How deep am I???

[Steven Rawles]

Being a bit of a newbie I was wondering does anyone know a way of telling the depth to which I have dived ? Is there some way of knowing by the amount of times I've had to equalise on my way down?I appreciate that I'm probably clutching at straws with this theory,due to increased pressure at depth and of course no two people are the same but short of splashing out on an expensive bit of tech I'm a bit stumped !!

 

[Bill McIntyre]

An expensive bit of tech is the way to go. Something like an Aeris f.10 will tell you how deep your last dive was, how long your bottom time was, and even more important, how long your surface interval is.

Herre is an example from a friend's watch last week. One of his buddies had shot a yellowtail that tied up in the kelp on the bottom and he dove to cut it out. You can clearly see that he dove to 95 feet, spent a total of 1:32 under water, and had been on the surface for 5:32 after the dive.

Don't be intimidated by the depth and time- there is no way I could do that either. I'm just posting the photo to show you what a good watch can tell you. Its expensive, but its worth it.

 

[Steven Rawles]

i expect I will end up with something like very soon but I was just curious to know if there was a low tech way of telling

 

[cdavis]

Something like the F10 will pay big dividends, but if you can't swing the coin, they used to make el cheapo capillary depth guages, for very little. Clunky, but will give you an idea of depth and somebody should still make'em. Alternatively, make a sounding line and measure your depth. You could probably make your own capillary guage if you can get a decent line measurement of 33 ft.

 

[landshark sa]

As the other guys mentioned, a dive watch is a invaluable piece of dive equipment, not just for temp and depth but also for dive intervals.

Other than that, if you are diving with a buoy use the float line. Mark off lengths of 5m or so and then leave your gun at the bottom after a dive and count the marks as you ascend.

Although less accurate, paying attention to the underwater fauna and flora could also provide some clues to how deep you are. Around here Bull Kelp usually only grow to around 10-12m in length, if I dive in on a rocky bottom and I come to the far edge of a kelp bed I know that’s more or less the depth there. Another example is in the areas I mostly dive a certain type of bream species of fish we target are most prolific at around 15-20m. So if I start seeing the smaller fish of this species I know I'm reaching around 15m and once I encounter the larger ones I should be around 20m. Any deeper they generally start to give way to other reef species. Not an exact science I know, but if you add all these clues together one can get a general idea of depth.

 

[Steven Rawles]

I really like the measured float line best low tech approach so far, also leaves my hands free !nice one

 

[Mr. X]

I usually use my float-line as a rough depth gauge. I attach my float line to my speargun. I often use a fairly short float-lines - to reduce tangle and/or winder-drag - and had to switch to slightly longer one a while back when I noticed that I was "getting to the end of my tether".

Alternatively is sometimes possible to see the bottom & estimate depth in body lengths. The time and effort to ascend can give an indication of depth - but perhaps too late by then . These are all just rough guides.

The Aeris f.10 mentioned above costs hundreds of dollars (Mako sell them). There ought to be a much cheaper waterproof watch with a depth gauge - or perhaps altimeter capabable of below sea-level reading - out there by now. If that floats your boat, try googling to see what is around.

 

[J Campbell]

Get an old syringe, seal tightly the output end. Lube up the plunger so it slides easily in and out. Now, when at the surface, be sure the syringe is clear of all water and containing only air, place the plunger in the top so it is held in place good, but don't push it down. Now dive. The air volume in the syringe at 34 feet will be half of what is was at the surface; 68 feet = 1/4 volume; 102 feet = 1/8 volume, etc.

 

[Bill McIntyre]

Get an old syringe, seal tightly the output end. Lube up the plunger so it slides easily in and out. Now, when at the surface, be sure the syringe is clear of all water and containing only air, place the plunger in the top so it is held in place good, but don't push it down. Now dive. The air volume in the syringe at 34 feet will be half of what is was at the surface; 68 feet = 1/4 volume; 102 feet = 1/8 volume, etc.

But this is the beginner spearfishing forum. Is it practical to be looking at a syringe while spearfishing?

 

[J Campbell]

But this is the beginner spearfishing forum. Is it practical to be looking at a syringe while spearfishing?

Yes, definitely less practical than looking at a dive watch.

 

[Steven Rawles]

Well I like it ! Low tech yet Scientific lol

 

[landshark sa]

Another option is to check depths and structure of the area you will be targeting before you go.

