RE: [PSUBS-MAILIST] K-250 Restoration in Sandpoint Officially Underway

Very cool, it's great to have another K boat in the process of being resurrected.

To clean those viewports without detriment to the acrilic use mineral spirits. Silicone sealant is a bear to get off. It's even tough to remove from the hull by sandblasting, because the grains of sand tend to bounce off without removing the silicone where they would cut right through paint in a second.

I agree with Jon, given the viewports have a finite shelf life the proper course of action is to replace them. If I were you I'd send the old ones to Greg Cottrell for evaluation and/or to serve as models for replacements. BTW the coning tower viewports are not standard on a K-250. The tricky bit in fabrication will be matching the conical angle to the seats -- the match has to be very precise and is specced in PVHO and Stachiw's book.

Good luck with the project, I'm looking forward to another operational K-250. Since I have a K-250 myself, let me know if you need anything like detailed photos of components to use as a reference in the restoration.

I'll have to check the K250 drawings again, but I don't believe the current plans call for tapered viewports. A tapered design would be more safe, but not a requirement for the 250 foot depth limitation of the K250 hull. Regarding the viewport integrity, I recommend you get a copy of the ASME PVHO viewport standards and/or Jerry Stachiw's "Handbook of Acrylics" for guidance on whether the viewports are still viable. US Federal regulations for commercial submersibles requires replacement after 10,000 diving cycles or 10 years, which ever comes first. The crush depth of your viewports is an unknown. You have to consider their age and condition, and without actually setting up a test environment to simulate the maximum depth plus a safety factor you may never know at what depth they will fail. A brand new flat viewport rated for 350 feet of water depth has dimensions of 1.25 x 8 inches, and requires a one inch width seat (6 inch exposed diameter inside the sub). There are too many variables associated with your existing viewports I think, to accurately calculate a safe water depth for them and they should be replaced.

Also, assuming the viewports fit within the requirements of less than 10,000 dive cycles and less than 10 years old, any buffing or other machining of the lens to restore them will introduce new stresses and require an annealing process to relieve those stresses. Again, let the ASME and Stachiw references be your guide here.

I got two words for ya: Hot and Humid. I got a chance to start working on the K-250 yesterday. I carefully removed all three view ports. Drained most of the water and did some clean-up. I scraped and poked all around the inside of the hull, and so far I have not found anything but surface rust. We'll know more when the sandblasting is done. I'll be sandblasting the three view port flanges this morning and see how much of the interior piping and hardware we can removed today, to get ready for sandblasting.

When I removed the large 2 inch thick acrylic view port, about 6 inches of water came gushing out. On that view port and the small port conning tower view port they used some crappy white silicone that didn't hold very well and looked bad to boot. The starboard conning tower view port was seated in clear silicone and had the metal seating surface painted. The port side seating surface was bare steel and lightly rusted. The taped screw holes on the conning tower view ports, didn't have any grease on the threads and so there was some light rust on the threads.

Here is the Frappr link to the pics I took yesterday.

http://www.frappr.com/?a=viewphoto&id=2628470&pid=6212256

The large front view port after I cleaned it up, looks really good with no crazing, yellowing, or scratches. It looks like we can just polish it and anneal it. That view port is in a mostly shaded protected position, so it didn't get much sun.

The conning tower view ports have some light crazing on just the interior surface. I'm not sure why but it would be interesting to know why? Perhaps the sunlight was focusing on the inside of these view ports from the dome and that combined with the heat did the damage. There are some very light scratches that should be able to be buffed out and no yellowing. Are the type of conning tower view ports we have on this K-250, with the beveled seating standard on K-250's and if so what is there crush depth? They are 1.20" thick by 6-9/16" on the exterior diameter and 5-3/8" for the interior diameter with a 1/8" flat round surface next the the exterior face. Is there a good solvent for cleaning silicone off of acrylic that won't damage the acrylic or do I just have to buff it off?

More data to come about the identity of this K-250. But for now I have sandblasting to get to.

Regards,

Brent Hartwig

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