If you want to connect in series you need to be sure that panel(s) are not partly shaded, even by small objects. Series is regularly done in power stations sited in the open. Boat panels are most often wired in parallel. If your panels do not have diodes internal you will probably need to have them external. This prevents the shaded panel from getting overheated by the unshaded panel trying to force current
the wrong way through the panel. Your charge controler should prevent back current
from the batteries when the sun is down. Make sure your charge controler is rated both for the amps and for the open circuit voltage.
If your boat is 12 volts and your panels are nominal 12 volts you can use a PWM type charger
. You will not get much benefit from an MPPT
unless the panel voltage is significantly above your battery
voltage. (likewise if the panels are 24 and the boat is 24)
I encourage you to follow my link in post 65 to Handy Bob. His blog is well worth the read before you design your system. Particularly interesting are the photos showing how only a very small shadow puts a wrench in the system. Bob is big on Morningstar PWM and MPPT charge controlers. I've read a lot of data on various manufacturer's products. I tend to like their stuff too based on the specs and manuals
In our case, we needed big power. My 3 panels are 220 watts; 54 volts open circuit and the boat is 24 VDC. This requires MPPT to control the charging
feed to the batteries. I will be wired parallel.