[PSUBS-MAILIST] Bouyancy

[via Personal_Submersibles]

Scott, Alec, Vance, and all,
 
A 3/4" vent is going to be about 2.25 times as big in cross  section as the 
1/2" vent.  A 1" vent would be about 4 times as big as the  1/2". What are 
your thoughts/comments on 3/4", 1" or any other  size vent vs another?
 
Thanks,
Jim  
 
 
In a message dated 6/11/2014 5:45:10 P.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

James,
I totally agree with you on the 1/2 inch vents being way to small.  
Eventually I am going to switch mine out to 3/4"
Thanks,
Scott Waters









Sent from my U.S. Cellular©  Smartphone


James Frankland via Personal_Submersibles  
<personal_submersibles at psubs.org> wrote:
Hi All,
 
A member has asked me to post a description of what was going on with  
bouyancy on my dive.  Which was as follows:
 
I'd asked the crane driver to be prepared for the first dive to hold me  
just below the surface as i was expecting to be a little out of control.   

At first, i got a bubble stuck in the forward tank.  Ive put quite a  large 
lip on the inside of the tanks in an attempt to cope with Guernsey  seas.  
I could see the bubble stuck through the forward dome and i  squished myself 
right up into the front to try and force it a bit more  level so it could 
escape out of the vent.  It didnt make any difference  and then all the lead 
i had inside, slid along the deck right to the back,  making the entire 
situation worse.  Closed vents, blew mains and  re-surfaced.
 
Next attempt, i got the bubble stuck in the aft tank.  This wasnt as  bad 
because the motor cut away allows air to escape so i got under a little  
further, but not enough.  I flooded the variable in an attempt to get  under.  
Still no good, so i asked the divers to shove on the back.   This got the 
boat under, but then because of the total lack of air in any  tanks, i sank to 
the bottom like a stone.  Depth was 6m (20ft).  I  expected to stop on the 
crane ropes, but the driver must have misunderstood me  and before i knew it, 
the bottom was in sight and then i was down with a  gentle bump.  
 
I sat for a bit talking to my brother on the radio and then shut the  
variable vent and pumped a little air into the tank.  I slowely started  to rise. 
 Flooded it again and started to sink.  Really quite  straight forward.  
 
Blowing the VBT completely brought me up fairly quickly until i seemed to  
be just awash with the surface.  Filling the mains then brought me right  
out.  
 
I did several more test dives after that and as long as i evened out the  
venting of the main tanks to avoid the bubbles, i could dive without the  
divers assistance.  
 
I next got the boat neutral just off the bottom and then used the motors  
to drive up and down. I was not aware at the time that one motor was not  
working but it still seemed quite responsive and i could drive all the way up  
to the top or down to the bottom, stopping anywhere in between.
 
I need to add some extra vents to the main tanks to prevent the air  pocket 
from occuring again, and also those half inch vents are far too  small.  It 
takes forever to vent the main tanks.  Thats one for a  winter modification.
 
I think that was it.
Regards
James
 
 


_______________________________________________
Personal_Submersibles  mailing  list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20140611/cea0133b/attachment.html>