Housing/gear considerations for deep diving

[chipi 1]

Hi everyone. 

I am on my way to spend more and more time in 60-100m range of depth in sea with my Nikon D850 in Sea & Sea housing and I am curious what are some extra considerations about the gear, tips and tricks and/or whatever knowledge that could be useful to make sure my kit survives :-) and I get good shots.

Example:

1. Electrical va optical cables. I use electrical.

2. How big vacuum to set? I started pulling out more air with pump when going deep. 

3. What do you think of survivability of extra connections like bulkheads for strobes, vacuum ventil etc

4. What about condensation inside and temperature ranges?

5. Acrylic va glass dome ports in terms of strength and depth rating

6. Depth rating of viewfinder assemblies?

7. How much should I trust that small plastic window on back of the housing. Looks vert fragile even if housing is 100m rated

8. What does it really mean 100m rated? Tested to 150m so definitlly good on 100m?

9. What about ambiental exposure in those low light conditions down there. Sometimes it is pitch black and no blues. How far to go with ISO and get still a good compromise on size of the grain/noise

And so on and on. Maybe for somebody this is a routine and some proven tips are just around the corner.

Thanks,

Marko 

[ChrisRoss 150]

Hi Marko,

some comments on your list

2. Vacuum, there is no need to change this it is only there to pre-load the o-rings and to provide a means to leak check.  O-rings seal better with more pressure up to the point they physically fail which will be much deeper than you will be going.

3. if they are rated for 100m no reason to expect different survivability - all it has to do is keep shape and the o-rings won't give you any more problem than at shallow depths and small parts are inherently very strong.  Similar o-rings withstand 200 bar in your scuba tanks.  As long as the joint is designed according to well established guidelines o- rings can seal really very high pressures - 10 bar mechanically speaking is fairly trivial, though for the human body it's another matter all together.

4. no different to cold water diving - aluminium housings tend to be less prone to condensation in any case - just take normal precautions as you would on shallow dives

5. there is nothing inherently different about acrylic vs glass,  I think acrylic has a higher strength as it seems some of the items with a deeper rating are acrylic.  Just go by the vendor depth rating.  It is a relatively simple engineering calculation to work out the strength required to withstand the pressure.  The Pressure at 100m is 10 bar but your scuba tank holds air at 200 bar - 10 bar is not that high a pressure from a mechanical perspective and a hemisphere is a very strong shape.

6. the vendor will design them for a certain depth - why would you not trust this rating?

7. Again this is designed as part of the housing acrylic plastic is really very strong

8. it will be designed to withstand the external pressure - relatively straight forward engineering calculations and guidelines.  Depending on the manufacturer they will then test each housing - this is more checking there are no defects that would cause a problem than confirming the housing as designed can withstand the pressure. 

[chipi 1]

Thanks Chris for detailed comments. All makes sence. Cheers!

[simonK 10]

I have had a 230mm dome crack at 70m, it was rated 100m. So recommend you stick to smaller domes for the deeper stuff, or at least do a test dive with an empty housing if you must have a big dome.

[trimix125 73]

Hi,
at 100m its 11 bar ;-))
A difference can be that the pressure puts so much power to the orings that pressing / turning gets a lot harder...
Was once with a Subal video 8 housing a lot deeper than planned, and couldnt simply switch it on, because the switch was a knob, and i couldnt turn it... Non of the sealings was leaking, simply too tight.
Point can be that the springs have to be changed to stronger ones for deep diving. Thats what is the most difference between normal and deep housings.
Regars,
Wolfgang

[Algwyn 12]

If you dive to 100m, you'll reach the limit of the Sea & Sea depth rating, which probably increases the risks of flooding.

For deep diving, have you considered switching to an Easydive housing? They are designed for deep diving, up to 150m. It's one of the few housing actually designed for deep diving.

[r4e 24]

Hi,

1. There is little difference between optical and electrical cords if they are properly manufactured. Electrical cables might have more physical strength against getting snagged in your other gear. But thereafter the cable might be less reliable.

2. I wouldn't add vacuum pressure for deeper dives. It increases pressure difference between the inside and outside of the housing and thus could slightly reduce MOD for the housing. E.g. a housing with 100m specs and a normal 0.2 bar vacuum, would, in theory, reduce to MOD 98m if you increase the vacuum to 0.4 bar. Increasing vacuum is totally unnecessary unless you have trouble of a vacuum sensor circuit not being temperature compensated. Then you might receive false alarms when descending into colder water, if you pump just to the minimum threshold in room temperature.

3. Strength of small components is not likely to be a limiting factor.

4. Condensation risk is dependent on temperature difference, air moisture (when closing housing) and housing material. A metal housing will conduct heat/cold faster and therefore the metal parts will sooner become cold than the dome, thus collecting the majority of moisture and reducing likelihood of condensation in the dome area. Depth will affect only via water temperature. E.g. here in Finland almost all diving to anything deeper than 30m will be around 4-6 degrees celsius. However, even with a metal housing, condensation is possible if you do not pay attention to closing procedures. E.g. if you are sweating in a 30+ celcius climate and place the camera into the housing with sweaty hands and drip some of your sweat into the housing and then leave the housing in the sun for a while, all that moisture will become partial pressure steam into the air of the housing. If you then make a fast descent to 4 degree water, you might have condensation even inside the dome. (done that).

5. The manufacturer should specify depth ratings for each dome model separately. Please note that there are both glass and acrylic domes that are specified to only 40m. However, the depth rating is for a new dome without scratches and/or microcracks. These faults are likely to decrease depth tolerance.

6. The viewfinder falls under the small components topic. It is the outer glass that takes the pressure difference. In most cases it is straight glass with sufficient thickness. However, I want to point out that in some housing the view finder is attached to an acrylic back window. If you use a longer 45 or 180 degree viewfinder on your housing and you happen to bump a tank against the viewfinder, there will be momentary dynamic forces in addition to the static water pressure.

7. The back window is designed by the housing manufacturer to be thick enough. In most cases it is a straight acrylic sheet without curvature and most of them range between 5-10 mm thickness. In addition to thickness, the critical design question is the surface area. It is often the surface area of the acrylic window that will limit the maximum depth. This is quite apparent for Blackmagic camera housings and some of the monitor/recorder housings, especially one with larger screen size.

8. Different manufacturers have different procedures for this. For example, some manufacturers just perform a test to this nominal depth, but, design and manufacture all the items robust enough for much bigger depths. They just don't claim any higher figures. In Europe/EU there is regulation concerning pressure vessels and how the maximum operational pressure and test pressure should relate to each other. I wonder how many, if any, of the manufacturers have paid attention to these rules.

We perform hydrostatic testing for our customers' u/w camera gear and do perform various kinds of tests upto static pressures matching 150m water depth. However, these are static tests. If you bump your acrylic (or glaas) dome into a tank, DPV, ship wreck or solid rock at 150m depth, there will be the combined effect of static and dynamic forces at very small points of contact and an implosion is possible. Some of our customers have been shooting stuff at 150m and I have warned them about this combined risk.