Minimal battery size for minimal components?

[great white]

My 12 foot tinny is very weight sensitive because, well......it's only a 12 footer.



To that end, I'm not intending to run a trolling motor. Wouldn't have much use for it the way I use my boat. I also have a johnny 2 hp (used as emergency propulsion if the 8 hp dies) on the transom that I have converted to electronic ignition and will idle so low you can almost count the sparks. The 2 HP can do trolling duty if I ever decide to do a down-rigger, which would fit the type of fishing I occasionally do. Yeah, I could probably drop the 20 lb johhny and run a trolling motor instead, but that means a bigger battery and less (for my purposes) utility I can get from the gas motor. After the big trolling battery, wiring, mounting and trolling motor, I'd probably have more weight than just running the 2 hp johnny.

So all my battery will have to run is:

1. 200 GPH bilge pump used for daily duties. Draws 1.7 amps, rated 10 gph @ 5 feet lift, not much more than a washer motor pump really.
2. 2000 GPH pump. Backup in case I hole the hull and the 200 gph can't keep up, 11 amp draw, 1200 gph @ 5 feet lift.
3. An led bow light and stern light. Removable type, I almost never run the boat after dark.

Even my fish finder is an older (and portable) humminbird 100 wide and it runs off it's own bank of 2 six volt batteries. I really just use it for a depth sounder as I go where I know there is fish when I want to fish. Seems a little "unsporting" to me to use a fish finder anyways. I'm not that serious about catching anyways. As I mantioned, I'm more interested in where the bottom is.

The main motor (johhny 8 hp) will plane the boat right now with me and my gear in it, but will plow with two full size guys. I'm usually by myself, so that's not a problem. But I don't want to add much more weight than I already have and as batteries get bigger, the get really heavy, really fast.

Here's a couple older pictures of what's already in the boat:

It's since been fully carpeted (bottom deck is foam standing mats) and the rear bench has been reduced a bit (radio and slots have been removed to move the tiller seat aft to a more comfortable running position). It still planes and floats like it used to, but you can see why I'm concerned about adding more weight than needed.

How small a battery do you think I can get away with?

I actually have a couple motorcycle batteries I have been considering trying. What I really need it for is to run the bilge pumps in the event of an emergency. The rest of the time the batteries are just along for the ride.....

 

[great white]

So it looks like this:

The small pump draws 1.7 amps. That means for a 12 ahr battery it can run for 7 hrs. Call it 5 to be safe since you don't get full draw right down to zero rated amps n a battery.

The bigger pump draws 11 amps. That mans less than an hour running. Call it a 45 mins to be safe.

It's beginning to sound like a 10-14 ahr battery will fill my needs and still keep the weight down. I never more than about 5 minuets run from shore so no worries about making land before the batteries die if there is a leak. If it's a big gashing hole I'm hooped anyways.

I'll install an LED warning light trigger under deck (with a honkin' big red LED above deck!) so I will know if the water is rising past a specific level which means it's time to flick on the big pump and head for shore.

My LED running lights are minimal draw at best and 99.5% of the time they won't be used at al so that's not really a factor.

A small solar panel mounted on each wing box will help to keep some charge in it while out on the water. Not enough to make a big difference, but even a trickle of free power is good power!

 

[earl60446]

Seems like you got it under control and know what you are doing. I would use the cycle battery you already have if it were me.
Tim