If I switch to a deep cycle battery for my main battery to start the motor, run livewells, run lights, and two fishfinders  will I have to charge this battery when I get off the water?  Currently I have a starting battery and the motor charges it up when we have it running.  I have always trickle charged my deep cycles before getting a bass boat so I am not sure what kind of a job the alternator will do. I just want to make sure that if I need to get another charger I can do it in this long off season

It has more to do with how long the run is from your fishing spot(s) back to the trailer rather than type of battery.  If you are running everything from a single battery you have a balancing act to how much power you can use against how much charge your alternator puts out and how long you run it.

You can do the math, measure load currents, make estimates of duty cycle %, alternator output, running time etc., but the simplest way is to try it and monitor battery voltage carefully as you gain experience.

But one way or another you will probably need a half way decent shore power charger.  The ones Walmart sells with the digital readout for about $80 are excellent smart chargers.

Unless you spend a lot of time running the big motor at higher speeds you will need to charge the battery along with the TM batteries.

When I got my first bass boat battery state of charge was always an issue. Then I got smart and bought an on board 3 bank charger so one plug in did the total job - no more issues.

Yea thats what I just started thinking about.  We have pretty small lakes around here and a "run" from spot to spot is only a couple of minutes at most.  I have a 2 bank charger that came with the boat for the TM batteries and wasnt sure if I should get another charger or not.  Thanks for all the help.