Honorable Mention for Hydrosta's Retractable Thrusters in the Nomination for
After winning the 'Innovation of the Year' award earlier this January, Hydrosta's Retractable Thrusters have received an honourable mention in the nomination for 'Ship of the Year.' Huygens Engineers conducted the mechanical analysis and provided design support for the certification of the Retractable Thrusters. Our team calculated and analyzed Hydrosta’s design, tested according to compliance with Lloyd’s standards, and thoroughly documented the process. This collaboration with Hydrosta's design team has been very fulfilling. In addition to traditional analysis, our work included extensive simulations involving the non-linear material properties of rubber.
In the nomination, the KNVTS wrote:
"The most striking innovative solution is the retractable propulsion, consisting of two electric thrusters tilting out of the hull just aft of the keel, developed in close collaboration between Royal Huisman and Hydrosta. Sarissa is not the first sailing yacht with such retractable thrusters, but the integration of the electric motors into the struts of the thrusters is an absolute first. This integration made it possible to flexibly mount the thrusters, including the casing (technically part of the hull), resulting in a significant reduction in noise and vibration levels."
Twan Verweij, our lead engineer on this project, shares some insights into the complexities of this impressive project: "It is an extremely lightweight design that, in addition to the required robustness, must also operate as quietly as possible. The mechanical optimization required a targeted approach, because the solution space is limited when thruster and ship are designed and built in parallel. This project was particularly challenging and interesting for me, because it encompassed many aspects: from strength and fatigue analysis of the structure, to evaluating the drive technology. From thermal aspects, to analysis-driven optimization of the vibration characteristics of the innovative mounting. Huygens Engineers carried out all analysis in-house, and outcomes were embedded in the design in close cooperation with the client."
Modeling of Rubber
The design is lightweight and strong, but also quiet. To dampen the sound and vibrations of the motor, the motor is suspended in multiple pre-tensioned rubber mountings.
Twan: "Rubber is non-linear; the more the material deforms, the stiffer it reacts. This makes it challenging in the analysis and requires smart choices in modeling to achieve usable results: conventional methods for assessing vibration properties require linear behavior. By making informed decisions after extensive reseach, we succeeded in obtaining usable results, which were validated in collaboration with Rubber Design. An aspect not to be underestimated is the design of the mounting for creep, ensuring that the thruster behaves as designed both now and in the future."
Success Story
A good design can lead to remarkable analysis results that translate impressively into real-world performance. This became evident during the commissioning phase. When determining the harmonic response through the unconventional mounting, it was predicted that the transmitted vibrations from the thruster to the hull would be practically negligible across the entire spectrum of propeller blade frequencies. What does "practically negligible" mean in terms of sound production in the ship during commissioning? The thruster was silent. Too silent? At 50% power, a malfunction was suspected during commissioning: no vibrations and no noise. Until looking behind the ship, where the churning water mass was undeniable. Huygens Engineers looks back on the collaboration with Hydrosta with great satisfaction. Together, we achieved an outstanding result!
