controls.....
...there are many tiller steered boats that have engine controls mounted in the cockpit. A quick look through west marine, boat us, defender or even sailet.com catalogues will show you a few.(I've provided a link to the West Marine Engine systems page)The single lever types, where throttle and gearshift are linked to one handle, all have a safety lever to prevent the operator from shifting gears at high rpm. Once in gear, however, engaging the safety stop is not necessary to adjust the throttle. Before investing in a new unit (they are very expensive) make sure your cables are good. I suggest replacing the cables first, it'll cost less than $50. Then make your decision about replacing the control box.