CONCLUSIONS
The Leg 179 HDS tests were designed to be a test of the overall HDS concept in actual sea conditions. As such, the tests provided a wealth of data that, with further study, should provide a clear indication as to the direction in which the HDS development should proceed. The hammer drill itself shows great promise of being able to penetrate subsea hard-rock environments. Although the hammer drill performed well considering the sea state during the testing, a dialogue with the manufacturer will be established to address issues such as the short stroke length to open and close the bypass, the valve cracking problem, and galling of the piston and lower bushing.
It is evident that the underreaming bits designed for conventional land-based hammer drill operations, such as those used during Leg 179, are not suitable for drilling in casing in offshore deep water with an unsupported BHA. Ideas for new design underreaming bits are already being formulated. The HDS casing running tools and reentry cone were not deployed during Leg 179. However, they were land tested before Leg 179, and no problems were encountered. So, at this time, no redesign of these tools is planned. In general, confidence remains high with the overall HDS. The benefits of the HDS to ODP and the science community as a whole are well worth continuing with the HDS development.