Inspired by Fredrik Ljungström’s circular arc hull design, the OK Hull was created by Rafnar's founder Össur Kristinsson, who dedicated six years to the development of the scalable platform. The research process involved tank testing over 100 different one-metre models before building a six-metre prototype.
Össur Kristinsson (all images by Andrew Johansson)
Following extensive studies on the six-metre, the yard began to construct larger prototypes before settling on Leiftur, a 10m RIB and Þorbjörn, an experimental 12m fibreglass boat. We were invited on a sea trial in ever-changing weather conditions to highlight the qualities of the boats promised by Rafnar, and they didn’t disappoint.
Unlike a traditional RIB hull form, the OK Hull does not rise up and plane, nor does it plough through the sea like a displacement vessel. And yet when we opened up the throttle of the two 250hp engines (Leiftur is fitted with outboards while Þorbjörg has inboards), the boats increased speed and reached in excess of 30 knots. This is thanks to its special hull shape, which directs water under the boat in a more efficient way to reduce drag.
“These boats don’t behave in the same way as others,” explained captain Mike Hasted, who worked together with the team on the project. “When you come alongside a boat in a traditional RIB, you have to maintain a certain speed to keep it on the plane. With Leiftur, you have much better control over the speed and the boat behaves much better.”
While there are differences in performance between the models, they delivered a comfortable ride in open water. Manoeuvring at speed was impressive with tight turns achieved without sliding and a high level of grip at the stern. It is this overall performance that grabbed the attention of the Icelandic Coast Guard, which will take delivery of its first custom Leiftur in mid May 2015.
“It has been proven that this craft works extremely well for us in our operations in Icelandic waters,” said Georg Larusson, CEO of the Icelandic Coast Guard, which has aided the shipyard in testing the 10m over the past 18 months after it was approached by Rafnar's CEO Björn Jónsson.