A fire that began between the interior and exterior hulls of a charter fishing boat Monday afternoon caused about $20,000 worth of damage on the boat. Workers were welding a plate between the two hulls on the boat to get it up to Coast Guard codes when the sparks caused urethane insulation to catch fire, according to Kevin Bowman, deputy chief of the Tarpon Springs Fire Department. The fire spread across the ceiling and under the wheelhouse of the boat, which was at Anclote Marine Ways, 1082 Island Ave., Bowman said. It took firefighters 30 minutes to contain the blaze, he said. Bowman said fighting the fire was complicated because the boat was raised on a shoring device. Firefighters had to climb 20 feet to get into the boat, which had 400 gallons of fuel on board, Bowman said. Firefighters used a foam system to put out the flames as a precautionary measure because fuel does not dilute in water, he said. The boat was owned by Fred Standard of Crystal River. No one was injured.