ferro-cement submarine versus conventional concrete

tugboat
Better thinking about it, the form would probably be better of standing upright (the way it's in the finished boat). That way you can walk thru the mold and access it from all sides. The mold itself would be any cheap plywood. Adding removable panels on the mold would be a good idea to ensure a good filling. Also you can drill holes up to an inch diameter that allow air out, but not much concrete.

I think you could reduce the amount of moulds by 3 or 4, if you desing the structure symmetrical both sides of the longitudal centerline. Only the bow and stern caps and probably the second piece from the stern would have to be unique.

Ask a competing offer for transporting about eight 2 meters long and 2,4 (8ft) dia segments, should be a fraction of the cost of half the hull.

I think I'll do a quick sketch of my idea so we're on the same page of things.

Lurvio

 

Great Lurvio--thanks...ill get you the sketches too...and the drawings of how i plan to make the frames etc..but maybe your idea is easier...

be back soon

Doug

 

There's a lot of mis-inormation here ( every statement imparts misinformarion really ) that suggests you should seek some good professional advice.

The military don't use titanium except for special uses,
Steel boats don't fall apart ( and you say you have seen this )
Ferro cement has the weakest shear strength of anything other than cross grain wood and is nearly always always holed by moderate side impact

And for the prize to suggest a sub is not going to be more stressed than a surface vessel

You are also jumping to grand fallacies about conrete, the fatigue strength is low for high stress situations. All the examples you quote are effectively static loads with small variations. This is considerably different to large stress ranges.
Unless you run some very detailed FEA models you are going to have a massive heavy structure to get enough FOSafety to cover your unkowns.

Steel would be a much better material.

How many conrcete high pressure tanks have you seen? Despite all the advantages of ease of construction, low maintenance etc, ask yourself why.

 

LyndonJ
The high pressure concrete tank (or lack of) is because that needs high tensile strenght, which concrete doesn't have. In a sub the pressure is compressional, in which concrete is good.

Otherwise I agree to your post, to a point. And a good construction engineer with a lot of experience on concrete has to be consulted to make the needed calculations on the structure and loads.

Lurvio

 

Yes but if it's just a matter of 'dropping in rebar' then even hoop stress is compressive on the inside and the rebar carries the tensile. It could be done, it would be heavy and eventually I suspect it would start leaking apart on the 300th refill.

Just wanted to get some thinking going on any other basis than heresay urban myth and fantasy.

 

half hull vrs round c-pipe sections

LyndonJ -
I shall first make a comment on the high pressure tanks,in that the hoop stress may appear so, but it is not compressive on the inside of the rebar, as you might hope it to be.


I should first say that I am not a sub designer, but have studied engineering at university.


tugboat -
I would like to comment on the half hull as compared to round c-pipe sections.
The round c-pipe sections are excellent integral compressive hull sections.
Two half hulls put together, would have much higher compressive loads around the seams then you would expect.
You are thinking that you can reinforce your seams to be as strong as an integral round section, and that will be much more difficult then it looks.
You would probably need load bearing beams going through the center of your walking space in the hulls from where the seams are joined together, to the other side.


You do not have an integrated uniform hull section to distribute the load properly, as compared to a round c-pipe sections.
If you sink your test sub deep enough, I would expect that is what will cause the first breakdowns.
Hopefully your test sub with no one in it, will show this.


I should add here that the half hull method should work, but it is the matter of the working depth wanted.
I expect that you get much deeper operating depth with the round c-pipe sections, and you want to be very sure what your safe depth for a half hull construction is.


I would like to hear other people's views on this specific area.

Gilbert.

 

Yes, a very poignent consoderation.

Just a t hought, if you can build at the edge of the water, the Japanese launch huge ships rolling them on chopped piano wire,

 

Well the 'dropping on rebar' in this case would be a pre-welded rebar cage.

As stated before, I'm no engineer but I have a pretty good idea how the stresses go in structures. And I have to agree with DocScience on this one.

tugboat
A qualified structural (concrete) engineer can pretty much tell you without a calculator, what wall thicknesses you need and how to place the rebar. Just tell him/her (damn english) the measures of the boat and how deep you want to get. Add to that a safety factor of at least 6x and you'll be on the ball park.

Lurvio

 

Hmmmm

There's a lot of circular concrete structures in hydro infrastructure under pressure, but that's not really the point I was trying to get across.

It's the cyclic loads, the long term effects of direct crack and micro fatigue cracking in the matrix and their effect I was suggesting, perhaps not directly enough.

