ferro-cement submarine versus conventional concrete

Hull failure 45 meters(metres).

 

Now I'm even more concerned :!:

Impact resistance of 19kpsi ? That sounds like a full penetration shear failure, but in reality punch shear from a collision not directly on the rebar is little better than 1/2 inch-1inch of plaster. There was a thread on this recently and some good pictures posted of holes in ferro boats.

As for the just do-it to prove it approach : Tis is a SUBMERSIBLE sudden catastrophic failure = death.
How do you find in real life that your hull suddenly spalls and develops a small hole or not so small on the 100th dive ?

What will you factor of safety be?

Failure of brittle materials is catastrophic, yield of metals is not so a collision that smashes a hole in a brittle material boat will often just dent a metal boat.

Yeah I did my honours project in a very detailed FEA of spherical cavity reinforced concrete structures under load, particulalry looking at the steel matrix interaction and I think unless you have a perfect sphere you are going to get cracking even on the first dive and that's ok, but its what these cracks do over repeated cycles that is the concern.

Do you know that reinforced concrete cracks and that that is acceptable ?

Finally there's a big distinction between boats and ships, global stresses on ships have split them cross ways in cold weather becasue of poor notch toughness.

 

oh dear - sounds so simple on paper, but extrapolate that out, and you will see why the WWII subs are so complex.

lets just look at "8. dive planes"

These require thru-hulls for controls, and unless you have external motors operated by hydraulics, you have got the problematic concrete/steel movable shaft problem for a start. Thats a major engineering effort in a steel sub, let alone concrete. Lets say you solve it.

Ok, first voyage - underway, cruising on elecric motor. Now, half throttle, 7 degree bow plane - (using hand operated wheels lets say. The bow starts to submerge. Handraulicly (no automatic computer driven systems or other operators) you adjust your "soft ballast" (say electric pumps) to lose a bit of bouyancy - you over or under compensate, the sub rolls abit to port, you adjust the plane angles, adjust the bouyancy, this is while steering and managing prop rpm ....

When you visit that WWII sub, notice how there are specialist control positions - one person for trim and ballast, one for bow planes, one for steering and prop speed - and like all good movies with the Captain looking grave and saying "make it so" in his best Shaun Connery voice.

Everyone will tell you over and over, its not the major bits like hull and hatches, its all the "little" bits like efffective, efficient, complex control bits and pieces that determine safe (survivable) operation.

Time to expand that list by a factor of a 100.

Oh - have I mentioned insurance ???

 

hey guys--i know your intentions are that you just dont wanna see a nice guy(me) get killed- and i appreciate the concern...i sorta kinda know what im doing--well im learning a lot too but im aware of the risks...

lyndonj- this is great--ok first- since you are an engineer who has studied concrete--whats your opinion on doing a split mold aprox 4-6 inches thick but using highly reinforced concrete?..or the ferro-cement layering method? you have a lot of knowledge and obviously i could benefit from it..i would really like to know which of the two types of construction would be better -if you HAD to choose???
... as for punctures--hmmm i could find many more examples of wooden and steel boats punctures ripped open etc from collisions, reefs etc
steel is not impervious to rupture either... there is always risk...btw lyndonj, please send me a post with those fc pics i sure would like to see them--there is no material i know of impervious to being holed..and compared to steel especially older steel- concrete as you know gets stronger with age. but holing a four inch thick extra-reinforced concrete slab --thats gonna be hard dont you think?
a spall should not be a problem--spalls are usually just on the surface. a chip(spall) of the hull would not cause a leak especially at two atm-

the cyclic loads...well only time can tell..if i see weak points--it gets drydocked till i repair them--obviously i will have regular inspections..but steel cyclic loads are just as bad maybe worse than concrete- think of the steel coathanger effect.
concrete will be almost rigid. steel hulls hog and sag and it fatigues easily. many ships lost from that...i can find no examples of concrete ships lost due to structural failure...nada.

.. also i plan to epoxy and glass the hull to stop spalling...i dont see an issue there...at the surface you simply add a layer of surface repair topcoat concrete...done! you can repair cement underwater...

saftey factor
-if the hull can withsatnd 300 ft roughly, then i would only go to 100ft max and operational about 40-60 ft. about the same as on the uc3 which is a big influence in my design criteria,... i guess the factor would be 60/300 or or a factor of 80%. hope those figures are what your looking for...please explain notch toughness???

reinforced concrete does crack but rarely and only if the pour was not done right..and even then its easy to fix a crack...but ferro-cement rarely cracks...have you ever seen how it if fixed? quite easy...
steel has as many problems as concrete...
whenever i am walking downa sidewalk i look for spalls...they dont seem to me to be big trouble..but thats my opinion..

