Speed trials are an important stage in the delivery of a ship. The speed and power are measured at sea to confirm that the ship's performance in specified conditions--- usually deep water, no wind and no waves --- agreeswith the contract. As actual conditions are often different,procedures are in place to correct the measurements for environmental effects. The latest guidelines have resulted from the STA (Ship Trial Analysis) Joint-Industry Project (Van den Boom et al, 2013).Large or fast ships need really deep water to avoid all effects of limited water depths, and this may not be found within an acceptable distance from the yard. E.g. for today's large containerships, water depths over 100 m may be needed to keep the effect on required power below 1%. Therefore, frequently trials are conducted in water that is too shallow, causing incipient shallowwater effects that lead to a reduction of the speedachieved. A correction procedure is thus desired for such effects. The ITTC Recommended Procedure (ITTC, 2014) prescribes to apply Lackenby's correction for this. However, this is still considered a weak point, experience suggesting that the corrections may be too large.