Re: [PSUBS-MAILIST] In my search for a simple, cheap pressure hull ...

[AndrePevestorf@aol.com]

Hi Folks,

Some remarks about fiberglass an low cost pressure hulls..
Iīve just finished looking through some books about composites and want to reflect what I found...
+   composites (fiberglass / epoxi) is a really nice high-tech material. (I have worked with this stuff too..)
+   You are able to build structures with a relativ hight stiffeness by a relativ low wight
+   composite constructions have a better fatigue behavior
+   by knowing the exactly forceflow itīs possible to create constructions with a very high level of material utilization 
+   with composites ist not a problem to form complex shapes 

BUT:

-   to use the capabilitys of composites ist neceessary to fullfill a lot of requirements...everything is important! Storing conditions, humidity, temperature,...the color of the shirt youīre wearing.... J
-   everything is relativ... and a good ratio from stiffness to wight is important if you want to build a bridge or so but SUBs is definitly not really stressed by there own wight... to optain a sufficient strong pressure hull only the absolut stiffness is important...and that means coalfiber and a lot of money too...
-   normally SUBs doesnīt vibrate so much...except You run over 60kn ... J
-   are there somebody who knows the exact forceflow of his construction? Are You shure to lay the fibres in 90 degree direction or might it better to lay them in 45 degree or better unidirectional...???
-   the quest to resist the enormous water pressure is not a design competition...the answer is simple...the best is a hollowsphere. Next the cylinder. I guess this will be the next 1000 years so.... 

comparing the advantages and disadvantages I would come to the conclusion that fiberglass is not automatically the right way to low cost pressure hulls for PSUBs.

Our qualitymanager told me that it make no sence to use a technology if you have not enough control over the process. All advantages of the new technology will by canceled by the tribut to the randoms... itīs a little like driving a Porsche with 300 Horsepower at night, unknown area, offroad.....J maybe funny too.....

For everybody how want to use fiberglass I can give some data next days ... but believe me...itīs not so funny to calculate with orthotrope material behavior...and keep in mind that fiberglass has only a small reserve in way of yielding! So You have to use a higher safety factor than steel!  3 (someone named it here) is OK!

How to build a low cost PSUB ?

Reduce the cost means reducing the uncertainty. Sheet steel is easy to by and You can be sure that the strengh may be granted. Welding is uncertainly for all non profis. But everybody can drill a hole and turn a screw....I hope so... J

Using simple geometrie, granted steel, screws (or rivets) instad of welding means not generally a reducing of wight or time to build or so but it means a certain construction easy to calculate and you can reach the deep with fewer material because you dont need such a high safety factor. And this saves your money at least.

Simple is safe. And can be inexpensive too.

Hope You enjoy my “German-English”


--AP