[PSUBS-MAILIST] Re: sub question

[Ray Keefer <Ray.Keefer@Sun.COM>]

Hi Heath & Kev,

I assume we are talking about a one atmosphere sub. See below for my
comments.

> From: Heath & Kev <tampa.trio@verizon.net>
> To: <ray@psubs.org>
> Subject: sub question
> Date: Sat, 4 Jan 2003 14:31:52 -0500
> Content-Transfer-Encoding: 7bit
> X-Authentication-Info: Submitted using SMTP AUTH LOGIN at out006.verizon.net 
from [127.0.0.1] at Sat, 4 Jan 2003 13:31:52 -0600
> 
> i was just on your web site, and saw some really nice subs.
> but they all looked very heavy. my question is 
> could carbon fiber be used for the shell of a sub, with the proper steel
> suport's instead of an all steel shell...

While steel hulls might be heavier they are typically not heavy enough
to submerge their whole volume of displacement. They require
additional ballast to be added. While a carbon fiber hull might be
lighter then a steel hull you have the same problem with forcing the
hull under water and will have to add ballast. With the lighter
carbon fiber hull you will have to add even more ballast. The end
result is that to displace the same volume of water the combined
weight of the hull and ballast will be the same whether the hull is
steel or carbon fiber.

> i dont know that much about steel, or how to work with it

You can learn or have someone fabricate the pressure hull for you.

> but carbon fiber being so easy to mold and repair, and the fact that i 
> make carbon fiber parts for cars and racing gocarts it would be very 
> easy for me to make a shell..

For an ambient pressure sub I would say great. For an one atmosphere
sub I would say in theory you can use an alternate material for the hull. 
Here are some thoughts to consider:

1. How do you calculate the crush depth? Steel and other metals
   (alumimum and titanium) are well understood. Fiberglass? Not well
   understood. You will have to make several hulls and test till they
   crush to get a general feel as to where it will typically fail.
   
2. How do you control the layup process to make sure you have a homogeneously
   strong hull? No weak points? No stress points? How to you make sure
   the hull you are intending to use is as strong as the one you tested?
   Again you will have to  test hulls but the x number of hulls you 
   tested does not guarantee the x+1 hull is the same. You can get close
   if you tightly control the temperature, humidity, layup wrapping,
   the expoxy mix, and air pressure for each and every hull.
   
3. Use your carbon fiber skills to make MBT or external fairlings. Use 
   steel for the pressure hull.
   
4. Parts for cars and racing gocarts do not have to withstand external
   pressure (pounds per square inch). At 50 feet we are talking 21 psi. 
   Which doesn't sound like much. However for a hull 13 feet long 
   (156") and a diameter of 3 feet (36", a assumption since
   you didn't specify) you get the surface area (of a cylinder for a 
   quick and dirty calculation) of 19678.93 square inches or a total of
   413257.62 pounds of pressure.  Until you do the testing you 
   really don't know if the hull will have to be 3/8" thick, or 1/2", 
   or 7/8" thick. You also don't know how many ribs you will have to
   have or how strong or how thick. Until you try it and test it 
   you will not know for sure and to do it right you will have to
   build several hulls.


> this is my plan..
> i want to build a sub for 2 to 3 people, 10 to 13 feet long
> single file seating, with a max depth of 50 feet, man and battery power, and 
the proper safety equipment..
> do you think it can be done and do you think the coast guard will approve it
> 

Currently Coast Guard requirements are minimal unless your sub is for hire.
Then you get into certification issues which get very expensive real
fast. As far as I know the American Bureau of Shipping does not
certify hulls that are not metallic or acrylic (spherical or cylindrical). 
They might make an exception if you do an extensive amount of
imperical testing but you will have to check with them.

> thanks for your help.
> 
> 
> p.s i tried to post this message on the web site but it would not go through
> 

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Regards,
Ray