What gauge does the wiring harness have to be to support 24v system? thanks

It's not the voltage that's the primary determinate of gauge - it's the amperage and distance - check this chart.

Across the top is the length from battery to device, far left is max current, bulk of chart is what wire gauge to use.

 

Thanks for the chart. I'm trying to see if its worth paying to upgrade from 12v to 24v for accessories on new purchase aluminum boat 

4 minutes ago, elway1983 said:

Thanks for the chart. I'm trying to see if its worth paying to upgrade from 12v to 24v for accessories on new purchase aluminum boat 

The only 'accessory' that would need 24v would be a trolling motor. Sonar, lights, etc all run on 12v. If you're talking a second battery to extend the time-on-water, you'd connect the two batteries in parallel (positive to positive, negative to negative) and still have only 12v...it's the AH ratings that would add together in that case...and both batteries should be the same AH rating.

What's the reasoning behind 12v, 24v and 36 volt? I just want to have enough juice to last 8-10 hours fishing with equipment.

Just now, elway1983 said:

What's the reasoning behind 12v, 24v and 36 volt? I just want to have enough juice to last 8-10 hours fishing with equipment.

As I said - Trolling motors are the only items that have differing voltage. Higher voltage TMs draw less power for the same amount of thrust.

Example: A MinnKota 12v 50# TM draws 50amps at max speed, a 24v 70# only draws 42 amps at max.

The trade off is double the cost for batteries, and double the weight. As a SLA battery weighs close to 65-70lbs - that's a lot of weight in a small space.

 

Adding a second battery if you're running a 12v TM will extend your running time, but sonar, lights, etc will take 2amps or less total...so a 20AH SLA battery will run those for 5 hours without draining it too much.

Thanks for your help

 

5 minutes ago, elway1983 said:

Thanks for your help

 

Just in summary

 

If you're running a 12v TM - you can add a second battery in parallel (pos-pos, neg-neg) to double your running time....

 

and you don't have to change ANY of your wiring.

In my opinion, if you're buying a new boat - there isn't any substitute for electric power.   Purchase the strongest trolling motor your boat will hold.   Pay for the wiring upgrade - it will be worth it in the long run.   I wish I had a 36 volt trolling motor on my boat - just for so many things.   You can hold in the wind better - you can cut across the cove quicker without having to start up your big motor -

you can crawl along the shore line or drop off line much easier - it is just better if you can afford it.  If you can't fit a 36 volt unit on to your boat - then go with a 24 - go with as much power as you can afford.