Modifying my BMCLs for the Hammerhead Extreme CCR

I've started to make a few adjustments to my new Hammerhead CCR this week, in general the unit works a dream; but one minor concern I had is that the unit doesn't breath well as you move to a head down position due to air becoming trapped in the bottom of the lungs and not being able to reach the shoulder mounted T-pieces.

I don't really plan on being in a head down position too often, however wreck or cave diving can often require this and I didn't like the idea of restricted or unbreathable operation when more than likely being in a restriction.

Hose wraps on BMCL T-pieces

The modification suggested by Randy from SubGravity was the addition of the standard scuba hose wraps into the the lungs.  I actually didn't dive the unit without the wraps inside the lungs so can't comment on any improvement but I felt the sharp edges of the wraps could increase the risk of puncturing the lungs, while the performance with the wraps still made breathing slightly more difficult when horizontal and noticeably difficult when orientated head down.

I wanted something softer inside the lungs that gave a greater opening area to keep an airway between the t-pieces and the bottom of the lungs, initially I was thinking of a 1 inch diameter chemical braided hose (like a large diameter hose pipe) but was a little worried about the effect on minimum loop volume - a long length of large diameter hose would create quite a bit of dead space which I didn't want to carry in the lungs.  The hose also needed to be soft enough to not interfere with the lungs or risk damage, but firm enough to avoid collapse when under a negative pressure in the lung.

Standard firm garden hose with holes

I weighed up a few different options and had intended to try two or three different options, namely a standard garden hose, a slightly larger hose and the larger 3/4 inch hose.  My final choice was just to go with the garden hose as the hardware store nearby only had that in stock unless I bought the full 20m hose!  I had two choices, soft or firmer and went for the firmer hose type.

I cut the hoses to reach from the t-piece to around 10cm/4" from the bottom of the lungs - this could mean I couldn't quite work them at absolute minimum loop volume but was willing to sacrificial that to avoid the end been sealed or increased risk of water in the hoses.

To stop water entailment from the bottom of the lungs into the breathing loop, and to allow gas movement from anywhere in the counter lung, I drilled several large holes in the hoses.  I had originally intended to drill more larger holes but found they made the hose shape more flexible and was concerned the hoses could close up and reduce the breathing area when under a negative pressure in the lung.

Hose connection on BMCL T-piece

The hose was then tied using a cave line with two half hitches to the counter lung t-pieces, keeping the hose and as close as possible to the t-piece connection.

Performance wise I definitely noticed a significant improvement in the work of breathing when fully horizontal, head down was still noticeable harder to breath but it did prevent the complete close-up of the lungs - although the breathing resistance was still very high.

I've since added a second hose to each counter lung to double the hose opening are, the second hose was added in the same way as the firs.  Adding the second hose seems to line up well with the t-piece water trap openings.

I've not yet had a chance to dive the unit with the second hose so can't compare performance, however I'm hoping there's a further improvement - logic would suggest breathing should be easier again given the increased hose sectional area in each lung.  Sadly I don't think I'll get a chace to dive the unit again for almost 2 weeks due to other commitments but as soon as I do I'll give an update on how it works!