Measuring Depth

[Brian Hamilton]

I was wondering how you all measure depth of a dive site before you actually dive there. Unfortunately I do not have access to a boat with depth sounding gear and dive straight off the rocks.

I currently use a string marked at metre intervals with a weight tied to the end. This system has proven to be innacurate as I have to throw the weight a good distance offshore to clear the rocks and seaweed. As a result of this the string lies at an angle between the weight and the waters surface so the readings can be really far of the mark.

Have any of you encountered similar problems and if so you did you solve it? I guess some kind of float to hold the string vertical would be the answer but I can't figure out how to put it all together.

Any ideas?

Brian

 

[efattah]

I usually just dive down and find out how deep it is.


Eric Fattah
BC, Canada

 

[Alun]

you could try that system whilst floating in the water... should work better. just use a scuba diving reel. most take 50m+ of line.
make sure the weight at the bottom won't snag on anything.
another option is buy an Admiralty chart covering your area. may not show great detail but should give you a rough idea of depths.

 

[fjohnson]

I use a flashlight-size portable Polar Vision sonar - here's a link that has info on it. Even works through the ice.. that's what it was designed for http://www.cabelas.com/information/...eld-Sonar-and-Flex-Stand-Handheld0010513.html
Was a little spendy but the kids gave me a gift cert. so I used it on this. Works very good, but was not so waterproof as is stated. I had to seal the cap with silicone in order to keep it dry while it's floating around in my innertube float.
Fred

 

[Brian Hamilton]

Thanks for the reply guys. Unfortunately the admiralty charts for the area I dive are about one hundred years old and are not very accurate.

I only dive with a buddy but go out to measure different sites on my own so I am not going to dive to check out depths.

The handheld sonar seems like a good idea, I will have to try and see where it can be purchased in the UK.

Cheers,

Brian

 

[Jon]

It depends

If I am diving on a shipwreck, I look at the bottom finder on the boat before I jump in, plus I have access to good charts and can check ahead of time.

IF I am diving a local lake, I can look up lake maps from our D.N.R. website.

If I am diving a quarry, with no charts to it, I have a Diverite wreckreel that I have marked off with knots, and magic marker, every 10'. I can keep this clipped off to my float and drop it down, with a 1 pound weight at the end, and see how far it goes.

For training warm-up's, I have a rope with tape marks on it every 10'.

In some cases, as Eric mentioned, I just swim down and look at my D-3.

Jon

 

[Pezman]

Jersey Jim rigged up an inexpensive depth sounder (about $75) on a boogie board and powered the whole thing with a gel-cell. We used that and a GPS (also Jersey Jim's) to find some deeper holes at Dutch Springs. You can even see divers on the depth sounder, so it may have some value as a sort of safety device.

You may also be able to get aerial photos at Terraserver and mark them up w/ the coordinates of your favorite spots.

At this point, we probably know the quarry's underwater terrain better than most of the SCUBA guys, since we are far more mobile on the surface. We also out-gunned the SCUBA guys during the annual Easter Egg hunt. I suppose that the next challenge is to beat them at the underwater pumpkin carving contest