 

Hi LyndonJ-i believe the military doers not use standard steel i do know titanium is used-anmd i heard or read somewhere its used for the hull sections.perhaps not all the hull but for parts of it...??- but i also know they dont use cheap standard steel for the hull either- it actuallyis kept secret and i suspect its very special..this actually does not support my argument for concrete--i am not aiming for a deep diving submarine. 60-100ft is about my max. it is positivley bouyant (slightly) at all times.

there will only be one stress submerged as a rule- compressive-
what i meant to imnpart was- more varieties of stress on the surface as opposed to basic compressive stresses
i think yours is a matter of opinion about misinformation--may i submit to you--how much research have you done on fc vessels?
they have 19000-21000 psi impact resistance.there are some great books on the material..they tend to absorb the stress over a greater area and i think your misinformed about the tolerance to holes. Check out the u.s. navy guide to ferro-cement boatbuilding volume 2.

bottom line for me--i just know it will work..i dont care about math or forces etc-except to what i am able to substantiate through practical application...-

what works to find out is real life trials. can be huge diff between theoretical engineering and practical..btw i didnt say I have SEEN boats break apart only that I know of them --the edmund fitzgerald being one--and its my contention that it was metal fatigue and the weight of the ore--i have worked on vessels as a decklhand and no way did that boat go down cuz of mis-dogged hatches.
concrete pressure vessels -its only my opinion but i think people go with whats conventional..people arwe afraid to try new things -so concrete pressure vessels could work if designed properly...they use water tanks in FC thats a lot of force acting on the sides of 25 000 gallon atnk...maybe not as much as a propane tank etc but its viable..but thats my opinion..i have stated all this is merely my perception...if you think im misinformed..so be it...guess ill have to see what happens if/when i build...

 

Thanks Gilbert
the test sub is a model not sure of the sclae but i think its 1" to 1 ft i can go measure it but im too lazy right now..but when i made the plug for a mold-i think i made an easy scale...ill use a thinner wall to to compensate for the scale and for a safety factor...but ultimately
there is only one way to find out--and thats to sink one..we shall see...

 

Lurvio--one way (to figure out operational depth) i thought of doing this was to take 1 inch steel in comparison to concrete at X thickness and use youngs modulus of elasticity solve for X...this should give me the required thickness in relation to the strength of steel at the same depths.

the engineers on here should know this is equation perhaps they know others that would work?

btw sorry for my typing errors- not at the usual computer today...

 

A model is always a good idea, but for pressure testing it has some problems. You have to scale down every component in the material, sand/gravel particle size and the steels parts at least. Your succesting 1:12 scale, I'd personally build something like 1:5 scale for seeing what it really looks and 1:2 scale for load testing. You dont have to make the test piece a complete hull, a section with suitable caps will do just fine.

Lurvio

 

You can go to Oconomowoc and look at a WWII submarine in detail. They give a great tour some old timers that served on them. It will open your eyes to the complexity of the systems.

 

hi Gonzo- thanks-ill definitely go check out the site...cool


even Carsten Standfuss's(see the euronaut) sub is incredibly complex for a civil sub.for the older ww11 and newer nuke classes they have to be complex!! remember i am one person--it has to be designed so I can manage the sub alone- kittridge subs are not too bad..even they-inMHO- are overly complex.... the subs you mentioned -you have to remember those are military systems not civil ones...this is what usually throws poeple off-

at least in theory, civil systems can be extremely simple and cost effective--no torpedos, electronics-actuators, phase converters, compressors, sonar dive chambers etc etc ad infintum-
i have spent two years finding simple effective and cost effective solutions to complex problems while keeping the systems simple...Ask me how ive solved any system id be happy to tell you -if i didnt think it was necessary i didn't add it in..for me its about preferences...personal preference

a simple designed civil sub needs(not including all the details on how to set them up build them etc etc):

1. a pressure hull
2. an engine/drive train/diesel tanks
3.an electric engine/batts/charger
4. a prop
5. an air snorkel intake(and even that isnt truly necessary if you just minimalize(not totally avoid) those situation where the weather is so rough you cannot open a hatch for air.
6. an exhaust
7. (for mine)- pumps- high volume
8. dive planes
9. a hatch
10 view ports
11. plumbing for basics
12, lights- bitts- nav system(in my case visuals as in a small watercraft)- and a strobe
13 solid ballast/and soft ballast tanks.
14-cheap effective seals
15-an emergency ballast release system(a weight drop system is very easily done)!!

i dont plan on using a static dive system- you can eliminate about 50% of the complexity by dynamic diving. this i have tested over and over on models.

there are a few more basics but thats about it...

some on here are going to disagree with my methods...no probs...like i say---the final say will be the finished vessel should it get built...
disagree and argue all you want folks-- engineers-submariners and experienced builders cannot even agree on many things!! there are no right or wrong --only - what works!!.

Lurvio--the scale shouldnt matter--its still a 1 atm chamber- at whatever hull thickness with an empty space inside- either it will fail or it won't at any specific thickness and depth...hence, why even build it to any particular scale since you still cant know till the full size one is built....i understand what your saying--and appreciate your input--for me it seems like a lot of expense??? i am still going to do my drop test but
ill research it a bit more just to make sure im am correct about the scaling etc...
thanks!