Active Heave Compensated Drilling

The DOSECC AHC800 is an active heave compensated (AHC) coring rig that is capable of retrieving continuous core to depths of 800 m (water + sediment) in shallow marine and deep lacustrine environments. The system is modular and designed to fit on a variety of drilling platforms. The AHC800 uses the same suite of proven sampling tools as does DOSECCs GLAD800.

The AHC800 senses the heave of the vessel using a taut line deployed through the moonpool or over the side of the vessel. The vertical motion of the vessel is relayed to a computer that in turn activates hydraulic controls. The AHC800 is powered by a 450 hp diesel engine.

Based on the success of the GLAD800 system, the United States Office of Naval Research requested that DOSECC design and build an active heave compensated rig. The rig, designated the AHC800, is specifically designed to collect core samples on the continental shelves. The rig can be operated from the larger UNOLS research vessels (R/V Knorr, R/V Melville) that have moonpools. The rig can also be accommodated on the icebreaker R/V Palmer that is being fitted with a moonpool. In addition, the rig could be cantilevered over the side or stern on vessels without moonpools. The rig is also suitable to use on vessels of opportunity on large lakes, such as Lake Malawi in Africa.

The AHC800 underwent sea trials in November, 2001 and a three-week drilling program in September-October 2002.

Download or Review our AHC Brochure: Front and Back.

AHC800 Specifications are provided below.

Video of sea trial of AHC800 aboard the R/V Knorr. The ship is heaving with the waves; the drillers are stationary with respect to the horizon.

Quicktime video, ~ 3 minutes

The AHC800 has undergone sea trials mounted on the R/V Knorr. The trials utilized a moonpool located to the aft and starboard of the pivot point of the vessel. Positioning utilized the Knorr’s GPS system controlling one bow and two stern thrusters.

Counter:

Heave Design Parameters

Vertical Ship Heave: 8 feet (2.4 m)

Wave Period: 8 Seconds

Cal. Maximum Velocity: 3.14 feet/sec. (0.95 m/s)

Feed Holdback: 40,000 Pounds Maximum

Heave Acceleration: 0.077 G

Calculated Heave System Parameters

Heave Force: 52,400 Pounds Maximum

Heave Compensation: 4 feet/sec. Velocity Maximum (1.2 m/s)

Heave Acceleration: 0.1 G

Heave Cylinders: 2 @ 5.00” Bore x 3.5” Double Rod

System Pressure: Calculated Working Pressure 3900 PSI, Max. Continuous 5000 PSI

Heave Stroke: 8 Foot (2.4 m) Stroke (10 Foot Available)

Peak Oil GPM: 250 GPM

Oil Flowrate: 125 GPM (16.63 Gallons/Period)

Heat Rejection: 120 Horsepower Average

Outside Supply Items

Cooling Water Supply: 75 GPM Sea Water (filtered)

Compressed Air: 50 SCFM @ 100 PSIG 35-degree Pressure Dew Point

Electrical: 120 / 60 VAC, 30 amp capacity

The AHC on land, shows the general configuration of the system.