft dia. so if not its a no go. the other way in steel is 5/16 th steel wrapped around 1/2 inch rings and then 1/4 inch stringers spaced 6 inches apart..this makes a strong matrix.

 

 but we will want to investigate-within one month-  three small scaled test models:

they  will be:

 

 65 inches long (1.8   meters?) and 6.5 inches wide all are scaled models

 

1. a pressure cylinder using concrete full thickness conventional at about 1 or 2 inches thick (scaled)

2. a ferro-cement cylinder with 4 layers of mesh and steel rebar. the full hull is 8 layers.

3.  fer-a lite cylinder made same as 2. but using FAL instead.. this might act the same as cement--

OH YEA! what is the best mix to use for high strength concrete? im guessing here but

 need at least 30 mpa ?  would i use  stone aggregates?..plastisizers? glass fibers? air entrainment?

 

in all cases they will be reinforced. but we will do a vacuum test on each to see what happens --or a drop test in a neaby lake--depth 600 ft or 100 fathoms. The split mold might work really well-- it is the whale shape--or teardrop shape..two halves are made--then joined. im guessing again here but 6-8 inches of concrete??? would be a good operating thickness for 200-300 ft?

let me know your thoughts on that?

 

 

-- Edited by u-boatdreams on Monday 26th of September 2011 06:20:50 AM

Hi wil- wow--once again you are right--i talked to an engineer today- i asked him about the steel pressure vessel and forces exerted externally- and then on a side note- i asked him about concrete as a pressure vessel...--he insisted that it makes a great pressure vessel because- it handles compressive forces exceptionally well-- he cited that thats why they use it for pillars and other structural uses. so the result of this is-forget steel-costly and complicated and i dont want to fear the buckling--(after i saw how easily it buckled in those vids--i didn't feel comfortable) so i am going to build the pressure hull out of concrete. in fact i calculated a 6 ft i.d. pipe to be 1700.00.0 cdn, using 40 mpa and 32 mpa was 10.00 less per cubic meter. the pressure vessel in steel was -for the same diameter-- $10,000 in 5/16th inch! about 8x's the price of concrete-

and now i am certain its stronger due to the fact  i have had it confirmed by engineers more than once.and yea -other strucures... I once did beleive a concrete vessel could be used--

 

and after today its how i will be building the pressure hull. now this does bring up other problems-

 

1. how to attach things to the hull-- how to attach thru hulls, etc, and attaching the exo-shell to the concrete pressure hull... will epoxy work to add the sail??..i.e. could i prefab a concrete or fc. sail and attach it to the pressure hull for entry using epoxy?? what about hatches????

 

what would you suggest as the mix ratio? and reinforcing? i dont have the concrete civil eng. handbook--could you provide a link? i thought if i followed the concrete scientific paper you sent me--made the hull to those parameters i.e. use the same ratio of reinforcemnts and concrete type etc..then it should be able to handle a 200 ft s.o.d.?? any help is appreciated here Wil-- you are right about concrete though--im now convinced. so if i understand correctly--concrete just compresses more and more under pressure making it elastic in a sense?

-- Edited by u-boatdreams on Monday 26th of September 2011 11:33:34 AM

-- Edited by u-boatdreams on Monday 26th of September 2011 06:04:03 PM

i get it now--this is why cold joints are not an issue--they compress into themselves under pressure....water cannot penetrate ...aha light bulb just went on...

One of the problems of thick concrete walls is EXACTLY the weight.  if the sub runs aground and you have a type of submarine that can raise itself up to 1/3 hull diameter, then this can release it from the grounding. if the subs weight from the hull is so inherently heavy-then if the sub get stranded on anything such as a reef, then its not going to dislodge easily--if the shell is lighter--say 1/4 the weight of neutral--then you at least can dislodge it...this is one of my big problems with thick walled subs..

 

as seen in scientific papers ferro-cement is very crack resistant and its compressive strength is huge--no buckling issues--yes its a little more costly to make--but then you just ballast the hull with two walls of concrete inside the hull. i.e the bow section and stern seciton would be filled  completely with cheap concrete mix and scrap steel for ballast. the tanks will be big enough to float the sub at her lines 1/3 of it being freeboard.

the other issue- as mentioned is that few cranes can lift heavy hull sections. there currently are-to my knowledge no trucks that can haul a 58 ft x 120 000 lb load. the hydraulic trailer maxes out at 50 000 lbs. these are serious issues in practicality.

 

of course you could make smaller sections--but you still have to have them moved and everytrip costs. plus there is an added technical challenge in assembling them.

 

 why dont i  just use fc. its proven--they use it for watertight tanks all the time. and there  was talk using them for pressure boilers in steam applications. i would prefer to build one hull install engine and hatches etc on land then -launch and add ballast as required.

-- Edited by u-boatdreams on Tuesday 27th of September 2011 11:17:31 AM

weight is only a problem if you plan a lighweight surface boat - in a submarine enough weight to overcome bouyancy is a reqired feature - not a problem.

I doubth that your "ran aground scenario" will work - according to my stranding tests i prefer a strong hull that works itself into the reef and refloat at high tide over a light hull that allows that the reef works itself into it.

The crack resistance of a material is a function of its elastic features - elastic is something you do not want - elastic is exaclty what the tank plating in the video above has and brings up the buckling.

Why would you make the walls thinn and light to invite buckling - and then have a structurally useless weight casted in front and stern - why not distribute the material into the wall where it is double useful - as ballast and as anti buckling measure.

I understand that weight can be a transport issue - and you have to create a viable compromise. Instead creating the hull according to your land transport capabilities, i would try to find a way to skip the land transport and heavy lifting need.

Reading List:

Basic Concrete Engineering for Builders with CDROM / Design of Concrete Structures / Strength Design for Reinforced - Concrete Hydraulic Structures Engineering Manual on CD / Design of Offshore Concrete Structures / Construction of Marine and Offshore Structures, Second Edition (Civil Engineering - Advisors) / The Dock Manual: Designing/Building/Maintaining / Theory and Design of Concrete Shells / Thin Shell Concrete Structures / design procedures of reinforced concrete shell structures (JGJT 22-98) / Understanding Structures / Concrete Planet: The Strange and Fascinating Story of the World's Most Common Man-made Material / Concrete Construction Manual (Construction Manuals (englisch)) / Large Wind Turbines: Design and Economics / Dynamics of Offshore Structures / Offshore Technology in Civil Engineering / Design of Offshore Concrete Structures / Concrete in the Marine Environment (Modern Concrete Technology)