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RE: [PSUBS-MAILIST] Double O-Ring On A Hatch

Frank,
 
It's great to feel your passion for getting your sub project underway after you went to the convention. 
 
With sub design I've found there is allot of trade offs when considering different designs like; strength, weight, performance, cost, available tools and skills needed, etc. I spend a fair bit of time thinking about ways to lower my CG to improve my metacentric height. I learned allot from the RV Needlefish project in this area. I hope he plans to lighten his hatch and conning tower and enlarges his saddle tanks so we can see the sub totally functional.
 
I was just thinking last night about whether I would use the cut-out dome from a conning tower collar cut-out on a 48" sphere pressure hull, for a sub I'm working on, for the hatch. I know it's not as domed as allot of hatches and end caps, but I've seen allot of hatches with just that sort of lightly domed hatch. It would be even stronger by the addition of the flange ring to it. This is the way Idabel's hatch was made.  On your sub, you have that same section that is not removed from the bottom head, that will be with-standing all the same basic pressures. Although you might have some supports I don't know about down there. Also the bottom area of your sub will need to be extra strong in case you hit the ocean floor to hard.  The Alicia sub and the Atlantis tourist sub I just posted pics of, also have a lightly domed hatch. Thickness, type of steel or other material used, and heat treating makes allot of difference of course.
 
I just noticed that Karls hatch flanges on the Idabel are conical down and into the sub with the O-ring in the top flange. This is a little like the Uboat Worx subs but in reverse. Also note that the flanges are very small and very light and he's gone down past 2000 FSW.  Chew on that. ; )'  
 
I would expect he gets a little wet from the water in the flange gap coming in on him every time he comes to the surface and opens the hatch. Although very little since the O-ring is towards the outside of the flange.
 
http://www.frappr.com/?a=viewphoto&id=4001713&pid=7567828
 
The Alicia sub had a much taller conning tower in it's conceptual drawings, then it ended up with in the end product. In the drawings it looks like they would get at least the 30" you are talking about from the surface of the water. But in the end, I don't think they got much more then 14" to 16" and they are ABS certified. Here is a pic I just took of the Alicias hatch. Sorry but my digital screen capture is not working, so I did it the old way.
 
http://www.frappr.com/?a=viewphoto&id=4001713&pid=7567969
 
http://www.frappr.com/?a=viewphoto&id=4001713&pid=7567726
 
I also noticed a short part at the beginning of the NOVA show, with Paul Moorhouse working on the 2D CAD drawings of Alicia, showing the hatch at the same level as the main deck of the sub, but my pics of it came out to grainy.
 
Do you or anyone else have more pics of the various Atlantis tourist sub's hatches. I didn't get any good pics of the top area of the hatches, since they were open and hidden from my view when I was on board the sub, and my digital camera doesn't have rapid shot capabilities, and the Atlantis Sub staff herded use into and off of the sub pretty quickly.
 
In one of my pic of the Atlantis sub you'll notice the wave guard around the bow hatch. That guard of course is not retractable for hydrodynamics when submerged. In regards to inflatable's here's a link showing a integrated bow fat sac that might work if you use two of them or the like on your sub.
 
http://www.overtons.com/modperl/product/details.cgi?r=view&i=12406&pdesc=Fly_High_Pro_X_Series_Fat_Sacs_Integrated_Bow_Sac_ea_12_x_12_x_50_750_lbs_each

 
Regards,
Brent Hartwig


From: ShellyDalg@aol.com
Date: Mon, 20 Aug 2007 22:11:12 -0400
Subject: Re: [PSUBS-MAILIST] Double O-Ring On A Hatch
To: personal_submersibles@psubs.org

Brent. I too took a ride on Atlantis, and checked out the hatch very closely.  The ring groove on mine will be on the bottom ring, where it will be subject to abrasion from entering/exiting the sub. I did it this way because I wanted the thicker flange ( with the groove ) to be part of the hull. A lighter ring on the hatch makes it weigh less, and the heavier ring on the hull adds strength to the hull opening. It's a trade-off. I don't anticipate replacement of the ''O'' ring to be a big deal, and in fact may be a good idea to replace on a regular basis so the groove can be cleaned more often.
Some of the subs I've seen have  relatively thin flanges, but they all have a tower to add strength. I am trying to minimize the tower height to aid in dropping the hydro drag. My testing showed me that with bigger ballast tanks, I can achieve reasonable freeboard height without a tall tower. I also want to keep the top half of the sub as light as possible, to keep the center of gravity low and the center of buoyancy high.
 I will however need a splash guard to keep waves from washing over the open hatch.( still working on that design.)
I think ABS calls for 30 inches minimum, but I won't get that much at the hatch. I'm making the hatch opening  rise above the hull by only 2 inches, so a splash guard that lays flat when submerged is what I'm working on.
I have some ideas, but haven't spent a lot of time on that yet. I'm leaning toward an inflatable device like maybe an inner tube type affair, to deflect the waves but also have some ideas to have a plexi screen that would pop up when I'm surfaced.  I will be able to get the 30 inches with whatever the final design ends up being.
 My hatch flanges are pretty thick, and so are heavy. The hull ring is 1-1/2 inch thick X 2 inch wide while the hatch ring is 1 inch X 2 inch. The hull dome is 3/8 inch like the hull but has a taller radius than the lid I'm cutting out of the hull for the hole. The tower is only 6 inches long overall, giving me just enough tube on the inside to attach the inside stiffeners and gussets to. Frank D.



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