FEATURE | O’Hara Corporation’s Bering Sea factory trawler gets efficiency-enhancing upgrades

FISHING/AQUACULTURE WEEK
Alaska Spirit (Photo: O'Hara Corporation)

O’Hara Corporation, a fishing company based in Rockland, Maine, is presently overseeing a project aimed at modernising one of its existing factory trawlers.

Originally built by Halter Marine Services as an offshore supply vessel for operations in the Gulf of Mexico in 1974, the 204-foot (62-metre) Alaska Spirit has been fishing in the Bering Sea just off its namesake state since 1989, when it was brought to Murakami Shipyard in Japan to undergo conversion to a head and gut factory trawler. O’Hara said it has committed to a complete overhaul to improve habitability and efficiency as well as to optimise the performance of the vessel, which has been used to catch Atka mackerel, Pacific Ocean perch, yellowfin sole, rock sole, pollock, and cod.

The multi-year modernisation project began in 2017, shortly after O’Hara acquired the vessel and selected Seattle-based naval architects Elliott Bay Design Group (EBDG) as its designated engineering partner. EBDG said project planning has been very intentional to ensure vessel operations were not negatively impacted. The designers further claimed that, as a result, the modernisation work completed thus far occurred during normal downtime, meaning no seasons have been missed during the process.

Upgrades to Alaska Spirit included a new generator and hydraulic engines, a new factory, conversion of underutilised aft tanks to stores, replacement of pilothouse port lights with windows, habitability upgrades, and a complete redesign of the trawl deck. EBDG has provided engineering support for much of this work while the US Coast Guard provided oversight in accordance with the Alternate Compliance and Safety Agreement (ACSA).

For habitability, O’Hara and EBDG refurbished the crew quarters by incorporating upgrades to the staterooms, the laundry area, and the showers and toilet spaces. The two companies are currently in the planning phase for galley and mess area upgrades to complete the accommodation improvements.

3D model overlaid with vessel scan (Photo: EBDG)

EBDG also added silencers to the exhaust lines of all diesel engines to substantially reduce onboard noise pollution for the crew. The designers said that, prior to installation, noise on the trawl deck measured approximately 130 dB – well above the 110 dB that researchers at Purdue University claim to be the average human pain threshold  – whenever the main engines, the generator, and the hydraulic engines were operating. Following installation of silencers, the sound level dropped to 85 dB.

For the silencers, EBDG engineered two new stacks and rebuilt an existing one. The starboard stack aft of the amidships gantry houses the main engine silencer, and the port stack outboard of the gantry houses two silencers for the new Caterpillar C18 generators installed. The port stack forward of the gantry was modified to allow installation of a silencer on the new Caterpillar C32 hydraulic engine.

When the vessel was converted for fishing in 1989, the crew relied solely upon burtoning gear. There were no net reels installed and spare nets were carried outboard of the trawl fence. O’Hara has since removed the forward burtoning gear and installed a knuckle boom crane. New trawl winches began being installed in 2020, and an equipment room is being constructed around the crane pedestal.

This year, the existing trawl machine located at the forward end of the trawl deck will be removed. In its place will be a pair of net reels and a new Gilson gantry. The base of the gantry and reel foundations are being incorporated into an enlarged changing room for the deck crew. All these modifications have been analysed using finite element analysis (FEA) software, an innovative tool that helps designers and engineers predict how an object will react to real-world physical effects such as heat and vibration.

Throughout the modification process, O’Hara considered several different vessel options, one being the addition of a bulbous bow. EBDG investigated the addition by utilising CFD analysis.

Four different bulb geometries were considered in three conditions of vessel loading. The conclusion of the analysis was that dramatic changes in vessel trim meant a bulb could significantly improve vessel efficiency for a particular loading, but would have comparable penalties to efficiency in other conditions of loading. As a side benefit of the analysis, EBDG and O’Hara determined that modifications to the bow thruster grating, a relatively inexpensive change, could realise an efficiency gain of over one per cent. Ultimately, though, O’Hara decided not to install a bulbous bow.

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