Will a 12 volt starting battery with1000ca and 135rc and 800a run a fish finder that has 500 watts and 4000 peak watts for 8 hours?
4000 watts / 12V = 333.3 amps, no commercial sonar set transducer would have a 300+ amps draw. Your basic question is an obvious misnomer and requires you to get an appropriate size generation set. Any transducer requiring 300+ amps DC at 12V would require a Maxwell super capacitor to pulse ping. A standard fish sonar will operate all day long on a deep cycle battery like you have. Your load figure is probably in milliamps, not an actual electrical load rated in watts. That would mean half an amp to 4 amps maximum battery current draw in milliamps. Most of the electrical consumption is for the neon sweeper and motor to spin it around.
duck you sucker!
1,000 cca--I assume?--is 330 A/Hrs, that's 33 amps for 10 hour rate. 500 w /12 = 41 amps. So, it will for a little while. How long duration is this 4,000 w peak? How often? These figure sound high, even for a Ship Radar. I can see the short sonar pulses being at these peaks, but your continuous, average load cannot be near this high. I had a very early Lowrance unit, it was small and would run on a 10 A/Hr Motorcycle battery for an hour. If you really want a good battery, make sure it is marine grade deep cycle. Often, starting short-cycles can't take a sustained load like even 5 amps for 12 hours. Weren't designed for it.
Far safer to have a separate battery to power the fishfinder if you really need one!
should do so - despite the high power figures for a depth sounder they only put out very brief pulses. I'd expect the fishfinder to average about 2 Amp current. I assume because you have a starting battery you also have a motor which will bew running & putting charge back into the battery anyway. Tip starting batteries dont like being taken below about 2/3 charge - if runnnig the fish finder is all it is t obe used for a deep cycle battery would be a better choice.