Drag levels and energy requirements on a SCUBA diver

The popularity of sport diving has increased rapidly since its inception in the 1950’s. Over this period, the trend has been to increase the amount of equipment carried by the diver. There are many undoubted safety advantages associated with the additional kit, but under some conditions, it can impose an additional burden in the form of increased drag. The purpose of this paper is to identify the drag penalties for a number of simple SCUBA configurations. This is achieved through scale model experiments conducted in a wind tunnel. Some comments on the associated energy requirements are made, and from these, the effect on a diver’s bottom time is briefly addressed. The configurations tested include a study of the effect of the equipment configuration and the effect of small changes to the diver incidence. The tests show that the addition of a pony cylinder gives a 10% increase in drag compared to a conventional octopus set-up. When a dive knife, large torch and a Surface Marker Bouy (SMB) are also added this increases to 29%. Over the range tested, the average effect of swimming at a head up incidence to the flow is to increase the drag coefficient by 0.013/degree. This amounts to 16% at 5 degrees and 49% at 15 degrees. Estimates of the effect of the drag changes on bottom time show that particularly at the higher speeds the drag increases result in approximately similar percentage reductions in bottom time. Some simple suggestions for drag reduction are proposed.