****rwatson- thanks for the input--i always enjoy your humour.

have you checked out the UC3 nautilus yet? go see it on youtube. quite a feat.
60 ft by 6 ft beam diveable to 300 meters -amateur built? by a man with a grade 8 education!
do you know how the "malen" a swedish sub was built??..i actually talked with the malens designer about dive planes...seals etc...i learned a lot from him...
or how about the 60 ft amateur sub "spurdog"?

here is where the fun begins--- yes--you have mentioned insurance many times- and we have discussed that but not with my project-
i have no need for insurance in my one-off sub-- i am not building commercially- there are no laws requiring that here for non commercial experimental subs cuz there arent any!....just as you dont need insurance to drive a runabout or a private yacht unless you want to insure it for sinking.
commercial vessels -yes- commercially built and sold -probably...

maybe in your area thats different but here---no insurance is needed in my country for a pleasure vessel except at certain marina's for property damage...but np--i am not going to keep it at a marina anyway.
now lets address your scenario-
dive planes--rwatson--i dont know your background--you seem wise in matters legal- perhaps you are a lawyer or paralegal or something in that area???(i swear that pic you have posted is a pic of jeff bridges playing fidel castro!!) but what do you know about seals? or o-rings? or high perfomance pressure seals?- dry seals. pressure seals?, oil seals, ambient seals?...if you know about them- problem solved. in a tube for instance using o-rings- once in the tube- water pressure expands the greased butylene rubber rings against the walls of the shaft tube for the dive planes..viola sealed.

for 150.00 i get two commercially made 3/4 inch i.d. high performance rotary seals good to 250 psi!! for my dive plane shaft...done! the dive plane mechanism is simple- a shaft connected to a worm gear. also cheap effective and simple as well as simply managed while underway and cheap. does not need computers, battery energy or actuators etc...no electronics means less chance of failures...and no diff between steel or concrete,..in c-subs the shaft is epoxied into the hull and blanks put in the hull during the casting for the shaft log- the shaft log tube is sealed with epoxy...no issue...
did i mention my sub will not be statically dived?..thus no pump water needs to be adjusted while underway submerged..the main pumps adjust that prior to the dive on the surface bringing it to easily controlled slightly positive bouyancy. of course everyday pressure washers at 1600 psi could easily deal with a static dive. again no issue...steering and prop rpm controls?...no different from a boat rolling and controlling that underway...in fact submerged running has almost no movement...almost...but not severe enough to cause your aforementioned issues--again no issue...
to address your concerns regarding the manned stations on a military sub--this is because it was and is necessary for emergency dives...
the earliest subs were not complex and they worked fine...they had hand cranks for propulsion!...midget subs used one or two people...the turtle had one man to operate a much more complex sub than mine...google it--see what he had to do...but he managed..he started to suffocate-true..(laugh) ..but he could handle static diving, trim,ballast, propulsion etc etc..all alone...again no issue..
ill stick to my list...
hatches are welded on to the rebar trusses before the pour--something called starter rods which would connect steel items such as bitts and hatches etc. but remember you can also simply put bolts into the concrete at the pour too..not very hard ... simple effective steel plates with internal dog systems will work fine...the water pressure keeps them sealed watertight.

Sean Connery's voice--" yesh- well rwatson--"
you make shum good pwoints "nothinggg i caaant handle"


rwatson..please tell me which method you prefer??.i would like to hear which one you think is best --dont worry about the details..let me worry about that..ok? i truly want to know how you would approach a concrete design...even though you may never...

 

look at this thread (just click on this ):
http://www.boatdesign.net/forums/boat-design/we-love-ferro-cement-but-beware-21436-4.html

see the pics in post 54

and unfortuantely some good input was removed from another memer who resigned.

Notice that the steel has only yielded and yet the hull is compromised due to the brittle failure of the plaster.

 

Tuggy, me ol' mate - the only way to do something like a sub is to do it proper like.

Look at the ads for commercially available submersables, they are everywhere on the internet. They work, you can earn a living with them. the planning and engineering is done, you dont have to pay an engineer to calculate the nth degree of pressure/performance/weight etc

Hey, maybe you can ask Welmer if he wants to sell one of his spare concrete hulls!

This is a fun discussion, but we both know that you are not going to pour two to three years of your life and say $250,000 + into a lump of concrete that may or may not work and you cannot insure against perils by sea and land.

