Re: Materials/parts...

[shawl@torchlake.com (Jonathan Shawl)]

Thanks for the extra input Phil, it is good advice.
I forgot to mention, my hatch tower is reinforced on the inside. It makes for
cleaner lines on the outside.
Also I am not saying my sub is the best way to do it. I would change many
things if I started over, and I might.
I have a 500 gallon tank that is almost a sphere the straight part is about 12"
long but it is about  5' dia. It would be much roomier than a 36" dia 10' long
tube.
Jon Shawl


>........ Propane tanks are excellent starting points and  they are
>very cheap because of high volume. Since the thickness vs the dia  is
>typically such that the tank will have to be ring stiffened ( the internal
>pressure inflates the tank so that the failure mode is material yield .
>.whereas external pressure causes failure at a much lower pressure through
>assymetric buckling) you can get in through the hatch cut- out and weld the
>rings inside in two or more pieces. You should use a doubler plate over the
>hatch to hull area 'cause the stress is unacceptably high in the right
>angle joint - a way around that is to use a T stiffener externally,
>perpendicular to the weld - this isn't too often done because not many know
>that it can be! Hope this helps!
>Regards
>Phil Nuytten