Kind of new to wiring... I've always just hooked the wires onto the battery when I needed something when boating as a kid- didn't know about breakers, load, etc. Now I have my own boat and I'm trying to educate myself.
I've read some posts on here and came up with a diagram for a small aluminum boat I will be putting a battery on. I have a 43# bow mounted troller to hook up, and will be getting lights and float bilge pump. Motor is pull start (for now). I'll be closing the bow off with a plywood cover, giving the troller a mounting spot, and I'll also be placing the battery inside (through a lockable hatch).
I like the idea of a kill switch in case someone starts fooling around with switches.
I was hoping to purchase or make a simple switch panel with a single 20 amp breaker on the lead. Here's the diagram I came up with, please let me know if anything seems wrong, or any advice
You are on the right track but there are several additional things you need to consider.
1) Nav lights. These lights require a three pole (ON-OFF-ON) switch because the bow and stern lights are operated in a specific way. Underway both must be on. When anchored only the stern light is on. You have the option of using two separate ON-OFF switches if you wish (one for the nav and one for the anchor light.
2) The battery needs to be a deep cycle for the troller. What gauge wire you use for the troller depends on the current draw (40 amps max) and the length of the run of wire (up and back). So you need to consult an "ampacity" chart. If the run is very short as you imply, then perhaps 10 gauge is ok but #8 would be best, especially if you ever get a bigger motor.
3) The "kill" switch you refer to is really a standard heavy duty switch and is better termed "Master Power". It must be capable of handling the maximum current drawn through that circuit.
4) The 20 amp fuse/breaker is in the wrong place. It needs to be within six inches of the battery and the switch must be after it -- not before it. More on this later.
5) You do not indicate if the panel includes a fuse panel or not but you do need separate fuses for each circuit branched off the panel. In your diagram, consider a dead short in any of the three circuits with 16 gauge wire. 16 gauge wire can safely handle 10 amps. You have a 20 amp fuse feeding those three circuits. That means the wire would burn up before the fuse blew. Add a combination switch/fuse panel, or a separate fuse panel with about 4 - 6 slots, or a combo switch/breaker panel. Nav lights and bilge pump can use 7.5 amp fuses.
6) The trolling motor breaker is in the wrong place. It needs to be within six inches of the battery. Its purpose is to protect the wiring TO the motor. Where you have it would result in a certain fire if there was a short anywhere between the connector and the battery. If the trolling motor has an internal short that pops the breaker the motor is shot anyway so thats why breakers and fuses are installed at the source, not the destination.
Even though it is a short run, I'd go a little larger on the trolling motor wire. 8ga, and if you can 6ga., if you ever step up to a 55lb thrust. Downsize to a 40amp manual reset breaker near the positive post. I'd go with a prebuilt panel which has individual fuses per leg. Try to get one with a couple of extra circuits for the future. For relying on one battery, get the largest Deep Cycle you can. When you add elec start motor, you can just get a new starting battery, placed near the transom, and you could easily move the panel powered items to it.
PS: I see that I'm the slow typer again! ST covered most of my items, and then some.
No need for 8 gauge to the panel. You are not going to pull 40 amps through that circuit -- EVER. Heavy wire is hard to deal with especially when you get into confined spaces. 10 gauge is very adequate and even 12 gauge would be sufficient. 16 gauge for the branch circuits is actually bigger than it would need to be but due to vibration, that's the smallest that should be used. 18 gauge would suffer frequent breakage.