The hobby shop should have warned you to charge your batteries and let them drain at least a couple times until they are consistent on run time. Rechargable batteries when they are new, with MY experience, aren't ready to be trusted until this is done.

The person selling this boat did not have or did not share that knowlege which caused your root problem with the rudder and made you shut it down.

I do not own what you have or looked at the instructions, but I HAVE worked in a hobby shop before and always warned people of this "untold" problem with rechargables.