Thanks for the response. I came back on another email about the Nekton/Delta boats, which use the same arrangement with staggering success. And there is no reinforcement at the hull joint. The shell is welded straight to the box with a couple or three inches sticking through. On top of which, the Delta is 42" diameter and only has two ribs, one forward and one aft of the conning tower (which has an extensive arc of reinforcement, as you will be able to see from photos on their web page).
From: Dan H. <firstname.lastname@example.org>
Sent: Mon, 10 Apr 2006 08:42:16 -0400
Subject: Re: [PSUBS-MAILIST] structural question
I'm not the guy to do the calculations but I'd bet you would need to reinforce the slot your taking out of the hull tube similar to the way you have to reinforce around a viewport. The forces in the hull tube would be trying to close your slot and would have to be carried across the opening with something substantial. More then just the ribs in that area.
Also, with the batteries in a box like that you would loose the protection in case of a battery explosion. The way it is now, the pod end cap will blow off but you won't flood or get hit. But, Maybe battery explosions aren't such a big problem as I was led to believe.
----- Original Message -----
Sent: Sunday, April 09, 2006 1:22 PM
Subject: [PSUBS-MAILIST] structural question
I'm planning on another K-sub, but thinking about a box keel like the Nektons and Delta had, rather than pods. Has anyone got an idea about how to figure structure on something like that? The Nekton's box was 9/16" wall, flat side and bottom, and reinforced with flat plates running athwartships on 18" centers (more or less). The hulls were the same thickness and the same material (A516 Grade 70).
I'm wondering if there would be any penalty to building a 1/2" thick box with 1/4" dividers matched to the ring stiffeners in the hull (ie., 12" centers). The box would be a foot square in cross section, and if all seems well, would be welded through a slot in the hull and covered inside with a reinforced aluminum deck plate gasketed and vented for charging. If the pressure hull is six feet long in the cylinder, that would give me room for a grunch of 85 amp deep cycle batteries (more than called for) and still not kill my payload.
Anyone not familiar with K-subs might think all this sounds pretty heavy. Have a look at the lead load in Dan's boat, if you think we don't have it to spare.