I was speaking generically of small engines, including outboards, motorcycles, etc. For example, regulated alternators didn't appear on outboard motors until the mid-eighties, when increased electrical power demands necessitated higher-output alternators.
Shunting regulators are quite common on motorcycles, and I assume that's the design used on most small engines. It's really the only way you can implement a regulator using SCRs. Silicon-controlled rectifiers are curious devices: you can turn them on but not off. (A triac is just two SCRs back-to-back in parallel.) The behavior of SCRs isn't a problem when switching ac, since the signal turns itself off every half cycle. Now in the case of lighting dimmers, SCRs are used exactly as you describe: the SCR is triggered partway through the half cycle, so only a portion of the waveform is passed to the load. But lighting dimmers are open-loop devices with no feedback loop. Voltage regulators are closed-loop devices; they need a means of turning the power OFF as well as on. Since an SCR can't turn off, the solution is to short out the stator output using the SCR as a shunt.
The link below has the schematic for a rudimentary shunting regulator, and a good discussion of the theory of operation.
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