Purpose-built chase vessels for seismographic research
Rederij Groen, a Scheveningen-based service supplier to the offshore industry, initially contracted Saltwater Engineering in 2010 for a preliminary design of two dedicated chase vessels for seismographic research. The preliminary design consisted of the hull lines, a general arrangement and a technical specification. The initial design brief called for a tonnage below 500GT, comfortable accommodation above the main deck, a practical aft working deck and a spacious wheelhouse with good views both forward and aft.
The design of the Astra-G and Aquarius-G was primarily based on her seakeeping behaviour at low speed. Saltwater Engineering concluded that a sharp bow, with U-shaped sections and minimal bowflair, along with V-shaped stern sections would yield the best result. At low speeds stern slamming becomes an important issue, V-shaped stern frames help reducing the force of the impact.
Out-of-the-box thinking resulted in a design with a relatively high centre of gravity, resulting in a GM below one meter, and thus gentler transverse accelerations and more comfortable motions. The principle is based on the hull of cable laying vessels, which also spend most of their time at low speeds.
Saltwater also designed an important add-on, the quick release towing hook that was integrated onto the aft deck. Saltwater Engineering provide Rederij Groen with detailed FEM calculations and workshop drawings. The bollard pull was tested at 21.5 tons.