Bushwalk Australia

Hi Everyone...
Just a curious question on hydrostatic head - and how it stacks up in the real world...

Just noticing the HH values for tents, varying from 1000mm to around 6000mm (for rainflys mainly)

Anyone have any experience with this? I've had a tent which has a rainfly that said 3000mm - but wicked through like a cotton sheet...
But on the other hand - I've had lower spec rainflys, that I could've camped underwater and still stayed dry...

Just seeing what people have found, advice etc...

I believe the generally accepted minimum hh for tent flys is 1500mm while for a decently waterproof floor 3000 or 5000mm seem to be the go. The surface does need to be clean and preferably with a dwr finish so the water beads and runs off. As usual what is printed on the packet/advert isn't always correct. The level of proofing applied can vary widely even on the same roll of fabric.

I have just purchased a cheap blood pressure kit ($15.50 for gauge, cuff and stethoscope) http://www.ebay.com.au/itm/182469649769 with the intention of making a water head tester. There is a post on this on bpl https://backpackinglight.com/forums/topic/44977/.

Cheers,
I was wondering whether the DWR plays more of a role than I initially though... 1000mm HH with great DWR vs 3000mm HH and poor/no DWR...

What about Silnylon, which has no DWR?

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DWR can play a huge part as it is essentially using surface tension as free waterproofing, if the fabric itself never gets wet, it doesn't need to hold anything out.

I suspect that because Sil doesn't have any DWR that's why the thinner stuff is prone to misting under direct raindrop impact. So the heavier stuff would be much more resistant to that, I have no idea what the pressures involved would be, but I'm sure a raindrop on impact imparts a lot of pressure in a very small spot.

Aztec,
Simply because a tent is claimed to have a 3000mm waterhead, it does not mean that it has.

There are many tents on the market with a 1200mm waterhead rating and from well known brands, for example MSR, BA and Nemo, coincidentally all three brands are made by the same company.
Eureka even sells tents with a published 800mm rating.
At Tarptent years ago we used a type of silnylon that was rated 1200mm. Under big blobs dropped from trees it could mist.
On that fabric I never had penetration otherwise even under severe thunderstorm.
We now use a silnylon that is rated 3000 mm.

Just for the sake of comparison...

Our Hilleberg Nallo has 3000mm head for the fly and 5000mm for the floor.

Our tent is from 2008, so it's old technology.

A 2017 Nallo has 5000mm head for the fly and 15,000mm for the floor.
The Nallo is a mid-weight Hilleberg model.
The more serious models have 5500mm for the fly and 20,000mm for the floor.

Yeah, the old saying you get what you pay for...