JohnNicholson wrote:
You either

a) Die of hyperthermia
b) Drown
c) Starve

or possibly and most likely a combination of all three which is why OHA is a grade 5 cave and should not be underestimated. Added to that, any attempt at a rescue from its deeper reaches would be very very difficult even in non flood conditions.

timwatts wrote:
Although you could always exit through the second entrance (if you find it soon...)

preciexactly!

Tim
I'd still like to get an overlay of the OHA system onto an OS map. I still reckon that by drawing an arc rotating it around using the 'end' of the cave as a scribe will give us an idea where the end might be, ie somewhere on that arc, I'm particularly interested where it would intersect with the river.
Has Mick got one?

tim's got one frank

got some more elevation data at home somewhere too.

Oh yes
That will do for starters
Thanks

Interesting
If you look at the plan of poachers the end of the cave shows it quite a distance from where it actually is, am I correct?

I also notice some small squares on the map, is this anything significant? Known sinks for example?

Is the river flowing at the moment? And does it ever flow along the river bed near the entrance?

The river bed was looking remarkably vegetation free...

Tim et al,

Have you thought of using a ground transmitter/receiver to locate the aven from the surface. The molephone is a rather sophisticated version on this, but something cruder may suffice. You need a source of low frequency radio waves in the aven - this can be just be a simple 2 transistor multivibrator running at 1khz from a 12v motorcycle battery. You hammer a couple of metal rods about 8-10' apart in the aven and couple them up to the oscillator output and then retire to the surface. a standard 7AH battery should run the oscillator for a few days. On the surface you need a similar pair of probes, a small amplifier and a pair of headphones. You could space the probes about 3' apart using a wooden frame (like the timeteam resistance survey) and then wander around poking it into the ground and listening for the tone. The louder it gets the closer you are. For real sophistication add recfifier and meter to show the signal strength. The electrical field will travel quite long distances in damp ground - what we have now and you should be able to locate within about 10 metres.

There are a few caveats: Ground resistance isn't uniform and so you may get a strong signal from a point not immediately above the aven if there is conduit of conductive damp soil while the surrounds are rock or a specially damp area with the rest dryish soil. But its probably more reliable than smoke testing.

Dave

PS. If you don't have any tame electronics experts I could probably knock something up for you, but I am not sure I would want to brave the sumps to fit it at present

Frank, blue dots are photos that show on google earth on which the overlay was added to.

Dave, we have somone who works for maplin in our numbers so have somone who can knock one up. (and has offered to do so iirc)

I have indeed started to put together schematics etc. The coils will be the hardest part, Copper isn't cheap. The multivibrator itself is easy enough, as is the power source (I have enough Li-Ion's to light up a cave rave for days). I was going to go for lower frequencies, but we'll see what happens. This is not likely to happen before Xmas though.

if you have a look through CREG website i remember theres some PCB templates and component lists and instructions for tried and tested methods for winding coils on there somewhere. Not got time to search just now coz bit hectic at work but have a look and i'm sure you'll find it.

I you want to obtain parts from work and make one up either I or UCET will cover the costs.

bcra.org.uk/creg/

yer i think it was on Brians page.... radiolocation.tripod.com/

I'm a subscriber (paid up) for CREG so let me know if u need any past journals - but that said its only £4 or £5 a year to join yourself if you fancy it.

ohh and whoever was asking - yes the river regualarly flows on the surface under wetter conditions - when the flow rate via the caves reaches is maximum flow capacity and the sink holes back up until everythings flowing on the surface.

No need to cover costs, I'm happy to do it, but time will play just as much a factor. I have had a brief look at CREG, and found a few bits. My problem is trying to make a low, *reliable* frequency. The lower it is, the farther it travels, so I want to go as low as is practical.

ECW is way cheaper from ebay, I guesstimate I'll need about 1-1.5KG of 24SWG for both coils. The electronics can probably be made fairly intelligent if needs be, micro-controllers are cheap these days.

EDIT

Will 30M vertically and 70M horizontally Max (for Radiolocation, not comms), be enough for our immediate purposes?

I already have that page, and one it links to, bookmarked. I plan on making, at least to begin with, a "basic 2", operating frequency 1.75Khz.

yer - basic 2 was the one i was looking at a while back - got as far as etching a PCB ready for it but god only knows where thats gone now.

HI- Can any one tell what in situ ropes are in place to sump one.

i can assure you all I did not put no wire in, I had 10 years of that shit hole before the club got formed
and can anyone put there hand on heart and say murph was our trip,no because I hate the shithole .