Delmar System engineers provide offshore technical support to assist with the installation and recovery of all mooring systems. Our offshore support includes a wide variety of products and installation methodologies.
MODU Mooring Installation and Recovery Assistance
- Model line catenaries both real time and in the future
- Provide positioning guidance for all vessels
- Calculate component payouts needed to make preset connections safely and efficiently
- Monitor rudder clearances to anchor handling vessels during preset connections
- Assisting with anchor placement for conventionally installed systems
- Calculating mooring loads for proper load sharing between vessels
Modeling Line Catenaries
Our Del-Cat mooring software is used to calculate mooring line catenary shapes throughout the entire mooring process. Clearances to any assets (such as pipelines, umbilicals, etc.) are noted. Catenaries are also modeled ahead of time to determine boat positions and payouts necessary to help make safe and efficient connections or disconnections.
Monitoring Rudder Clearances
As mooring operations are being conducted, it is necessary to ensure that the mooring component does not come into contact with the rudders of the anchor handling boat/vehicle (AHV). Sometimes it is required for the AHV to turn the boat heading in order to make preset connections and disconnections. If sufficient component is not paid out by the MODU or AHV, rudder contact can occur. This contact can then lead to damage to the AHV’s rudder or mooring equipment, which can be especially critical if operations are being conducted over assets.
For conventionally installed mooring systems, the anchor is stretched with the AHV after the proper components are paid out by the rig. Therefore, the anchor placement is highly dependent upon the payouts and vessel positions at the time the anchor is set on bottom. Delmar can run catenaries in these cases to assist with getting the anchor closer to the proposed position. Modeling the stretch of the line is also important to ensure much of the mooring component is off bottom prior to cutting power on the AHV and setting the anchor in the mud.
Especially for cases with heavy mooring component, like with long chain sections, it is important that the rig and anchor handling vessel load share the weight of the mooring component. If too much weight is supported by one side during installation or recovery, damage to the winch can occur. Delmar can run catenaries and calculate mooring weights to help ensure a safe operation and mitigate equipment damage.
The Bruce DENNLA (Drag Embedment Near Normal Load Anchor) can be preset ahead of rig arrival on location for systems where taut or semi-taut (minimal grounded length) systems are being used. Delmar can provide technical support to monitor the line catenaries as the anchors are being set and later proof-loaded.
Once the AHV (anchor handling vessel) has set the DENNLA on bottom near the proposed anchor location, it begins to pay out mooring components as it moves away from the anchor down the proposed heading of the mooring line. Once a sufficient amount of component is paid out, the vessel powers up. Excessive uplift or bollard pull may result in the anchor slipping, causing lost time with it needing to be reset. Too little power may result in the anchor not penetrating properly.
Once the DENNLA is set, the AHV will back off of its power and recover component until there will be ~40° of uplift at the anchor for the pin shear condition. Once this has been done, the boat will again power up and put sufficient tension at the anchor to shear the pin. It is extremely important for the catenary to be monitored in this condition since too high of an anchor angle may result in slippage. Too little power or insufficient uplift may result in the pin not shearing.
Delmar’s OMNI-Max® anchor is a gravity-installed VLA (vertically loaded anchor). The anchor has a 360° rotating arm so that it can be loaded in any direction which can be important in cases such as multiple line failures during an extreme storm event or if it is planned to do several batch operations from the same mooring pattern by winching the vessel around a field (without moving anchors).
Delmar can provide technical support in the field to make sure the OMNI-Max anchors are installed properly. Other technical support includes:
- Water depth verification at seabed
- Anchor tip depth verification (just before anchor release)
- Released anchor location
- Arm heading verification (just before anchor release)
- Measured anchor tip penetration (note any differences to calculated penetrations if soil data is available)
For recovery, it is important to note the new anchor tip penetration prior to pulling the anchor out of the mud, especially if the line was subjected to any high tensions from a storm event. Once the new penetration has been calculated, the maximum recovery tension needed by the winch on the anchor handling vessel is logged as well.