Use of concrete.

[Erik Michael Muller <emm03@uow.edu.au>]

Hi!, I too am new, and have had the thought of small subs in my head for a
long time, which i think is the best way to have it before you plunge
straight in!.

I have a question regarding the use of concrete in personal subs, and I 
notice that concrete subs were discussed a little before, so please forgive 
me if i am going over old ground.  
I would have thought that the excellent compressive strength of concrete
would have been an enormous advantage. Coupled with the kind of 'sealing'
that you might get from pouring concrete.
Because i havent bothered to find out the density of concrete and do the
sums, i am unaware how large a submarine is required to achive some kind of 
boyancy, my guess however is quite large.  Anyone fill me in on this?

I though also that concrete is significantly cheaper than steel/iron per
ton, and could significantly reduce cost??

Maybe i am all just too ignorant, in which case i apologise for wasting
peoples time! 
otherwise please set me straight or fill me in etc.

Thanks!
E.M.