Considering a low cost Charge controller is not the best option. It is the Charge controller who will make the difference in your daily production.
240 W of panels will produce as an average, each day :
240 (Watt/h of you 12V panels
X 0,8 (for cable losses and heat)
= 192 W/H
X ? 5 hours a day of peak sun = 960 W/H per day .
* The number of hours of peak sun on a boat
is very difficult to evaluate:
1/ If you are in a marina and your panels are not directly facing the sun, you will produce very little
2/ If part of your panels are shaded, you could loose up to 75 % of your panel capacity, depending on the type of panels, ....and the type of charge controler used.
960 W/H per day in 12V is the equivalent of 80 Amps . (960 divided by 12)
This means you should produce 80 Amp of current
each sunny day.
If you plan on using these 80 amps each day, and you want to discharge your batteries at a maximum of 50% of their capacity (25% is too low , Deep cycle batteries can easily handle 50%) ,plus you want to have a minimum of 2 days autonomy, this means you need to have a battery bank of :
80 divide by 0,5 = 160 Amp/h
2 days = 160 X 2 = 320 Ah...... in 12V
The best option for you will be a set of 2 real good quality 6V battery of 350 Ah.
This is not the correct place to advertise but if you need any additional information you can send me a message with your email
address and I will give you more details.