In the ever-evolving world of subsea operations, innovation knows no bounds. One groundbreaking solution that has been making waves is the MDL PVLS - the world’s first road-transportable vertical lay system - and its multi-tasking iteration, the PVLR. Both offer a convenient alternative to a pipelay vessel for those smaller or isolated scopes that demand vertical handling.

But what if we told you that there’s also a way to lay vertically using a horizontal lay system?

An industry-proven alternative to the base case VLS approach is a modular spread of portable equipment that can be installed efficiently on a vessel of choice, reducing the ‘all-up’ day rate of an installation vessel.

The key to selecting the correct modular spread for your project lies in considering the maximum top tension foreseen during installation or recovery and the properties of the flexible product.

At MDL, we are specialists in the delivery and operation of such modular spreads, which can also replicate the functionality of a VLS - like the MDL Horizontal Lay System.

Horizontal Lay Systems (HLS) are not new in the SURF market; what differentiates the MDL design is the packaging of an array of handling aids within the system’s footprint - very much like the PVLS.

Fixing Friction

The MDL HLS's convenient features have made it a hugely popular system worldwide for umbilical installation and riser retrieval and it has been the system of choice for a SURF decommissioning programme off South America.

However, even advanced systems face challenges. Our HLS excelled in many aspects but encountered limitations when handling recovered pipes over the HLS chute. Friction between the flexible product and the chute significantly reduced recovery capacity, even with a high line pull-capacity tensioner.

While the HLS could provide an outboard tension of 100Te with a single-unit MDL tensioner and a 4.5m chute, the required load capacity for recovery was 185Te.

Did that mean the Contractor was going to be forced down the route of using a costly pipelayer for the retrieval scopes? Not for us. We're all about lean solutions, and some further engineering and exploration led us to the answer: we needed a wheel.

MDL Wheeled Horizontal Lay System

The WHLS keeps true to the base HLS design by offering a portable, compact, and cost-effective solution applicable on vessels of opportunity – that is, any “bare back” tonnage available locally, optimising schedules, budgets and project CO2 impact.

The system maintains all the features facilitating recovery of various lengths and diameters of products, including: an integrated hang-off for handling end fittings; davits for overhead handling of products; integrated work platform for over the side or moonpool scopes and an adjustable wheel position to accommodate various product diameters.

By incorporating a wheel into the HLS design, we boost recovery capacity to match the tensioner's capability without extra space or weight from additional steel structures. The 2-point contact from the wheel profile on the product results in reduced MBR requirements, opening up the OD window for wider application.

The first MDL WHLS has now shipped to its new owner in Brazil - but should we consider adding one to our rental fleet? Reach out to our team if you're interested in the MDL WHLS or want to discuss improvements for lay, retrieval, or mechanical handling operations in your sector.