The Swedish Transport Agency has noted a number of accidents in which the external factors that affect a voyage may not have been fully taken into account. Among other things, trailers and barges have come loose.
Trying to assess wave height through weather forecasts, either by experience or with the help of wave height nomograms, can be uncertain and time-consuming. The Swedish Meteorological and Hydrological Institute (SMHI) has a relatively high-resolution forecast model with a graphical interface that it well suited to shipping.
The service is public and is available at: http://www.smhi.se/oceanweb/surface-layers without a subscription. Read more about the models at http://www.smhi.se/2.153/sakerhet-och-beredskap/oceanografiska-prognoser/oceanografiska-modelldata-for-48-timmar-1.13209