Re: Weight of subs.

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

Hi Sean,

> I was just working out some equations and discovered that my sub needs to be  > unusually heavy to be nuetrally bouyant.

You do need to calculate weight as close as you can during the design stages.
Keep in mind that not all the weight is added ballast. Some of your weight is
the hull, structure, ribs, motors, batteries.... There is a lot of details
involved in calculating weight. 

Measureing weight is an easier way to determine weight. During construction
you can weight the pieces as long as you do the weighing before the chunks get
to large or heavy. 

Or once built pull your sub on trailer to a truck scale. Once with empty
trailer then with sub on trailer.

Caculating bouyancy is even worse. Every structure that is imersed in water
displaces water which reduces its apparent weight in water. So your dive
plane may weigh 10 pounds in air but 9 pounds underwater. 

In any case it is much better to err your design to the more bouyant side.
That way you can add ballast in the form of weight.

> 18096 lbs or 9 tons. This seems VERY heavy to me!

Depends on the size of the sub At 18096 pounds you get 283 cubic feet of
space if you use the rough 64 pounds/cubic foot. Which fits into a cylinder 
of (roughly):

Length	Diameter
22ft    4ft
14ft	5ft
10ft	6ft
7.4ft   7ft
5.63ft	8ft
4.5ft   9ft
3.6ft	10ft

You have demonstrated one of the disadvantages of a sub having a large 
interior air space, weight. Either you keep it in water, build a large
trailer, or scale it down.

Regards,
Ray