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Boxing clever

Ship & Boat international: Sept/Oct 2016

The new vessel Triploid, named after a species of bivalve, is definitely an original. Gary Wordsworth, founder of Othniel Oysters, has teamed up with naval architect Ian Darley to create a boat with one specific operation in mind: oyster harvesting.

Darley explains that Wordsworth has, over the years, developed farming methods which differ somewhat from the more common approach. “These oysters are not grown on ropes the way they do it in France; they are in their natural habitat on the bottom,” he says, adding that they are better for it. However, the issue is collecting the oysters efficiently.

This approach has resulted in a unique shape for the new Othniel Oysters vessel, as well as a focus on utilising as much local know-how as possible. The vessel was constructed by Poole-based yard Marine and General Services Ltd.

Operations on the square-ish, 0.6m draught vessel (tailored for the shallow 2m depths of the oyster beds in Poole Harbour in the UK) are centred around a long conveyor belt. This runs in a recess along most of the port side, so there is a 1.5m-wide bite taken out of the 6m beam hull.

High-pressure water is injected into the dredge head at the lower end of the conveyor. The agitated water and silt lifts the oysters off the bottom and deposits them on the conveyor.  The SPP KP122, 150mm-bore suction / 100mm-bore delivery pump is powered by an Iveco IK6H diesel engine mounted underdeck forward.

These oysters are then gently shunted up until they get to the deck – the effective angle of the conveyor determining the overall length of the 15.25m vessel – where they are sorted, on a second, transverse conveyor. “The detritus and those oysters that are too small are deposited into a waste well and land on the harbour bottom in almost the same place as they were picked up,” says Darley. He adds that, once again, local ingenuity has been key: Poole’s Weldtec Metal Fabrications and Finishes has built the whole system to the specifications of Wordsworth’s design.

Deck clearance
Since the harvester will be operated by a two-man crew, there’s an alternative second helm positioned at the rear near the end, close to the transverse conveyor. Interestingly, the forward-placed, fibreglass wheelhouse – moulded by local manufacturer, Martyn Schmitt – has overcome Darley’s original scepticism by being “much more cost effective than a steel structure and far easier to maintain,” as well as allowing for preformed, integrated housing for controls and so on.

The general design is an evolution of Wordsworth’s original conversion vessel. However, everybody admits that the first version of the vessel had become somewhat cluttered. “The brief was to clear a lot of the junk from the deck,” says Darley. Subsequently, a fair amount of work has been done to place as much of the kit below in the machinery spaces as possible.

As a result, the 6m beam still holds a lot of clear deck space – enough to carry no less than 14 Euro-pallets (each sized 1.2m x 1m); these are where the bagged oysters (which can survive two weeks out of water) are transported.

However this did take some juggling, Darley admits. He says: “Given the shallow hull, the area beneath the deck is obviously quite compact but we had to leave room for maintenance – we didn’t want people to have to wiggle in on their bellies.”

Engine selection
Propelling the boat along at its usual, stately 5knots pace are a pair of 63kW JCB J444 NA engines from Mermaid, with a Newage PRM 500 reverse reduction gearbox.  While speed is obviously not the issue here, these engines were chosen because of their longer stroke length, slower revolution and general robustness; these will take the vessel to 7knots for its weekly run to the processing plant. Blokland box coolers avoid sucking in the churned up silt from the shallow bed below.

There is a belt-driven hydraulic pump on each main engine to power the capable Amco Veba V815M 3SCE knuckle boom crane which has a 1.18tonne lifting capacity at 10.16m reach – this is necessary to pick up and place the Euro-pallets on the deck of the processing vessel. It also drives the conveyors and the small hoist winch mounted on the derrick that positions the conveyor and dredge head. Also beneath the deck are 500litre-capacity Tek Tanks, to hold the fuel, and a stainless steel hydraulic oil tank, a simpler option than building in integrated steel compartments.

Interestingly, this is only the second vessel that has been built at the Marine and General Services Ltd yard. Normally, this firm constructs water treatment plants for cruise ships, but Wordsworth – who is both a champion of local firms and a Poole Harbour Commissioner – wanted to keep the build close by.

There was one last issue: the harvester, when loaded with those pallets, will still have quite a high windage and it was necessary to find a balance between space, draught and freeboard “to stop the whole boat skittering around like a leaf on a pond”. So, Darley explains, the operational displacement was pushed to about 40tonnes by the integration of internal ballast.

“To most people this will be just a simple box... but there’s a lot of thought gone into this particular box,” Darley concludes.