Standard Disclosure on Seasickness: If you get motion sickness easily (e.g. riding in a car), you will probably become seasick. Otherwise, incidences of seasickness are highly variable depending on each person and the particular conditions. I have seen the most experienced sailors get seasick in relatively mild conditions. On the other hand, in over thirty years of sailing with a large number of beginners on inshore waters (and the Delaware River certainly qualifies) I have had only one person who was so uncomfortable so as to classify as being seasick. Tips to avoid seasickness:

1) Do not sail hungover;
2) Stay on deck where your eyes can reference the horizon;
3) Avoid eating heavy, rich foods before and during sailing;
4) Stay comfortable -avoid getting chilled or overheated;
5) Relax and stay involved in the activity aboard.

Dramamine and other medicines do work for some people (Bonine or Marezine may cause less drowsiness); I have not used any but I think you may have to take them some hours before sailing if you want it to be effective.