Eliminating fossil fuels entirely is not feasible for high-latitude yachts: Heating and hot water are usually diesel-powered. So is propulsion, given remote areas with limited infrastructure. Accommodating tight schedules does not help. The goal, therefore, is to minimize its use - for environmental reasons, to save money and to avoid noise.
Other than avoiding waste with very good insulation and efficient systems and optimized generation off the engines this means taking advantage of non-consumable power-generation – in particular wind and solar.
Ideally, the engine won’t need to be run just for power generation.
Generating electricity, while the engine it is used for propulsion is no big deal: The extra load of highly efficient generator heads doesn’t require much fuel anyways.
Given the combined input of wind and solar, the need for generation off the engine will be rare. It can be combined with water-making and heating off the engine if needed. That way very little energy is wasted.