The motor the "Reef racer" uses stock is similar to a Graupner Speed-400, the hull cannot really accomodate a gear drive and the 4800 Kv motor you first used is probably too much load for your battery which drop voltage under load, hence the LVC. I use similar power in 18" monos and hydros but with 2200 mA/20C cells. Some esc will cut-off when they become too hot. In these boats I use CC thunderbird-36 with a cold plate for the esc. A lower Kv motor will stress your battery/esc less will still giving more speed than a stock brushed motor. The "Reef racer" like the "Zig-Zag" has a limit in maximum speed before stability becomes a problem. The stock prop being submerged is too big for high Vv brushless. All my mini boats are surface drive and I use Octura X427 to X430 maximum on 2 cells for the mono and 3 with the hydro. Were do you run your boat?
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