[PSUBS-MAILIST] Stability & Buoyancy

Sat Nov 30 16:16:06 EST 2013

Jon and all,

The A-boat sail was pirated directly from the Pisces mold and serves as a splash guard for emergency egress on the surface. The initial MBT design was for a wraparound set of tanks, which were expanded to the broad topped triple tank setup that is still on board today. Maybe that was an ABS requirement for larger tanks. I don't know. You can't see it, but the primary tanks are U-shaped on the bottom and mostly flat on top. They straddle the hull with a central vent each and stainless steel straps running from one side to the other and out the bottom openings to bolt to the pressure hull.

Perry designed their conning tower as a primary observation point for the pilot and built accordingly. With Aquarius, it was definitely secondary (used mostly around structure and while surfacing or on the surface, and often with creative invective as the ports are so damned small). Remember the old cameras? A compact one was the size of an Aladdin thermos, and the pan and tilt units were big and clunky and expensive. These days, small cameras can do a lot of that from-the-top kind of viewing.

The A-boat sail itself is screwed down to the deck and is completely free flooding, essentially open all the way around to the space under and between the MBTs under the outer skin. The open portion in back of the conning tower provides a route for the aft lift strap, which is why you usually see the lift rig sort of draped out of the sail and onto the deck forward. If you look carefully, you can see the pressure hull and a ring stiffener back there.

A side note is that the same sail drained through rubber scuppers on a Pisces. The idea was that you after you were on the surface, it would drain down enough to allow the crow to open the hatch in an emergency. A lap full of water was probably eminent if you had to do it, but you also probably wouldn't lose the sub.

I ran Leo for a season (Pisces with a big window) but never had the need to see if the scuppers were effective. That's a good thing. Eventually, we replaced the main hatch with a regular conning tower built by Hyco and did away with the sail entirely, which was an infinite improvement for the close observation work in bad conditions we often did in the Gulf of Mexico where we were operating.

These days, they have cameras and light systems that can see more than what the US Navy calls the Mark I Human Eyeball, but back then, I was all there was, and no matter what kind of equipment we had, I always wanted to SEE stuff for myself. Still do, come to that. If I wasn't so stubborn about it, I'd probably be running ROVs, which isn't any fun at all in comparison. Like our Dr. Phil says, ROVs are like phone sex. Okay in a pinch, but nothing like the real thing.

Vance

-----Original Message-----
From: Jon Wallace <jonw at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sat, Nov 30, 2013 11:18 am
Subject: Re: [PSUBS-MAILIST] Stability & Buoyancy

      Excellent point and great photo to illustrate it.  I notice that      the sail on Nutyco's Aquarius is completely vacant aft of the      hatch to quickly release trapped water and of course doubles to      provide easy access for entry.  Also the deck/ballast is high (at      the hatch thru-hull) and very wide providing excellent stability.

      On 11/30/2013 5:51 AM, MerlinSub at t-online.de wrote:

                  Hi Alan, 

        additional the sub can dynamic unstable during surfacing.

        There is a lot of water in the free flooding open sail.
        If you surface fast and with to small opening in the 
        bottom of the free flooding sail the extra weight can 
        move the CG so high that the sub tends to get heavy 
        side angles during surfacing until the water rush out. 

        The picture 8382a shows the higher waterlevel during surfacing 
        in the sail and the MBT sadlle tanks still under water 
        but for this sub the extra weight was not critical.

        But on a military one with there tons of 
        water in the sail during a fast emergency surfacing 
        it can be a problem. 

        By the way Euronaut has no Kingston valve without any problem
        and a positve GB alltimes greater than 2". 
        On dive station or surfaced. 
        And great openings in the bottom of the sail. 

        Boats without Kingston valve tends to lost some 
        bouancy during rough sea. The tanks and the seastage
        work like a air pump and some water enter the tanks.

        On the otherside a boat with Kingston and a 
        compressed air blow out system can blow away the 
        tanks very fast if you forget to open the Kingstons 
        during blowing the tanks or have a air leak 
        in the in the pipe to the tanks.

        vbr Carsten  

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