I own a 22ft custom built boat with a volvo penta 250 horse power (inboard) engine.. on my last outing (early morning (so a bit damp)) the boat was going smoothly until the engine started eraticly looseing and gaining revs.. i cut the engine. had a look in the box etc thought it must be the petrol filter. i started the engine again and started putting along slowly when sudenly the voltage went way up and the red light came on and the gps warning aswell... now my thoughts was it is the ultanator playing up... i got it checked and that isnt the problem... so id just like to know if anyone has any suggestions to what most likely could be the case here?

I had an inboard motor and the regulator overcharged the battery which makes the battery

its not a cpu motor... and has external regulator.