Last evening I epoxy-ed the deck onto the hull. First batch of epoxy on the beams, side of the hull and the forward "box". After it had set in, I added extra epoxy all round to make the hull and deck stronger and watertight.
I also epoxy-ed both push knees in place.
Yesterday I got a 6V 7Ah lead-acid from a local electronics shop.
Those batteries are mass produced and cheap so I thought I'd give it a shot. Cost me 22€ including the Faston blade connectors. I had some Tamiya connectors laying around for the other en of the battery cable (ESC is fitted with Tam-plug which is my default "low current connector")
Battery is 1070g (2-1/3lb) so ballast had to be adjusted compared to my initial 7.2V 6-cell NIMH setup. That's when hook & look comes in very handy, yet is really strong (can turn the boat upside down with the 6V battery in it, won't move.
At first ballast was setup (at home) so that the tug would sit flat on water. Waterline strictly parallel to the deck, and right at the bottom (say 5mm) of the transom.
Including the battery that was approximately 3700g (8lb) of ballast.
It looked nice in the bathtub ... but once on the pond the springer had an identity crisis and behaved like a submarine. It would Dive! Dive! Dive! the moment throttle was barely applied.
I removed 4 lead ingots (around 1400g / 3lb) so that the bow would get up. By the way did I mention hook & loop is frigging strong ? Had to remove the battery to get some wiggle room to remove two of the lead ingots. Cold and wet fingers didn't help either ...
With some of the ballast off, things were a bit more manageable. Tug still "dives" a little when full ahead but I might keep it that way and just go easy on the throttle. Extra power will still be useful when pushing or towing.
Here's a video of the tug once ballast was adjusted. I was on my own so I took my GoPro. Its wide angle means you don't have to point it very carefully but it also means you can barerly see the tug once it is 15ft away. There's some slow-motion (everything looks better in slo-mo !) at 01'30", 02'52", 04'50", 05'10", 05'35" and 06'45". Watch in HD !