> water can soak right through silnylon (even if rated to 1200 mm) -- but no
> complaints from users of quality, well-maintained nylon tent floors rated to just 800 mm.

I have to say I have problems with this statement as it stands.
First, saying that a fabric rated to 800 mm will better withstand water than a fabric rated at 1200 mm just seems totally wrong to me.
Second, my blue tent has a standard silnylon floor and that floor lasted at least 4 years of intense use without showing any signs of leaking.

Sorry, but ...

Cheers

Roger:

I never said "that a fabric rated to 800 mm "will" better withstand water than a fabric rated at 1200 mm -- because that's simply ridiculous. What I am saying is that some fabrics rated higher have had water seep through whereas other different fabrics or differently coated fabrics with ostensibly lower hh ratings have not.

My contention is that there may well be other considerations at work here -- in addition to mm ratings. A straight comparison of mm ratings -- I highly suspect -- is not giving us a complete picture -- or even a good picture -- of a fabric's performance in the rain (or atop a puddle). I know from reading that some people have experienced water seeping through their silnylon tent floors -- although I myself have not experienced this with my silnylon tent floor -- at least not yet (and apparently neither have you, Roger).

If it were just a simple equation -- as Richard apparently likes to see it -- then your silnylon tent floor and mine should both have experienced water seepage -- every single time -- just like 2+2 should equal 4 every single time! But that's just not the case, is it?

Edited by ben2world on 02/20/2010 18:03:53 MST.

Richard:

Tables and calculations can be a good starting point -- although sometimes, they are just entertaining.

Scouts all across the nation have used cheap, 800 mm rated tent floors and flies for decades in rain or shine, puddle and dry -- and no, despite your calculations -- they do not all suffer wet knee caps and buttocks every time a small puddle collects under their tents (due to careless site selection or what have you). Indeed, these tents have apparently performed "well enough" that they actually have a pretty darn good reputation for decades now -- for three season use.

Not saying that the calculations are necessarily invalid or worthless -- but I am saying that using straight calculations to predict outcome as you have done in your post above -- and elsewhere -- does not correlate highly with what's out there in the wilds -- or at campsites.

Your tables are good starting points for comparisons -- assuming everything else is held constant. The latter constraint that everything be held constant for the comparisons to be valid is what makes such comparisons difficult in actuality. Indeed, the 800 mm Eureka versus the 1,200 mm silnylon tent floors discussed above seems like a paradox! But my view is that they are not paradox -- but simply that hh / mm is just one of several (or perhaps many) factors at play!

Edited by ben2world on 02/20/2010 18:08:52 MST.

I have a typical floorless shelter/tent, and in a few months I will need to use it in a very wet place. I expect rain puddles, and there is only so much that you can do with tent location when the ground is basically flat. Obviously, I need to construct a bathtub floor of sorts to insert in there, and it will be about 6.5 feet by 2.5 feet. The upturned edge will need to be at least a half inch to keep water out.

I made one out of coated nylon, and it turned out several ounces too heavy. I mean, it is too heavy when the bathtub floor weighs more than the entire top of the shelter/tent.

Now I have some yardage of spinnaker fabric and some Momentum fabric. Gut instinct tells me that the spinnaker fabric would be better there. Alternatively, I have a painter's dust tarp of 0.7 mil plastic. It's pretty light, waterproof, not very durable, but I can't upturn the edge or sew it.

Weight is a factor at play here, but durability is not. This only needs to last through the puddles for six nights or so. Any suggestions? Meanwhile, I will get the sewing machine warmed up.
--B.G.--

I suspect that some of the difference between one 800mm rated floor and another has to do with consistency of the coating. In other words some "800mm" floors may have areas that are only, say, 600mm and others have more like a 1000mm or so coating. To get that difference the coating does not need to be that much thinner or thicker.
Franco

Ben,

Floors and HH are simple to explain and I just covered that in my prior post where I poked a little good natured fun at you (sorry). Hydrostatic head rating relative to fly fabrics and single wall tents field performance was last explained by me in a response to Richard Matthews' post on 4/6/07. I can’t find that old discussion thread URL using the BPL search feature or the just stepping through the posts under my profile. If any one can find that discussion thread, please post the URL. Fortunately I saved a copy of my response to Richard’s question in my files and so I will repost my old explanation. I used the term how “heavy” rain was in the old forum thread. The rain drop diameter, temperature, and wind all contribute to this factor and I created a spreadsheet to explain this earlier in this forum thread.

In 2007 Richard asked, " Would the amount of tension applied to the fabric change the PSI?

