Re: [PSUBS-MAILIST] Ballast

[Carsten Standfuss <Merlinsub@t-online.de>]

What is the difference between soft and hard ballast?

I?m planning to use only sealed ballast tanks (valves at top and bottom)
to help maintain neutral buoyancy at varying depths.  I have assumed
that soft ballast
would be an open bottom ballast tank that would allow buoyancy to change
with depth, but have talked myself into the possiblity that hard ballast
might
actually refer to hard weight (trim, drop).  Also, the term variable
ballast would mean any ballast tank that air could be added to or
subtracted from, right?

Thaks,

Cliff

Hi Cliff

If the free surface of a tank get to big because the tank get to big the
boat get pretty unstable and dive and drive like a dolphin. For this
reason since about 1900 the bigger boats use bigger softtank to get
freeboard. About 10-30% of the displacemnet of the boat. This tanks can
be have vales only on the top (US-style) or vales on top and bottom
(Russian-style) but the are not pressure tight  - and allways full of
air -on the surface or complete filled with water (dived). To bouancy
the boat it is useful to have small hard tanks about 3-5% of the
displacement of the boat (with a small watersurfacearea) - means
pressure tight tanks which can contains between 0-100 % of volume of
water even under oustside pressure. 

Sgt.Peppers has only softtanks and the neutral bouancy was hard to fix
with lead bars - needs 3-4 test dives before one real dive. Now the boat
gets an additional hard tank to make it perfect neutral. 

Euronaut has two softtanks of 5000 liter each on both ends, additional
two hardtanks of 700 Liter at both ends. And a moveable 0,5 t
hard-weight on a 2 meter long track. And two 500 liters diesel
trimmtanks on both ends. 

Smaller boaths of K-style for two or one person have about two soft
tanks at the bow and stern and one hard tank in the center.  

All boats before 1900 with only big hardtanks were pretty unstable. 

best regards Carsten




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