We were working on Tatiana, the ship’s small boat. There has been a problem with the motor tilt. There are two controls, one on the console and the other is on the outboard motor itself. I started trouble shooting the trim. While I was working on it I noticed one of the ground weirs from the engine to the hull was starting to overheat. This meant there was a grounding problem as well. I went though and tested all the weirs with an amp clamp meter. To find where the electricity was finding its way back through the hull. There are two batteries on the boat, a start battery and an auxiliary battery. The start battery was grounded to the aluminum hull with two weirs for some reason. I looked closer and tested all the battery cables and discovered that they were wired completely wrong. The tilt was getting its power though the starter cable from the start battery. The problem is the negative return was attached to the auxiliary battery negative. The auxiliary negative cabe was hooked up to the start battery. So the two were switched. This is why the power was finding its way back to the stat battery through the weirs that grounded it to the hull. The fact that the battery was grounded to the hull was weird. There is no good reason for it on this boat let alone the fact it was done with two wires is even stranger. The batters should have been wired in parallel which they weren’t which gave me a hit to what the two ground weirs were from. Whoever did the wiring for the battery last used the paralleling wires as a ground and then switched up the two negative cables. I re-wired everything correctly and removed the battery ground from the hull. There is no good reason to ground the battery on this aluminum boat with two batteries as the only power source. First it caused me problems with figuring out the tilt issue. It’s also a fire hazard because the grounding wire that the power was going through was too small for the load and started to smoke from all the amps going through it. This could start a fire if it went on long enough. Another problem this presents is the battery ground could cause a shock hazard. If you were touching the hull and then touched the engine or something else that was getting power to it you could get a shock. Without a battery ground this would be impossible the only way you could get shocked is if you were touching the negative battery post while touching the engine or something else receiving power. Once I finished rewiring the batteries I tested everything out and everything worked.