I built mine from the original Matchbox kit in 1982, still have it and as yet not started its refit number 6 - i think - anyway, its also sank once due to U weed dragging her down and luckily was recovered by a safety marshal at the water when an event was ongoing (this has been mentioned before years ago).
From experience the weight of ballast which was to use a battery as part of that was 6lb in old money, the RC was an Acoms - so a standard 2002 servo for the rudder, a bobs board and 2002 servo, a receiver and 4 x AA cell battery pack, the motor is a 6v decaperm with a reduction gear, i think that is still in there, the motors battery power was either 2 or 4 C cell batteries, and yes it didn't last long, but it did work, in the following refits the battery was changed to gel block that became the ballast, futaba radio gear that included (and I think is still inside it) a M20 ? speed controller, and various cosmetic changes, if I was to do the next refit it would entail redoing the access as currently the whole top, bar the front anchor area, is removed for full access, I will have to do some photos.