You've made incredible progress. I'm really impressed and your building skills. For Ballasting I've found these weights to be convenient View: https://www.amazon.com/CK-Auto-Adhesive-EasyPeel-Motorcycles/dp/B06XDHXRT7
I don't know yet. I have narrowed it down to either receiver or esc. I think its just a soldering problem.
You have some great photos of the exterior of the boat. Would it be possible to get some interior photos? What are the dimensions?
Something’s soldered to your receiver? If you have a servo tester try plugging that into your esc instead of the receiver to narrow it down. If you don’t have one I recommend picking one up. There pretty cheap.
This is a fully 3d printed ship. Includes all mounting for motors pumps, servos, water channeling designed in. I'll try to do a write-up and post it with the .STL files. This is based on a a ferry that ran from Ireland to Iceland as a.troop transport in WWII called the St. Claire. Since all transport ships in WWCC get the same speed, her small size and quick turning make her a difficult target.
OK, I did a quick writeup and zipped all of the .STL files into a resource called "R.M.S. St Claire". Build one for yourself... she's relatively quick to put together and has proven to be very competitive in WWCC battles.