My experience suggests that the silnylon tarp pitched very taut will have more misting than the same tarp draped over a pack."

In 2007 I answered as follows:

Think of rain in terms of droplets crashing into the fabric. Each one has a mass and velocity depending on how “heavy” the rain is. This gives it a penetrating ability and is proportional to its kinetic energy... a bit like a bullet from a gun: heavier, faster bullets have more energy. (Kinetic energy = 1/2 mass times velocity squared.). The ability for a silnylon fabric to absorb the energy of the rain is dependant on a number of factors:

• Fabric weight
• Fabric porosity
• The angle of collision
• How much the fabric can move

It is as Richard said, “My experience suggests that a silnylon tarp pitched very taught will have more misting than the same tarp draped over a pack.” And as Tom said, “So other factors have to be involved which influence this (waterproofness)”.

The porosity, in a large measure, determines the PSI rating. The angle of collision can be just about anything, with perpendicular being the worse case scenario. The energy absorbed from the collision depends on how the fabric moves and how the rain drop distorts. It is the force the fabric exerts on the water acting over a certain distance (energy = force times distance) or the work done by the fabric. This is similar to a Kevlar bullet proof vest which distorts to slow down the bullet.

Richard:

Yes, we certainly agree that there are indeed many factors at play here. Maybe one day, scientists will have a fuller understanding of all these factors and interplays to be able to write the proper software to arrive at meaningfully predictive results. In the meantime, we use the tools we have -- plus what we all try to pass off as "common sense". :)

Was this thread about the new Black Diamond fabric for its single wall tents?
When will Henry begin selling the spray cans of liquid glass for our tarptents?
If durability is not an issue, why not use cuben for the temporary tent floor ($$$)?
Googled ".8 ounce fabric" and got a bunch of listings for 8 ounce fabric. Didn't realize that Google had removed the decimal point, and almost ordered a bunch of biohazard bags.
Is BPL getting to be too hard?
Good try, Ben, with the sanity thing!

Yes, this was a really strange thread. Started out talking about Nano and then Richard, with no info on Nano at all, started talking Hydostatic head. Informative as it was...was difficult to follow. Then OSMO was confused with NANO, and then both were confused with the spray-on-glass, which is NOT nano. *phew*

Did anyone ever figure out how breathable and water-resistant Nano is? Is this just epic with a gross green color?

Bob,

Re "Now I have some yardage of spinnaker fabric and some Momentum fabric. Gut instinct tells me that the spinnaker fabric would be better there. Alternatively, I have a painter's dust tarp of 0.7 mil plastic. It's pretty light, waterproof, not very durable, but I can't upturn the edge or sew it."

I made upturned corners in a GG polychro ground cloth by folding in the corners making a kind of dart, then glueing and clamping. It Still flattens out along the sides but one possibility to "lift" the sides would be thin ( less than 1 inch wide) cross wise sections of 3/4" or 1" inside diameter foam pipe insulation. A one inch wide section must weigh @ a gram and you'd halve that to make a section of "rib" or also you could lay some sticks along the edge to keep the sides turned up. Chancey but very light. I wasn't trying to get a fool-proof tub; just trying to make it less likely that rain water would easily flow over the edges. I suppose you could also do a little trenching/berm building around the edges to keep the edges of the ground cloth turned up. This is all very minimalist but still if you're not in some drain channel and under a tarp it shouldn't take much.

You could also do the same ( fold in the corners ) on a piece of tyvek; then install like 3 light grommets down eack side and clip/connect those with strings of 1/16th shock cord. probably weigh @ 3 oz.

Any more reviews on how the new tent material performs?
I'm looking at a Firstlight and hoping someone here got to play with there tent this winter.

Edited by lightingboy on 04/28/2011 09:51:56 MDT.

My Highlite has performed admirably on the three different trips that I have used it. Every time we pitched above tree-line and had no issues with wind stability. Only one of those times did I deploy the guy lines. There was evident misting or condensation dislodgment from hail impact during a particularly powerful snow/hail/thunderstorm that lasted the bulk of one night in SW Asia @ 12,000ft in October last year. Either way, I imagine the HH of hail in 45mph wind is off the charts and I was pleased with how it held up in the challenging weather. The other two trips had zero condensation issues and each time we had two people in there. Hope that helps a bit. /a

how about heavy constant rain?

wondering if itll wet out like epic and suddenly fail

I have not had the pleasure of sustaining blowing rain yet in that tent, although we did have a wet snow storm the night following the hail, with no issues. We were also using the BD vestibule and had both vents open slightly.