That could very well be it. I had coastal capitals in the last few games. I will try getting a slightly better starting position in the next game (maybe this evening) - if the problem still arises I will post a screenshot afterwards.
I usually prefer a coastal start for my capital, provided it has far more land tiles than water tiles. Being coastal will provide the capital with better trade routes, and I tend to emphasize commerce in my capital more than production. Why? Bureaucracy will boost the commerce output for a good long while. Granted, it boosts production too; however, because your capital city is your
first city, it will also have your earliest cottages, meaning they should be near maturity when you're running Bureaucracy, unlike newer cities with newer cottages. It will also likely have a larger population than newer cities, meaning more cottage tiles can be worked. Finally, because Bureaucracy boosts both commerce
and production, your capital's builds will have to be divided between buildings that enhance both types of yields (forge, market, university, grocer, factory, etc.). A pure production city can just focus on production-enhancing builds.
To have a super-production (Ironworks) city, select a site with sufficient food and several riverside tiles, and preferably NO water tiles whatsoever--so a completely in-land city. That way you can take advantage of things like watermills, levees, and hydro plants.
For more information on building a riverside ironworks city, see the link in my sig to my Intermediate tactics guide.