I use a combination of Garmin marine maps and Navionics when scouting areas before a dive trip.

All the mainstream fish finder / GPS manufacturers have apps available but in most instances you have to purchase the relevant detail map for your geographic location as the base maps don't have enough detail to make it useful from a diving perspective.

On my boat I use a Garmin chart plotter which has a feature called QuickDraw contours. When enabled, it creates a high definition contour map of the ocean floor as you cruise along. Amazing technology and the ocean floor structure data I now have is absolutely priceless. But you need all the relevant paraphernalia (plotter, transducer, map etc) in order to create these contour maps.

Navionics however has a free website / web app (https://webapp.navionics.com/) which has a cool feature called SonarChart which provides pretty high resolution contours of the ocean floor. Below is screen shot of an area (Anvil Rock) I dive regularly off Cape Point.

Cape Point:

Anvil Rock with the SonarChart feature turned on:

Because its not directly tied to a GPS coordinate it's not as accurate as the Garmin QuickDraw but I have plotted and mapped the Cape Point area extensively with my Garmin and can tell you that the Navionics is pretty darn close, so a very useful tool to check structure and depths.

 

[Mr. X]

Get an old syringe, seal tightly the output end. .... The air volume in the syringe at 34 feet will be half of what is was at the surface; 68 feet = 1/4 volume; 102 feet = 1/8 volume, etc.

Clever & I have a some cheap syringes in my workshop (for measuring 2-stroke oil, bar oil, etc.) - although 38 feet will likely be as far as I am likely to go - so might need to work on the calibration. I have a couple of very big syringes and many small ones - I guess there are pros & cons to each option (e.g. bulk vs. accuracy). Have you tried this while diving Mark?

Charts is a good idea. I bought some old out-of-date paper charts for dorset some years ago; charts become "invalid" for shipping as conditions change over time. It was interesting to review them but I haven't look at them for years; I tend to look at Google maps arial views now instead - no depth info tho'. Paper charts tend to be rather specific or rather too broad - it's not a cheap option. But if you already have access to modern computerized charts that might be a good option.

 

[J Campbell]

@james Bond - No, I have not tried using a syringe, I have an Oceanic F.10 watch. But if you try it let me know how it goes!

 

[mariusshobo]

Mark the buoy line from 5 to 5 meters with a permanent marker and sink the buoy anchor. Then you'll know the depth.
As for bottom time, monitor it in a safe environment, as a pool, if this is important for you. You can use any water resistant watch.

 

[Bill McIntyre]

Mark the buoy line from 5 to 5 meters with a permanent marker and sink the buoy anchor. Then you'll know the depth.
As for bottom time, monitor it in a safe environment, as a pool, if this is important for you. You can use any water resistant watch.

Sigh. Were talking spearfishing, not line diving. Or is he supposed to move the buoy after each dive?

 

[Steven Rawles]

Great shout on the navionics website unbelievably useful! Nice one landshark

 

[Naisan Geula]

another simple way: buy a used depth gauge from your local scuba shop or on ebay. They run from $10-$30 for a decent one.

Search ebay for "scuba depth gauge."

Make sure the one you get has a little wire next to the needle that will stay at the deepest depth the needle gets to - many have a little flathead screw on the front that you can reset after each dive with your fingernail.

 

[Mr. X]

Interesting, I just found this £17 depth gauge: https://www.scubaland.co.uk/capillary-depth-gauge-xml-350_428_7590-45466.html?currency=GBP

But the helpful description means it would be unsuitable for me:

Capillary Depth Gauge:

Capillary Depth Gauge (also known as a bubble depth gauge) is the simplest instrument designed for diving to measure the depth in which you find yourself. It consists of a tube that is stoppered on one end and attached to a scale plate. This depth gauge is very accurate in shallow waters, but its accuracy reduces in deeper waters. Additionally, you will need to have good eyesight and light to read this gauge.

 

[Mr. X]

Sigh. Were talking spearfishing, not line diving. Or is he supposed to move the buoy after each dive?

Bill, some spearos do this regularly, i.e. attach their dive buoy to a weight/anchor, drop it at a likely spot and then dive around it. I think Magpie in Guernsey described using a window sash weigh as his anchor when doing this some years ago. Probably not useful in the giant kelp forests you fish for white bass though.

I prefer to attach my floatline to my speargun (fear of loss) but some find float lines an unwelcome encumberance while spearing. Perhaps useful around tangle hazards, like wrecks too?