Heck, just to get some kind of sensible engineering calculations and getting a design done, finding a place you can roll the behemoth into the water from that you can afford, and a million and one other issues - you have to be a rich man mate.

And, if you were a rich man - you wouldnt be fussed with the minor issue of the cost of the hull. Ferrocement hulls have been proven in use by conventional yachts - but what percentage are they in use ? 10%, 15% or much less. Hull expense is such a small part of the overall cost, and ferrocement isnt all that much cheaper than steel and fibreglass if you factor in the labour.

But hey, by all means keep up the research and the mental exercise. I suspect that floating concrete edifices will become common in the future, but whether they will ever be very submersable is a real hard question.

 

They are all submersible, but are they refloatable?

 

aha! elementary my dear watson!- the sum calculated to build would be 1/10th of your estimate to build or about 25 000 -even in steel...remember necessity is the mother of simplicity and cost effectiveness....

my guess is operational in less than five years building singlehandedly!! it would run to 60- 80 ft ft operational.

so it sounds to me like you have issued a challenge!! (wringing hands in glee)..
tell you what monsieur watson--if i go ahead and build this thing..say starting sometime between now and end of summer(here its approaching summer i guess i should say winter where you are)regardless of materials
what are you willing to risk as a gentlmans wager?-- i build it and it works for that sum- you pay insurance?? (laughing)

i am fairly certain i can build a working submarine for at or under 25 000 u.s
in steel or concrete...i already have the powerplant- prop, 900 gpm pump...the site--the capabilities to move it for 500.00 u.s.--im on my way...if i so choose--
i had recently thought about changing my design- using a ww2 design- only because it would run more on the surface and thats what the ww2 u-boats were designed for...anyway...im going to challenge you-- sit down with a graph paper pen and a calculator--and design one...why not??...its fun even if you never build...
you might find that you can do more than you may think in solving problems...insurance aside... let me know matey!

 

Oh no - they will blame me for your demise .... taking on a dare.

Before anything else, you had better define what it is you are aiming for

1) Minimum depth achieved with you on board
2) Number of dives with you on board
3) Maximum speed
4) Maximum range

$25,000 won't build you a decent surface boat of that length, let alone one that is supposed to submerge. I giggle violently at your proposal you crazy canadian.

 

Let him dream on folks................

he knows better anyway.

Just another example of a newbie coming here for confirmation of his preposition, not for advice, hints and assistance.

Do´nt waste your time mates.

Regards
Richard

 

Apex, you are right but it's good natured.

Sorry my opinion as an engineer that knows a little about concrete is that you should use steel for this application, not concrete or Al alloy or wood or polycarbonate or carbon fibre-epoxy Just high strength steel.

 

Steel makes good weapons.

Concrete makes good targets.

Submarines are mainly weapons. Use steel.

I am not speaking as an engineer but as an engineer's assistant.

 

Apex--tsk tsk you must be trying to start a war---does the word hypocrite mean anything to you???

Funny apex -since you know me so well-- and to you- not worthy of "wasting time on" as you put--funny thing is - you invested your time in answering (negatively) my post!

you just did the very thing you are telling others not to do--reply to my post!?.
so why bother???

(laughing) i don't care what goes in in your mind...offer something constructive..maybe ill consider your opinion...when you build 5 boats let me know...

 

I once saw a rectangular steel box that had been sinked to about 6 km depth. The box had about 40 cm sides and 10 cm thick walls. The walls had pressed inward more than 5 cm on all sides.

 

sorry to go off topic for my final post here- but maybe some will get this-

****Know that there are three types of people:

Inferior,Mediocre and Superior

The Inferior are said to be those
Who by any of the various means
Strive for their for own benefit
To Merely attain pleasures of our everyday mortal life

The Mediocre are said to be those
Who turn their back on life's pleasures
And also refrain from evil deeds,
Yet merely pursue a personal Peace

The Superior are said to be those
Who, through understanding their own suffering,
Deeply desire to completely end
The suffering of all beings

which one do you choose to be?


i've learned a lot from certain people on here- but mostly i've learned-- don't share your dreams with anyone. to try is the "real" waste of time --

btw -for the ones trying to discourage me -(god only knows why?)
-good luck to you..you'll need it more than me...
do you want to know why i will succeed and the mudslingers wont??--superior attitude!! its simple...

rwatson--you have opposed this- but it has been a healthy opposition- i respect that and Ill miss our debates...

lyndonj- thanks--i appreciate you offering some sound advice as well-

to lurvio- thanks...!

to the others-- well...we reap what we sow don't we?