I am currently in the planning stages for a hydronic radiant floor heating system, zoned with removeable panels to access the bilges for a dutch barge conversion. I have been trying to calculate the heat load requirements for a hydronic radiant floor heating system for this barge. However, almost all references to calculate heat loads for hydronic radiant floor heating are for domestic homes. As the barge sits in the water, I am having a very hard time trying to find how to calculate the proper heat load requirements for the portion of the vessel below the waterline. Any help would be greatly appreciated. Thanks. 
Google is your friend. There are many sites with the heat transfer coefficients of the materials in your boat and the formulas for calculating heat transfer.
Assume this is to convert to a house barge? The hull will need enough thermal insulation, and a way to keep it dry, and keep the bilges free to let water flow through the limberholes.
Once you have made the hull relatively tight insulation wise, it should take little heat to keep it snug. I would imagine the amount of linear meters of radiant heat strips would be proportional to cubic feet over the whole vessel.
If you are trying to do this with little or no insulation, it is a crapshoot. The amount of hull under water, exposed topsides, and deck would make this a trial and error method.