Vance,
According to Stachiw the cylindrical acrylic performs worse than disc or spherical in terms of optical, but he doesn't really give a description of how bad it is. The larger the diameter, the less optical distortion is perceived. He states that a diameter of 42 inches, 4inch thick, has acceptable optical qualities. The fabrication of an acrylic conning tower however appears to be much less involved than a steel conning tower with multiple disc viewports.
Jon
vbra676539@aol.com wrote:
> Steve and James,
>
> If you go to the Submersible Systems Technologies web site and look at > the Vista Ranger, you will see a good picture of Steve's hatch, or at > least of the PC-1402's hatch, which they used on the new acrylic > cylinder conning tower. I do like the idea (the acrylic conning tower) > but wonder about distortion and crash protection. I have, in > fact, seen some used in pretty rugged circumstances, so I may be just > hanging with what I know.
>
> For instance, Vickers built the LRs based on Perry's PC-15 dimensions. > The hulls were spun fiberglass and the conning towers were all acrylic > like you see on the Ranger. The crews ran the hell out of them (we > were all in direct competition in those days, and we ALL ran the hell > out of whatever we had). In any case, Vickers never had any trouble > with the LRs that I heard of aside from the fact that they were tubby > as all get out and hard to manage in cross currents and the like. The > subs had crash guards on deck to help protect the acrylic, and they > were monumentally heavy. To be fair, they did have the spare payload, > so I guess it worked out. Just on the face of it, the acrylic tube > looks to me like simpler construction, and maybe even cheaper than the > Perry's as you don't have all the multiple bits and pieces to build > and weld and machine and clad and paint and...well, and so on.
>
> Mind you, the PC-12 class from Perry has continued in service (in the > tourist industry mostly), and they have done, literally, tens of > thousands of dives without incident. That's a hard record to beat for > sheer toughness. Keep in mind, you don't wear dress shoes when you're > working. You wear steel toed brogans or work boots--heavier, more > expensive perhaps, but very hard to beat when you drop a hammer on > your toe. The steel conning towers are kind of like that, I think. > Sort of a Wolverine safety boot with viewports.
>
> Vance
>
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