In 1993, IMO resolution A751(18) was accepted. Since 1993, ship designs focussed on complying with these standards. For the Netherlands, MARIN gathered the full-scale results of about 100 ships. Performance with respect to IMO A751 requirements was demonstrated in the 2002 meeting of the IMO-DE. It was shown that most ships fulfilled the IMO recommendations. The ships not fulfilling the requirements sailed anyway, manually, or by using an advanced autopilot. Based on the gathered manoeuvring properties of the vessels, the following observations are made. The current standards are focussing much on conventional vessels: displacement ships propelled by standard propulsions (propeller(s) and rudder(s)). For vessels with other propulsion means, the rules are flexible. Also sailing in shallow and restricted water (most critical manoeuvring situations) are not dealt with. The impact of environment (wind, waves and other vessels) is also not taken into account. Because there are no criteria for that, under the economic pressure ships will be constructed "just" fulfilling the design criteria (so-called fit-for-purpose). However, other aspects are also important. On these subjects a set of criteria is proposed and ways to test or verify the designs are discussed.

　

 The danger of introducing manoeuvring criteria is that ships are designed that are just fulfilling the criteria. Under economic pressure it could then be said that the ship is "good" manoeuvrable, while this would be not the case as "good" manoeuvrable may also be defined by other factors.

 When looking at criteria, one should make distinctions between safety criteria and mission related criteria. Safety criteria will define a minimum level of manoeuvrability. Ships not fulfilling these criteria are substandard and should obtain a penalty: more training is required, special means should be put on board or in the ultimate case, the ship would not be allowed to sail. This most severe penalty should not be carried out often, as that would jeopardise the common ground for solid criteria.

 In this paper, the as-is situation is analysed. Some drawbacks are sketched and additional criteria (quantities and norms) are proposed. Furthermore, ways to verify compliance with these criteria are proposed. The objective remains that ships sailing in our waters should have adequate controllability, both for their own safety and the safety of others.

　

 Since 10 years, IMO criteria are advised in many countries, although there is no obligatory character.

 Most national administrations take part in recommending that "IMO manoeuvres" are carried out on sea trials of newly built vessels. Also in the Netherlands, for every vessel built in the Netherlands or sailing under Dutch flag, IMO manoeuvres are carried out. The gathered results of about 5 years full-scale trials are summarised in Figures 1 , 2 and 3.

 MARIN gathered these results and made comparisons between the sea trial results and the IMO criteria. It is observed that for ships under Dutch flag or built by Dutch shipyards, most vessels comply with the criteria. Some ships are not fulfilling the criteria. For the "Dutch" vessels, the most difficult criterion is the criterion for the first overshoot angle of the 10/10 zigzag test. This means that there are ships that are course unstable up to an unsatisfactory degree (at least according to the IMO standards).

　

　

　

　

　

　

 Although some vessels do not comply with the criteria, all ships are delivered and are sailing. The feeling of the designers and sailors is that the vessels are indeed course unstable. In general, it is the feeling of the designers that the criteria for overshoot angles is realistic. This is also confirmed by the conclusions by Rhee [1]. The vessels that do not comply with the criteria are indeed course unstable, although the degree of instability or unacceptability can be under discussion.

 The following question arises: will, by pursuing the present line of IMO A751(18), substandard ships be eliminated? This is the motivation to investigate the other and enhanced criteria for manoeuvring.