Hi Roger, boat looks good but sounds like it's wanting more power. I'd change to LiPos (say 3s 2200mAh) as they are much lighter and have much better starting power than most similar voltage batteries and hold their power well. Your motors are only about 1250 KV (revs per volt) so will need to be spinning at about 10-12000 and stay at that level to have decent lasting thrust and speed, and LiPos are really suited for this requirement. You could use a 2s 2200 mAh LiPo on your centre motor and a 3s for your outers (I'm assuming you have 2 ESCs)
Your motors should only draw about 3.3A at 12v each(according to Dougs' spec info) -free running,-(in the water, maybe 8A max,- you'll need a watt meter between your battery and ESC to check this properly so you can get an accurate figure- this will show you which way you need to go,-prop/voltage wise) anything else is a guess.
If the motors are pulling say 20A and the ESC is getting warm (no problem as long as you can hold you finger on it) you can screw a small 12v fan onto the cooling fins to help cool it, and join it into your battery feed at a convenient spot (I solder a JST plug just behind the ESC- battery plug) so it can be un-plugged. You can also run it to a switch, (manual or electronic)
As Doug said, you will need a LiPo charger if you change to LiPos, but once you get the hang of LiPos I'm sure you won't go back. The easiest and most common charger is an I-MAX B6 (only a genuine one not a copy) which is fine for smaller batteries. You can also buy chargers which require no setting, specially for 2-3s batteries, which have no fancy settings to confuse you, they do nothing but balance charge, (I've used one for about 10years no problems, -they will also stop if they detect a dud cell)
The advantage of the better chargers is that they can charge, discharge, balance charge or storage charge. They also have a display so you can monitor what's happening,- fail-safes such as incorrect connection, wrong battery selected, battery temp sensors etc which let you know during setting up and charging. They also can charge different battery types, (LiPos, NiMh, li-on, NiCads etc.
Set function and B6 multi function charger examples shown. Tons of info everywhere if you decide to go the LiPo way. Nothing to be worried about if you are careful (driving a car's more dangerous😁)