Re: [PSUBS-MAILIST] VBT positioning

[MerlinSub@t-online.de (Carsten Standfuß)]

Hi Harry - welcome here.  

Harry Spillett schrieb:
> 
> Hello, I am new to the group so please excuses any errors in protocol I may
> make!
> 

Here is no protocol ..  just do not blame/flame somnebody.. 

> I live in Surrey England and have been doing my own research into
> submersibles and ROV's for some time. I have almost finished my first
> prototype ROV which I hope to get wet in the near future.
> 
> However in tandem with my ROV I am also sketching out preliminary designs
> for a single person submersible.
> 
> My question is:
> 
> I have noticed that on all most all existing designs I have seen the
> variable buoyancy tank is sited inside the pressure hull.
> Is this so that it does not have to withstand diving pressure? Ore is there
> another reason perhaps to do with the internal volume of the pressure hull.

Sgt.Peppers has one pressure tight (hard) regulator in the keel outside
the pressure hull under the center of bouancy . If the tank is inside it
is easier to build the vale and pipeing system. But in this small sub
was no space inside.
CSSX will have two hard regulator tanks outside - one in the bow, one in
the keel. 

The most reason for one regulator inside is that you can locate the tank
in the center of bouancy/gravity and it will not change your trim. 
That means on boats which are not  "to long" you can live with one 
regulator tank - instead two for trim purpose. 

TADPOLE for example has just one single tank for all purposes: 
Its in the middle axis of the two horizontal endcap hull as pressure
tight
regulator which is so big that it can also be use to make the freeboard. 
(In this sub the tank cylinder is also be used as structure part 
of the pressure hull himself.) 

If the tank inside is pressure tight or not depents on his construction. 
If the tank water is blowing out with compressed air against the 
outside water pressure it must be pressure tight. If you remove the
water
by a pump - only the pipeing forward the pump and the pump himself must
be pressure tight. In this case the tank can be for example a rubber
bag..

> 
> Following on from this, when the VBT is flooded is the air released vented
> into the pressure hull or to the sea.

Both is possible. The third solution : if you move the water in and out 
with a pump - let the air inside the tank - just a little compressed..
Save the air blow vale and pipeing. 

In general there are a lot of combinations of tanks possible : 

1.) One big hard regulator in the bouancy center (TADPOLE)
or
2.) One Soft tank in the bow , one in the stern, 
    hard regulator in the bouancy center (K-250) 
or.)
3.) One Soft tank starboard, one softtank portside,
    hard regulator in the bouancy center (SGT.PEPPERS)
or
4.)  One Soft tank in the bow , one in the stern, 
    one hard regulator in the bow and one in the stern
    so can be use for trim purpose. (CSSX)
or 
5.) One Soft tank in the bow , one in the stern, 
    one trim regulator in the bow and one in the stern, 
    one hard regulator near the center of bouancy (bigger boats)  
    
There are much more combinations. For the reason that with 
just one hard regulator you can not change the trim angle 
- some of the boats with just one regulator have 
longitudinal moveable trim weights - in Sgt.Peppers the Pilot
which can go about 2/3 foot forward or aft. In other boats 
the batteries or the drop weights or a seperate lead weight. 

Carsten

> 
> Once again I hope I have followed correct procedure and look forward to your
> thoughts. It is comforting to know there is a pool of like minded people I
> can turn to for advice rather than pull my hair out alone!
> 
> Regards
> 
> Harry Spillett