Self Elevating Units – Part 3 Reader Feedback
Mar 31, 2015 News Archive
I am happy to report that we had good feedback on Part 3 of our Self Elevating Units series. One point in particular we’d like to share is a comment by Colin Nelson, who has over 30 years’ experience working on jack-up operational and design issues with drilling contractor and marine warranty survey entities.
Colin’s comment, has to do with the published ratings of a unit (usually done for marketing purposes). In some cases, especially for liftboats, we have seen combinations of high wind speeds with very low wave heights that are almost impossible to co-exist. This is Colin’s initial comment:
“I would point out though that we must try to avoid errors which have been made in the past where there may have been significant inconsistencies between components of metocean criteria which were applied together – in other words high wind speeds with no current, or mismatched wind and wave assumptions.”
- Colin Nelson
Our response was that the use of such “unrealistic metocean combinations” is mostly due to the fact that unrestricted service notation can be obtained simply by proving that the design can handle 100knot wind speed with any wave. So, many times we’ll see designs that show 100knot wind speed with 1m waves (and 1knot wind-driven current). This is most prevalent on liftboats than jackups, though.
Colin followed up with the following comment, which corroborates the need for the industry to have a clear distinction when discussing the capabilities of a unit. Colin’s closing comment is shown below.
“In my view, one of the reasons for the implementation of site specific assessment for jack-ups across the industry is that operating expectations have been skewed by inappropriate claims of operability derived from unrealistic combinations of metocean criteria which are far removed, in some cases, from what occurs in the field. It was common a few decades ago, and I am disappointed if it is still going on as you suggest. We should all know better by now. Designers and builders need to work on projects which will be fit for purpose for the anticipated operating theater and lifetime of the vessel, and not merely generate work during the design and construction phase which could leave inherent legacy issues for the satisfactory operational performance later. Designers would be well advised, in my view, to highlight any client related specific requests to the contrary which might lead in this direction, because the client for the initial build may not retain ownership throughout the life of the unit – but the legacy will endure.”
- Colin Nelson