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Webster Telescopes Forum • View topic - Webster Shrouds are 100% Waterproof!
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 Post subject: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 3:58 pm 
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Posts: 122
We have received about a dozen emails lately asking about "other options" than our standard light shroud.

We have had the same military nylon Ripstop shrouds for almost 20 years, so this seemed rather odd.

Apparently, somebody is posting online that Ripstop is water permeable, and that it causes water to soak through and drip on the mirror!

The US Army itself classifies Ripstop as "water resistant". It is made with silicone so water beads and runs off, without it getting soaked.

To counter this false claim, I set up a test:

1. Piece of untreated, straight off of the bolt, cut of Ripstop
2. A 2oz glass of pure Detroit tap water
3. Common rubber band
4. Glass, wide mouth pickle jar


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 4:00 pm 
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Next, I formed the Ripstop into a "cup" of sorts using the rubber band and the Pickle jar:


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 4:05 pm 
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Next, I poured the entire shot glass of Detroit tap water into the newly formed cup.

I noted that no water ran through at all.

I noted that no water beaded up on the back side of the Ripstop at all.

I also noted that 2oz (60ml) of water is about 20000x more volume than any drop of dew I have ever seen, even in "Land of 7000 Lakes" Michigan.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 4:07 pm 
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Four hours later, still no water has beaded up on the back of the Ripstop, nor has any dripped into the jar.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 4:09 pm 
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Four hours latter, and still no drip.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 5:14 pm 
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I'll take another look at the jar in a few days and see if the Ripstop finally dripped.


So what have we learned from this test?

For the purpose of telescope shrouds, we can safely declare Ripstop to be 100% waterproof.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Apr 09, 2012 5:38 pm 
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How can dew drip on the mirror if it does not soak through the shroud?

On nights of really crazy moisture, dew can form on:
1. The spider vanes.
2. The inside of the UTA.
3. The Secondary Holder
4. The truss tubes.
5. The inside surface of the shroud.


On nights of crazy dew, what can I do to keep the primary mirror from having dew drops fall on it?
1. Open the front shroud flap and put the Mirrorbox cover back on.
2. Slide the shroud from the scope and shake it dry (Ripstop does not hold moisture, it will become very dry from shaking).
3. Wipe off the spider vanes, Trusses and UTA with a towel.
4. Repeat every 3-5 hours until sunrise.

Of course this could be a 5 minute process every few hours, but other than moving to a desert, there is always the chance of one or two nights a year with really heavy dew.


What if dew drips on my primary mirror?
1. Simply rinse it off with some Distilled Water. No need to scrub or wash the mirror.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Wed Apr 25, 2012 10:58 pm 
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After a few days the water simply evaporated. No water penetrated the Ripstop.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Sat Jun 02, 2012 12:49 pm 
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I suspect it was me who made the claim to which you refer, so I think I should clarify things. The point was not really whether the shroud is permeable to water, but that water droplets accumulated to problematic levels on the inside surface on a regular basis. During the "dew season" in the peak of summer I had raining droplets after about two or three hours on most nights. An Obsession owner I observed with commented that his nylon shroud also behaved this way and so he preferred to observe with no shroud at all. Of course YMMV depending on location (I'm on the east coast: Long Island and Catskills) and I'm sure there are plenty of areas where internal dewing does not occur at all.

I found the drips occurred sufficiently often to become an annoyance. Removing and shaking out the shroud didn't seem like a practical solution, although it is one I considered and even tried once.

Knowing that the shroud is impermeable to water is useful, since it indicates that the droplets are formed by condensation on the inside rather than seepage of water through the material. So water-proofing the shroud won't help. In any case, I didn't like the sound of water-proofing since I didn't want to risk chemicals ending up on the mirror.

In the end I fixed my problem by installing a lycra shroud. Unlike nylon, this material absorbs water and so doesn't rain dew onto the mirror. The downside to lyrca is that you need to dry it when it gets wet. So nylon has the advantage of being more practical whereas lycra works better in dew. Both materials have their plusses and minuses, but for me lycra ended up being the most suitable.


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 Post subject: Re: Webster Shrouds are 100% Waterproof!
PostPosted: Mon Jun 04, 2012 1:39 am 
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Joined: Thu Jul 02, 2009 11:48 am
Posts: 80
Location: Detroit Michigan
Thanks Rob,

I'm not sure if you were the cause of the emails or not, so no need to blame yourself.

We get a lot of dew here in Michigan (land of 11,000 lakes), so we feel your pain.

Unfortunately, we have determined that Lycra shrouds are not suitable for our scopes for several reasons:

1. Lycra is not durable enough. Lycra gets "runs" in it anywhere there is a hole or tear.

You can poke holes in Ripstop and the holes never get any bigger over the years. Take a look at 15 year old Ripstop shrouds and see; holes do not run or fray at all.

2. Lycra allows body heat to enter the telescope light path. This is important for high power viewing.

Ripstop holds your body heat out of the lightpath.

3. On smaller telescopes Lycra absorbs water and makes the telescope top heavy.

Ripstop absorbs no water, and thus keeps small scopes in balance.


All that being said, we are glad you found Lycra to be a suitable solution to your dew problem; it just has too many drawbacks for us to "officially" endorse it.

Thanks again for your input, we always appreciate it,

Eric

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Eric Webster
http://www.WebsterTelescopes.com


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