Kevmar,
It also depends on your overall goal with the solar. For example, maybe you want to meet all of your boat's electrical system's demands with solar. If so, then you will need to carefully plan out all of your electrical needs (use including loads, amp hour demands etc.) and ensure that your 'end' electrical system can meet those needs without having shore power, generator run time, etc.
However, if you are like me, I wanted to reduce generator run time without having to "redo" the entire system. I have a NT 37 and my main electrical draws are 12v (Novakool) fridge, separate additional small freezer, and misc. like lighting, anchor alarm, some TV at night, etc.
In my case, I decided that more ability is better when it comes to solar. I have never heard anyone say, I should have installed less solar capacity
. So I installed 2 large panels on my pilothouse roof. For my boat, this was the best location to avoid (at least some) of the shading. My panels total 570 watts. Next, invest in a good quality
MPPT solar controller. This is the "brains" of the system and is not an area to go low quality. Some good brands include Outback, Morningstar, Blue Seas, etc. (there are others). If your boat (location for solar panels) suffers from a fair amount of shading, you will be better to have a solar controller for each panel to ensure you get the "most" out of your system.
My system ensures that my batteries (house bank, not connected to start) get back to 100% full charge almost every day with no generator run time. On days with very heavy overcast or fog in the morning, I may run the generator every second day.
I hope you find at least some of that useful