While being towed at a 19.5-foot draft, the...

🔍 Key Concepts

• rolling period and stability – what does a short vs. long roll period generally tell you about initial stability (GM)? • effect of increased draft/ballast on GM for a semi-submersible or MODU being towed • operational limits in the MODU stability booklet regarding maximum allowable roll amplitude and roll period while under tow

💭 Think About

• Think about whether an 8‑second period with only 10° single‑amplitude rolls suggests the rig is too stiff (excessive GM) or too tender (insufficient GM). • Consider what happens to the center of gravity and center of buoyancy when you ballast a semi‑submersible deeper: does this usually increase or decrease GM? • Ask which option is the most cautious and directly addresses the observed motions, rather than just continuing as you are or changing course without fixing the underlying stability condition.

✅ Before You Answer

• Verify whether larger GM = shorter, snappier roll period and smaller angles, and smaller GM = longer, slower roll period and larger angles. • Check how ballasting from 19.5 ft to deeper drafts (45 ft or 60 ft) would normally affect the rig’s metacentric height (GM) and hence its rolling behavior. • Confirm which options actually change the rig’s stability condition versus just changing operating parameters like heading or simply continuing.

While being towed at a 19.5-foot draft, the DEEP DRILLER experiences single amplitude rolls of 10° with a period of 8 seconds. You should __________.

ballast the rig to a 45-foot draft and check the vessel motions

ballast the rig to a 60-foot draft and continue towing operations

alter course to bring the wind off the starboard beam

continue towing operations at a 19.5-foot draft

🔍 Key Concepts

💭 Think About

✅ Before You Answer