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I had an experience worth
relating on this topic of how to seal in a viewport. Originally I was using
white silicone sealant. The K-250 has both a flat acrylic viewport in the bow,
and an acrylic dome. Both were seated in silicone sealant. At fifty feet, I
suddenly felt a stream of something wet on my shoulder. It was the silicone
sealant pouring out of the seal as if it were water. The hatch had been
installed for months, but the sealant had not cured beneath the surface, and
with the pressure it extruded into the cabin. Not an experience you'd want to
repeat, the seal looked like it had just turned into milk.
On Greg Cottrell's
recommendation I'm now using a different product called Sikaflex-295. The
product literature actually says it's for underwater use, which sounds a lot
more reassuring than "exteriors". It has a special compound for preparing
the surfaces, to ensure a good bond. The downside is that it's *really* hard to remove a
viewport for maintenance. For those who haven't had the pleasure, the job is
already seriously nasty with silicone. I haven't had to remove a
viewport since sealing with Sikaflex, but I've seen what Greg ended up
doing to remove one of his -- cut the viewport up and remove it in
shards. To reduce maintenance, the viewports on the current
project sub are going to be sealed with o-rings, not bedded in
sealant.
thanks,
Alec The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it.
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
ShellyDalg@aol.com
Sent: Thursday, February 28, 2008 11:18 AM To: personal_submersibles@psubs.org Subject: Re: [PSUBS-MAILIST] FEA of a Basic Flat Acrylic Viewport Hello Dan. What type of urethane did you use to bed your lens in ? I much
prefer the urethane seal versus the O ring or gasket approach. My thought is
this.... with a 2 inch backing ring and a 3 inch thick lens, I have 5 inches of
seal for the water to get through, rather than 2 inch for a gasket, or 1/4 inch
for an O ring.
With urethane on the outside, covered by the retainer ring, the seal
increases to 7 inches.
I will be ordering the three pieces from Greg soon, and was planning on
calling the Sika Flex people for a recommendation. I'd appreciate any thoughts
and experience you could provide. Thanks, Frank D.
Also.....Nice work Brent! Delicious ideas to please the pickiest eaters. Watch the video on AOL Living. |