Hydrostatic Head Conversion

[JulianWormwood]

I need to buy a new lightweight tent, and one of the options I'm looking at doesn't give its hydrostatic head (a measurement I'm at home with), rather it gives a measurement in L/hr/m²

I've no way of relating this measurement to what I know. Is 450L/hr/m² the equivalent of light, heavy or torrential rain?

Is there a way of converting (even roughly) between this and hydrostatic head?

I go tent shopping tomorrow, so any help would be appreciated.

 

[gregorach]

That sounds like a measure of breathablity (technically moisture vapour transmission, or MVT), not waterproofness. It's almost the opposite of hydrostatic head.

 

[Jodie]

I'm assuming the hydrostatic head readings given in mm actually mean mmHg which
is actually a unit for pressure (mm's just a distance, which makes no sense).

No idea how the two relate though - litres per hour gives some indication of force or
pressure and the m2 would be the area so I can see how it would work, but not how
the two terms would be interchangeable.

Hopefully someone will come along and explain it but you should ask the mfr to
provide data that enables comparison

Didn't find anything useful on Google, don't know much about it. Good luck!

 

[combatblade1]

Is your tent a quechua? I would suggest that a tent which can stand having 450 litres of water an hour per suare meter chucked at it would be pretty substantial.

 

[Ogri the trog]

Is your tent a quechua? I would suggest that a tent which can stand having 450 litres of water an hour per suare meter chucked at it would be pretty substantial.

A kind of collapseable submarine comes to mind!

Ogri the trog

 

[dommyracer]

I'm assuming the hydrostatic head readings given in mm actually mean mmHg which
is actually a unit for pressure (mm's just a distance, which makes no sense).

Hydrostatic Head is measured in mm, with the mm referring to the height of a column of water that the fabric can withstand.

But as someone else said, the measurement given sounds more like a water transit measurement.

 

[gregorach]

Well, looking at the MVT figures for various fabrics over on Pennine Outdoor Fabrics, somebody somewhere has got either their maths or their units wrong. They give the MVT of their best 3-layer breathable membrane as 7,500 g/m^2/24hrs... And I calculate that the above-quoted figure of 450L/m^2/hr works out as 10.8 million g/m^2/24hrs - or over 1000 times more breathable than the figure given for Pennine's best membrane.

I'm not sure that air would have an MVT that high... Perhaps I've got my sums wrong.

 

[Glen]

Well, looking at the MVT figures for various fabrics over on Pennine Outdoor Fabrics, somebody somewhere has got either their maths or their units wrong. They give the MVT of their best 3-layer breathable membrane as 7,500 g/m^2/24hrs... And I calculate that the above-quoted figure of 450L/m^2/hr works out as 10.8 million g/m^2/24hrs - or over 1000 times more breathable than the figure given for Pennine's best membrane.

I'm not sure that air would have an MVT that high... Perhaps I've got my sums wrong.

Your figure look right to my quick glance, but I suspct there some confuson as to what's being measured and guessing from the original post wording that they mean tested waterproof in a 450L/m^2/hr "shower"

Might need to check my figures but :

450L over 1m^2 is 450000cm^3 over 10000cm^2
Giving a depth of 45cm ( or 18 inches ) per hour. Thats 0.75cm (or 0.3 inches) per minute
Sounds like quite a downpour to me but mustn't loose sight that these are probably sales oriented figures and its more likely to be an inch in around 3 minutes than 432 inches in a day.

Actually those figure do look more realistic than any other interpretaion I can think of.

 

[JulianWormwood]

Is your tent a quechua? I would suggest that a tent which can stand having 450 litres of water an hour per suare meter chucked at it would be pretty substantial.

Yup - we're looking at the Quencha T2 Ultralight Pro from Decathlon. It's a bit cheaper and a bit lighter than the Coleman Avior X2 which is the other option I'm looking at.

Obviously if people have a better reccomendation for under £100, I'll gladly listen.

 

[KAE1]

A useful example of hydrostatic head on this link;
http://www.kammo.co.uk/tests.html

See breathability on this site;
http://www.fjallraven.com/templates/mall1.asp

Hope this is of some help.

 

[scanker]

No experience of it, but the Aztec Rapido looks to be pretty good. £64.50 delivered from the site below.
http://www.outdoormegastore.co.uk/acatalog/Outdoor_Megastore_Aztec_Tents_295.html

Condensation may be a problem as it's single skin. I think the Esquina Solo is a bit bigger and standard fly/inner.
http://www.worldofcamping.co.uk/shop/Detail.asp?ProductID=359