Are Rebreathers Overly Restrictive on Vision and Mobility?

[AKmountaineer]

Let me first qualify this post by saying that I have yet to actually dive with a rebreather, but it seems that all of the pictures I've seen feature a diver with his head shrouded in fat hoses on 3 1/2 sides leaving only a little room for him to peer out over the top of an exceptionally large mouthpiece. Does the setup of these devices really cut down on visibility and head mobiliy as much as it appears to? Why is it necessary to have such fat hoses? Obviously you wouldn't want to be breathing through a straw, but it seems like half the current hose diameter would be adequate for gas exchange.

 

[wedivebc]

Let me first qualify this post by saying that I have yet to actually dive with a rebreather, but it seems that all of the pictures I've seen feature a diver with his head shrouded in fat hoses on 3 1/2 sides leaving only a little room for him to peer out over the top of an exceptionally large mouthpiece. Does the setup of these devices really cut down on visibility and head mobiliy as much as it appears to? Why is it necessary to have such fat hoses? Obviously you wouldn't want to be breathing through a straw, but it seems like half the current hose diameter would be adequate for gas exchange.

Because the gas is moved around the loop by lung power the work of breathing is very important to the diver, that is why the hoses tend to be large. As far as mobility is concerned I do find it easier to tilt my whole body to look beside me but there is no trouble tilting my head up and down. There is no lack of visibilty that I have noticed and the lack of bubbles filling your field of vision is a definate advantage.

 

[caveseeker7]

The work of breathing depends on a variety of factors regarding the gas path, among the the diameter of openings and hoses. Narrower hoses also translate into higher gas speeds within the loop, including the scrubber.
Both high WOB and reduced dwell time can affect CO2 build-up.

There are different types of corrugated hoses. In some the corrugation is spirally, which is eases cleaning and drying. But these can not be cut to length. There are also hoses with circular corrugation, which allow the hoses to be cut to the ideal length for the user. This is one way to keep hose interference to a mininmum.

As for mobility, the reason that the hoses are as long is to insure the needed mobility. The large DSV keeps them far enough apart that they usually don't interfere much.

If you look at list of successfull photographers and filmmakers using rebreather it becomes apparent that limited vision can't be a major issue. Howard Hall, Wes Skiles, Curt Bowen, Jill Heinerth, the list goes on and on. The advantages certainly outweight any inconvinience caused by the hoses. There are plenty of photographers still using twin hose regs to avoid bubble interference.
Also, consider that rebreathers are frequently used by other "working divers", from Fish & Game to NOAA to UC Davis researchers tagging sharks and military divers disposing of ordenance.