Personally I'd avoid Lithium Polymer (LiPo) batteries on a boat (or in a house or car for that matter). They are VERY touchy, and if left for a while need to be discharged to a safe storage
voltage. Great care has to be exercised in how they are charged, and how they are discharged. To the extent you can get explosion proof charging
bags to put them in while charging
(I have an explosion protection charging bag, and I use it), and shipping
options can be severely curtailed due to the risks involved in carrying them. As Boeing and others have discovered, they are a bit prone to bursting into flames (as well as exploding).
Never let a 12v battery
get below 12.2v, and it will last, and last (so called deep discharge batteries also get damaged if voltages go below this, and can only withstand maybe a bit more damage than 'ordinary' batteries, maybe not too). At 12.2v you are at about a 50% charge level.
An acquaintance has been testing solar panels
for getting on 30 years. He hasn't had a monocrystalline Class A cell perform as low as specified age would indicate, ALL of them have surpassed their specification, and are still performing well at 20+ years.
He hasn't had a polycrystalline solar
panel last usefully more than 5 years yet (hopefully that is changing/will change).
charge controllers are very nice, it is possible to pick up extremely well made PWM charge controllers at very good prices (e.g. I got a pile of Highway Authority heavy duty 30 amp 12v ones for £10 each). I will use mine on the small 12v system which won't have many amps flowing through it (lots of amps at 12v are bad news for the infrastructure cabling, connections, and fittings). 15 amps through a 30 amp charge controller should help provide long term reliability
, as well as sensible infrastructure costs (cabling for example gets seriously pricey, beyond 170 amps, and if you utilise a lot at 12v, amp handling ramps up really fast). For DC make sure your cabling is multi strand rather than solid core
too. I know it works better, but it is supposed to be because DC travels on the outside of the strands, so the more strands the better (I am not actually that sure about that, but it is more flexible and easier to work with anyway, so any excuse I suppose, and I haven't felt the need to delve right into it as yet).
My 'serious' system (not on a boat) is 48v for the sensible amperages, and for that there will be a big MPPT
charge controller, 48v battery banks, and I have a humungous 8kw/24kw 230v pure sine wave inverter (I can hardly lift
the darned thing it is so heavy, almost all transformers).
You used to be able to get towed generators for boats, is there anybody still making them?
eta: Yes Aquair still do them.