By K.Steiner-Dicks on Feb 2, 2015

Conventional ROVs are generally designed to operate in subsurface currents of up to 1.5 ms-1 but, in Mojo’s experience, many struggle above 1.0 ms-1. Conventional ROVs can therefore be a key operating limitation in the design (and cost) of the marine operations for tidal energy installations, where subsurface current speeds of 5.0 ms-1, are the norm in high energy tidal sites.

For this reason, Mojo and IKM joined forces in mid-2014 to bid for EU funding, from the Maritime Technologies (MARTEC II) call, to develop a HF ROV capable of being operated from the HF4 in high energy tidal sites. The project is being administered by InnovateUK.

The ROV will be capable of being operated from Mojo’s ground tidal energy vessel, the Hi Flo 4 (HF4).

A significant proportion of overall tidal energy costs are in array installation and, between 2012 and 2014, Mojo Maritime designed and developed the HF4, an offshore construction vessel (OCV) capable of lifting the heaviest envisaged tidal turbines and of dynamically positioning in up to 5.0 ms-1 (10 knots) of tidal stream.

“These operational advantages will feed through into installation benefits,” says Mojo, who has witnessed early analysis using its Mermaid vessel in medium energy tidal sites.

“HF4 can install tidal arrays in half the time and at a third of the cost of conventional methods,” says Mojo.

Mojo claims that HF4 can offer levelised costs of energy for tidal arrays of £118 per MWH, which is already below that of many envisaged offshore wind projects, and Mojo is now working with its ship-owning partner, Hammonia Reedeira, to select a yard to build the first-of-class HF4, with an anticipated delivery date target of late 2016.