Welcome to the forum. I am sure you will find a wealth of information here. But it takes
some research filtering through all the threads to find exactly what you are looking for.
A 13 Kg servo is a very powerful one. That said, we need to know more information on
your intended boat size and intention of use.
There is a vast difference between a small tug plodding along and a large screaming high speed racing boat. Their set up is entirely different from each other.
With the 15 Amp ESC it would match a fairly modest size boat with a relatively small propeller to not overload the ESC. What is the motor capable of handling in the way of Voltage and Amperage?
These things need to be considered together to have a balanced system that matches
the boat of choice.
Please give us more information and I am sure the folks here can help.