Increasing the freedom in optimisation generally increases the chance of finding better results. In particular, allowing asymmetric sterns can lead to significant additional savings of 2-5%. As the gains of the asymmetric aftbody build on similar physical effects as other propulsion saving devices (e.g. fins, spoilers) where gains are generally found to be higher for full hull forms (bulkers and tankers) than for slender hull forms (containerships, multi-purpose vessels, LNG tankers), the same trends are expected for asymmetric hull shapes. The asymmetric stern improves propulsive efficiency similar to pre-swirl devices, albeit with much higher structural robustness, avoiding potential problems with vibration and fatigue strength. The time appears ripe for a renaissance of this idea from the 1970s.
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