Re: [PSUBS-MAILIST] RE: payload

["Brian Cox" <ojaivalleybeefarm@dslextreme.com>]

Water would be heavyer

Brian

----- Original Message ----- 
From: "Andy Jensen" <drewacard@charter.net>
To: <personal_submersibles@psubs.org>
Cc: <ShellyDalg@aol.com>
Sent: Tuesday, December 05, 2006 07:37
Subject: Re: [PSUBS-MAILIST] RE: payload


> I was thinking about using an oil kept in side the sub and pumping it into an expandable bladder out side the sub using either an electric or hand hydraulic pump.
> 
> one through hull and one valve. A truck inner tube in a small thin tank open tank.
> using water to force the oil back in.  Most hydraulic connections are rated at 3000PSI working pressure should give me plenty of over head for 600'.
> 
> It seems to simple so what am I missing?
> 
> Andy J.
> 
> 
> 
> ---- ShellyDalg@aol.com wrote: 
> Kory. I have always thought trim tanks were to adjust trim, not compensate  
> for varying loads.
> Water density changes with temperature and salinity, but not very much. It  
> is possible to run into a salty current or water layer and trim can be added or 
>  reduced to compensate.
> Sometimes subs have forward and aft trim tanks to change the angle of the  
> sub while still maintaining neutral buoyancy.
> Adding lead ballast before a dive, depending on load, is easier than having  
> a separate, large system with associated piping and tanks which  requires 
> maintenance, cost, and monitoring.
> With a few dives, you know how much added weight your sub needs to  reach 
> neutral, and then you adjust with weights from there for added  passengers, 
> cargo, new equipment, or whatever.
> Trim tanks need to be at one atmosphere, whether full or empty.
> Ballast tanks are ambient. 
> If your trim tank is half full and open to the sea, ( like a ballast tank  ) 
> the air will compress when you get deeper, and you'll start sinking  fast.
> Large, one atmosphere tanks for trim will require heavy walled tanks, fill  
> valves, drain valves, pressure monitoring, and take up room and add weight  
> because they're thick steel.
> And you have to flush them out after every dive so they don't  corrode.
> Better to have small tanks for trim and carry some lead.
> Just my opinion....Frank D.
> 
> 
> 
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