A tough challenge was set for Ijmuiden based Offshore Ship Designers (OSD) when Silverburn Shipping Group was looking for a shallow draft offshore supply vessel for Caspian Sea service.
It has to be capable of worldwide AHTS service, but also has to be optimised for the Caspian Sea and Russian rivers, which are a very tough environment. The vessel will have to be capable of 40 tons bollard pull while on a shallow draft of 2.5m. It also requires a significant load carrying capability at this draft and must be able to break ice up to 70 cm thick.
Silverburn insisted that the vessel had to be a very rugged and simple design, able to operate and be maintained without extensive support. There are no high quality shipyards close to the expected operating areas if repairs are needed. No high tensile steel could be used and a conventional dual diesel direct drive power plant with shrouded propellers was chosen. The challenge for OSD was to design a vessel which is strong enough to break ice yet light enough to carry cargo on a shallow draft.
Model tests at Aker Arctic show that it can be done. The basic design challenge has been met by increasing the beam of the vessel to generate load capacity on a shallow draft. This is at the expense of some seakeeping ability, as the vessel now has a high GM. OSD has conducted 1:10 scale model tests at Aker Arctic to ensure the hull form can break ice to Finnish/Swedish Ice Class 1A standards. The tests showed that the extreme B/D ratio will deliver the performance required and the design is now out to tender at a number of yards.
Main dimensions for the design are LOA 49.6m, beam 16.5m, seagoing draft 3.5m, and shallow draft 2.5 m.
