Ship speed limits are legal and save fuel

Setting mandatory global and regional speed limits for shipping is legally and technically feasible and does not require major administrative and economic burdens for enforcement. Reduced speed results in dramatic reductions in ship emissions - CO2, air pollution and particulates - and does not pose technical, operational or safety dangers. The preliminary findings of the first ever study on the feasibility of speed limits for ships, suggest that a global speed limit agreed at the IMO can be enforced by States as a condition of entry into ports so long as the measure is not discriminatory as far as the ship flag is concerned. The speed limit study- carried out by CE Delft, the University of Southampton and the International Council on Clean Transportation (ICCT) and commissioned by T&E and Seas at Risk - recommended that an international agreement on a global measure would be the best way of implementing speed limits for shipping.

http://www.transportenvironment.org/News/2011/10/Seminar-on-slow-steaming-and-speed-limiters-for-shipping-4-October-2011/