Hydrostatic head - clue or con?

Argos TigerPaw 2000mm hydrostatic head

vango tempest  3000mm hydrostatic head

i know what one id rather have when it pours down.

The above was a reply to a comment I made on another thread....which made me think

In over 30 something years of camping experience, I have never had an identifiable problem with a lower rated tent leaking in comparison to a higher rated tent - on the occaisions where I have been subjected to monsoonal rain, I have been camping close to someone else who has been using a "better" and "more water resistant" tent.....and we both ended up seemingly equally damp.

In fact, thinking about it, the longest period that I had in consistant rain (several days) was in a cotton Force 10 which, arguably isnt strictly waterproof like Paramo isnt a waterproof, and was dry throughout....

So, the question is....are we being blinded by science and do hydrostatic head figures actually mean much? Are we being conned by marketing speak?

Hydrostatic heads are how much vertical water a fabric can hold without anything getting through. In that manner they are no con. If people begin to buy garments/tents on this data and nothing else then they're conning themselves.

Most tents have their hydrostatic head ratings based on their polyurethane floor, and I think this is a pretty good estimate of how long the fabric will last: a lightweight/cheap tent has generally a lower HH and so will last less long while being 'waterproof'.

How high a HH must be to keep out driven rain I do not know, but a bit of maths should sort it. I'm sure someone's done it before so tracking those figures could be helpful, but to be classed as 'waterproof' I think something must have an HH of 3000 mm, making that Argos tent, above, not actually 'waterproof'. 

Look here

Interesting point Mr F....our own estemed Mr Gear suggests the BS standard is 1000mm....

But you mid paragraph is a good point, or may have been if it hadnt been for the Trail test some time ago, where some of the top end tents failed much earlier than the cheaper ones......

But....really what I'm asking is...for most of us...does it make much difference between 2000 and 3000 given the amount of humidity involved anyway?

First up, there's more than one way you can measure HH, a bit like there's more than one way you can measure fill power (US values for the same thing are higher than EU values with the same basic description and the same down, for example, so first thing is you can't be sure that Brand X's claimed n,000 mm HH is quite the same as Y-Camp's claimed n,000 mm HH.

And HH is also something that's going to degrade with wear and tear, and to be frank most of us don't camp enough to make it too much of a worry.  But in the longer term and with harder use and more UV etc., higher HHs will take longer to get leaky than lower ones.

But for most of us most of the time in the UK, especially with a fairly new tent, it's a non-issue in the field.  But marketing like it because it's an Actual Number they can put by a bullet point and sound impressive, and people who put too much store in what marketing tells them like it for the same reason, especially if it's a bigger number than someone else's

Pete.

Aaah, Pete,

So it is all about piddling up trees is it?

Ben, could be a number of factors, at least one of which boils down to everyone makes the odd lemon, and nobody will fully test every piece of fabric or every finished tent for full waterproofness (maybe the seamer had a hangover or just got distracted, or the fabric coating machine blew a fuse or got  a blockage that went un-noticed etc.).

What I'd suggest is that if you took 500 expensive Macpacs and 500 £45 Vangos and pitched them all the same way in an identical simulated tropical downpour then more of the Vangos would leak and sooner than the Macpacs.  Not much solace if you're in one of the leaky Macs, but your chances are probably better if you take them there. No QA is perfect, but more is better.

Pete.

To Ben: Jack's waterproof being dripped inside, bad pitching, it going in the sea, and Alpine conditions generally being easy compared to the UK (who sweats in the Alps, I mean, really?!).

If Mr Gear reckons it's 1000 mm for waterproof then that'll be right - the 3000 mm figure was off the top of my head. 

A quick calculation (also, please shoot this down if someone can actually do maths): 

Basic low level of waterproofing: 1000 mm water = 100 cm.

Assume 1cm^2 area then that's 100 g weight on 1 cm^2

Now take the same approach to a bloke (let's call him 'Chubby') kneeling on his tent floor with standing water underneath it.

100 kg Chubby on 100 cm^2 area. That's 1000 g weight on 1 cm^2.   

So, following that shoddy maths and huge rounding up, unless Chubby has a 10000 mm HH his tent will let water through when he kneels on it. I Seem to remember Paramo has a low HH so if water is pushed into the fabric you'll get wet, only for it to be 'pumped out' again.

So, following that shoddy maths and huge rounding up, unless Chubby has a 10000 mm HH his tent will let water through when he kneels on it.

I'm not convinced.  A lot of grounsheets have significantly lower HH than that but don't leak when kneeled on...

Pete.

"I Seem to remember Paramo has a low HH so if water is pushed into the fabric you'll get wet, only for it to be 'pumped out' again. " wrong analogy it is extremely difficult to push water through paramo - unless you really want to sit and wriggle about in a puddle of adequate depth.

it's less about static head that raindrop force. my tarp is "waterproof". i can lie on it kneel on it and it's fine. when taut under heavy rain (i.e. chucking it down like i need to build an ark) the occasional drop will come through as a very fine spray. not enough to be a problem for me. i've no idea what the hh is for it. if the tent has an inner then this spray won't be a problem either i would imagaine.

i'm asking for trouble now. in general 3 season use by normal people how often would you encounter really nasty, heavy wind blown rain that would need the extra hh. in such conditions i would be more worried about the tent disintegrating than getting a bit damp?

is this potentially a bit more "received" wisdom (like you HAVE to wear boots)?

Mr Fuller's backup the envelope Maths look fine, It's just the Physics that needs a tune. (simplification) When mr chubby kneels on the ground sheet his knees are supported by the ground under the sheet. The fabric is just squeezed a bit like if you put at the bottom of swimming pool. Hence no leeks.

Parky Again wrote (see)

you'll get wet, only for it to be 'pumped out' again. " wrong analogy it is extremely difficult to push water through paramo - unless you really want to sit and wriggle about in a puddle of adequate depth.

to be honest lentenrose i haven't a clue. at a guess i would think it has to do with angles. and angle will deflect the raindrop whereas a raindrop will collide with all its force on a perpendicular plane. (back of a fag packet thinking and logic) my green tarp is bob's large single one. my cuben fibre one just doesn't worry about water (only so far tested by blasting the shower at it).

the fine spray was experienced during a "summer shower" - always a novelty in the south east - when i'd set the tarp up as an overhead shelter for lunch; and just in time too before a waterfall started. it rolled away into the distance before giving it the full light and sound show (technical meteorological terms). later that afternoon i was entertained by a torrential horizontal downpour. if i were caught out in that at night i would just classify it as being unlucky - and in the south east i would have made camp in some sheltered spot anyway (me camping guv? surely not!)

not having experience elsewhere in the uk i would tentatively suggest that just how often do you get really bad conditions (remember i'm talking about normal people ) that would probably put any tent under strain in the "three season" mode? is it worth worrying about? would you pitch somewhere exposed anyway?

sometimes i think we can easily get sucked into the marketing bs and can end up with something grossly over-engineered for its intended use.

i believe a quality tent will outlast a cheap tent. but on the other side you can buy 5 cheap tents for one quality one and which would last the longest and hence which is cheapest in the long run?

lol with the paramo. a very heavy groundsheet!

Parky Again wrote (see)

double sided sticky tape and bin bags are out then.

Why?

Ok...if they are value grade bin bags I agree, but I have found the biohazard grade bags excellent...