[PSUBS-MAILIST] Bouyancy

Thu Jun 12 19:58:58 EDT 2014

Dan / Scott,
I'm a bit puzzled by this.
There wouldn't be water in the line initially unless the valve exit was facing upward & rain 
or wave splash entered it. Does water enter in as the sub bobbles about & the ballast
air exit dips below the water? I guess then the water in the line would be held in place
by the small air pressure in the ballast tank, which wouldn't be enough to force the water up & out, 
but is enough to hold it in position.
Alan

________________________________
 From: Dan H. via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Friday, June 13, 2014 3:03 AM
Subject: Re: [PSUBS-MAILIST] Bouyancy

Scott,  
To clear the lines, I screwed a T onto each of the 
through hulls that feed air to the MBTs.  (on the open end under the 
MBTs)  Then I fashioned a piece of copper tubing that directs a stream of 
air right into the MBT vent line but not actually connected to 
it.   I put a restriction in the other end of the T to create 
enough back pressure so the tubing emits a pretty good blast of air directed at 
the vent port.  

To vent the MBTs, I open the conning tower vent 
valves then give the tank blow valve a turn till I see the water blow up and out 
the vents.  That seems to clear the lines and then it vents 
properly. 
 It's not a great fix but it 
works.
----- Original Message ----- 
>From: swaters via  Personal_Submersibles 
>To: Personal Submersibles General  Discussion 
>Sent: Wednesday, June 11, 2014 10:37  PM
>Subject: Re: [PSUBS-MAILIST]  Bouyancy
>
>
>Dan,
>I have the exact same problem with hydrolocking in the vents. I have to  open the hatch and blow the water out with my mouth. Pain in the butt.
>Thanks,
>Scott Waters
>
>
>
>
>
>
>
>
>Sent from my U.S. Cellular©  Smartphone
>"Dan H. via Personal_Submersibles" <personal_submersibles at psubs.org>  wrote:
>
>If I were to do mine over again, I wouldn't vent it as it is in the  plans. Instead of running piping from the MBTs to the conning tower, I  would run linkage, and have the actual valves mounted on the MBT.  
> 
>Besides slow venting, my biggest problem is getting water in the piping  that won't escape to let the air come through when venting.  A homemade  mushroom valves made from bathroom sink drains controlled by linkage  going to the conning tower, or anywhere easy to reach in the hull, would solve  all the problems.  
> 
>My thought, Dan H.
>----- Original Message ----- 
>>From: via Personal_Submersibles 
>>To: personal_submersibles at psubs.org 
>>Sent: Wednesday, June 11, 2014 9:53  PM
>>Subject: Re: [PSUBS-MAILIST]  Bouyancy
>>
>>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
>>> 
>>> 
>>>
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