[PSUBS-MAILIST] Bouyancy

Wed Jun 11 22:31:04 EDT 2014

Agreed. Big valves on the tanks. Good plan.
Vance

-----Original Message-----
From: Dan H. via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wed, Jun 11, 2014 10:12 pm
Subject: Re: [PSUBS-MAILIST] Bouyancy

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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